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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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SPDX-License-Identifier: GPL-2.0+/* * Read-Copy Update mechanism for mutual exclusion (tree-based version) * * Copyright IBM Corporation, 2008 * * Authors: Dipankar Sarma <dipankar@in.ibm.com> * Manfred Spraul <manfred@colorfullife.com> * Paul E. McKenney <paulmck@linux.ibm.com> * * Based on the original work by Paul McKenney <paulmck@linux.ibm.com> * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. * * For detailed explanation of Read-Copy Update mechanism see - * Documentation/RCU */
#define pr_fmt(fmt) "rcu: " fmt
#include <linux/types.h>#include <linux/kernel.h>#include <linux/init.h>#include <linux/spinlock.h>#include <linux/smp.h>#include <linux/rcupdate_wait.h>#include <linux/interrupt.h>#include <linux/sched.h>#include <linux/sched/debug.h>#include <linux/nmi.h>#include <linux/atomic.h>#include <linux/bitops.h>#include <linux/export.h>#include <linux/completion.h>#include <linux/kmemleak.h>#include <linux/moduleparam.h>#include <linux/panic.h>#include <linux/panic_notifier.h>#include <linux/percpu.h>#include <linux/notifier.h>#include <linux/cpu.h>#include <linux/mutex.h>#include <linux/time.h>#include <linux/kernel_stat.h>#include <linux/wait.h>#include <linux/kthread.h>#include <uapi/linux/sched/types.h>#include <linux/prefetch.h>#include <linux/delay.h>#include <linux/random.h>#include <linux/trace_events.h>#include <linux/suspend.h>#include <linux/ftrace.h>#include <linux/tick.h>#include <linux/sysrq.h>#include <linux/kprobes.h>#include <linux/gfp.h>#include <linux/oom.h>#include <linux/smpboot.h>#include <linux/jiffies.h>#include <linux/slab.h>#include <linux/sched/isolation.h>#include <linux/sched/clock.h>#include <linux/vmalloc.h>#include <linux/mm.h>#include <linux/kasan.h>#include <linux/context_tracking.h>#include "../time/tick-internal.h"
#include "tree.h"#include "rcu.h"
#ifdef MODULE_PARAM_PREFIX#undef MODULE_PARAM_PREFIX#endif#define MODULE_PARAM_PREFIX "rcutree."
/* Data structures. */static void rcu_sr_normal_gp_cleanup_work(struct work_struct *);
static DEFINE_PER_CPU_SHARED_ALIGNED(struct rcu_data, rcu_data) = { .gpwrap = true,};
int rcu_get_gpwrap_count(int cpu){ struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
return READ_ONCE(rdp->gpwrap_count);}EXPORT_SYMBOL_GPL(rcu_get_gpwrap_count);
static struct rcu_state rcu_state = { .level = { &rcu_state.node[0] }, .gp_state = RCU_GP_IDLE, .gp_seq = (0UL - 300UL) << RCU_SEQ_CTR_SHIFT, .barrier_mutex = __MUTEX_INITIALIZER(rcu_state.barrier_mutex), .barrier_lock = __RAW_SPIN_LOCK_UNLOCKED(rcu_state.barrier_lock), .name = RCU_NAME, .abbr = RCU_ABBR, .exp_mutex = __MUTEX_INITIALIZER(rcu_state.exp_mutex), .exp_wake_mutex = __MUTEX_INITIALIZER(rcu_state.exp_wake_mutex), .ofl_lock = __ARCH_SPIN_LOCK_UNLOCKED, .srs_cleanup_work = __WORK_INITIALIZER(rcu_state.srs_cleanup_work, rcu_sr_normal_gp_cleanup_work), .srs_cleanups_pending = ATOMIC_INIT(0),#ifdef CONFIG_RCU_NOCB_CPU .nocb_mutex = __MUTEX_INITIALIZER(rcu_state.nocb_mutex),#endif};
/* Dump rcu_node combining tree at boot to verify correct setup. */static bool dump_tree;module_param(dump_tree, bool, 0444);/* By default, use RCU_SOFTIRQ instead of rcuc kthreads. */static bool use_softirq = !IS_ENABLED(CONFIG_PREEMPT_RT);#ifndef CONFIG_PREEMPT_RTmodule_param(use_softirq, bool, 0444);#endif/* Control rcu_node-tree auto-balancing at boot time. */static bool rcu_fanout_exact;module_param(rcu_fanout_exact, bool, 0444);/* Increase (but not decrease) the RCU_FANOUT_LEAF at boot time. */static int rcu_fanout_leaf = RCU_FANOUT_LEAF;module_param(rcu_fanout_leaf, int, 0444);int rcu_num_lvls __read_mostly = RCU_NUM_LVLS;/* Number of rcu_nodes at specified level. */int num_rcu_lvl[] = NUM_RCU_LVL_INIT;int rcu_num_nodes __read_mostly = NUM_RCU_NODES; /* Total # rcu_nodes in use. */
/* * The rcu_scheduler_active variable is initialized to the value * RCU_SCHEDULER_INACTIVE and transitions RCU_SCHEDULER_INIT just before the * first task is spawned. So when this variable is RCU_SCHEDULER_INACTIVE, * RCU can assume that there is but one task, allowing RCU to (for example) * optimize synchronize_rcu() to a simple barrier(). When this variable * is RCU_SCHEDULER_INIT, RCU must actually do all the hard work required * to detect real grace periods. This variable is also used to suppress * boot-time false positives from lockdep-RCU error checking. Finally, it * transitions from RCU_SCHEDULER_INIT to RCU_SCHEDULER_RUNNING after RCU * is fully initialized, including all of its kthreads having been spawned. */int rcu_scheduler_active __read_mostly;EXPORT_SYMBOL_GPL(rcu_scheduler_active);
/* * The rcu_scheduler_fully_active variable transitions from zero to one * during the early_initcall() processing, which is after the scheduler * is capable of creating new tasks. So RCU processing (for example, * creating tasks for RCU priority boosting) must be delayed until after * rcu_scheduler_fully_active transitions from zero to one. We also * currently delay invocation of any RCU callbacks until after this point. * * It might later prove better for people registering RCU callbacks during * early boot to take responsibility for these callbacks, but one step at * a time. */static int rcu_scheduler_fully_active __read_mostly;
static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp, unsigned long gps, unsigned long flags);static void invoke_rcu_core(void);static void rcu_report_exp_rdp(struct rcu_data *rdp);static void rcu_report_qs_rdp(struct rcu_data *rdp);static void check_cb_ovld_locked(struct rcu_data *rdp, struct rcu_node *rnp);static bool rcu_rdp_is_offloaded(struct rcu_data *rdp);static bool rcu_rdp_cpu_online(struct rcu_data *rdp);static bool rcu_init_invoked(void);static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf);static void rcu_init_new_rnp(struct rcu_node *rnp_leaf);
/* * rcuc/rcub/rcuop kthread realtime priority. The "rcuop" * real-time priority(enabling/disabling) is controlled by * the extra CONFIG_RCU_NOCB_CPU_CB_BOOST configuration. */static int kthread_prio = IS_ENABLED(CONFIG_RCU_BOOST) ? 1 : 0;module_param(kthread_prio, int, 0444);
/* Delay in jiffies for grace-period initialization delays, debug only. */
static int gp_preinit_delay;module_param(gp_preinit_delay, int, 0444);static int gp_init_delay;module_param(gp_init_delay, int, 0444);static int gp_cleanup_delay;module_param(gp_cleanup_delay, int, 0444);static int nohz_full_patience_delay;module_param(nohz_full_patience_delay, int, 0444);static int nohz_full_patience_delay_jiffies;
// Add delay to rcu_read_unlock() for strict grace periods.static int rcu_unlock_delay;#ifdef CONFIG_RCU_STRICT_GRACE_PERIODmodule_param(rcu_unlock_delay, int, 0444);#endif
/* Retrieve RCU kthreads priority for rcutorture */int rcu_get_gp_kthreads_prio(void){ return kthread_prio;}EXPORT_SYMBOL_GPL(rcu_get_gp_kthreads_prio);
/* * Number of grace periods between delays, normalized by the duration of * the delay. The longer the delay, the more the grace periods between * each delay. The reason for this normalization is that it means that, * for non-zero delays, the overall slowdown of grace periods is constant * regardless of the duration of the delay. This arrangement balances * the need for long delays to increase some race probabilities with the * need for fast grace periods to increase other race probabilities. */#define PER_RCU_NODE_PERIOD 3 /* Number of grace periods between delays for debugging. */
/* * Return true if an RCU grace period is in progress. The READ_ONCE()s * permit this function to be invoked without holding the root rcu_node * structure's ->lock, but of course results can be subject to change. */static int rcu_gp_in_progress(void){ return rcu_seq_state(rcu_seq_current(&rcu_state.gp_seq));}
/* * Return the number of callbacks queued on the specified CPU. * Handles both the nocbs and normal cases. */static long rcu_get_n_cbs_cpu(int cpu){ struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
if (rcu_segcblist_is_enabled(&rdp->cblist)) return rcu_segcblist_n_cbs(&rdp->cblist); return 0;}
/** * rcu_softirq_qs - Provide a set of RCU quiescent states in softirq processing * * Mark a quiescent state for RCU, Tasks RCU, and Tasks Trace RCU. * This is a special-purpose function to be used in the softirq * infrastructure and perhaps the occasional long-running softirq * handler. * * Note that from RCU's viewpoint, a call to rcu_softirq_qs() is * equivalent to momentarily completely enabling preemption. For * example, given this code:: * * local_bh_disable(); * do_something(); * rcu_softirq_qs(); // A * do_something_else(); * local_bh_enable(); // B * * A call to synchronize_rcu() that began concurrently with the * call to do_something() would be guaranteed to wait only until * execution reached statement A. Without that rcu_softirq_qs(), * that same synchronize_rcu() would instead be guaranteed to wait * until execution reached statement B. */void rcu_softirq_qs(void){ RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || lock_is_held(&rcu_lock_map) || lock_is_held(&rcu_sched_lock_map), "Illegal rcu_softirq_qs() in RCU read-side critical section"); rcu_qs(); rcu_preempt_deferred_qs(current); rcu_tasks_qs(current, false);}
/* * Reset the current CPU's RCU_WATCHING counter to indicate that the * newly onlined CPU is no longer in an extended quiescent state. * This will either leave the counter unchanged, or increment it * to the next non-quiescent value. * * The non-atomic test/increment sequence works because the upper bits * of the ->state variable are manipulated only by the corresponding CPU, * or when the corresponding CPU is offline. */static void rcu_watching_online(void){ if (ct_rcu_watching() & CT_RCU_WATCHING) return; ct_state_inc(CT_RCU_WATCHING);}
/* * Return true if the snapshot returned from ct_rcu_watching() * indicates that RCU is in an extended quiescent state. */static bool rcu_watching_snap_in_eqs(int snap){ return !(snap & CT_RCU_WATCHING);}
/** * rcu_watching_snap_stopped_since() - Has RCU stopped watching a given CPU * since the specified @snap? * * @rdp: The rcu_data corresponding to the CPU for which to check EQS. * @snap: rcu_watching snapshot taken when the CPU wasn't in an EQS. * * Returns true if the CPU corresponding to @rdp has spent some time in an * extended quiescent state since @snap. Note that this doesn't check if it * /still/ is in an EQS, just that it went through one since @snap. * * This is meant to be used in a loop waiting for a CPU to go through an EQS. */static bool rcu_watching_snap_stopped_since(struct rcu_data *rdp, int snap){ /* * The first failing snapshot is already ordered against the accesses * performed by the remote CPU after it exits idle. * * The second snapshot therefore only needs to order against accesses * performed by the remote CPU prior to entering idle and therefore can * rely solely on acquire semantics. */ if (WARN_ON_ONCE(rcu_watching_snap_in_eqs(snap))) return true;
return snap != ct_rcu_watching_cpu_acquire(rdp->cpu);}
/* * Return true if the referenced integer is zero while the specified * CPU remains within a single extended quiescent state. */bool rcu_watching_zero_in_eqs(int cpu, int *vp){ int snap;
// If not quiescent, force back to earlier extended quiescent state. snap = ct_rcu_watching_cpu(cpu) & ~CT_RCU_WATCHING; smp_rmb(); // Order CT state and *vp reads. if (READ_ONCE(*vp)) return false; // Non-zero, so report failure; smp_rmb(); // Order *vp read and CT state re-read.
// If still in the same extended quiescent state, we are good! return snap == ct_rcu_watching_cpu(cpu);}
/* * Let the RCU core know that this CPU has gone through the scheduler, * which is a quiescent state. This is called when the need for a * quiescent state is urgent, so we burn an atomic operation and full * memory barriers to let the RCU core know about it, regardless of what * this CPU might (or might not) do in the near future. * * We inform the RCU core by emulating a zero-duration dyntick-idle period. * * The caller must have disabled interrupts and must not be idle. */notrace void rcu_momentary_eqs(void){ int seq;
raw_cpu_write(rcu_data.rcu_need_heavy_qs, false); seq = ct_state_inc(2 * CT_RCU_WATCHING); /* It is illegal to call this from idle state. */ WARN_ON_ONCE(!(seq & CT_RCU_WATCHING)); rcu_preempt_deferred_qs(current);}EXPORT_SYMBOL_GPL(rcu_momentary_eqs);
/** * rcu_is_cpu_rrupt_from_idle - see if 'interrupted' from idle * * If the current CPU is idle and running at a first-level (not nested) * interrupt, or directly, from idle, return true. * * The caller must have at least disabled IRQs. */static int rcu_is_cpu_rrupt_from_idle(void){ long nmi_nesting = ct_nmi_nesting();
/* * Usually called from the tick; but also used from smp_function_call() * for expedited grace periods. This latter can result in running from * the idle task, instead of an actual IPI. */ lockdep_assert_irqs_disabled();
/* Check for counter underflows */ RCU_LOCKDEP_WARN(ct_nesting() < 0, "RCU nesting counter underflow!");
/* Non-idle interrupt or nested idle interrupt */ if (nmi_nesting > 1) return false;
/* * Non nested idle interrupt (interrupting section where RCU * wasn't watching). */ if (nmi_nesting == 1) return true;
/* Not in an interrupt */ if (!nmi_nesting) { RCU_LOCKDEP_WARN(!in_task() || !is_idle_task(current), "RCU nmi_nesting counter not in idle task!"); return !rcu_is_watching_curr_cpu(); }
RCU_LOCKDEP_WARN(1, "RCU nmi_nesting counter underflow/zero!");
return false;}
#define DEFAULT_RCU_BLIMIT (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ? 1000 : 10) // Maximum callbacks per rcu_do_batch ...#define DEFAULT_MAX_RCU_BLIMIT 10000 // ... even during callback flood.static long blimit = DEFAULT_RCU_BLIMIT;#define DEFAULT_RCU_QHIMARK 10000 // If this many pending, ignore blimit.static long qhimark = DEFAULT_RCU_QHIMARK;#define DEFAULT_RCU_QLOMARK 100 // Once only this many pending, use blimit.static long qlowmark = DEFAULT_RCU_QLOMARK;#define DEFAULT_RCU_QOVLD_MULT 2#define DEFAULT_RCU_QOVLD (DEFAULT_RCU_QOVLD_MULT * DEFAULT_RCU_QHIMARK)static long qovld = DEFAULT_RCU_QOVLD; // If this many pending, hammer QS.static long qovld_calc = -1; // No pre-initialization lock acquisitions!
module_param(blimit, long, 0444);module_param(qhimark, long, 0444);module_param(qlowmark, long, 0444);module_param(qovld, long, 0444);
static ulong jiffies_till_first_fqs = IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD) ? 0 : ULONG_MAX;static ulong jiffies_till_next_fqs = ULONG_MAX;static bool rcu_kick_kthreads;static int rcu_divisor = 7;module_param(rcu_divisor, int, 0644);
/* Force an exit from rcu_do_batch() after 3 milliseconds. */static long rcu_resched_ns = 3 * NSEC_PER_MSEC;module_param(rcu_resched_ns, long, 0644);
/* * How long the grace period must be before we start recruiting * quiescent-state help from rcu_note_context_switch(). */static ulong jiffies_till_sched_qs = ULONG_MAX;module_param(jiffies_till_sched_qs, ulong, 0444);static ulong jiffies_to_sched_qs; /* See adjust_jiffies_till_sched_qs(). */module_param(jiffies_to_sched_qs, ulong, 0444); /* Display only! */
/* * Make sure that we give the grace-period kthread time to detect any * idle CPUs before taking active measures to force quiescent states. * However, don't go below 100 milliseconds, adjusted upwards for really * large systems. */static void adjust_jiffies_till_sched_qs(void){ unsigned long j;
/* If jiffies_till_sched_qs was specified, respect the request. */ if (jiffies_till_sched_qs != ULONG_MAX) { WRITE_ONCE(jiffies_to_sched_qs, jiffies_till_sched_qs); return; } /* Otherwise, set to third fqs scan, but bound below on large system. */ j = READ_ONCE(jiffies_till_first_fqs) + 2 * READ_ONCE(jiffies_till_next_fqs); if (j < HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV) j = HZ / 10 + nr_cpu_ids / RCU_JIFFIES_FQS_DIV; pr_info("RCU calculated value of scheduler-enlistment delay is %ld jiffies.\n", j); WRITE_ONCE(jiffies_to_sched_qs, j);}
static int param_set_first_fqs_jiffies(const char *val, const struct kernel_param *kp){ ulong j; int ret = kstrtoul(val, 0, &j);
if (!ret) { WRITE_ONCE(*(ulong *)kp->arg, (j > HZ) ? HZ : j); adjust_jiffies_till_sched_qs(); } return ret;}
static int param_set_next_fqs_jiffies(const char *val, const struct kernel_param *kp){ ulong j; int ret = kstrtoul(val, 0, &j);
if (!ret) { WRITE_ONCE(*(ulong *)kp->arg, clamp_val(j, 1, HZ)); adjust_jiffies_till_sched_qs(); } return ret;}
static const struct kernel_param_ops first_fqs_jiffies_ops = { .set = param_set_first_fqs_jiffies, .get = param_get_ulong,};
static const struct kernel_param_ops next_fqs_jiffies_ops = { .set = param_set_next_fqs_jiffies, .get = param_get_ulong,};
module_param_cb(jiffies_till_first_fqs, &first_fqs_jiffies_ops, &jiffies_till_first_fqs, 0644);module_param_cb(jiffies_till_next_fqs, &next_fqs_jiffies_ops, &jiffies_till_next_fqs, 0644);module_param(rcu_kick_kthreads, bool, 0644);
static void force_qs_rnp(int (*f)(struct rcu_data *rdp));static int rcu_pending(int user);
/* * Return the number of RCU GPs completed thus far for debug & stats. */unsigned long rcu_get_gp_seq(void){ return READ_ONCE(rcu_state.gp_seq);}EXPORT_SYMBOL_GPL(rcu_get_gp_seq);
/* * Return the number of RCU expedited batches completed thus far for * debug & stats. Odd numbers mean that a batch is in progress, even * numbers mean idle. The value returned will thus be roughly double * the cumulative batches since boot. */unsigned long rcu_exp_batches_completed(void){ return rcu_state.expedited_sequence;}EXPORT_SYMBOL_GPL(rcu_exp_batches_completed);
/* * Return the root node of the rcu_state structure. */static struct rcu_node *rcu_get_root(void){ return &rcu_state.node[0];}
/* * Send along grace-period-related data for rcutorture diagnostics. */void rcutorture_get_gp_data(int *flags, unsigned long *gp_seq){ *flags = READ_ONCE(rcu_state.gp_flags); *gp_seq = rcu_seq_current(&rcu_state.gp_seq);}EXPORT_SYMBOL_GPL(rcutorture_get_gp_data);
/* Gather grace-period sequence numbers for rcutorture diagnostics. */unsigned long long rcutorture_gather_gp_seqs(void){ return ((READ_ONCE(rcu_state.gp_seq) & 0xffffULL) << 40) | ((READ_ONCE(rcu_state.expedited_sequence) & 0xffffffULL) << 16) | (READ_ONCE(rcu_state.gp_seq_polled) & 0xffffULL);}EXPORT_SYMBOL_GPL(rcutorture_gather_gp_seqs);
/* Format grace-period sequence numbers for rcutorture diagnostics. */void rcutorture_format_gp_seqs(unsigned long long seqs, char *cp, size_t len){ unsigned int egp = (seqs >> 16) & 0xffffffULL; unsigned int ggp = (seqs >> 40) & 0xffffULL; unsigned int pgp = seqs & 0xffffULL;
snprintf(cp, len, "g%04x:e%06x:p%04x", ggp, egp, pgp);}EXPORT_SYMBOL_GPL(rcutorture_format_gp_seqs);
#if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_VIRT_XFER_TO_GUEST_WORK))/* * An empty function that will trigger a reschedule on * IRQ tail once IRQs get re-enabled on userspace/guest resume. */static void late_wakeup_func(struct irq_work *work){}
static DEFINE_PER_CPU(struct irq_work, late_wakeup_work) = IRQ_WORK_INIT(late_wakeup_func);
/* * If either: * * 1) the task is about to enter in guest mode and $ARCH doesn't support KVM generic work * 2) the task is about to enter in user mode and $ARCH doesn't support generic entry. * * In these cases the late RCU wake ups aren't supported in the resched loops and our * last resort is to fire a local irq_work that will trigger a reschedule once IRQs * get re-enabled again. */noinstr void rcu_irq_work_resched(void){ struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
if (IS_ENABLED(CONFIG_GENERIC_ENTRY) && !(current->flags & PF_VCPU)) return;
if (IS_ENABLED(CONFIG_VIRT_XFER_TO_GUEST_WORK) && (current->flags & PF_VCPU)) return;
instrumentation_begin(); if (do_nocb_deferred_wakeup(rdp) && need_resched()) { irq_work_queue(this_cpu_ptr(&late_wakeup_work)); } instrumentation_end();}#endif /* #if defined(CONFIG_NO_HZ_FULL) && (!defined(CONFIG_GENERIC_ENTRY) || !defined(CONFIG_VIRT_XFER_TO_GUEST_WORK)) */
#ifdef CONFIG_PROVE_RCU/** * rcu_irq_exit_check_preempt - Validate that scheduling is possible */void rcu_irq_exit_check_preempt(void){ lockdep_assert_irqs_disabled();
RCU_LOCKDEP_WARN(ct_nesting() <= 0, "RCU nesting counter underflow/zero!"); RCU_LOCKDEP_WARN(ct_nmi_nesting() != CT_NESTING_IRQ_NONIDLE, "Bad RCU nmi_nesting counter\n"); RCU_LOCKDEP_WARN(!rcu_is_watching_curr_cpu(), "RCU in extended quiescent state!");}#endif /* #ifdef CONFIG_PROVE_RCU */
#ifdef CONFIG_NO_HZ_FULL/** * __rcu_irq_enter_check_tick - Enable scheduler tick on CPU if RCU needs it. * * The scheduler tick is not normally enabled when CPUs enter the kernel * from nohz_full userspace execution. After all, nohz_full userspace * execution is an RCU quiescent state and the time executing in the kernel * is quite short. Except of course when it isn't. And it is not hard to * cause a large system to spend tens of seconds or even minutes looping * in the kernel, which can cause a number of problems, include RCU CPU * stall warnings. * * Therefore, if a nohz_full CPU fails to report a quiescent state * in a timely manner, the RCU grace-period kthread sets that CPU's * ->rcu_urgent_qs flag with the expectation that the next interrupt or * exception will invoke this function, which will turn on the scheduler * tick, which will enable RCU to detect that CPU's quiescent states, * for example, due to cond_resched() calls in CONFIG_PREEMPT=n kernels. * The tick will be disabled once a quiescent state is reported for * this CPU. * * Of course, in carefully tuned systems, there might never be an * interrupt or exception. In that case, the RCU grace-period kthread * will eventually cause one to happen. However, in less carefully * controlled environments, this function allows RCU to get what it * needs without creating otherwise useless interruptions. */void __rcu_irq_enter_check_tick(void){ struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
// If we're here from NMI there's nothing to do. if (in_nmi()) return;
RCU_LOCKDEP_WARN(!rcu_is_watching_curr_cpu(), "Illegal rcu_irq_enter_check_tick() from extended quiescent state");
if (!tick_nohz_full_cpu(rdp->cpu) || !READ_ONCE(rdp->rcu_urgent_qs) || READ_ONCE(rdp->rcu_forced_tick)) { // RCU doesn't need nohz_full help from this CPU, or it is // already getting that help. return; }
// We get here only when not in an extended quiescent state and // from interrupts (as opposed to NMIs). Therefore, (1) RCU is // already watching and (2) The fact that we are in an interrupt // handler and that the rcu_node lock is an irq-disabled lock // prevents self-deadlock. So we can safely recheck under the lock. // Note that the nohz_full state currently cannot change. raw_spin_lock_rcu_node(rdp->mynode); if (READ_ONCE(rdp->rcu_urgent_qs) && !rdp->rcu_forced_tick) { // A nohz_full CPU is in the kernel and RCU needs a // quiescent state. Turn on the tick! WRITE_ONCE(rdp->rcu_forced_tick, true); tick_dep_set_cpu(rdp->cpu, TICK_DEP_BIT_RCU); } raw_spin_unlock_rcu_node(rdp->mynode);}NOKPROBE_SYMBOL(__rcu_irq_enter_check_tick);#endif /* CONFIG_NO_HZ_FULL */
/* * Check to see if any future non-offloaded RCU-related work will need * to be done by the current CPU, even if none need be done immediately, * returning 1 if so. This function is part of the RCU implementation; * it is -not- an exported member of the RCU API. This is used by * the idle-entry code to figure out whether it is safe to disable the * scheduler-clock interrupt. * * Just check whether or not this CPU has non-offloaded RCU callbacks * queued. */int rcu_needs_cpu(void){ return !rcu_segcblist_empty(&this_cpu_ptr(&rcu_data)->cblist) && !rcu_rdp_is_offloaded(this_cpu_ptr(&rcu_data));}
/* * If any sort of urgency was applied to the current CPU (for example, * the scheduler-clock interrupt was enabled on a nohz_full CPU) in order * to get to a quiescent state, disable it. */static void rcu_disable_urgency_upon_qs(struct rcu_data *rdp){ raw_lockdep_assert_held_rcu_node(rdp->mynode); WRITE_ONCE(rdp->rcu_urgent_qs, false); WRITE_ONCE(rdp->rcu_need_heavy_qs, false); if (tick_nohz_full_cpu(rdp->cpu) && rdp->rcu_forced_tick) { tick_dep_clear_cpu(rdp->cpu, TICK_DEP_BIT_RCU); WRITE_ONCE(rdp->rcu_forced_tick, false); }}
/** * rcu_is_watching - RCU read-side critical sections permitted on current CPU? * * Return @true if RCU is watching the running CPU and @false otherwise. * An @true return means that this CPU can safely enter RCU read-side * critical sections. * * Although calls to rcu_is_watching() from most parts of the kernel * will return @true, there are important exceptions. For example, if the * current CPU is deep within its idle loop, in kernel entry/exit code, * or offline, rcu_is_watching() will return @false. * * Make notrace because it can be called by the internal functions of * ftrace, and making this notrace removes unnecessary recursion calls. */notrace bool rcu_is_watching(void){ bool ret;
preempt_disable_notrace(); ret = rcu_is_watching_curr_cpu(); preempt_enable_notrace(); return ret;}EXPORT_SYMBOL_GPL(rcu_is_watching);
/* * If a holdout task is actually running, request an urgent quiescent * state from its CPU. This is unsynchronized, so migrations can cause * the request to go to the wrong CPU. Which is OK, all that will happen * is that the CPU's next context switch will be a bit slower and next * time around this task will generate another request. */void rcu_request_urgent_qs_task(struct task_struct *t){ int cpu;
barrier(); cpu = task_cpu(t); if (!task_curr(t)) return; /* This task is not running on that CPU. */ smp_store_release(per_cpu_ptr(&rcu_data.rcu_urgent_qs, cpu), true);}
static unsigned long seq_gpwrap_lag = ULONG_MAX / 4;
/** * rcu_set_gpwrap_lag - Set RCU GP sequence overflow lag value. * @lag_gps: Set overflow lag to this many grace period worth of counters * which is used by rcutorture to quickly force a gpwrap situation. * @lag_gps = 0 means we reset it back to the boot-time value. */void rcu_set_gpwrap_lag(unsigned long lag_gps){ unsigned long lag_seq_count;
lag_seq_count = (lag_gps == 0) ? ULONG_MAX / 4 : lag_gps << RCU_SEQ_CTR_SHIFT; WRITE_ONCE(seq_gpwrap_lag, lag_seq_count);}EXPORT_SYMBOL_GPL(rcu_set_gpwrap_lag);
/* * When trying to report a quiescent state on behalf of some other CPU, * it is our responsibility to check for and handle potential overflow * of the rcu_node ->gp_seq counter with respect to the rcu_data counters. * After all, the CPU might be in deep idle state, and thus executing no * code whatsoever. */static void rcu_gpnum_ovf(struct rcu_node *rnp, struct rcu_data *rdp){ raw_lockdep_assert_held_rcu_node(rnp); if (ULONG_CMP_LT(rcu_seq_current(&rdp->gp_seq) + seq_gpwrap_lag, rnp->gp_seq)) { WRITE_ONCE(rdp->gpwrap, true); WRITE_ONCE(rdp->gpwrap_count, READ_ONCE(rdp->gpwrap_count) + 1); } if (ULONG_CMP_LT(rdp->rcu_iw_gp_seq + ULONG_MAX / 4, rnp->gp_seq)) rdp->rcu_iw_gp_seq = rnp->gp_seq + ULONG_MAX / 4;}
/* * Snapshot the specified CPU's RCU_WATCHING counter so that we can later * credit them with an implicit quiescent state. Return 1 if this CPU * is in dynticks idle mode, which is an extended quiescent state. */static int rcu_watching_snap_save(struct rcu_data *rdp){ /* * Full ordering between remote CPU's post idle accesses and updater's * accesses prior to current GP (and also the started GP sequence number) * is enforced by rcu_seq_start() implicit barrier and even further by * smp_mb__after_unlock_lock() barriers chained all the way throughout the * rnp locking tree since rcu_gp_init() and up to the current leaf rnp * locking. * * Ordering between remote CPU's pre idle accesses and post grace period * updater's accesses is enforced by the below acquire semantic. */ rdp->watching_snap = ct_rcu_watching_cpu_acquire(rdp->cpu); if (rcu_watching_snap_in_eqs(rdp->watching_snap)) { trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti")); rcu_gpnum_ovf(rdp->mynode, rdp); return 1; } return 0;}
#ifndef arch_irq_stat_cpu#define arch_irq_stat_cpu(cpu) 0#endif
/* * Returns positive if the specified CPU has passed through a quiescent state * by virtue of being in or having passed through an dynticks idle state since * the last call to rcu_watching_snap_save() for this same CPU, or by * virtue of having been offline. * * Returns negative if the specified CPU needs a force resched. * * Returns zero otherwise. */static int rcu_watching_snap_recheck(struct rcu_data *rdp){ unsigned long jtsq; int ret = 0; struct rcu_node *rnp = rdp->mynode;
/* * If the CPU passed through or entered a dynticks idle phase with * no active irq/NMI handlers, then we can safely pretend that the CPU * already acknowledged the request to pass through a quiescent * state. Either way, that CPU cannot possibly be in an RCU * read-side critical section that started before the beginning * of the current RCU grace period. */ if (rcu_watching_snap_stopped_since(rdp, rdp->watching_snap)) { trace_rcu_fqs(rcu_state.name, rdp->gp_seq, rdp->cpu, TPS("dti")); rcu_gpnum_ovf(rnp, rdp); return 1; }
/* * Complain if a CPU that is considered to be offline from RCU's * perspective has not yet reported a quiescent state. After all, * the offline CPU should have reported a quiescent state during * the CPU-offline process, or, failing that, by rcu_gp_init() * if it ran concurrently with either the CPU going offline or the * last task on a leaf rcu_node structure exiting its RCU read-side * critical section while all CPUs corresponding to that structure * are offline. This added warning detects bugs in any of these * code paths. * * The rcu_node structure's ->lock is held here, which excludes * the relevant portions the CPU-hotplug code, the grace-period * initialization code, and the rcu_read_unlock() code paths. * * For more detail, please refer to the "Hotplug CPU" section * of RCU's Requirements documentation. */ if (WARN_ON_ONCE(!rcu_rdp_cpu_online(rdp))) { struct rcu_node *rnp1;
pr_info("%s: grp: %d-%d level: %d ->gp_seq %ld ->completedqs %ld\n", __func__, rnp->grplo, rnp->grphi, rnp->level, (long)rnp->gp_seq, (long)rnp->completedqs); for (rnp1 = rnp; rnp1; rnp1 = rnp1->parent) pr_info("%s: %d:%d ->qsmask %#lx ->qsmaskinit %#lx ->qsmaskinitnext %#lx ->rcu_gp_init_mask %#lx\n", __func__, rnp1->grplo, rnp1->grphi, rnp1->qsmask, rnp1->qsmaskinit, rnp1->qsmaskinitnext, rnp1->rcu_gp_init_mask); pr_info("%s %d: %c online: %ld(%d) offline: %ld(%d)\n", __func__, rdp->cpu, ".o"[rcu_rdp_cpu_online(rdp)], (long)rdp->rcu_onl_gp_seq, rdp->rcu_onl_gp_state, (long)rdp->rcu_ofl_gp_seq, rdp->rcu_ofl_gp_state); return 1; /* Break things loose after complaining. */ }
/* * A CPU running for an extended time within the kernel can * delay RCU grace periods: (1) At age jiffies_to_sched_qs, * set .rcu_urgent_qs, (2) At age 2*jiffies_to_sched_qs, set * both .rcu_need_heavy_qs and .rcu_urgent_qs. Note that the * unsynchronized assignments to the per-CPU rcu_need_heavy_qs * variable are safe because the assignments are repeated if this * CPU failed to pass through a quiescent state. This code * also checks .jiffies_resched in case jiffies_to_sched_qs * is set way high. */ jtsq = READ_ONCE(jiffies_to_sched_qs); if (!READ_ONCE(rdp->rcu_need_heavy_qs) && (time_after(jiffies, rcu_state.gp_start + jtsq * 2) || time_after(jiffies, rcu_state.jiffies_resched) || rcu_state.cbovld)) { WRITE_ONCE(rdp->rcu_need_heavy_qs, true); /* Store rcu_need_heavy_qs before rcu_urgent_qs. */ smp_store_release(&rdp->rcu_urgent_qs, true); } else if (time_after(jiffies, rcu_state.gp_start + jtsq)) { WRITE_ONCE(rdp->rcu_urgent_qs, true); }
/* * NO_HZ_FULL CPUs can run in-kernel without rcu_sched_clock_irq! * The above code handles this, but only for straight cond_resched(). * And some in-kernel loops check need_resched() before calling * cond_resched(), which defeats the above code for CPUs that are * running in-kernel with scheduling-clock interrupts disabled. * So hit them over the head with the resched_cpu() hammer! */ if (tick_nohz_full_cpu(rdp->cpu) && (time_after(jiffies, READ_ONCE(rdp->last_fqs_resched) + jtsq * 3) || rcu_state.cbovld)) { WRITE_ONCE(rdp->rcu_urgent_qs, true); WRITE_ONCE(rdp->last_fqs_resched, jiffies); ret = -1; }
/* * If more than halfway to RCU CPU stall-warning time, invoke * resched_cpu() more frequently to try to loosen things up a bit. * Also check to see if the CPU is getting hammered with interrupts, * but only once per grace period, just to keep the IPIs down to * a dull roar. */ if (time_after(jiffies, rcu_state.jiffies_resched)) { if (time_after(jiffies, READ_ONCE(rdp->last_fqs_resched) + jtsq)) { WRITE_ONCE(rdp->last_fqs_resched, jiffies); ret = -1; } if (IS_ENABLED(CONFIG_IRQ_WORK) && !rdp->rcu_iw_pending && rdp->rcu_iw_gp_seq != rnp->gp_seq && (rnp->ffmask & rdp->grpmask)) { rdp->rcu_iw_pending = true; rdp->rcu_iw_gp_seq = rnp->gp_seq; irq_work_queue_on(&rdp->rcu_iw, rdp->cpu); }
if (rcu_cpu_stall_cputime && rdp->snap_record.gp_seq != rdp->gp_seq) { int cpu = rdp->cpu; struct rcu_snap_record *rsrp;
rsrp = &rdp->snap_record; rsrp->cputime_irq = kcpustat_field(CPUTIME_IRQ, cpu); rsrp->cputime_softirq = kcpustat_field(CPUTIME_SOFTIRQ, cpu); rsrp->cputime_system = kcpustat_field(CPUTIME_SYSTEM, cpu); rsrp->nr_hardirqs = kstat_cpu_irqs_sum(cpu) + arch_irq_stat_cpu(cpu); rsrp->nr_softirqs = kstat_cpu_softirqs_sum(cpu); rsrp->nr_csw = nr_context_switches_cpu(cpu); rsrp->jiffies = jiffies; rsrp->gp_seq = rdp->gp_seq; } }
return ret;}
/* Trace-event wrapper function for trace_rcu_future_grace_period. */static void trace_rcu_this_gp(struct rcu_node *rnp, struct rcu_data *rdp, unsigned long gp_seq_req, const char *s){ trace_rcu_future_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq), gp_seq_req, rnp->level, rnp->grplo, rnp->grphi, s);}
/* * rcu_start_this_gp - Request the start of a particular grace period * @rnp_start: The leaf node of the CPU from which to start. * @rdp: The rcu_data corresponding to the CPU from which to start. * @gp_seq_req: The gp_seq of the grace period to start. * * Start the specified grace period, as needed to handle newly arrived * callbacks. The required future grace periods are recorded in each * rcu_node structure's ->gp_seq_needed field. Returns true if there * is reason to awaken the grace-period kthread. * * The caller must hold the specified rcu_node structure's ->lock, which * is why the caller is responsible for waking the grace-period kthread. * * Returns true if the GP thread needs to be awakened else false. */static bool rcu_start_this_gp(struct rcu_node *rnp_start, struct rcu_data *rdp, unsigned long gp_seq_req){ bool ret = false; struct rcu_node *rnp;
/* * Use funnel locking to either acquire the root rcu_node * structure's lock or bail out if the need for this grace period * has already been recorded -- or if that grace period has in * fact already started. If there is already a grace period in * progress in a non-leaf node, no recording is needed because the * end of the grace period will scan the leaf rcu_node structures. * Note that rnp_start->lock must not be released. */ raw_lockdep_assert_held_rcu_node(rnp_start); trace_rcu_this_gp(rnp_start, rdp, gp_seq_req, TPS("Startleaf")); for (rnp = rnp_start; 1; rnp = rnp->parent) { if (rnp != rnp_start) raw_spin_lock_rcu_node(rnp); if (ULONG_CMP_GE(rnp->gp_seq_needed, gp_seq_req) || rcu_seq_started(&rnp->gp_seq, gp_seq_req) || (rnp != rnp_start && rcu_seq_state(rcu_seq_current(&rnp->gp_seq)))) { trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Prestarted")); goto unlock_out; } WRITE_ONCE(rnp->gp_seq_needed, gp_seq_req); if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) { /* * We just marked the leaf or internal node, and a * grace period is in progress, which means that * rcu_gp_cleanup() will see the marking. Bail to * reduce contention. */ trace_rcu_this_gp(rnp_start, rdp, gp_seq_req, TPS("Startedleaf")); goto unlock_out; } if (rnp != rnp_start && rnp->parent != NULL) raw_spin_unlock_rcu_node(rnp); if (!rnp->parent) break; /* At root, and perhaps also leaf. */ }
/* If GP already in progress, just leave, otherwise start one. */ if (rcu_gp_in_progress()) { trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedleafroot")); goto unlock_out; } trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("Startedroot")); WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags | RCU_GP_FLAG_INIT); WRITE_ONCE(rcu_state.gp_req_activity, jiffies); if (!READ_ONCE(rcu_state.gp_kthread)) { trace_rcu_this_gp(rnp, rdp, gp_seq_req, TPS("NoGPkthread")); goto unlock_out; } trace_rcu_grace_period(rcu_state.name, data_race(rcu_state.gp_seq), TPS("newreq")); ret = true; /* Caller must wake GP kthread. */unlock_out: /* Push furthest requested GP to leaf node and rcu_data structure. */ if (ULONG_CMP_LT(gp_seq_req, rnp->gp_seq_needed)) { WRITE_ONCE(rnp_start->gp_seq_needed, rnp->gp_seq_needed); WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed); } if (rnp != rnp_start) raw_spin_unlock_rcu_node(rnp); return ret;}
/* * Clean up any old requests for the just-ended grace period. Also return * whether any additional grace periods have been requested. */static bool rcu_future_gp_cleanup(struct rcu_node *rnp){ bool needmore; struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
needmore = ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed); if (!needmore) rnp->gp_seq_needed = rnp->gp_seq; /* Avoid counter wrap. */ trace_rcu_this_gp(rnp, rdp, rnp->gp_seq, needmore ? TPS("CleanupMore") : TPS("Cleanup")); return needmore;}
/* * Awaken the grace-period kthread. Don't do a self-awaken (unless in an * interrupt or softirq handler, in which case we just might immediately * sleep upon return, resulting in a grace-period hang), and don't bother * awakening when there is nothing for the grace-period kthread to do * (as in several CPUs raced to awaken, we lost), and finally don't try * to awaken a kthread that has not yet been created. If all those checks * are passed, track some debug information and awaken. * * So why do the self-wakeup when in an interrupt or softirq handler * in the grace-period kthread's context? Because the kthread might have * been interrupted just as it was going to sleep, and just after the final * pre-sleep check of the awaken condition. In this case, a wakeup really * is required, and is therefore supplied. */static void rcu_gp_kthread_wake(void){ struct task_struct *t = READ_ONCE(rcu_state.gp_kthread);
if ((current == t && !in_hardirq() && !in_serving_softirq()) || !READ_ONCE(rcu_state.gp_flags) || !t) return; WRITE_ONCE(rcu_state.gp_wake_time, jiffies); WRITE_ONCE(rcu_state.gp_wake_seq, READ_ONCE(rcu_state.gp_seq)); swake_up_one(&rcu_state.gp_wq);}
/* * If there is room, assign a ->gp_seq number to any callbacks on this * CPU that have not already been assigned. Also accelerate any callbacks * that were previously assigned a ->gp_seq number that has since proven * to be too conservative, which can happen if callbacks get assigned a * ->gp_seq number while RCU is idle, but with reference to a non-root * rcu_node structure. This function is idempotent, so it does not hurt * to call it repeatedly. Returns an flag saying that we should awaken * the RCU grace-period kthread. * * The caller must hold rnp->lock with interrupts disabled. */static bool rcu_accelerate_cbs(struct rcu_node *rnp, struct rcu_data *rdp){ unsigned long gp_seq_req; bool ret = false;
rcu_lockdep_assert_cblist_protected(rdp); raw_lockdep_assert_held_rcu_node(rnp);
/* If no pending (not yet ready to invoke) callbacks, nothing to do. */ if (!rcu_segcblist_pend_cbs(&rdp->cblist)) return false;
trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbPreAcc"));
/* * Callbacks are often registered with incomplete grace-period * information. Something about the fact that getting exact * information requires acquiring a global lock... RCU therefore * makes a conservative estimate of the grace period number at which * a given callback will become ready to invoke. The following * code checks this estimate and improves it when possible, thus * accelerating callback invocation to an earlier grace-period * number. */ gp_seq_req = rcu_seq_snap(&rcu_state.gp_seq); if (rcu_segcblist_accelerate(&rdp->cblist, gp_seq_req)) ret = rcu_start_this_gp(rnp, rdp, gp_seq_req);
/* Trace depending on how much we were able to accelerate. */ if (rcu_segcblist_restempty(&rdp->cblist, RCU_WAIT_TAIL)) trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccWaitCB")); else trace_rcu_grace_period(rcu_state.name, gp_seq_req, TPS("AccReadyCB"));
trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbPostAcc"));
return ret;}
/* * Similar to rcu_accelerate_cbs(), but does not require that the leaf * rcu_node structure's ->lock be held. It consults the cached value * of ->gp_seq_needed in the rcu_data structure, and if that indicates * that a new grace-period request be made, invokes rcu_accelerate_cbs() * while holding the leaf rcu_node structure's ->lock. */static void rcu_accelerate_cbs_unlocked(struct rcu_node *rnp, struct rcu_data *rdp){ unsigned long c; bool needwake;
rcu_lockdep_assert_cblist_protected(rdp); c = rcu_seq_snap(&rcu_state.gp_seq); if (!READ_ONCE(rdp->gpwrap) && ULONG_CMP_GE(rdp->gp_seq_needed, c)) { /* Old request still live, so mark recent callbacks. */ (void)rcu_segcblist_accelerate(&rdp->cblist, c); return; } raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ needwake = rcu_accelerate_cbs(rnp, rdp); raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ if (needwake) rcu_gp_kthread_wake();}
/* * Move any callbacks whose grace period has completed to the * RCU_DONE_TAIL sublist, then compact the remaining sublists and * assign ->gp_seq numbers to any callbacks in the RCU_NEXT_TAIL * sublist. This function is idempotent, so it does not hurt to * invoke it repeatedly. As long as it is not invoked -too- often... * Returns true if the RCU grace-period kthread needs to be awakened. * * The caller must hold rnp->lock with interrupts disabled. */static bool rcu_advance_cbs(struct rcu_node *rnp, struct rcu_data *rdp){ rcu_lockdep_assert_cblist_protected(rdp); raw_lockdep_assert_held_rcu_node(rnp);
/* If no pending (not yet ready to invoke) callbacks, nothing to do. */ if (!rcu_segcblist_pend_cbs(&rdp->cblist)) return false;
/* * Find all callbacks whose ->gp_seq numbers indicate that they * are ready to invoke, and put them into the RCU_DONE_TAIL sublist. */ rcu_segcblist_advance(&rdp->cblist, rnp->gp_seq);
/* Classify any remaining callbacks. */ return rcu_accelerate_cbs(rnp, rdp);}
/* * Move and classify callbacks, but only if doing so won't require * that the RCU grace-period kthread be awakened. */static void __maybe_unused rcu_advance_cbs_nowake(struct rcu_node *rnp, struct rcu_data *rdp){ rcu_lockdep_assert_cblist_protected(rdp); if (!rcu_seq_state(rcu_seq_current(&rnp->gp_seq)) || !raw_spin_trylock_rcu_node(rnp)) return; // The grace period cannot end while we hold the rcu_node lock. if (rcu_seq_state(rcu_seq_current(&rnp->gp_seq))) WARN_ON_ONCE(rcu_advance_cbs(rnp, rdp)); raw_spin_unlock_rcu_node(rnp);}
/* * In CONFIG_RCU_STRICT_GRACE_PERIOD=y kernels, attempt to generate a * quiescent state. This is intended to be invoked when the CPU notices * a new grace period. */static void rcu_strict_gp_check_qs(void){ if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) { rcu_read_lock(); rcu_read_unlock(); }}
/* * Update CPU-local rcu_data state to record the beginnings and ends of * grace periods. The caller must hold the ->lock of the leaf rcu_node * structure corresponding to the current CPU, and must have irqs disabled. * Returns true if the grace-period kthread needs to be awakened. */static bool __note_gp_changes(struct rcu_node *rnp, struct rcu_data *rdp){ bool ret = false; bool need_qs; const bool offloaded = rcu_rdp_is_offloaded(rdp);
raw_lockdep_assert_held_rcu_node(rnp);
if (rdp->gp_seq == rnp->gp_seq) return false; /* Nothing to do. */
/* Handle the ends of any preceding grace periods first. */ if (rcu_seq_completed_gp(rdp->gp_seq, rnp->gp_seq) || unlikely(rdp->gpwrap)) { if (!offloaded) ret = rcu_advance_cbs(rnp, rdp); /* Advance CBs. */ rdp->core_needs_qs = false; trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuend")); } else { if (!offloaded) ret = rcu_accelerate_cbs(rnp, rdp); /* Recent CBs. */ if (rdp->core_needs_qs) rdp->core_needs_qs = !!(rnp->qsmask & rdp->grpmask); }
/* Now handle the beginnings of any new-to-this-CPU grace periods. */ if (rcu_seq_new_gp(rdp->gp_seq, rnp->gp_seq) || unlikely(rdp->gpwrap)) { /* * If the current grace period is waiting for this CPU, * set up to detect a quiescent state, otherwise don't * go looking for one. */ trace_rcu_grace_period(rcu_state.name, rnp->gp_seq, TPS("cpustart")); need_qs = !!(rnp->qsmask & rdp->grpmask); rdp->cpu_no_qs.b.norm = need_qs; rdp->core_needs_qs = need_qs; zero_cpu_stall_ticks(rdp); } rdp->gp_seq = rnp->gp_seq; /* Remember new grace-period state. */ if (ULONG_CMP_LT(rdp->gp_seq_needed, rnp->gp_seq_needed) || rdp->gpwrap) WRITE_ONCE(rdp->gp_seq_needed, rnp->gp_seq_needed); if (IS_ENABLED(CONFIG_PROVE_RCU) && rdp->gpwrap) WRITE_ONCE(rdp->last_sched_clock, jiffies); WRITE_ONCE(rdp->gpwrap, false); rcu_gpnum_ovf(rnp, rdp); return ret;}
static void note_gp_changes(struct rcu_data *rdp){ unsigned long flags; bool needwake; struct rcu_node *rnp;
local_irq_save(flags); rnp = rdp->mynode; if ((rdp->gp_seq == rcu_seq_current(&rnp->gp_seq) && !unlikely(READ_ONCE(rdp->gpwrap))) || /* w/out lock. */ !raw_spin_trylock_rcu_node(rnp)) { /* irqs already off, so later. */ local_irq_restore(flags); return; } needwake = __note_gp_changes(rnp, rdp); raw_spin_unlock_irqrestore_rcu_node(rnp, flags); rcu_strict_gp_check_qs(); if (needwake) rcu_gp_kthread_wake();}
static atomic_t *rcu_gp_slow_suppress;
/* Register a counter to suppress debugging grace-period delays. */void rcu_gp_slow_register(atomic_t *rgssp){ WARN_ON_ONCE(rcu_gp_slow_suppress);
WRITE_ONCE(rcu_gp_slow_suppress, rgssp);}EXPORT_SYMBOL_GPL(rcu_gp_slow_register);
/* Unregister a counter, with NULL for not caring which. */void rcu_gp_slow_unregister(atomic_t *rgssp){ WARN_ON_ONCE(rgssp && rgssp != rcu_gp_slow_suppress && rcu_gp_slow_suppress != NULL);
WRITE_ONCE(rcu_gp_slow_suppress, NULL);}EXPORT_SYMBOL_GPL(rcu_gp_slow_unregister);
static bool rcu_gp_slow_is_suppressed(void){ atomic_t *rgssp = READ_ONCE(rcu_gp_slow_suppress);
return rgssp && atomic_read(rgssp);}
static void rcu_gp_slow(int delay){ if (!rcu_gp_slow_is_suppressed() && delay > 0 && !(rcu_seq_ctr(rcu_state.gp_seq) % (rcu_num_nodes * PER_RCU_NODE_PERIOD * delay))) schedule_timeout_idle(delay);}
static unsigned long sleep_duration;
/* Allow rcutorture to stall the grace-period kthread. */void rcu_gp_set_torture_wait(int duration){ if (IS_ENABLED(CONFIG_RCU_TORTURE_TEST) && duration > 0) WRITE_ONCE(sleep_duration, duration);}EXPORT_SYMBOL_GPL(rcu_gp_set_torture_wait);
/* Actually implement the aforementioned wait. */static void rcu_gp_torture_wait(void){ unsigned long duration;
if (!IS_ENABLED(CONFIG_RCU_TORTURE_TEST)) return; duration = xchg(&sleep_duration, 0UL); if (duration > 0) { pr_alert("%s: Waiting %lu jiffies\n", __func__, duration); schedule_timeout_idle(duration); pr_alert("%s: Wait complete\n", __func__); }}
/* * Handler for on_each_cpu() to invoke the target CPU's RCU core * processing. */static void rcu_strict_gp_boundary(void *unused){ invoke_rcu_core();}
// Make the polled API aware of the beginning of a grace period.static void rcu_poll_gp_seq_start(unsigned long *snap){ struct rcu_node *rnp = rcu_get_root();
if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE) raw_lockdep_assert_held_rcu_node(rnp);
// If RCU was idle, note beginning of GP. if (!rcu_seq_state(rcu_state.gp_seq_polled)) rcu_seq_start(&rcu_state.gp_seq_polled);
// Either way, record current state. *snap = rcu_state.gp_seq_polled;}
// Make the polled API aware of the end of a grace period.static void rcu_poll_gp_seq_end(unsigned long *snap){ struct rcu_node *rnp = rcu_get_root();
if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE) raw_lockdep_assert_held_rcu_node(rnp);
// If the previously noted GP is still in effect, record the // end of that GP. Either way, zero counter to avoid counter-wrap // problems. if (*snap && *snap == rcu_state.gp_seq_polled) { rcu_seq_end(&rcu_state.gp_seq_polled); rcu_state.gp_seq_polled_snap = 0; rcu_state.gp_seq_polled_exp_snap = 0; } else { *snap = 0; }}
// Make the polled API aware of the beginning of a grace period, but// where caller does not hold the root rcu_node structure's lock.static void rcu_poll_gp_seq_start_unlocked(unsigned long *snap){ unsigned long flags; struct rcu_node *rnp = rcu_get_root();
if (rcu_init_invoked()) { if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE) lockdep_assert_irqs_enabled(); raw_spin_lock_irqsave_rcu_node(rnp, flags); } rcu_poll_gp_seq_start(snap); if (rcu_init_invoked()) raw_spin_unlock_irqrestore_rcu_node(rnp, flags);}
// Make the polled API aware of the end of a grace period, but where// caller does not hold the root rcu_node structure's lock.static void rcu_poll_gp_seq_end_unlocked(unsigned long *snap){ unsigned long flags; struct rcu_node *rnp = rcu_get_root();
if (rcu_init_invoked()) { if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE) lockdep_assert_irqs_enabled(); raw_spin_lock_irqsave_rcu_node(rnp, flags); } rcu_poll_gp_seq_end(snap); if (rcu_init_invoked()) raw_spin_unlock_irqrestore_rcu_node(rnp, flags);}
/* * There is a single llist, which is used for handling * synchronize_rcu() users' enqueued rcu_synchronize nodes. * Within this llist, there are two tail pointers: * * wait tail: Tracks the set of nodes, which need to * wait for the current GP to complete. * done tail: Tracks the set of nodes, for which grace * period has elapsed. These nodes processing * will be done as part of the cleanup work * execution by a kworker. * * At every grace period init, a new wait node is added * to the llist. This wait node is used as wait tail * for this new grace period. Given that there are a fixed * number of wait nodes, if all wait nodes are in use * (which can happen when kworker callback processing * is delayed) and additional grace period is requested. * This means, a system is slow in processing callbacks. * * TODO: If a slow processing is detected, a first node * in the llist should be used as a wait-tail for this * grace period, therefore users which should wait due * to a slow process are handled by _this_ grace period * and not next. * * Below is an illustration of how the done and wait * tail pointers move from one set of rcu_synchronize nodes * to the other, as grace periods start and finish and * nodes are processed by kworker. * * * a. Initial llist callbacks list: * * +----------+ +--------+ +-------+ * | | | | | | * | head |---------> | cb2 |--------->| cb1 | * | | | | | | * +----------+ +--------+ +-------+ * * * * b. New GP1 Start: * * WAIT TAIL * | * | * v * +----------+ +--------+ +--------+ +-------+ * | | | | | | | | * | head ------> wait |------> cb2 |------> | cb1 | * | | | head1 | | | | | * +----------+ +--------+ +--------+ +-------+ * * * * c. GP completion: * * WAIT_TAIL == DONE_TAIL * * DONE TAIL * | * | * v * +----------+ +--------+ +--------+ +-------+ * | | | | | | | | * | head ------> wait |------> cb2 |------> | cb1 | * | | | head1 | | | | | * +----------+ +--------+ +--------+ +-------+ * * * * d. New callbacks and GP2 start: * * WAIT TAIL DONE TAIL * | | * | | * v v * +----------+ +------+ +------+ +------+ +-----+ +-----+ +-----+ * | | | | | | | | | | | | | | * | head ------> wait |--->| cb4 |--->| cb3 |--->|wait |--->| cb2 |--->| cb1 | * | | | head2| | | | | |head1| | | | | * +----------+ +------+ +------+ +------+ +-----+ +-----+ +-----+ * * * * e. GP2 completion: * * WAIT_TAIL == DONE_TAIL * DONE TAIL * | * | * v * +----------+ +------+ +------+ +------+ +-----+ +-----+ +-----+ * | | | | | | | | | | | | | | * | head ------> wait |--->| cb4 |--->| cb3 |--->|wait |--->| cb2 |--->| cb1 | * | | | head2| | | | | |head1| | | | | * +----------+ +------+ +------+ +------+ +-----+ +-----+ +-----+ * * * While the llist state transitions from d to e, a kworker * can start executing rcu_sr_normal_gp_cleanup_work() and * can observe either the old done tail (@c) or the new * done tail (@e). So, done tail updates and reads need * to use the rel-acq semantics. If the concurrent kworker * observes the old done tail, the newly queued work * execution will process the updated done tail. If the * concurrent kworker observes the new done tail, then * the newly queued work will skip processing the done * tail, as workqueue semantics guarantees that the new * work is executed only after the previous one completes. * * f. kworker callbacks processing complete: * * * DONE TAIL * | * | * v * +----------+ +--------+ * | | | | * | head ------> wait | * | | | head2 | * +----------+ +--------+ * */static bool rcu_sr_is_wait_head(struct llist_node *node){ return &(rcu_state.srs_wait_nodes)[0].node <= node && node <= &(rcu_state.srs_wait_nodes)[SR_NORMAL_GP_WAIT_HEAD_MAX - 1].node;}
static struct llist_node *rcu_sr_get_wait_head(void){ struct sr_wait_node *sr_wn; int i;
for (i = 0; i < SR_NORMAL_GP_WAIT_HEAD_MAX; i++) { sr_wn = &(rcu_state.srs_wait_nodes)[i];
if (!atomic_cmpxchg_acquire(&sr_wn->inuse, 0, 1)) return &sr_wn->node; }
return NULL;}
static void rcu_sr_put_wait_head(struct llist_node *node){ struct sr_wait_node *sr_wn = container_of(node, struct sr_wait_node, node);
atomic_set_release(&sr_wn->inuse, 0);}
static int rcu_normal_wake_from_gp = 1;module_param(rcu_normal_wake_from_gp, int, 0644);static struct workqueue_struct *sync_wq;
#define RCU_SR_NORMAL_LATCH_THR 64
/* Number of in-flight synchronize_rcu() calls queued on srs_next. */static atomic_long_t rcu_sr_normal_count;static int rcu_sr_normal_latched; /* 0/1 */
static void rcu_sr_normal_complete(struct llist_node *node){ struct rcu_synchronize *rs = container_of( (struct rcu_head *) node, struct rcu_synchronize, head); long nr;
WARN_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && !poll_state_synchronize_rcu_full(&rs->oldstate), "A full grace period is not passed yet!\n");
/* Finally. */ complete(&rs->completion); nr = atomic_long_dec_return(&rcu_sr_normal_count); WARN_ON_ONCE(nr < 0);
/* * Unlatch: switch back to normal path when fully * drained and if it has been latched. */ if (nr == 0) (void)cmpxchg_relaxed(&rcu_sr_normal_latched, 1, 0);}
static void rcu_sr_normal_gp_cleanup_work(struct work_struct *work){ struct llist_node *done, *rcu, *next, *head;
/* * This work execution can potentially execute * while a new done tail is being updated by * grace period kthread in rcu_sr_normal_gp_cleanup(). * So, read and updates of done tail need to * follow acq-rel semantics. * * Given that wq semantics guarantees that a single work * cannot execute concurrently by multiple kworkers, * the done tail list manipulations are protected here. */ done = smp_load_acquire(&rcu_state.srs_done_tail); if (WARN_ON_ONCE(!done)) return;
WARN_ON_ONCE(!rcu_sr_is_wait_head(done)); head = done->next; done->next = NULL;
/* * The dummy node, which is pointed to by the * done tail which is acq-read above is not removed * here. This allows lockless additions of new * rcu_synchronize nodes in rcu_sr_normal_add_req(), * while the cleanup work executes. The dummy * nodes is removed, in next round of cleanup * work execution. */ llist_for_each_safe(rcu, next, head) { if (!rcu_sr_is_wait_head(rcu)) { rcu_sr_normal_complete(rcu); continue; }
rcu_sr_put_wait_head(rcu); }
/* Order list manipulations with atomic access. */ atomic_dec_return_release(&rcu_state.srs_cleanups_pending);}
/* * Helper function for rcu_gp_cleanup(). */static void rcu_sr_normal_gp_cleanup(void){ struct llist_node *wait_tail, *next = NULL, *rcu = NULL; int done = 0;
wait_tail = rcu_state.srs_wait_tail; if (wait_tail == NULL) return;
rcu_state.srs_wait_tail = NULL; ASSERT_EXCLUSIVE_WRITER(rcu_state.srs_wait_tail); WARN_ON_ONCE(!rcu_sr_is_wait_head(wait_tail));
/* * Process (a) and (d) cases. See an illustration. */ llist_for_each_safe(rcu, next, wait_tail->next) { if (rcu_sr_is_wait_head(rcu)) break;
rcu_sr_normal_complete(rcu); // It can be last, update a next on this step. wait_tail->next = next;
if (++done == SR_MAX_USERS_WAKE_FROM_GP) break; }
/* * Fast path, no more users to process except putting the second last * wait head if no inflight-workers. If there are in-flight workers, * they will remove the last wait head. * * Note that the ACQUIRE orders atomic access with list manipulation. */ if (wait_tail->next && wait_tail->next->next == NULL && rcu_sr_is_wait_head(wait_tail->next) && !atomic_read_acquire(&rcu_state.srs_cleanups_pending)) { rcu_sr_put_wait_head(wait_tail->next); wait_tail->next = NULL; }
/* Concurrent sr_normal_gp_cleanup work might observe this update. */ ASSERT_EXCLUSIVE_WRITER(rcu_state.srs_done_tail); smp_store_release(&rcu_state.srs_done_tail, wait_tail);
/* * We schedule a work in order to perform a final processing * of outstanding users(if still left) and releasing wait-heads * added by rcu_sr_normal_gp_init() call. */ if (wait_tail->next) { atomic_inc(&rcu_state.srs_cleanups_pending); if (!queue_work(sync_wq, &rcu_state.srs_cleanup_work)) atomic_dec(&rcu_state.srs_cleanups_pending); }}
/* * Helper function for rcu_gp_init(). */static bool rcu_sr_normal_gp_init(void){ struct llist_node *first; struct llist_node *wait_head; bool start_new_poll = false;
first = READ_ONCE(rcu_state.srs_next.first); if (!first || rcu_sr_is_wait_head(first)) return start_new_poll;
wait_head = rcu_sr_get_wait_head(); if (!wait_head) { // Kick another GP to retry. start_new_poll = true; return start_new_poll; }
/* Inject a wait-dummy-node. */ llist_add(wait_head, &rcu_state.srs_next);
/* * A waiting list of rcu_synchronize nodes should be empty on * this step, since a GP-kthread, rcu_gp_init() -> gp_cleanup(), * rolls it over. If not, it is a BUG, warn a user. */ WARN_ON_ONCE(rcu_state.srs_wait_tail != NULL); rcu_state.srs_wait_tail = wait_head; ASSERT_EXCLUSIVE_WRITER(rcu_state.srs_wait_tail);
return start_new_poll;}
static void rcu_sr_normal_add_req(struct rcu_synchronize *rs){ /* * Increment before publish to avoid a complete * vs enqueue race on latch. */ long nr = atomic_long_inc_return(&rcu_sr_normal_count);
/* * Latch when threshold is reached. Checking for an exact match * restricts cmpxchg() to a single context. * * This latch is intentionally relaxed and best-effort. Concurrent * set/clear can race and temporarily lose the latch, which is OK * because it only selects between the fast and fallback paths. */ if (nr == RCU_SR_NORMAL_LATCH_THR) (void)cmpxchg_relaxed(&rcu_sr_normal_latched, 0, 1);
/* Publish for the GP kthread/worker. */ llist_add((struct llist_node *) &rs->head, &rcu_state.srs_next);}
/* * Initialize a new grace period. Return false if no grace period required. */static noinline_for_stack bool rcu_gp_init(void){ unsigned long flags; unsigned long oldmask; unsigned long mask; struct rcu_data *rdp; struct rcu_node *rnp = rcu_get_root(); bool start_new_poll; unsigned long old_gp_seq;
WRITE_ONCE(rcu_state.gp_activity, jiffies); raw_spin_lock_irq_rcu_node(rnp); if (!rcu_state.gp_flags) { /* Spurious wakeup, tell caller to go back to sleep. */ raw_spin_unlock_irq_rcu_node(rnp); return false; } WRITE_ONCE(rcu_state.gp_flags, 0); /* Clear all flags: New GP. */
if (WARN_ON_ONCE(rcu_gp_in_progress())) { /* * Grace period already in progress, don't start another. * Not supposed to be able to happen. */ raw_spin_unlock_irq_rcu_node(rnp); return false; }
/* Advance to a new grace period and initialize state. */ record_gp_stall_check_time(); /* * A new wait segment must be started before gp_seq advanced, so * that previous gp waiters won't observe the new gp_seq. */ start_new_poll = rcu_sr_normal_gp_init(); /* Record GP times before starting GP, hence rcu_seq_start(). */ old_gp_seq = rcu_state.gp_seq; /* * Critical ordering: rcu_seq_start() must happen BEFORE the CPU hotplug * scan below. Otherwise we risk a race where a newly onlining CPU could * be missed by the current grace period, potentially leading to * use-after-free errors. For a detailed explanation of this race, see * Documentation/RCU/Design/Requirements/Requirements.rst in the * "Hotplug CPU" section. * * Also note that the root rnp's gp_seq is kept separate from, and lags, * the rcu_state's gp_seq, for a reason. See the Quick-Quiz on * Single-node systems for more details (in Data-Structures.rst). */ rcu_seq_start(&rcu_state.gp_seq); /* Ensure that rcu_seq_done_exact() guardband doesn't give false positives. */ WARN_ON_ONCE(IS_ENABLED(CONFIG_PROVE_RCU) && rcu_seq_done_exact(&old_gp_seq, rcu_seq_snap(&rcu_state.gp_seq)));
ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq); trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("start")); rcu_poll_gp_seq_start(&rcu_state.gp_seq_polled_snap); raw_spin_unlock_irq_rcu_node(rnp);
/* * The "start_new_poll" is set to true, only when this GP is not able * to handle anything and there are outstanding users. It happens when * the rcu_sr_normal_gp_init() function was not able to insert a dummy * separator to the llist, because there were no left any dummy-nodes. * * Number of dummy-nodes is fixed, it could be that we are run out of * them, if so we start a new pool request to repeat a try. It is rare * and it means that a system is doing a slow processing of callbacks. */ if (start_new_poll) (void) start_poll_synchronize_rcu();
/* * Apply per-leaf buffered online and offline operations to * the rcu_node tree. Note that this new grace period need not * wait for subsequent online CPUs, and that RCU hooks in the CPU * offlining path, when combined with checks in this function, * will handle CPUs that are currently going offline or that will * go offline later. Please also refer to "Hotplug CPU" section * of RCU's Requirements documentation. */ WRITE_ONCE(rcu_state.gp_state, RCU_GP_ONOFF); /* Exclude CPU hotplug operations. */ rcu_for_each_leaf_node(rnp) { local_irq_disable(); /* * Serialize with CPU offline. See Requirements.rst > Hotplug CPU > * Concurrent Quiescent State Reporting for Offline CPUs. */ arch_spin_lock(&rcu_state.ofl_lock); raw_spin_lock_rcu_node(rnp); if (rnp->qsmaskinit == rnp->qsmaskinitnext && !rnp->wait_blkd_tasks) { /* Nothing to do on this leaf rcu_node structure. */ raw_spin_unlock_rcu_node(rnp); arch_spin_unlock(&rcu_state.ofl_lock); local_irq_enable(); continue; }
/* Record old state, apply changes to ->qsmaskinit field. */ oldmask = rnp->qsmaskinit; rnp->qsmaskinit = rnp->qsmaskinitnext;
/* If zero-ness of ->qsmaskinit changed, propagate up tree. */ if (!oldmask != !rnp->qsmaskinit) { if (!oldmask) { /* First online CPU for rcu_node. */ if (!rnp->wait_blkd_tasks) /* Ever offline? */ rcu_init_new_rnp(rnp); } else if (rcu_preempt_has_tasks(rnp)) { rnp->wait_blkd_tasks = true; /* blocked tasks */ } else { /* Last offline CPU and can propagate. */ rcu_cleanup_dead_rnp(rnp); } }
/* * If all waited-on tasks from prior grace period are * done, and if all this rcu_node structure's CPUs are * still offline, propagate up the rcu_node tree and * clear ->wait_blkd_tasks. Otherwise, if one of this * rcu_node structure's CPUs has since come back online, * simply clear ->wait_blkd_tasks. */ if (rnp->wait_blkd_tasks && (!rcu_preempt_has_tasks(rnp) || rnp->qsmaskinit)) { rnp->wait_blkd_tasks = false; if (!rnp->qsmaskinit) rcu_cleanup_dead_rnp(rnp); }
raw_spin_unlock_rcu_node(rnp); arch_spin_unlock(&rcu_state.ofl_lock); local_irq_enable(); } rcu_gp_slow(gp_preinit_delay); /* Races with CPU hotplug. */
/* * Set the quiescent-state-needed bits in all the rcu_node * structures for all currently online CPUs in breadth-first * order, starting from the root rcu_node structure, relying on the * layout of the tree within the rcu_state.node[] array. Note that * other CPUs will access only the leaves of the hierarchy, thus * seeing that no grace period is in progress, at least until the * corresponding leaf node has been initialized. * * The grace period cannot complete until the initialization * process finishes, because this kthread handles both. */ WRITE_ONCE(rcu_state.gp_state, RCU_GP_INIT); rcu_for_each_node_breadth_first(rnp) { rcu_gp_slow(gp_init_delay); raw_spin_lock_irqsave_rcu_node(rnp, flags); rdp = this_cpu_ptr(&rcu_data); rcu_preempt_check_blocked_tasks(rnp); rnp->qsmask = rnp->qsmaskinit; WRITE_ONCE(rnp->gp_seq, rcu_state.gp_seq); if (rnp == rdp->mynode) (void)__note_gp_changes(rnp, rdp); rcu_preempt_boost_start_gp(rnp); trace_rcu_grace_period_init(rcu_state.name, rnp->gp_seq, rnp->level, rnp->grplo, rnp->grphi, rnp->qsmask); /* * Quiescent states for tasks on any now-offline CPUs. Since we * released the ofl and rnp lock before this loop, CPUs might * have gone offline and we have to report QS on their behalf. * See Requirements.rst > Hotplug CPU > Concurrent QS Reporting. */ mask = rnp->qsmask & ~rnp->qsmaskinitnext; rnp->rcu_gp_init_mask = mask; if ((mask || rnp->wait_blkd_tasks) && rcu_is_leaf_node(rnp)) rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags); else raw_spin_unlock_irq_rcu_node(rnp); cond_resched_tasks_rcu_qs(); WRITE_ONCE(rcu_state.gp_activity, jiffies); }
// If strict, make all CPUs aware of new grace period. if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) on_each_cpu(rcu_strict_gp_boundary, NULL, 0);
/* * Immediately report QS for the GP kthread's CPU. The GP kthread * cannot be in an RCU read-side critical section while running * the FQS scan. This eliminates the need for a second FQS wait * when all CPUs are idle. */ preempt_disable(); rcu_qs(); rcu_report_qs_rdp(this_cpu_ptr(&rcu_data)); preempt_enable();
return true;}
/* * Helper function for swait_event_idle_exclusive() wakeup at force-quiescent-state * time. */static bool rcu_gp_fqs_check_wake(int *gfp){ struct rcu_node *rnp = rcu_get_root();
// If under overload conditions, force an immediate FQS scan. if (*gfp & RCU_GP_FLAG_OVLD) return true;
// Someone like call_rcu() requested a force-quiescent-state scan. *gfp = READ_ONCE(rcu_state.gp_flags); if (*gfp & RCU_GP_FLAG_FQS) return true;
// The current grace period has completed. if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp)) return true;
return false;}
/* * Do one round of quiescent-state forcing. */static void rcu_gp_fqs(bool first_time){ int nr_fqs = READ_ONCE(rcu_state.nr_fqs_jiffies_stall); struct rcu_node *rnp = rcu_get_root();
WRITE_ONCE(rcu_state.gp_activity, jiffies); WRITE_ONCE(rcu_state.n_force_qs, rcu_state.n_force_qs + 1);
WARN_ON_ONCE(nr_fqs > 3); /* Only countdown nr_fqs for stall purposes if jiffies moves. */ if (nr_fqs) { if (nr_fqs == 1) { WRITE_ONCE(rcu_state.jiffies_stall, jiffies + rcu_jiffies_till_stall_check()); } WRITE_ONCE(rcu_state.nr_fqs_jiffies_stall, --nr_fqs); }
if (first_time) { /* Collect dyntick-idle snapshots. */ force_qs_rnp(rcu_watching_snap_save); } else { /* Handle dyntick-idle and offline CPUs. */ force_qs_rnp(rcu_watching_snap_recheck); } /* Clear flag to prevent immediate re-entry. */ if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) { raw_spin_lock_irq_rcu_node(rnp); WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags & ~RCU_GP_FLAG_FQS); raw_spin_unlock_irq_rcu_node(rnp); }}
/* * Loop doing repeated quiescent-state forcing until the grace period ends. */static noinline_for_stack void rcu_gp_fqs_loop(void){ bool first_gp_fqs = true; int gf = 0; unsigned long j; int ret; struct rcu_node *rnp = rcu_get_root();
j = READ_ONCE(jiffies_till_first_fqs); if (rcu_state.cbovld) gf = RCU_GP_FLAG_OVLD; ret = 0; for (;;) { if (rcu_state.cbovld) { j = (j + 2) / 3; if (j <= 0) j = 1; } if (!ret || time_before(jiffies + j, rcu_state.jiffies_force_qs)) { WRITE_ONCE(rcu_state.jiffies_force_qs, jiffies + j); /* * jiffies_force_qs before RCU_GP_WAIT_FQS state * update; required for stall checks. */ smp_wmb(); WRITE_ONCE(rcu_state.jiffies_kick_kthreads, jiffies + (j ? 3 * j : 2)); } trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("fqswait")); WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_FQS); (void)swait_event_idle_timeout_exclusive(rcu_state.gp_wq, rcu_gp_fqs_check_wake(&gf), j); rcu_gp_torture_wait(); WRITE_ONCE(rcu_state.gp_state, RCU_GP_DOING_FQS); /* Locking provides needed memory barriers. */ /* * Exit the loop if the root rcu_node structure indicates that the grace period * has ended, leave the loop. The rcu_preempt_blocked_readers_cgp(rnp) check * is required only for single-node rcu_node trees because readers blocking * the current grace period are queued only on leaf rcu_node structures. * For multi-node trees, checking the root node's ->qsmask suffices, because a * given root node's ->qsmask bit is cleared only when all CPUs and tasks from * the corresponding leaf nodes have passed through their quiescent state. */ if (!READ_ONCE(rnp->qsmask) && !rcu_preempt_blocked_readers_cgp(rnp)) break; /* If time for quiescent-state forcing, do it. */ if (!time_after(rcu_state.jiffies_force_qs, jiffies) || (gf & (RCU_GP_FLAG_FQS | RCU_GP_FLAG_OVLD))) { trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("fqsstart")); rcu_gp_fqs(first_gp_fqs); gf = 0; if (first_gp_fqs) { first_gp_fqs = false; gf = rcu_state.cbovld ? RCU_GP_FLAG_OVLD : 0; } trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("fqsend")); cond_resched_tasks_rcu_qs(); WRITE_ONCE(rcu_state.gp_activity, jiffies); ret = 0; /* Force full wait till next FQS. */ j = READ_ONCE(jiffies_till_next_fqs); } else { /* Deal with stray signal. */ cond_resched_tasks_rcu_qs(); WRITE_ONCE(rcu_state.gp_activity, jiffies); WARN_ON(signal_pending(current)); trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("fqswaitsig")); ret = 1; /* Keep old FQS timing. */ j = jiffies; if (time_after(jiffies, rcu_state.jiffies_force_qs)) j = 1; else j = rcu_state.jiffies_force_qs - j; gf = 0; } }}
/* * Clean up after the old grace period. */static noinline void rcu_gp_cleanup(void){ int cpu; bool needgp = false; unsigned long gp_duration; unsigned long new_gp_seq; bool offloaded; struct rcu_data *rdp; struct rcu_node *rnp = rcu_get_root(); struct swait_queue_head *sq;
WRITE_ONCE(rcu_state.gp_activity, jiffies); raw_spin_lock_irq_rcu_node(rnp); rcu_state.gp_end = jiffies; gp_duration = rcu_state.gp_end - rcu_state.gp_start; if (gp_duration > rcu_state.gp_max) rcu_state.gp_max = gp_duration;
/* * We know the grace period is complete, but to everyone else * it appears to still be ongoing. But it is also the case * that to everyone else it looks like there is nothing that * they can do to advance the grace period. It is therefore * safe for us to drop the lock in order to mark the grace * period as completed in all of the rcu_node structures. */ rcu_poll_gp_seq_end(&rcu_state.gp_seq_polled_snap); raw_spin_unlock_irq_rcu_node(rnp);
/* * Propagate new ->gp_seq value to rcu_node structures so that * other CPUs don't have to wait until the start of the next grace * period to process their callbacks. This also avoids some nasty * RCU grace-period initialization races by forcing the end of * the current grace period to be completely recorded in all of * the rcu_node structures before the beginning of the next grace * period is recorded in any of the rcu_node structures. */ new_gp_seq = rcu_state.gp_seq; rcu_seq_end(&new_gp_seq); rcu_for_each_node_breadth_first(rnp) { raw_spin_lock_irq_rcu_node(rnp); if (WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp))) dump_blkd_tasks(rnp, 10); WARN_ON_ONCE(rnp->qsmask); WRITE_ONCE(rnp->gp_seq, new_gp_seq); if (!rnp->parent) smp_mb(); // Order against failing poll_state_synchronize_rcu_full(). rdp = this_cpu_ptr(&rcu_data); if (rnp == rdp->mynode) needgp = __note_gp_changes(rnp, rdp) || needgp; /* smp_mb() provided by prior unlock-lock pair. */ needgp = rcu_future_gp_cleanup(rnp) || needgp; // Reset overload indication for CPUs no longer overloaded if (rcu_is_leaf_node(rnp)) for_each_leaf_node_cpu_mask(rnp, cpu, rnp->cbovldmask) { rdp = per_cpu_ptr(&rcu_data, cpu); check_cb_ovld_locked(rdp, rnp); } sq = rcu_nocb_gp_get(rnp); raw_spin_unlock_irq_rcu_node(rnp); rcu_nocb_gp_cleanup(sq); cond_resched_tasks_rcu_qs(); WRITE_ONCE(rcu_state.gp_activity, jiffies); rcu_gp_slow(gp_cleanup_delay); } rnp = rcu_get_root(); raw_spin_lock_irq_rcu_node(rnp); /* GP before ->gp_seq update. */
/* Declare grace period done, trace first to use old GP number. */ trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("end")); rcu_seq_end(&rcu_state.gp_seq); ASSERT_EXCLUSIVE_WRITER(rcu_state.gp_seq); WRITE_ONCE(rcu_state.gp_state, RCU_GP_IDLE); /* Check for GP requests since above loop. */ rdp = this_cpu_ptr(&rcu_data); if (!needgp && ULONG_CMP_LT(rnp->gp_seq, rnp->gp_seq_needed)) { trace_rcu_this_gp(rnp, rdp, rnp->gp_seq_needed, TPS("CleanupMore")); needgp = true; } /* Advance CBs to reduce false positives below. */ offloaded = rcu_rdp_is_offloaded(rdp); if ((offloaded || !rcu_accelerate_cbs(rnp, rdp)) && needgp) {
// We get here if a grace period was needed (“needgp”) // and the above call to rcu_accelerate_cbs() did not set // the RCU_GP_FLAG_INIT bit in ->gp_state (which records // the need for another grace period). The purpose // of the “offloaded” check is to avoid invoking // rcu_accelerate_cbs() on an offloaded CPU because we do not // hold the ->nocb_lock needed to safely access an offloaded // ->cblist. We do not want to acquire that lock because // it can be heavily contended during callback floods.
WRITE_ONCE(rcu_state.gp_flags, RCU_GP_FLAG_INIT); WRITE_ONCE(rcu_state.gp_req_activity, jiffies); trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("newreq")); } else {
// We get here either if there is no need for an // additional grace period or if rcu_accelerate_cbs() has // already set the RCU_GP_FLAG_INIT bit in ->gp_flags. // So all we need to do is to clear all of the other // ->gp_flags bits.
WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags & RCU_GP_FLAG_INIT); } raw_spin_unlock_irq_rcu_node(rnp);
// Make synchronize_rcu() users aware of the end of old grace period. rcu_sr_normal_gp_cleanup();
// If strict, make all CPUs aware of the end of the old grace period. if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) on_each_cpu(rcu_strict_gp_boundary, NULL, 0);}
/* * Body of kthread that handles grace periods. */static int __noreturn rcu_gp_kthread(void *unused){ rcu_bind_gp_kthread(); for (;;) {
/* Handle grace-period start. */ for (;;) { trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("reqwait")); WRITE_ONCE(rcu_state.gp_state, RCU_GP_WAIT_GPS); swait_event_idle_exclusive(rcu_state.gp_wq, READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_INIT); rcu_gp_torture_wait(); WRITE_ONCE(rcu_state.gp_state, RCU_GP_DONE_GPS); /* Locking provides needed memory barrier. */ if (rcu_gp_init()) break; cond_resched_tasks_rcu_qs(); WRITE_ONCE(rcu_state.gp_activity, jiffies); WARN_ON(signal_pending(current)); trace_rcu_grace_period(rcu_state.name, rcu_state.gp_seq, TPS("reqwaitsig")); }
/* Handle quiescent-state forcing. */ rcu_gp_fqs_loop();
/* Handle grace-period end. */ WRITE_ONCE(rcu_state.gp_state, RCU_GP_CLEANUP); rcu_gp_cleanup(); WRITE_ONCE(rcu_state.gp_state, RCU_GP_CLEANED); }}
/* * Report a full set of quiescent states to the rcu_state data structure. * Invoke rcu_gp_kthread_wake() to awaken the grace-period kthread if * another grace period is required. Whether we wake the grace-period * kthread or it awakens itself for the next round of quiescent-state * forcing, that kthread will clean up after the just-completed grace * period. Note that the caller must hold rnp->lock, which is released * before return. */static void rcu_report_qs_rsp(unsigned long flags) __releases(rcu_get_root()->lock){ raw_lockdep_assert_held_rcu_node(rcu_get_root()); WARN_ON_ONCE(!rcu_gp_in_progress()); WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags | RCU_GP_FLAG_FQS); raw_spin_unlock_irqrestore_rcu_node(rcu_get_root(), flags); rcu_gp_kthread_wake();}
/* * Similar to rcu_report_qs_rdp(), for which it is a helper function. * Allows quiescent states for a group of CPUs to be reported at one go * to the specified rcu_node structure, though all the CPUs in the group * must be represented by the same rcu_node structure (which need not be a * leaf rcu_node structure, though it often will be). The gps parameter * is the grace-period snapshot, which means that the quiescent states * are valid only if rnp->gp_seq is equal to gps. That structure's lock * must be held upon entry, and it is released before return. * * As a special case, if mask is zero, the bit-already-cleared check is * disabled. This allows propagating quiescent state due to resumed tasks * during grace-period initialization. */static void rcu_report_qs_rnp(unsigned long mask, struct rcu_node *rnp, unsigned long gps, unsigned long flags) __releases(rnp->lock){ unsigned long oldmask = 0; struct rcu_node *rnp_c;
raw_lockdep_assert_held_rcu_node(rnp);
/* Walk up the rcu_node hierarchy. */ for (;;) { if ((!(rnp->qsmask & mask) && mask) || rnp->gp_seq != gps) {
/* * Our bit has already been cleared, or the * relevant grace period is already over, so done. */ raw_spin_unlock_irqrestore_rcu_node(rnp, flags); return; } WARN_ON_ONCE(oldmask); /* Any child must be all zeroed! */ WARN_ON_ONCE(!rcu_is_leaf_node(rnp) && rcu_preempt_blocked_readers_cgp(rnp)); WRITE_ONCE(rnp->qsmask, rnp->qsmask & ~mask); trace_rcu_quiescent_state_report(rcu_state.name, rnp->gp_seq, mask, rnp->qsmask, rnp->level, rnp->grplo, rnp->grphi, !!rnp->gp_tasks); if (rnp->qsmask != 0 || rcu_preempt_blocked_readers_cgp(rnp)) {
/* Other bits still set at this level, so done. */ raw_spin_unlock_irqrestore_rcu_node(rnp, flags); return; } rnp->completedqs = rnp->gp_seq; mask = rnp->grpmask; if (rnp->parent == NULL) {
/* No more levels. Exit loop holding root lock. */
break; } raw_spin_unlock_irqrestore_rcu_node(rnp, flags); rnp_c = rnp; rnp = rnp->parent; raw_spin_lock_irqsave_rcu_node(rnp, flags); oldmask = READ_ONCE(rnp_c->qsmask); }
/* * Get here if we are the last CPU to pass through a quiescent * state for this grace period. Invoke rcu_report_qs_rsp() * to clean up and start the next grace period if one is needed. */ rcu_report_qs_rsp(flags); /* releases rnp->lock. */}
/* * Record a quiescent state for all tasks that were previously queued * on the specified rcu_node structure and that were blocking the current * RCU grace period. The caller must hold the corresponding rnp->lock with * irqs disabled, and this lock is released upon return, but irqs remain * disabled. */static void __maybe_unusedrcu_report_unblock_qs_rnp(struct rcu_node *rnp, unsigned long flags) __releases(rnp->lock){ unsigned long gps; unsigned long mask; struct rcu_node *rnp_p;
raw_lockdep_assert_held_rcu_node(rnp); if (WARN_ON_ONCE(!IS_ENABLED(CONFIG_PREEMPT_RCU)) || WARN_ON_ONCE(rcu_preempt_blocked_readers_cgp(rnp)) || rnp->qsmask != 0) { raw_spin_unlock_irqrestore_rcu_node(rnp, flags); return; /* Still need more quiescent states! */ }
rnp->completedqs = rnp->gp_seq; rnp_p = rnp->parent; if (rnp_p == NULL) { /* * Only one rcu_node structure in the tree, so don't * try to report up to its nonexistent parent! */ rcu_report_qs_rsp(flags); return; }
/* Report up the rest of the hierarchy, tracking current ->gp_seq. */ gps = rnp->gp_seq; mask = rnp->grpmask; raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ raw_spin_lock_rcu_node(rnp_p); /* irqs already disabled. */ rcu_report_qs_rnp(mask, rnp_p, gps, flags);}
/* * Record a quiescent state for the specified CPU to that CPU's rcu_data * structure. This must be called from the specified CPU. */static voidrcu_report_qs_rdp(struct rcu_data *rdp){ unsigned long flags; unsigned long mask; struct rcu_node *rnp;
WARN_ON_ONCE(rdp->cpu != smp_processor_id()); rnp = rdp->mynode; raw_spin_lock_irqsave_rcu_node(rnp, flags); if (rdp->cpu_no_qs.b.norm || rdp->gp_seq != rnp->gp_seq || rdp->gpwrap) {
/* * The grace period in which this quiescent state was * recorded has ended, so don't report it upwards. * We will instead need a new quiescent state that lies * within the current grace period. */ rdp->cpu_no_qs.b.norm = true; /* need qs for new gp. */ raw_spin_unlock_irqrestore_rcu_node(rnp, flags); return; } mask = rdp->grpmask; rdp->core_needs_qs = false; if ((rnp->qsmask & mask) == 0) { raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } else { /* * This GP can't end until cpu checks in, so all of our * callbacks can be processed during the next GP. * * NOCB kthreads have their own way to deal with that... */ if (!rcu_rdp_is_offloaded(rdp)) { /* * The current GP has not yet ended, so it * should not be possible for rcu_accelerate_cbs() * to return true. So complain, but don't awaken. */ WARN_ON_ONCE(rcu_accelerate_cbs(rnp, rdp)); }
rcu_disable_urgency_upon_qs(rdp); rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags); /* ^^^ Released rnp->lock */ }}
/* * Check to see if there is a new grace period of which this CPU * is not yet aware, and if so, set up local rcu_data state for it. * Otherwise, see if this CPU has just passed through its first * quiescent state for this grace period, and record that fact if so. */static voidrcu_check_quiescent_state(struct rcu_data *rdp){ /* Check for grace-period ends and beginnings. */ note_gp_changes(rdp);
/* * Does this CPU still need to do its part for current grace period? * If no, return and let the other CPUs do their part as well. */ if (!rdp->core_needs_qs) return;
/* * Was there a quiescent state since the beginning of the grace * period? If no, then exit and wait for the next call. */ if (rdp->cpu_no_qs.b.norm) return;
/* * Tell RCU we are done (but rcu_report_qs_rdp() will be the * judge of that). */ rcu_report_qs_rdp(rdp);}
/* Return true if callback-invocation time limit exceeded. */static bool rcu_do_batch_check_time(long count, long tlimit, bool jlimit_check, unsigned long jlimit){ // Invoke local_clock() only once per 32 consecutive callbacks. return unlikely(tlimit) && (!likely(count & 31) || (IS_ENABLED(CONFIG_RCU_DOUBLE_CHECK_CB_TIME) && jlimit_check && time_after(jiffies, jlimit))) && local_clock() >= tlimit;}
/* * Invoke any RCU callbacks that have made it to the end of their grace * period. Throttle as specified by rdp->blimit. */static void rcu_do_batch(struct rcu_data *rdp){ long bl; long count = 0; int div; bool __maybe_unused empty; unsigned long flags; unsigned long jlimit; bool jlimit_check = false; long pending; struct rcu_cblist rcl = RCU_CBLIST_INITIALIZER(rcl); struct rcu_head *rhp; long tlimit = 0;
/* If no callbacks are ready, just return. */ if (!rcu_segcblist_ready_cbs(&rdp->cblist)) { trace_rcu_batch_start(rcu_state.name, rcu_segcblist_n_cbs(&rdp->cblist), 0); trace_rcu_batch_end(rcu_state.name, 0, !rcu_segcblist_empty(&rdp->cblist), need_resched(), is_idle_task(current), rcu_is_callbacks_kthread(rdp)); return; }
/* * Extract the list of ready callbacks, disabling IRQs to prevent * races with call_rcu() from interrupt handlers. Leave the * callback counts, as rcu_barrier() needs to be conservative. * * Callbacks execution is fully ordered against preceding grace period * completion (materialized by rnp->gp_seq update) thanks to the * smp_mb__after_unlock_lock() upon node locking required for callbacks * advancing. In NOCB mode this ordering is then further relayed through * the nocb locking that protects both callbacks advancing and extraction. */ rcu_nocb_lock_irqsave(rdp, flags); WARN_ON_ONCE(cpu_is_offline(smp_processor_id())); pending = rcu_segcblist_get_seglen(&rdp->cblist, RCU_DONE_TAIL); div = READ_ONCE(rcu_divisor); div = div < 0 ? 7 : div > sizeof(long) * 8 - 2 ? sizeof(long) * 8 - 2 : div; bl = max(rdp->blimit, pending >> div); if ((in_serving_softirq() || rdp->rcu_cpu_kthread_status == RCU_KTHREAD_RUNNING) && (IS_ENABLED(CONFIG_RCU_DOUBLE_CHECK_CB_TIME) || unlikely(bl > 100))) { const long npj = NSEC_PER_SEC / HZ; long rrn = READ_ONCE(rcu_resched_ns);
rrn = clamp(rrn, NSEC_PER_MSEC, NSEC_PER_SEC); tlimit = local_clock() + rrn; jlimit = jiffies + (rrn + npj + 1) / npj; jlimit_check = true; } trace_rcu_batch_start(rcu_state.name, rcu_segcblist_n_cbs(&rdp->cblist), bl); rcu_segcblist_extract_done_cbs(&rdp->cblist, &rcl); if (rcu_rdp_is_offloaded(rdp)) rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist);
trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCbDequeued")); rcu_nocb_unlock_irqrestore(rdp, flags);
/* Invoke callbacks. */ tick_dep_set_task(current, TICK_DEP_BIT_RCU); rhp = rcu_cblist_dequeue(&rcl);
for (; rhp; rhp = rcu_cblist_dequeue(&rcl)) { rcu_callback_t f;
count++; debug_rcu_head_unqueue(rhp);
rcu_lock_acquire(&rcu_callback_map); trace_rcu_invoke_callback(rcu_state.name, rhp);
f = rhp->func; debug_rcu_head_callback(rhp); WRITE_ONCE(rhp->func, (rcu_callback_t)0L); f(rhp);
rcu_lock_release(&rcu_callback_map);
/* * Stop only if limit reached and CPU has something to do. */ if (in_serving_softirq()) { if (count >= bl && (need_resched() || !is_idle_task(current))) break; /* * Make sure we don't spend too much time here and deprive other * softirq vectors of CPU cycles. */ if (rcu_do_batch_check_time(count, tlimit, jlimit_check, jlimit)) break; } else { // In rcuc/rcuoc context, so no worries about // depriving other softirq vectors of CPU cycles. local_bh_enable(); lockdep_assert_irqs_enabled(); cond_resched_tasks_rcu_qs(); lockdep_assert_irqs_enabled(); local_bh_disable(); // But rcuc kthreads can delay quiescent-state // reporting, so check time limits for them. if (rdp->rcu_cpu_kthread_status == RCU_KTHREAD_RUNNING && rcu_do_batch_check_time(count, tlimit, jlimit_check, jlimit)) { rdp->rcu_cpu_has_work = 1; break; } } }
rcu_nocb_lock_irqsave(rdp, flags); rdp->n_cbs_invoked += count; trace_rcu_batch_end(rcu_state.name, count, !!rcl.head, need_resched(), is_idle_task(current), rcu_is_callbacks_kthread(rdp));
/* Update counts and requeue any remaining callbacks. */ rcu_segcblist_insert_done_cbs(&rdp->cblist, &rcl); rcu_segcblist_add_len(&rdp->cblist, -count);
/* Reinstate batch limit if we have worked down the excess. */ count = rcu_segcblist_n_cbs(&rdp->cblist); if (rdp->blimit >= DEFAULT_MAX_RCU_BLIMIT && count <= qlowmark) rdp->blimit = blimit;
/* Reset ->qlen_last_fqs_check trigger if enough CBs have drained. */ if (count == 0 && rdp->qlen_last_fqs_check != 0) { rdp->qlen_last_fqs_check = 0; rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs); } else if (count < rdp->qlen_last_fqs_check - qhimark) rdp->qlen_last_fqs_check = count;
/* * The following usually indicates a double call_rcu(). To track * this down, try building with CONFIG_DEBUG_OBJECTS_RCU_HEAD=y. */ empty = rcu_segcblist_empty(&rdp->cblist); WARN_ON_ONCE(count == 0 && !empty); WARN_ON_ONCE(!IS_ENABLED(CONFIG_RCU_NOCB_CPU) && count != 0 && empty); WARN_ON_ONCE(count == 0 && rcu_segcblist_n_segment_cbs(&rdp->cblist) != 0); WARN_ON_ONCE(!empty && rcu_segcblist_n_segment_cbs(&rdp->cblist) == 0);
rcu_nocb_unlock_irqrestore(rdp, flags);
tick_dep_clear_task(current, TICK_DEP_BIT_RCU);}
/* * This function is invoked from each scheduling-clock interrupt, * and checks to see if this CPU is in a non-context-switch quiescent * state, for example, user mode or idle loop. It also schedules RCU * core processing. If the current grace period has gone on too long, * it will ask the scheduler to manufacture a context switch for the sole * purpose of providing the needed quiescent state. */void rcu_sched_clock_irq(int user){ unsigned long j;
if (IS_ENABLED(CONFIG_PROVE_RCU)) { j = jiffies; WARN_ON_ONCE(time_before(j, __this_cpu_read(rcu_data.last_sched_clock))); __this_cpu_write(rcu_data.last_sched_clock, j); } trace_rcu_utilization(TPS("Start scheduler-tick")); lockdep_assert_irqs_disabled(); raw_cpu_inc(rcu_data.ticks_this_gp); /* The load-acquire pairs with the store-release setting to true. */ if (smp_load_acquire(this_cpu_ptr(&rcu_data.rcu_urgent_qs))) { /* Idle and userspace execution already are quiescent states. */ if (!rcu_is_cpu_rrupt_from_idle() && !user) set_need_resched_current(); __this_cpu_write(rcu_data.rcu_urgent_qs, false); } rcu_flavor_sched_clock_irq(user); if (rcu_pending(user)) invoke_rcu_core(); if (user || rcu_is_cpu_rrupt_from_idle()) rcu_note_voluntary_context_switch(current); lockdep_assert_irqs_disabled();
trace_rcu_utilization(TPS("End scheduler-tick"));}
/* * Scan the leaf rcu_node structures. For each structure on which all * CPUs have reported a quiescent state and on which there are tasks * blocking the current grace period, initiate RCU priority boosting. * Otherwise, invoke the specified function to check dyntick state for * each CPU that has not yet reported a quiescent state. */static void force_qs_rnp(int (*f)(struct rcu_data *rdp)){ int cpu; unsigned long flags; struct rcu_node *rnp;
rcu_state.cbovld = rcu_state.cbovldnext; rcu_state.cbovldnext = false; rcu_for_each_leaf_node(rnp) { unsigned long mask = 0; unsigned long rsmask = 0;
cond_resched_tasks_rcu_qs(); raw_spin_lock_irqsave_rcu_node(rnp, flags); rcu_state.cbovldnext |= !!rnp->cbovldmask; if (rnp->qsmask == 0) { if (rcu_preempt_blocked_readers_cgp(rnp)) { /* * No point in scanning bits because they * are all zero. But we might need to * priority-boost blocked readers. */ rcu_initiate_boost(rnp, flags); /* rcu_initiate_boost() releases rnp->lock */ continue; } raw_spin_unlock_irqrestore_rcu_node(rnp, flags); continue; } for_each_leaf_node_cpu_mask(rnp, cpu, rnp->qsmask) { struct rcu_data *rdp; int ret;
rdp = per_cpu_ptr(&rcu_data, cpu); ret = f(rdp); if (ret > 0) { mask |= rdp->grpmask; rcu_disable_urgency_upon_qs(rdp); } if (ret < 0) rsmask |= rdp->grpmask; } if (mask != 0) { /* Idle/offline CPUs, report (releases rnp->lock). */ rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags); } else { /* Nothing to do here, so just drop the lock. */ raw_spin_unlock_irqrestore_rcu_node(rnp, flags); }
for_each_leaf_node_cpu_mask(rnp, cpu, rsmask) resched_cpu(cpu); }}
/* * Force quiescent states on reluctant CPUs, and also detect which * CPUs are in dyntick-idle mode. */void rcu_force_quiescent_state(void){ unsigned long flags; bool ret; struct rcu_node *rnp; struct rcu_node *rnp_old = NULL;
if (!rcu_gp_in_progress()) return; /* Funnel through hierarchy to reduce memory contention. */ rnp = raw_cpu_read(rcu_data.mynode); for (; rnp != NULL; rnp = rnp->parent) { ret = (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) || !raw_spin_trylock(&rnp->fqslock); if (rnp_old != NULL) raw_spin_unlock(&rnp_old->fqslock); if (ret) return; rnp_old = rnp; } /* rnp_old == rcu_get_root(), rnp == NULL. */
/* Reached the root of the rcu_node tree, acquire lock. */ raw_spin_lock_irqsave_rcu_node(rnp_old, flags); raw_spin_unlock(&rnp_old->fqslock); if (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) { raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags); return; /* Someone beat us to it. */ } WRITE_ONCE(rcu_state.gp_flags, rcu_state.gp_flags | RCU_GP_FLAG_FQS); raw_spin_unlock_irqrestore_rcu_node(rnp_old, flags); rcu_gp_kthread_wake();}EXPORT_SYMBOL_GPL(rcu_force_quiescent_state);
// Workqueue handler for an RCU reader for kernels enforcing struct RCU// grace periods.static void strict_work_handler(struct work_struct *work){ rcu_read_lock(); rcu_read_unlock();}
/* Perform RCU core processing work for the current CPU. */static __latent_entropy void rcu_core(void){ struct rcu_data *rdp = raw_cpu_ptr(&rcu_data); struct rcu_node *rnp = rdp->mynode;
if (cpu_is_offline(smp_processor_id())) return; trace_rcu_utilization(TPS("Start RCU core")); WARN_ON_ONCE(!rdp->beenonline);
/* Report any deferred quiescent states if preemption enabled. */ if (IS_ENABLED(CONFIG_PREEMPT_COUNT) && (!(preempt_count() & PREEMPT_MASK))) { rcu_preempt_deferred_qs(current); } else if (rcu_preempt_need_deferred_qs(current)) { guard(irqsave)(); set_need_resched_current(); }
/* Update RCU state based on any recent quiescent states. */ rcu_check_quiescent_state(rdp);
/* No grace period and unregistered callbacks? */ if (!rcu_gp_in_progress() && rcu_segcblist_is_enabled(&rdp->cblist) && !rcu_rdp_is_offloaded(rdp)) { guard(irqsave)(); if (!rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL)) rcu_accelerate_cbs_unlocked(rnp, rdp); }
rcu_check_gp_start_stall(rnp, rdp, rcu_jiffies_till_stall_check());
/* If there are callbacks ready, invoke them. */ if (!rcu_rdp_is_offloaded(rdp) && rcu_segcblist_ready_cbs(&rdp->cblist) && likely(READ_ONCE(rcu_scheduler_fully_active))) { rcu_do_batch(rdp); /* Re-invoke RCU core processing if there are callbacks remaining. */ if (rcu_segcblist_ready_cbs(&rdp->cblist)) invoke_rcu_core(); }
/* Do any needed deferred wakeups of rcuo kthreads. */ do_nocb_deferred_wakeup(rdp); trace_rcu_utilization(TPS("End RCU core"));
// If strict GPs, schedule an RCU reader in a clean environment. if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD)) queue_work_on(rdp->cpu, rcu_gp_wq, &rdp->strict_work);}
static void rcu_core_si(void){ rcu_core();}
static void rcu_wake_cond(struct task_struct *t, int status){ /* * If the thread is yielding, only wake it when this * is invoked from idle */ if (t && (status != RCU_KTHREAD_YIELDING || is_idle_task(current))) wake_up_process(t);}
static void invoke_rcu_core_kthread(void){ struct task_struct *t; unsigned long flags;
local_irq_save(flags); __this_cpu_write(rcu_data.rcu_cpu_has_work, 1); t = __this_cpu_read(rcu_data.rcu_cpu_kthread_task); if (t != NULL && t != current) rcu_wake_cond(t, __this_cpu_read(rcu_data.rcu_cpu_kthread_status)); local_irq_restore(flags);}
/* * Wake up this CPU's rcuc kthread to do RCU core processing. */static void invoke_rcu_core(void){ if (!cpu_online(smp_processor_id())) return; if (use_softirq) raise_softirq(RCU_SOFTIRQ); else invoke_rcu_core_kthread();}
static void rcu_cpu_kthread_park(unsigned int cpu){ per_cpu(rcu_data.rcu_cpu_kthread_status, cpu) = RCU_KTHREAD_OFFCPU;}
static int rcu_cpu_kthread_should_run(unsigned int cpu){ return __this_cpu_read(rcu_data.rcu_cpu_has_work);}
/* * Per-CPU kernel thread that invokes RCU callbacks. This replaces * the RCU softirq used in configurations of RCU that do not support RCU * priority boosting. */static void rcu_cpu_kthread(unsigned int cpu){ unsigned int *statusp = this_cpu_ptr(&rcu_data.rcu_cpu_kthread_status); char work, *workp = this_cpu_ptr(&rcu_data.rcu_cpu_has_work); unsigned long *j = this_cpu_ptr(&rcu_data.rcuc_activity); int spincnt;
trace_rcu_utilization(TPS("Start CPU kthread@rcu_run")); for (spincnt = 0; spincnt < 10; spincnt++) { WRITE_ONCE(*j, jiffies); local_bh_disable(); *statusp = RCU_KTHREAD_RUNNING; local_irq_disable(); work = *workp; WRITE_ONCE(*workp, 0); local_irq_enable(); if (work) rcu_core(); local_bh_enable(); if (!READ_ONCE(*workp)) { trace_rcu_utilization(TPS("End CPU kthread@rcu_wait")); *statusp = RCU_KTHREAD_WAITING; return; } } *statusp = RCU_KTHREAD_YIELDING; trace_rcu_utilization(TPS("Start CPU kthread@rcu_yield")); schedule_timeout_idle(2); trace_rcu_utilization(TPS("End CPU kthread@rcu_yield")); *statusp = RCU_KTHREAD_WAITING; WRITE_ONCE(*j, jiffies);}
static struct smp_hotplug_thread rcu_cpu_thread_spec = { .store = &rcu_data.rcu_cpu_kthread_task, .thread_should_run = rcu_cpu_kthread_should_run, .thread_fn = rcu_cpu_kthread, .thread_comm = "rcuc/%u", .setup = rcu_cpu_kthread_setup, .park = rcu_cpu_kthread_park,};
/* * Spawn per-CPU RCU core processing kthreads. */static int __init rcu_spawn_core_kthreads(void){ int cpu;
for_each_possible_cpu(cpu) per_cpu(rcu_data.rcu_cpu_has_work, cpu) = 0; if (use_softirq) return 0; WARN_ONCE(smpboot_register_percpu_thread(&rcu_cpu_thread_spec), "%s: Could not start rcuc kthread, OOM is now expected behavior\n", __func__); return 0;}
static void rcutree_enqueue(struct rcu_data *rdp, struct rcu_head *head, rcu_callback_t func){ rcu_segcblist_enqueue(&rdp->cblist, head); trace_rcu_callback(rcu_state.name, head, rcu_segcblist_n_cbs(&rdp->cblist)); trace_rcu_segcb_stats(&rdp->cblist, TPS("SegCBQueued"));}
/* * Handle any core-RCU processing required by a call_rcu() invocation. */static void call_rcu_core(struct rcu_data *rdp, struct rcu_head *head, rcu_callback_t func, unsigned long flags){ rcutree_enqueue(rdp, head, func); /* * If called from an extended quiescent state, invoke the RCU * core in order to force a re-evaluation of RCU's idleness. */ if (!rcu_is_watching()) invoke_rcu_core();
/* If interrupts were disabled or CPU offline, don't invoke RCU core. */ if (irqs_disabled_flags(flags) || cpu_is_offline(smp_processor_id())) return;
/* * Force the grace period if too many callbacks or too long waiting. * Enforce hysteresis, and don't invoke rcu_force_quiescent_state() * if some other CPU has recently done so. Also, don't bother * invoking rcu_force_quiescent_state() if the newly enqueued callback * is the only one waiting for a grace period to complete. */ if (unlikely(rcu_segcblist_n_cbs(&rdp->cblist) > rdp->qlen_last_fqs_check + qhimark)) {
/* Are we ignoring a completed grace period? */ note_gp_changes(rdp);
/* Start a new grace period if one not already started. */ if (!rcu_gp_in_progress()) { rcu_accelerate_cbs_unlocked(rdp->mynode, rdp); } else { /* Give the grace period a kick. */ rdp->blimit = DEFAULT_MAX_RCU_BLIMIT; if (READ_ONCE(rcu_state.n_force_qs) == rdp->n_force_qs_snap && rcu_segcblist_first_pend_cb(&rdp->cblist) != head) rcu_force_quiescent_state(); rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs); rdp->qlen_last_fqs_check = rcu_segcblist_n_cbs(&rdp->cblist); } }}
/* * RCU callback function to leak a callback. */static void rcu_leak_callback(struct rcu_head *rhp){}
/* * Check and if necessary update the leaf rcu_node structure's * ->cbovldmask bit corresponding to the current CPU based on that CPU's * number of queued RCU callbacks. The caller must hold the leaf rcu_node * structure's ->lock. */static void check_cb_ovld_locked(struct rcu_data *rdp, struct rcu_node *rnp){ raw_lockdep_assert_held_rcu_node(rnp); if (qovld_calc <= 0) return; // Early boot and wildcard value set. if (rcu_segcblist_n_cbs(&rdp->cblist) >= qovld_calc) WRITE_ONCE(rnp->cbovldmask, rnp->cbovldmask | rdp->grpmask); else WRITE_ONCE(rnp->cbovldmask, rnp->cbovldmask & ~rdp->grpmask);}
/* * Check and if necessary update the leaf rcu_node structure's * ->cbovldmask bit corresponding to the current CPU based on that CPU's * number of queued RCU callbacks. No locks need be held, but the * caller must have disabled interrupts. * * Note that this function ignores the possibility that there are a lot * of callbacks all of which have already seen the end of their respective * grace periods. This omission is due to the need for no-CBs CPUs to * be holding ->nocb_lock to do this check, which is too heavy for a * common-case operation. */static void check_cb_ovld(struct rcu_data *rdp){ struct rcu_node *const rnp = rdp->mynode;
if (qovld_calc <= 0 || ((rcu_segcblist_n_cbs(&rdp->cblist) >= qovld_calc) == !!(READ_ONCE(rnp->cbovldmask) & rdp->grpmask))) return; // Early boot wildcard value or already set correctly. raw_spin_lock_rcu_node(rnp); check_cb_ovld_locked(rdp, rnp); raw_spin_unlock_rcu_node(rnp);}
static void__call_rcu_common(struct rcu_head *head, rcu_callback_t func, bool lazy_in){ static atomic_t doublefrees; unsigned long flags; bool lazy; struct rcu_data *rdp;
/* Misaligned rcu_head! */ WARN_ON_ONCE((unsigned long)head & (sizeof(void *) - 1));
/* Avoid NULL dereference if callback is NULL. */ if (WARN_ON_ONCE(!func)) return;
if (debug_rcu_head_queue(head)) { /* * Probable double call_rcu(), so leak the callback. * Use rcu:rcu_callback trace event to find the previous * time callback was passed to call_rcu(). */ if (atomic_inc_return(&doublefrees) < 4) { pr_err("%s(): Double-freed CB %p->%pS()!!! ", __func__, head, head->func); mem_dump_obj(head); } WRITE_ONCE(head->func, rcu_leak_callback); return; } head->func = func; head->next = NULL; kasan_record_aux_stack(head);
local_irq_save(flags); rdp = this_cpu_ptr(&rcu_data); RCU_LOCKDEP_WARN(!rcu_rdp_cpu_online(rdp), "Callback enqueued on offline CPU!");
lazy = lazy_in && !rcu_async_should_hurry();
/* Add the callback to our list. */ if (unlikely(!rcu_segcblist_is_enabled(&rdp->cblist))) { // This can trigger due to call_rcu() from offline CPU: WARN_ON_ONCE(rcu_scheduler_active != RCU_SCHEDULER_INACTIVE); WARN_ON_ONCE(!rcu_is_watching()); // Very early boot, before rcu_init(). Initialize if needed // and then drop through to queue the callback. if (rcu_segcblist_empty(&rdp->cblist)) rcu_segcblist_init(&rdp->cblist); }
check_cb_ovld(rdp);
if (unlikely(rcu_rdp_is_offloaded(rdp))) call_rcu_nocb(rdp, head, func, flags, lazy); else call_rcu_core(rdp, head, func, flags); local_irq_restore(flags);}
#ifdef CONFIG_RCU_LAZYstatic bool enable_rcu_lazy __read_mostly = !IS_ENABLED(CONFIG_RCU_LAZY_DEFAULT_OFF);module_param(enable_rcu_lazy, bool, 0444);
/** * call_rcu_hurry() - Queue RCU callback for invocation after grace period, and * flush all lazy callbacks (including the new one) to the main ->cblist while * doing so. * * @head: structure to be used for queueing the RCU updates. * @func: actual callback function to be invoked after the grace period * * The callback function will be invoked some time after a full grace * period elapses, in other words after all pre-existing RCU read-side * critical sections have completed. * * Use this API instead of call_rcu() if you don't want the callback to be * delayed for very long periods of time, which can happen on systems without * memory pressure and on systems which are lightly loaded or mostly idle. * This function will cause callbacks to be invoked sooner than later at the * expense of extra power. Other than that, this function is identical to, and * reuses call_rcu()'s logic. Refer to call_rcu() for more details about memory * ordering and other functionality. */void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func){ __call_rcu_common(head, func, false);}EXPORT_SYMBOL_GPL(call_rcu_hurry);#else#define enable_rcu_lazy false#endif
/** * call_rcu() - Queue an RCU callback for invocation after a grace period. * By default the callbacks are 'lazy' and are kept hidden from the main * ->cblist to prevent starting of grace periods too soon. * If you desire grace periods to start very soon, use call_rcu_hurry(). * * @head: structure to be used for queueing the RCU updates. * @func: actual callback function to be invoked after the grace period * * The callback function will be invoked some time after a full grace * period elapses, in other words after all pre-existing RCU read-side * critical sections have completed. However, the callback function * might well execute concurrently with RCU read-side critical sections * that started after call_rcu() was invoked. * * It is perfectly legal to repost an RCU callback, potentially with * a different callback function, from within its callback function. * The specified function will be invoked after another full grace period * has elapsed. This use case is similar in form to the common practice * of reposting a timer from within its own handler. * * RCU read-side critical sections are delimited by rcu_read_lock() * and rcu_read_unlock(), and may be nested. In addition, but only in * v5.0 and later, regions of code across which interrupts, preemption, * or softirqs have been disabled also serve as RCU read-side critical * sections. This includes hardware interrupt handlers, softirq handlers, * and NMI handlers. * * Note that all CPUs must agree that the grace period extended beyond * all pre-existing RCU read-side critical section. On systems with more * than one CPU, this means that when "func()" is invoked, each CPU is * guaranteed to have executed a full memory barrier since the end of its * last RCU read-side critical section whose beginning preceded the call * to call_rcu(). It also means that each CPU executing an RCU read-side * critical section that continues beyond the start of "func()" must have * executed a memory barrier after the call_rcu() but before the beginning * of that RCU read-side critical section. Note that these guarantees * include CPUs that are offline, idle, or executing in user mode, as * well as CPUs that are executing in the kernel. * * Furthermore, if CPU A invoked call_rcu() and CPU B invoked the * resulting RCU callback function "func()", then both CPU A and CPU B are * guaranteed to execute a full memory barrier during the time interval * between the call to call_rcu() and the invocation of "func()" -- even * if CPU A and CPU B are the same CPU (but again only if the system has * more than one CPU). * * Implementation of these memory-ordering guarantees is described here: * Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst. * * Specific to call_rcu() (as opposed to the other call_rcu*() functions), * in kernels built with CONFIG_RCU_LAZY=y, call_rcu() might delay for many * seconds before starting the grace period needed by the corresponding * callback. This delay can significantly improve energy-efficiency * on low-utilization battery-powered devices. To avoid this delay, * in latency-sensitive kernel code, use call_rcu_hurry(). */void call_rcu(struct rcu_head *head, rcu_callback_t func){ __call_rcu_common(head, func, enable_rcu_lazy);}EXPORT_SYMBOL_GPL(call_rcu);
/* * During early boot, any blocking grace-period wait automatically * implies a grace period. * * Later on, this could in theory be the case for kernels built with * CONFIG_SMP=y && CONFIG_PREEMPTION=y running on a single CPU, but this * is not a common case. Furthermore, this optimization would cause * the rcu_gp_oldstate structure to expand by 50%, so this potential * grace-period optimization is ignored once the scheduler is running. */static int rcu_blocking_is_gp(void){ if (rcu_scheduler_active != RCU_SCHEDULER_INACTIVE) { might_sleep(); return false; } return true;}
/* * Helper function for the synchronize_rcu() API. */static void synchronize_rcu_normal(void){ struct rcu_synchronize rs;
init_rcu_head_on_stack(&rs.head); trace_rcu_sr_normal(rcu_state.name, &rs.head, TPS("request"));
if (READ_ONCE(rcu_normal_wake_from_gp) < 1 || READ_ONCE(rcu_sr_normal_latched)) { wait_rcu_gp(call_rcu_hurry); goto trace_complete_out; }
init_completion(&rs.completion);
/* * This code might be preempted, therefore take a GP * snapshot before adding a request. */ if (IS_ENABLED(CONFIG_PROVE_RCU)) get_state_synchronize_rcu_full(&rs.oldstate);
rcu_sr_normal_add_req(&rs);
/* Kick a GP and start waiting. */ (void) start_poll_synchronize_rcu();
/* Now we can wait. */ wait_for_completion(&rs.completion);
trace_complete_out: trace_rcu_sr_normal(rcu_state.name, &rs.head, TPS("complete")); destroy_rcu_head_on_stack(&rs.head);}
/** * synchronize_rcu - wait until a grace period has elapsed. * * Control will return to the caller some time after a full grace * period has elapsed, in other words after all currently executing RCU * read-side critical sections have completed. Note, however, that * upon return from synchronize_rcu(), the caller might well be executing * concurrently with new RCU read-side critical sections that began while * synchronize_rcu() was waiting. * * RCU read-side critical sections are delimited by rcu_read_lock() * and rcu_read_unlock(), and may be nested. In addition, but only in * v5.0 and later, regions of code across which interrupts, preemption, * or softirqs have been disabled also serve as RCU read-side critical * sections. This includes hardware interrupt handlers, softirq handlers, * and NMI handlers. * * Note that this guarantee implies further memory-ordering guarantees. * On systems with more than one CPU, when synchronize_rcu() returns, * each CPU is guaranteed to have executed a full memory barrier since * the end of its last RCU read-side critical section whose beginning * preceded the call to synchronize_rcu(). In addition, each CPU having * an RCU read-side critical section that extends beyond the return from * synchronize_rcu() is guaranteed to have executed a full memory barrier * after the beginning of synchronize_rcu() and before the beginning of * that RCU read-side critical section. Note that these guarantees include * CPUs that are offline, idle, or executing in user mode, as well as CPUs * that are executing in the kernel. * * Furthermore, if CPU A invoked synchronize_rcu(), which returned * to its caller on CPU B, then both CPU A and CPU B are guaranteed * to have executed a full memory barrier during the execution of * synchronize_rcu() -- even if CPU A and CPU B are the same CPU (but * again only if the system has more than one CPU). * * Implementation of these memory-ordering guarantees is described here: * Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst. */void synchronize_rcu(void){ unsigned long flags; struct rcu_node *rnp;
RCU_LOCKDEP_WARN(lock_is_held(&rcu_bh_lock_map) || lock_is_held(&rcu_lock_map) || lock_is_held(&rcu_sched_lock_map), "Illegal synchronize_rcu() in RCU read-side critical section"); if (!rcu_blocking_is_gp()) { if (rcu_gp_is_expedited()) synchronize_rcu_expedited(); else synchronize_rcu_normal(); return; }
// Context allows vacuous grace periods. // Note well that this code runs with !PREEMPT && !SMP. // In addition, all code that advances grace periods runs at // process level. Therefore, this normal GP overlaps with other // normal GPs only by being fully nested within them, which allows // reuse of ->gp_seq_polled_snap. rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_snap); rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_snap);
// Update the normal grace-period counters to record // this grace period, but only those used by the boot CPU. // The rcu_scheduler_starting() will take care of the rest of // these counters. local_irq_save(flags); WARN_ON_ONCE(num_online_cpus() > 1); rcu_state.gp_seq += (1 << RCU_SEQ_CTR_SHIFT); for (rnp = this_cpu_ptr(&rcu_data)->mynode; rnp; rnp = rnp->parent) rnp->gp_seq_needed = rnp->gp_seq = rcu_state.gp_seq; local_irq_restore(flags);}EXPORT_SYMBOL_GPL(synchronize_rcu);
/** * get_completed_synchronize_rcu_full - Return a full pre-completed polled state cookie * @rgosp: Place to put state cookie * * Stores into @rgosp a value that will always be treated by functions * like poll_state_synchronize_rcu_full() as a cookie whose grace period * has already completed. */void get_completed_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp){ rgosp->rgos_norm = RCU_GET_STATE_COMPLETED; rgosp->rgos_exp = RCU_GET_STATE_COMPLETED;}EXPORT_SYMBOL_GPL(get_completed_synchronize_rcu_full);
/** * get_state_synchronize_rcu - Snapshot current RCU state * * Returns a cookie that is used by a later call to cond_synchronize_rcu() * or poll_state_synchronize_rcu() to determine whether or not a full * grace period has elapsed in the meantime. */unsigned long get_state_synchronize_rcu(void){ /* * Any prior manipulation of RCU-protected data must happen * before the load from ->gp_seq. */ smp_mb(); /* ^^^ */ return rcu_seq_snap(&rcu_state.gp_seq_polled);}EXPORT_SYMBOL_GPL(get_state_synchronize_rcu);
/** * get_state_synchronize_rcu_full - Snapshot RCU state, both normal and expedited * @rgosp: location to place combined normal/expedited grace-period state * * Places the normal and expedited grace-period states in @rgosp. This * state value can be passed to a later call to cond_synchronize_rcu_full() * or poll_state_synchronize_rcu_full() to determine whether or not a * grace period (whether normal or expedited) has elapsed in the meantime. * The rcu_gp_oldstate structure takes up twice the memory of an unsigned * long, but is guaranteed to see all grace periods. In contrast, the * combined state occupies less memory, but can sometimes fail to take * grace periods into account. * * This does not guarantee that the needed grace period will actually * start. */void get_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp){ /* * Any prior manipulation of RCU-protected data must happen * before the loads from ->gp_seq and ->expedited_sequence. */ smp_mb(); /* ^^^ */
// Yes, rcu_state.gp_seq, not rnp_root->gp_seq, the latter's use // in poll_state_synchronize_rcu_full() notwithstanding. Use of // the latter here would result in too-short grace periods due to // interactions with newly onlined CPUs. rgosp->rgos_norm = rcu_seq_snap(&rcu_state.gp_seq); rgosp->rgos_exp = rcu_seq_snap(&rcu_state.expedited_sequence);}EXPORT_SYMBOL_GPL(get_state_synchronize_rcu_full);
/* * Helper function for start_poll_synchronize_rcu() and * start_poll_synchronize_rcu_full(). */static void start_poll_synchronize_rcu_common(void){ unsigned long flags; bool needwake; struct rcu_data *rdp; struct rcu_node *rnp;
local_irq_save(flags); rdp = this_cpu_ptr(&rcu_data); rnp = rdp->mynode; raw_spin_lock_rcu_node(rnp); // irqs already disabled. // Note it is possible for a grace period to have elapsed between // the above call to get_state_synchronize_rcu() and the below call // to rcu_seq_snap. This is OK, the worst that happens is that we // get a grace period that no one needed. These accesses are ordered // by smp_mb(), and we are accessing them in the opposite order // from which they are updated at grace-period start, as required. needwake = rcu_start_this_gp(rnp, rdp, rcu_seq_snap(&rcu_state.gp_seq)); raw_spin_unlock_irqrestore_rcu_node(rnp, flags); if (needwake) rcu_gp_kthread_wake();}
/** * start_poll_synchronize_rcu - Snapshot and start RCU grace period * * Returns a cookie that is used by a later call to cond_synchronize_rcu() * or poll_state_synchronize_rcu() to determine whether or not a full * grace period has elapsed in the meantime. If the needed grace period * is not already slated to start, notifies RCU core of the need for that * grace period. */unsigned long start_poll_synchronize_rcu(void){ unsigned long gp_seq = get_state_synchronize_rcu();
start_poll_synchronize_rcu_common(); return gp_seq;}EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu);
/** * start_poll_synchronize_rcu_full - Take a full snapshot and start RCU grace period * @rgosp: value from get_state_synchronize_rcu_full() or start_poll_synchronize_rcu_full() * * Places the normal and expedited grace-period states in *@rgos. This * state value can be passed to a later call to cond_synchronize_rcu_full() * or poll_state_synchronize_rcu_full() to determine whether or not a * grace period (whether normal or expedited) has elapsed in the meantime. * If the needed grace period is not already slated to start, notifies * RCU core of the need for that grace period. */void start_poll_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp){ get_state_synchronize_rcu_full(rgosp);
start_poll_synchronize_rcu_common();}EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_full);
/** * poll_state_synchronize_rcu - Has the specified RCU grace period completed? * @oldstate: value from get_state_synchronize_rcu() or start_poll_synchronize_rcu() * * If a full RCU grace period has elapsed since the earlier call from * which @oldstate was obtained, return @true, otherwise return @false. * If @false is returned, it is the caller's responsibility to invoke this * function later on until it does return @true. Alternatively, the caller * can explicitly wait for a grace period, for example, by passing @oldstate * to either cond_synchronize_rcu() or cond_synchronize_rcu_expedited() * on the one hand or by directly invoking either synchronize_rcu() or * synchronize_rcu_expedited() on the other. * * Yes, this function does not take counter wrap into account. * But counter wrap is harmless. If the counter wraps, we have waited for * more than a billion grace periods (and way more on a 64-bit system!). * Those needing to keep old state values for very long time periods * (many hours even on 32-bit systems) should check them occasionally and * either refresh them or set a flag indicating that the grace period has * completed. Alternatively, they can use get_completed_synchronize_rcu() * to get a guaranteed-completed grace-period state. * * In addition, because oldstate compresses the grace-period state for * both normal and expedited grace periods into a single unsigned long, * it can miss a grace period when synchronize_rcu() runs concurrently * with synchronize_rcu_expedited(). If this is unacceptable, please * instead use the _full() variant of these polling APIs. * * This function provides the same memory-ordering guarantees that * would be provided by a synchronize_rcu() that was invoked at the call * to the function that provided @oldstate, and that returned at the end * of this function. */bool poll_state_synchronize_rcu(unsigned long oldstate){ if (oldstate == RCU_GET_STATE_COMPLETED || rcu_seq_done_exact(&rcu_state.gp_seq_polled, oldstate)) { smp_mb(); /* Ensure GP ends before subsequent accesses. */ return true; } return false;}EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu);
/** * poll_state_synchronize_rcu_full - Has the specified RCU grace period completed? * @rgosp: value from get_state_synchronize_rcu_full() or start_poll_synchronize_rcu_full() * * If a full RCU grace period has elapsed since the earlier call from * which *rgosp was obtained, return @true, otherwise return @false. * If @false is returned, it is the caller's responsibility to invoke this * function later on until it does return @true. Alternatively, the caller * can explicitly wait for a grace period, for example, by passing @rgosp * to cond_synchronize_rcu() or by directly invoking synchronize_rcu(). * * Yes, this function does not take counter wrap into account. * But counter wrap is harmless. If the counter wraps, we have waited * for more than a billion grace periods (and way more on a 64-bit * system!). Those needing to keep rcu_gp_oldstate values for very * long time periods (many hours even on 32-bit systems) should check * them occasionally and either refresh them or set a flag indicating * that the grace period has completed. Alternatively, they can use * get_completed_synchronize_rcu_full() to get a guaranteed-completed * grace-period state. * * This function provides the same memory-ordering guarantees that would * be provided by a synchronize_rcu() that was invoked at the call to * the function that provided @rgosp, and that returned at the end of this * function. And this guarantee requires that the root rcu_node structure's * ->gp_seq field be checked instead of that of the rcu_state structure. * The problem is that the just-ending grace-period's callbacks can be * invoked between the time that the root rcu_node structure's ->gp_seq * field is updated and the time that the rcu_state structure's ->gp_seq * field is updated. Therefore, if a single synchronize_rcu() is to * cause a subsequent poll_state_synchronize_rcu_full() to return @true, * then the root rcu_node structure is the one that needs to be polled. */bool poll_state_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp){ struct rcu_node *rnp = rcu_get_root();
smp_mb(); // Order against root rcu_node structure grace-period cleanup. if (rgosp->rgos_norm == RCU_GET_STATE_COMPLETED || rcu_seq_done_exact(&rnp->gp_seq, rgosp->rgos_norm) || rgosp->rgos_exp == RCU_GET_STATE_COMPLETED || rcu_seq_done_exact(&rcu_state.expedited_sequence, rgosp->rgos_exp)) { smp_mb(); /* Ensure GP ends before subsequent accesses. */ return true; } return false;}EXPORT_SYMBOL_GPL(poll_state_synchronize_rcu_full);
/** * cond_synchronize_rcu - Conditionally wait for an RCU grace period * @oldstate: value from get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or start_poll_synchronize_rcu_expedited() * * If a full RCU grace period has elapsed since the earlier call to * get_state_synchronize_rcu() or start_poll_synchronize_rcu(), just return. * Otherwise, invoke synchronize_rcu() to wait for a full grace period. * * Yes, this function does not take counter wrap into account. * But counter wrap is harmless. If the counter wraps, we have waited for * more than 2 billion grace periods (and way more on a 64-bit system!), * so waiting for a couple of additional grace periods should be just fine. * * This function provides the same memory-ordering guarantees that * would be provided by a synchronize_rcu() that was invoked at the call * to the function that provided @oldstate and that returned at the end * of this function. */void cond_synchronize_rcu(unsigned long oldstate){ if (!poll_state_synchronize_rcu(oldstate)) synchronize_rcu();}EXPORT_SYMBOL_GPL(cond_synchronize_rcu);
/** * cond_synchronize_rcu_full - Conditionally wait for an RCU grace period * @rgosp: value from get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(), or start_poll_synchronize_rcu_expedited_full() * * If a full RCU grace period has elapsed since the call to * get_state_synchronize_rcu_full(), start_poll_synchronize_rcu_full(), * or start_poll_synchronize_rcu_expedited_full() from which @rgosp was * obtained, just return. Otherwise, invoke synchronize_rcu() to wait * for a full grace period. * * Yes, this function does not take counter wrap into account. * But counter wrap is harmless. If the counter wraps, we have waited for * more than 2 billion grace periods (and way more on a 64-bit system!), * so waiting for a couple of additional grace periods should be just fine. * * This function provides the same memory-ordering guarantees that * would be provided by a synchronize_rcu() that was invoked at the call * to the function that provided @rgosp and that returned at the end of * this function. */void cond_synchronize_rcu_full(struct rcu_gp_oldstate *rgosp){ if (!poll_state_synchronize_rcu_full(rgosp)) synchronize_rcu();}EXPORT_SYMBOL_GPL(cond_synchronize_rcu_full);
/* * Check to see if there is any immediate RCU-related work to be done by * the current CPU, returning 1 if so and zero otherwise. The checks are * in order of increasing expense: checks that can be carried out against * CPU-local state are performed first. However, we must check for CPU * stalls first, else we might not get a chance. */static int rcu_pending(int user){ bool gp_in_progress; struct rcu_data *rdp = this_cpu_ptr(&rcu_data); struct rcu_node *rnp = rdp->mynode;
lockdep_assert_irqs_disabled();
/* Check for CPU stalls, if enabled. */ check_cpu_stall(rdp);
/* Does this CPU need a deferred NOCB wakeup? */ if (rcu_nocb_need_deferred_wakeup(rdp, RCU_NOCB_WAKE)) return 1;
/* Is this a nohz_full CPU in userspace or idle? (Ignore RCU if so.) */ gp_in_progress = rcu_gp_in_progress(); if ((user || rcu_is_cpu_rrupt_from_idle() || (gp_in_progress && time_before(jiffies, READ_ONCE(rcu_state.gp_start) + nohz_full_patience_delay_jiffies))) && rcu_nohz_full_cpu()) return 0;
/* Is the RCU core waiting for a quiescent state from this CPU? */ if (rdp->core_needs_qs && !rdp->cpu_no_qs.b.norm && gp_in_progress) return 1;
/* Does this CPU have callbacks ready to invoke? */ if (!rcu_rdp_is_offloaded(rdp) && rcu_segcblist_ready_cbs(&rdp->cblist)) return 1;
/* Has RCU gone idle with this CPU needing another grace period? */ if (!gp_in_progress && rcu_segcblist_is_enabled(&rdp->cblist) && !rcu_rdp_is_offloaded(rdp) && !rcu_segcblist_restempty(&rdp->cblist, RCU_NEXT_READY_TAIL)) return 1;
/* Have RCU grace period completed or started? */ if (rcu_seq_current(&rnp->gp_seq) != rdp->gp_seq || unlikely(READ_ONCE(rdp->gpwrap))) /* outside lock */ return 1;
/* nothing to do */ return 0;}
/* * Helper function for rcu_barrier() tracing. If tracing is disabled, * the compiler is expected to optimize this away. */static void rcu_barrier_trace(const char *s, int cpu, unsigned long done){ trace_rcu_barrier(rcu_state.name, s, cpu, atomic_read(&rcu_state.barrier_cpu_count), done);}
/* * RCU callback function for rcu_barrier(). If we are last, wake * up the task executing rcu_barrier(). * * Note that the value of rcu_state.barrier_sequence must be captured * before the atomic_dec_and_test(). Otherwise, if this CPU is not last, * other CPUs might count the value down to zero before this CPU gets * around to invoking rcu_barrier_trace(), which might result in bogus * data from the next instance of rcu_barrier(). */static void rcu_barrier_callback(struct rcu_head *rhp){ unsigned long __maybe_unused s = rcu_state.barrier_sequence;
rhp->next = rhp; // Mark the callback as having been invoked. if (atomic_dec_and_test(&rcu_state.barrier_cpu_count)) { rcu_barrier_trace(TPS("LastCB"), -1, s); complete(&rcu_state.barrier_completion); } else { rcu_barrier_trace(TPS("CB"), -1, s); }}
/* * If needed, entrain an rcu_barrier() callback on rdp->cblist. */static void rcu_barrier_entrain(struct rcu_data *rdp){ unsigned long gseq = READ_ONCE(rcu_state.barrier_sequence); unsigned long lseq = READ_ONCE(rdp->barrier_seq_snap); bool wake_nocb = false; bool was_alldone = false;
lockdep_assert_held(&rcu_state.barrier_lock); if (rcu_seq_state(lseq) || !rcu_seq_state(gseq) || rcu_seq_ctr(lseq) != rcu_seq_ctr(gseq)) return; rcu_barrier_trace(TPS("IRQ"), -1, rcu_state.barrier_sequence); rdp->barrier_head.func = rcu_barrier_callback; debug_rcu_head_queue(&rdp->barrier_head); rcu_nocb_lock(rdp); /* * Flush bypass and wakeup rcuog if we add callbacks to an empty regular * queue. This way we don't wait for bypass timer that can reach seconds * if it's fully lazy. */ was_alldone = rcu_rdp_is_offloaded(rdp) && !rcu_segcblist_pend_cbs(&rdp->cblist); WARN_ON_ONCE(!rcu_nocb_flush_bypass(rdp, NULL, jiffies, false)); wake_nocb = was_alldone && rcu_segcblist_pend_cbs(&rdp->cblist); if (rcu_segcblist_entrain(&rdp->cblist, &rdp->barrier_head)) { atomic_inc(&rcu_state.barrier_cpu_count); } else { debug_rcu_head_unqueue(&rdp->barrier_head); rcu_barrier_trace(TPS("IRQNQ"), -1, rcu_state.barrier_sequence); } rcu_nocb_unlock(rdp); if (wake_nocb) wake_nocb_gp(rdp); smp_store_release(&rdp->barrier_seq_snap, gseq);}
/* * Called with preemption disabled, and from cross-cpu IRQ context. */static void rcu_barrier_handler(void *cpu_in){ uintptr_t cpu = (uintptr_t)cpu_in; struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
lockdep_assert_irqs_disabled(); WARN_ON_ONCE(cpu != rdp->cpu); WARN_ON_ONCE(cpu != smp_processor_id()); raw_spin_lock(&rcu_state.barrier_lock); rcu_barrier_entrain(rdp); raw_spin_unlock(&rcu_state.barrier_lock);}
/** * rcu_barrier - Wait until all in-flight call_rcu() callbacks complete. * * Note that this primitive does not necessarily wait for an RCU grace period * to complete. For example, if there are no RCU callbacks queued anywhere * in the system, then rcu_barrier() is within its rights to return * immediately, without waiting for anything, much less an RCU grace period. * In fact, rcu_barrier() will normally not result in any RCU grace periods * beyond those that were already destined to be executed. * * In kernels built with CONFIG_RCU_LAZY=y, this function also hurries all * pending lazy RCU callbacks. */void rcu_barrier(void){ uintptr_t cpu; unsigned long flags; unsigned long gseq; struct rcu_data *rdp; unsigned long s = rcu_seq_snap(&rcu_state.barrier_sequence);
rcu_barrier_trace(TPS("Begin"), -1, s);
/* Take mutex to serialize concurrent rcu_barrier() requests. */ mutex_lock(&rcu_state.barrier_mutex);
/* Did someone else do our work for us? */ if (rcu_seq_done(&rcu_state.barrier_sequence, s)) { rcu_barrier_trace(TPS("EarlyExit"), -1, rcu_state.barrier_sequence); smp_mb(); /* caller's subsequent code after above check. */ mutex_unlock(&rcu_state.barrier_mutex); return; }
/* Mark the start of the barrier operation. */ raw_spin_lock_irqsave(&rcu_state.barrier_lock, flags); rcu_seq_start(&rcu_state.barrier_sequence); gseq = rcu_state.barrier_sequence; rcu_barrier_trace(TPS("Inc1"), -1, rcu_state.barrier_sequence);
/* * Initialize the count to two rather than to zero in order * to avoid a too-soon return to zero in case of an immediate * invocation of the just-enqueued callback (or preemption of * this task). Exclude CPU-hotplug operations to ensure that no * offline non-offloaded CPU has callbacks queued. */ init_completion(&rcu_state.barrier_completion); atomic_set(&rcu_state.barrier_cpu_count, 2); raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags);
/* * Force each CPU with callbacks to register a new callback. * When that callback is invoked, we will know that all of the * corresponding CPU's preceding callbacks have been invoked. */ for_each_possible_cpu(cpu) { rdp = per_cpu_ptr(&rcu_data, cpu);retry: if (smp_load_acquire(&rdp->barrier_seq_snap) == gseq) continue; raw_spin_lock_irqsave(&rcu_state.barrier_lock, flags); if (!rcu_segcblist_n_cbs(&rdp->cblist)) { WRITE_ONCE(rdp->barrier_seq_snap, gseq); raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags); rcu_barrier_trace(TPS("NQ"), cpu, rcu_state.barrier_sequence); continue; } if (!rcu_rdp_cpu_online(rdp)) { rcu_barrier_entrain(rdp); WARN_ON_ONCE(READ_ONCE(rdp->barrier_seq_snap) != gseq); raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags); rcu_barrier_trace(TPS("OfflineNoCBQ"), cpu, rcu_state.barrier_sequence); continue; } raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags); if (smp_call_function_single(cpu, rcu_barrier_handler, (void *)cpu, 1)) { schedule_timeout_uninterruptible(1); goto retry; } WARN_ON_ONCE(READ_ONCE(rdp->barrier_seq_snap) != gseq); rcu_barrier_trace(TPS("OnlineQ"), cpu, rcu_state.barrier_sequence); }
/* * Now that we have an rcu_barrier_callback() callback on each * CPU, and thus each counted, remove the initial count. */ if (atomic_sub_and_test(2, &rcu_state.barrier_cpu_count)) complete(&rcu_state.barrier_completion);
/* Wait for all rcu_barrier_callback() callbacks to be invoked. */ wait_for_completion(&rcu_state.barrier_completion);
/* Mark the end of the barrier operation. */ rcu_barrier_trace(TPS("Inc2"), -1, rcu_state.barrier_sequence); rcu_seq_end(&rcu_state.barrier_sequence); gseq = rcu_state.barrier_sequence; for_each_possible_cpu(cpu) { rdp = per_cpu_ptr(&rcu_data, cpu);
WRITE_ONCE(rdp->barrier_seq_snap, gseq); }
/* Other rcu_barrier() invocations can now safely proceed. */ mutex_unlock(&rcu_state.barrier_mutex);}EXPORT_SYMBOL_GPL(rcu_barrier);
static unsigned long rcu_barrier_last_throttle;
/** * rcu_barrier_throttled - Do rcu_barrier(), but limit to one per second * * This can be thought of as guard rails around rcu_barrier() that * permits unrestricted userspace use, at least assuming the hardware's * try_cmpxchg() is robust. There will be at most one call per second to * rcu_barrier() system-wide from use of this function, which means that * callers might needlessly wait a second or three. * * This is intended for use by test suites to avoid OOM by flushing RCU * callbacks from the previous test before starting the next. See the * rcutree.do_rcu_barrier module parameter for more information. * * Why not simply make rcu_barrier() more scalable? That might be * the eventual endpoint, but let's keep it simple for the time being. * Note that the module parameter infrastructure serializes calls to a * given .set() function, but should concurrent .set() invocation ever be * possible, we are ready! */static void rcu_barrier_throttled(void){ unsigned long j = jiffies; unsigned long old = READ_ONCE(rcu_barrier_last_throttle); unsigned long s = rcu_seq_snap(&rcu_state.barrier_sequence);
while (time_in_range(j, old, old + HZ / 16) || !try_cmpxchg(&rcu_barrier_last_throttle, &old, j)) { schedule_timeout_idle(HZ / 16); if (rcu_seq_done(&rcu_state.barrier_sequence, s)) { smp_mb(); /* caller's subsequent code after above check. */ return; } j = jiffies; old = READ_ONCE(rcu_barrier_last_throttle); } rcu_barrier();}
/* * Invoke rcu_barrier_throttled() when a rcutree.do_rcu_barrier * request arrives. We insist on a true value to allow for possible * future expansion. */static int param_set_do_rcu_barrier(const char *val, const struct kernel_param *kp){ bool b; int ret;
if (rcu_scheduler_active != RCU_SCHEDULER_RUNNING) return -EAGAIN; ret = kstrtobool(val, &b); if (!ret && b) { atomic_inc((atomic_t *)kp->arg); rcu_barrier_throttled(); atomic_dec((atomic_t *)kp->arg); } return ret;}
/* * Output the number of outstanding rcutree.do_rcu_barrier requests. */static int param_get_do_rcu_barrier(char *buffer, const struct kernel_param *kp){ return sprintf(buffer, "%d\n", atomic_read((atomic_t *)kp->arg));}
static const struct kernel_param_ops do_rcu_barrier_ops = { .set = param_set_do_rcu_barrier, .get = param_get_do_rcu_barrier,};static atomic_t do_rcu_barrier;module_param_cb(do_rcu_barrier, &do_rcu_barrier_ops, &do_rcu_barrier, 0644);
/* * Compute the mask of online CPUs for the specified rcu_node structure. * This will not be stable unless the rcu_node structure's ->lock is * held, but the bit corresponding to the current CPU will be stable * in most contexts. */static unsigned long rcu_rnp_online_cpus(struct rcu_node *rnp){ return READ_ONCE(rnp->qsmaskinitnext);}
/* * Is the CPU corresponding to the specified rcu_data structure online * from RCU's perspective? This perspective is given by that structure's * ->qsmaskinitnext field rather than by the global cpu_online_mask. */static bool rcu_rdp_cpu_online(struct rcu_data *rdp){ return !!(rdp->grpmask & rcu_rnp_online_cpus(rdp->mynode));}
bool rcu_cpu_online(int cpu){ struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
return rcu_rdp_cpu_online(rdp);}
#if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU)
/* * Is the current CPU online as far as RCU is concerned? * * Disable preemption to avoid false positives that could otherwise * happen due to the current CPU number being sampled, this task being * preempted, its old CPU being taken offline, resuming on some other CPU, * then determining that its old CPU is now offline. * * Disable checking if in an NMI handler because we cannot safely * report errors from NMI handlers anyway. In addition, it is OK to use * RCU on an offline processor during initial boot, hence the check for * rcu_scheduler_fully_active. */bool notrace rcu_lockdep_current_cpu_online(void){ struct rcu_data *rdp; bool ret = false;
if (in_nmi() || !rcu_scheduler_fully_active) return true; preempt_disable_notrace(); rdp = this_cpu_ptr(&rcu_data); /* * Strictly, we care here about the case where the current CPU is * in rcutree_report_cpu_starting() and thus has an excuse for rdp->grpmask * not being up to date. So arch_spin_is_locked() might have a * false positive if it's held by some *other* CPU, but that's * OK because that just means a false *negative* on the warning. */ if (rcu_rdp_cpu_online(rdp) || arch_spin_is_locked(&rcu_state.ofl_lock)) ret = true; preempt_enable_notrace(); return ret;}EXPORT_SYMBOL_GPL(rcu_lockdep_current_cpu_online);
#endif /* #if defined(CONFIG_PROVE_RCU) && defined(CONFIG_HOTPLUG_CPU) */
// Has rcu_init() been invoked? This is used (for example) to determine// whether spinlocks may be acquired safely.static bool rcu_init_invoked(void){ return !!READ_ONCE(rcu_state.n_online_cpus);}
/* * All CPUs for the specified rcu_node structure have gone offline, * and all tasks that were preempted within an RCU read-side critical * section while running on one of those CPUs have since exited their RCU * read-side critical section. Some other CPU is reporting this fact with * the specified rcu_node structure's ->lock held and interrupts disabled. * This function therefore goes up the tree of rcu_node structures, * clearing the corresponding bits in the ->qsmaskinit fields. Note that * the leaf rcu_node structure's ->qsmaskinit field has already been * updated. * * This function does check that the specified rcu_node structure has * all CPUs offline and no blocked tasks, so it is OK to invoke it * prematurely. That said, invoking it after the fact will cost you * a needless lock acquisition. So once it has done its work, don't * invoke it again. */static void rcu_cleanup_dead_rnp(struct rcu_node *rnp_leaf){ long mask; struct rcu_node *rnp = rnp_leaf;
raw_lockdep_assert_held_rcu_node(rnp_leaf); if (!IS_ENABLED(CONFIG_HOTPLUG_CPU) || WARN_ON_ONCE(rnp_leaf->qsmaskinit) || WARN_ON_ONCE(rcu_preempt_has_tasks(rnp_leaf))) return; for (;;) { mask = rnp->grpmask; rnp = rnp->parent; if (!rnp) break; raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ rnp->qsmaskinit &= ~mask; /* Between grace periods, so better already be zero! */ WARN_ON_ONCE(rnp->qsmask); if (rnp->qsmaskinit) { raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ return; } raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */ }}
/* * Propagate ->qsinitmask bits up the rcu_node tree to account for the * first CPU in a given leaf rcu_node structure coming online. The caller * must hold the corresponding leaf rcu_node ->lock with interrupts * disabled. */static void rcu_init_new_rnp(struct rcu_node *rnp_leaf){ long mask; long oldmask; struct rcu_node *rnp = rnp_leaf;
raw_lockdep_assert_held_rcu_node(rnp_leaf); WARN_ON_ONCE(rnp->wait_blkd_tasks); for (;;) { mask = rnp->grpmask; rnp = rnp->parent; if (rnp == NULL) return; raw_spin_lock_rcu_node(rnp); /* Interrupts already disabled. */ oldmask = rnp->qsmaskinit; rnp->qsmaskinit |= mask; raw_spin_unlock_rcu_node(rnp); /* Interrupts remain disabled. */ if (oldmask) return; }}
/* * Do boot-time initialization of a CPU's per-CPU RCU data. */static void __initrcu_boot_init_percpu_data(int cpu){ struct context_tracking *ct = this_cpu_ptr(&context_tracking); struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
/* Set up local state, ensuring consistent view of global state. */ rdp->grpmask = leaf_node_cpu_bit(rdp->mynode, cpu); INIT_WORK(&rdp->strict_work, strict_work_handler); WARN_ON_ONCE(ct->nesting != 1); WARN_ON_ONCE(rcu_watching_snap_in_eqs(ct_rcu_watching_cpu(cpu))); rdp->barrier_seq_snap = rcu_state.barrier_sequence; rdp->rcu_ofl_gp_seq = rcu_state.gp_seq; rdp->rcu_ofl_gp_state = RCU_GP_CLEANED; rdp->rcu_onl_gp_seq = rcu_state.gp_seq; rdp->rcu_onl_gp_state = RCU_GP_CLEANED; rdp->last_sched_clock = jiffies; rdp->cpu = cpu; rcu_boot_init_nocb_percpu_data(rdp);}
static void rcu_thread_affine_rnp(struct task_struct *t, struct rcu_node *rnp){ cpumask_var_t affinity; int cpu;
if (!zalloc_cpumask_var(&affinity, GFP_KERNEL)) return;
for_each_leaf_node_possible_cpu(rnp, cpu) cpumask_set_cpu(cpu, affinity);
kthread_affine_preferred(t, affinity);
free_cpumask_var(affinity);}
struct kthread_worker *rcu_exp_gp_kworker;
static void rcu_spawn_exp_par_gp_kworker(struct rcu_node *rnp){ struct kthread_worker *kworker; const char *name = "rcu_exp_par_gp_kthread_worker/%d"; struct sched_param param = { .sched_priority = kthread_prio }; int rnp_index = rnp - rcu_get_root();
if (rnp->exp_kworker) return;
kworker = kthread_create_worker(0, name, rnp_index); if (IS_ERR_OR_NULL(kworker)) { pr_err("Failed to create par gp kworker on %d/%d\n", rnp->grplo, rnp->grphi); return; } WRITE_ONCE(rnp->exp_kworker, kworker);
if (IS_ENABLED(CONFIG_RCU_EXP_KTHREAD)) sched_setscheduler_nocheck(kworker->task, SCHED_FIFO, ¶m);
rcu_thread_affine_rnp(kworker->task, rnp); wake_up_process(kworker->task);}
static void __init rcu_start_exp_gp_kworker(void){ const char *name = "rcu_exp_gp_kthread_worker"; struct sched_param param = { .sched_priority = kthread_prio };
rcu_exp_gp_kworker = kthread_run_worker(0, name); if (IS_ERR_OR_NULL(rcu_exp_gp_kworker)) { pr_err("Failed to create %s!\n", name); rcu_exp_gp_kworker = NULL; return; }
if (IS_ENABLED(CONFIG_RCU_EXP_KTHREAD)) sched_setscheduler_nocheck(rcu_exp_gp_kworker->task, SCHED_FIFO, ¶m);}
static void rcu_spawn_rnp_kthreads(struct rcu_node *rnp){ if (rcu_scheduler_fully_active) { mutex_lock(&rnp->kthread_mutex); rcu_spawn_one_boost_kthread(rnp); rcu_spawn_exp_par_gp_kworker(rnp); mutex_unlock(&rnp->kthread_mutex); }}
/* * Invoked early in the CPU-online process, when pretty much all services * are available. The incoming CPU is not present. * * Initializes a CPU's per-CPU RCU data. Note that only one online or * offline event can be happening at a given time. Note also that we can * accept some slop in the rsp->gp_seq access due to the fact that this * CPU cannot possibly have any non-offloaded RCU callbacks in flight yet. * And any offloaded callbacks are being numbered elsewhere. */int rcutree_prepare_cpu(unsigned int cpu){ unsigned long flags; struct context_tracking *ct = per_cpu_ptr(&context_tracking, cpu); struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); struct rcu_node *rnp = rcu_get_root();
/* Set up local state, ensuring consistent view of global state. */ raw_spin_lock_irqsave_rcu_node(rnp, flags); rdp->qlen_last_fqs_check = 0; rdp->n_force_qs_snap = READ_ONCE(rcu_state.n_force_qs); rdp->blimit = blimit; ct->nesting = 1; /* CPU not up, no tearing. */ raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled. */
/* * Only non-NOCB CPUs that didn't have early-boot callbacks need to be * (re-)initialized. */ if (!rcu_segcblist_is_enabled(&rdp->cblist)) rcu_segcblist_init(&rdp->cblist); /* Re-enable callbacks. */
/* * Add CPU to leaf rcu_node pending-online bitmask. Any needed * propagation up the rcu_node tree will happen at the beginning * of the next grace period. */ rnp = rdp->mynode; raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */ rdp->gp_seq = READ_ONCE(rnp->gp_seq); rdp->gp_seq_needed = rdp->gp_seq; rdp->cpu_no_qs.b.norm = true; rdp->core_needs_qs = false; rdp->rcu_iw_pending = false; rdp->rcu_iw = IRQ_WORK_INIT_HARD(rcu_iw_handler); rdp->rcu_iw_gp_seq = rdp->gp_seq - 1; trace_rcu_grace_period(rcu_state.name, rdp->gp_seq, TPS("cpuonl")); raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
rcu_preempt_deferred_qs_init(rdp); rcu_spawn_rnp_kthreads(rnp); rcu_spawn_cpu_nocb_kthread(cpu); ASSERT_EXCLUSIVE_WRITER(rcu_state.n_online_cpus); WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus + 1);
return 0;}
/* * Has the specified (known valid) CPU ever been fully online? */bool rcu_cpu_beenfullyonline(int cpu){ struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu);
return smp_load_acquire(&rdp->beenonline);}
/* * Near the end of the CPU-online process. Pretty much all services * enabled, and the CPU is now very much alive. */int rcutree_online_cpu(unsigned int cpu){ unsigned long flags; struct rcu_data *rdp; struct rcu_node *rnp;
rdp = per_cpu_ptr(&rcu_data, cpu); rnp = rdp->mynode; raw_spin_lock_irqsave_rcu_node(rnp, flags); rnp->ffmask |= rdp->grpmask; raw_spin_unlock_irqrestore_rcu_node(rnp, flags); if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE) return 0; /* Too early in boot for scheduler work. */
// Stop-machine done, so allow nohz_full to disable tick. tick_dep_clear(TICK_DEP_BIT_RCU); return 0;}
/* * Mark the specified CPU as being online so that subsequent grace periods * (both expedited and normal) will wait on it. Note that this means that * incoming CPUs are not allowed to use RCU read-side critical sections * until this function is called. Failing to observe this restriction * will result in lockdep splats. * * Note that this function is special in that it is invoked directly * from the incoming CPU rather than from the cpuhp_step mechanism. * This is because this function must be invoked at a precise location. * This incoming CPU must not have enabled interrupts yet. * * This mirrors the effects of rcutree_report_cpu_dead(). */void rcutree_report_cpu_starting(unsigned int cpu){ unsigned long mask; struct rcu_data *rdp; struct rcu_node *rnp; bool newcpu;
lockdep_assert_irqs_disabled(); rdp = per_cpu_ptr(&rcu_data, cpu); if (rdp->cpu_started) return; rdp->cpu_started = true;
rnp = rdp->mynode; mask = rdp->grpmask; arch_spin_lock(&rcu_state.ofl_lock); rcu_watching_online(); raw_spin_lock(&rcu_state.barrier_lock); raw_spin_lock_rcu_node(rnp); WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext | mask); raw_spin_unlock(&rcu_state.barrier_lock); newcpu = !(rnp->expmaskinitnext & mask); rnp->expmaskinitnext |= mask; /* Allow lockless access for expedited grace periods. */ smp_store_release(&rcu_state.ncpus, rcu_state.ncpus + newcpu); /* ^^^ */ ASSERT_EXCLUSIVE_WRITER(rcu_state.ncpus); rcu_gpnum_ovf(rnp, rdp); /* Offline-induced counter wrap? */ rdp->rcu_onl_gp_seq = READ_ONCE(rcu_state.gp_seq); rdp->rcu_onl_gp_state = READ_ONCE(rcu_state.gp_state);
/* An incoming CPU should never be blocking a grace period. */ if (WARN_ON_ONCE(rnp->qsmask & mask)) { /* RCU waiting on incoming CPU? */ /* rcu_report_qs_rnp() *really* wants some flags to restore */ unsigned long flags;
local_irq_save(flags); rcu_disable_urgency_upon_qs(rdp); /* Report QS -after- changing ->qsmaskinitnext! */ rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags); } else { raw_spin_unlock_rcu_node(rnp); } arch_spin_unlock(&rcu_state.ofl_lock); smp_store_release(&rdp->beenonline, true); smp_mb(); /* Ensure RCU read-side usage follows above initialization. */}
/* * The outgoing function has no further need of RCU, so remove it from * the rcu_node tree's ->qsmaskinitnext bit masks. * * Note that this function is special in that it is invoked directly * from the outgoing CPU rather than from the cpuhp_step mechanism. * This is because this function must be invoked at a precise location. * * This mirrors the effect of rcutree_report_cpu_starting(). */void rcutree_report_cpu_dead(void){ unsigned long flags; unsigned long mask; struct rcu_data *rdp = this_cpu_ptr(&rcu_data); struct rcu_node *rnp = rdp->mynode; /* Outgoing CPU's rdp & rnp. */
/* * IRQS must be disabled from now on and until the CPU dies, or an interrupt * may introduce a new READ-side while it is actually off the QS masks. */ lockdep_assert_irqs_disabled(); /* * CPUHP_AP_SMPCFD_DYING was the last call for rcu_exp_handler() execution. * The requested QS must have been reported on the last context switch * from stop machine to idle. */ WARN_ON_ONCE(rdp->cpu_no_qs.b.exp); // Do any dangling deferred wakeups. do_nocb_deferred_wakeup(rdp);
rcu_preempt_deferred_qs(current);
/* Remove outgoing CPU from mask in the leaf rcu_node structure. */ mask = rdp->grpmask;
/* * Hold the ofl_lock and rnp lock to avoid races between CPU going * offline and doing a QS report (as below), versus rcu_gp_init(). * See Requirements.rst > Hotplug CPU > Concurrent QS Reporting section * for more details. */ arch_spin_lock(&rcu_state.ofl_lock); raw_spin_lock_irqsave_rcu_node(rnp, flags); /* Enforce GP memory-order guarantee. */ rdp->rcu_ofl_gp_seq = READ_ONCE(rcu_state.gp_seq); rdp->rcu_ofl_gp_state = READ_ONCE(rcu_state.gp_state); if (rnp->qsmask & mask) { /* RCU waiting on outgoing CPU? */ /* Report quiescent state -before- changing ->qsmaskinitnext! */ rcu_disable_urgency_upon_qs(rdp); rcu_report_qs_rnp(mask, rnp, rnp->gp_seq, flags); raw_spin_lock_irqsave_rcu_node(rnp, flags); } /* Clear from ->qsmaskinitnext to mark offline. */ WRITE_ONCE(rnp->qsmaskinitnext, rnp->qsmaskinitnext & ~mask); raw_spin_unlock_irqrestore_rcu_node(rnp, flags); arch_spin_unlock(&rcu_state.ofl_lock); rdp->cpu_started = false;}
#ifdef CONFIG_HOTPLUG_CPU/* * The outgoing CPU has just passed through the dying-idle state, and we * are being invoked from the CPU that was IPIed to continue the offline * operation. Migrate the outgoing CPU's callbacks to the current CPU. */void rcutree_migrate_callbacks(int cpu){ unsigned long flags; struct rcu_data *my_rdp; struct rcu_node *my_rnp; struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); bool needwake;
if (rcu_rdp_is_offloaded(rdp)) return;
raw_spin_lock_irqsave(&rcu_state.barrier_lock, flags); if (rcu_segcblist_empty(&rdp->cblist)) { raw_spin_unlock_irqrestore(&rcu_state.barrier_lock, flags); return; /* No callbacks to migrate. */ }
WARN_ON_ONCE(rcu_rdp_cpu_online(rdp)); rcu_barrier_entrain(rdp); my_rdp = this_cpu_ptr(&rcu_data); my_rnp = my_rdp->mynode; rcu_nocb_lock(my_rdp); /* irqs already disabled. */ WARN_ON_ONCE(!rcu_nocb_flush_bypass(my_rdp, NULL, jiffies, false)); raw_spin_lock_rcu_node(my_rnp); /* irqs already disabled. */ /* Leverage recent GPs and set GP for new callbacks. */ needwake = rcu_advance_cbs(my_rnp, rdp) || rcu_advance_cbs(my_rnp, my_rdp); rcu_segcblist_merge(&my_rdp->cblist, &rdp->cblist); raw_spin_unlock(&rcu_state.barrier_lock); /* irqs remain disabled. */ needwake = needwake || rcu_advance_cbs(my_rnp, my_rdp); rcu_segcblist_disable(&rdp->cblist); WARN_ON_ONCE(rcu_segcblist_empty(&my_rdp->cblist) != !rcu_segcblist_n_cbs(&my_rdp->cblist)); check_cb_ovld_locked(my_rdp, my_rnp); if (rcu_rdp_is_offloaded(my_rdp)) { raw_spin_unlock_rcu_node(my_rnp); /* irqs remain disabled. */ __call_rcu_nocb_wake(my_rdp, true, flags); } else { rcu_nocb_unlock(my_rdp); /* irqs remain disabled. */ raw_spin_unlock_rcu_node(my_rnp); /* irqs remain disabled. */ } local_irq_restore(flags); if (needwake) rcu_gp_kthread_wake(); lockdep_assert_irqs_enabled(); WARN_ONCE(rcu_segcblist_n_cbs(&rdp->cblist) != 0 || !rcu_segcblist_empty(&rdp->cblist), "rcu_cleanup_dead_cpu: Callbacks on offline CPU %d: qlen=%lu, 1stCB=%p\n", cpu, rcu_segcblist_n_cbs(&rdp->cblist), rcu_segcblist_first_cb(&rdp->cblist));}
/* * The CPU has been completely removed, and some other CPU is reporting * this fact from process context. Do the remainder of the cleanup. * There can only be one CPU hotplug operation at a time, so no need for * explicit locking. */int rcutree_dead_cpu(unsigned int cpu){ ASSERT_EXCLUSIVE_WRITER(rcu_state.n_online_cpus); WRITE_ONCE(rcu_state.n_online_cpus, rcu_state.n_online_cpus - 1); // Stop-machine done, so allow nohz_full to disable tick. tick_dep_clear(TICK_DEP_BIT_RCU); return 0;}
/* * Near the end of the offline process. Trace the fact that this CPU * is going offline. */int rcutree_dying_cpu(unsigned int cpu){ bool blkd; struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); struct rcu_node *rnp = rdp->mynode;
blkd = !!(READ_ONCE(rnp->qsmask) & rdp->grpmask); trace_rcu_grace_period(rcu_state.name, READ_ONCE(rnp->gp_seq), blkd ? TPS("cpuofl-bgp") : TPS("cpuofl")); return 0;}
/* * Near the beginning of the process. The CPU is still very much alive * with pretty much all services enabled. */int rcutree_offline_cpu(unsigned int cpu){ unsigned long flags; struct rcu_data *rdp; struct rcu_node *rnp;
rdp = per_cpu_ptr(&rcu_data, cpu); rnp = rdp->mynode; raw_spin_lock_irqsave_rcu_node(rnp, flags); rnp->ffmask &= ~rdp->grpmask; raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
// nohz_full CPUs need the tick for stop-machine to work quickly tick_dep_set(TICK_DEP_BIT_RCU); return 0;}#endif /* #ifdef CONFIG_HOTPLUG_CPU */
/* * On non-huge systems, use expedited RCU grace periods to make suspend * and hibernation run faster. */static int rcu_pm_notify(struct notifier_block *self, unsigned long action, void *hcpu){ switch (action) { case PM_HIBERNATION_PREPARE: case PM_SUSPEND_PREPARE: rcu_async_hurry(); rcu_expedite_gp(); break; case PM_POST_HIBERNATION: case PM_POST_SUSPEND: rcu_unexpedite_gp(); rcu_async_relax(); break; default: break; } return NOTIFY_OK;}
/* * Spawn the kthreads that handle RCU's grace periods. */static int __init rcu_spawn_gp_kthread(void){ unsigned long flags; struct rcu_node *rnp; struct sched_param sp; struct task_struct *t; struct rcu_data *rdp = this_cpu_ptr(&rcu_data);
rcu_scheduler_fully_active = 1; t = kthread_create(rcu_gp_kthread, NULL, "%s", rcu_state.name); if (WARN_ONCE(IS_ERR(t), "%s: Could not start grace-period kthread, OOM is now expected behavior\n", __func__)) return 0; if (kthread_prio) { sp.sched_priority = kthread_prio; sched_setscheduler_nocheck(t, SCHED_FIFO, &sp); } rnp = rcu_get_root(); raw_spin_lock_irqsave_rcu_node(rnp, flags); WRITE_ONCE(rcu_state.gp_activity, jiffies); WRITE_ONCE(rcu_state.gp_req_activity, jiffies); // Reset .gp_activity and .gp_req_activity before setting .gp_kthread. smp_store_release(&rcu_state.gp_kthread, t); /* ^^^ */ raw_spin_unlock_irqrestore_rcu_node(rnp, flags); wake_up_process(t); /* This is a pre-SMP initcall, we expect a single CPU */ WARN_ON(num_online_cpus() > 1); /* * Those kthreads couldn't be created on rcu_init() -> rcutree_prepare_cpu() * due to rcu_scheduler_fully_active. */ rcu_spawn_cpu_nocb_kthread(smp_processor_id()); rcu_spawn_rnp_kthreads(rdp->mynode); rcu_spawn_core_kthreads(); /* Create kthread worker for expedited GPs */ rcu_start_exp_gp_kworker(); return 0;}early_initcall(rcu_spawn_gp_kthread);
/* * This function is invoked towards the end of the scheduler's * initialization process. Before this is called, the idle task might * contain synchronous grace-period primitives (during which time, this idle * task is booting the system, and such primitives are no-ops). After this * function is called, any synchronous grace-period primitives are run as * expedited, with the requesting task driving the grace period forward. * A later core_initcall() rcu_set_runtime_mode() will switch to full * runtime RCU functionality. */void rcu_scheduler_starting(void){ unsigned long flags; struct rcu_node *rnp;
WARN_ON(num_online_cpus() != 1); WARN_ON(nr_context_switches() > 0); rcu_test_sync_prims();
// Fix up the ->gp_seq counters. local_irq_save(flags); rcu_for_each_node_breadth_first(rnp) rnp->gp_seq_needed = rnp->gp_seq = rcu_state.gp_seq; local_irq_restore(flags);
// Switch out of early boot mode. rcu_scheduler_active = RCU_SCHEDULER_INIT; rcu_test_sync_prims();}
/* * Helper function for rcu_init() that initializes the rcu_state structure. */static void __init rcu_init_one(void){ static const char * const buf[] = RCU_NODE_NAME_INIT; static const char * const fqs[] = RCU_FQS_NAME_INIT; static struct lock_class_key rcu_node_class[RCU_NUM_LVLS]; static struct lock_class_key rcu_fqs_class[RCU_NUM_LVLS];
int levelspread[RCU_NUM_LVLS]; /* kids/node in each level. */ int cpustride = 1; int i; int j; struct rcu_node *rnp;
BUILD_BUG_ON(RCU_NUM_LVLS > ARRAY_SIZE(buf)); /* Fix buf[] init! */
/* Silence gcc 4.8 false positive about array index out of range. */ if (rcu_num_lvls <= 0 || rcu_num_lvls > RCU_NUM_LVLS) panic("rcu_init_one: rcu_num_lvls out of range");
/* Initialize the level-tracking arrays. */
for (i = 1; i < rcu_num_lvls; i++) rcu_state.level[i] = rcu_state.level[i - 1] + num_rcu_lvl[i - 1]; rcu_init_levelspread(levelspread, num_rcu_lvl);
/* Initialize the elements themselves, starting from the leaves. */
for (i = rcu_num_lvls - 1; i >= 0; i--) { cpustride *= levelspread[i]; rnp = rcu_state.level[i]; for (j = 0; j < num_rcu_lvl[i]; j++, rnp++) { raw_spin_lock_init(&ACCESS_PRIVATE(rnp, lock)); lockdep_set_class_and_name(&ACCESS_PRIVATE(rnp, lock), &rcu_node_class[i], buf[i]); raw_spin_lock_init(&rnp->fqslock); lockdep_set_class_and_name(&rnp->fqslock, &rcu_fqs_class[i], fqs[i]); rnp->gp_seq = rcu_state.gp_seq; rnp->gp_seq_needed = rcu_state.gp_seq; rnp->completedqs = rcu_state.gp_seq; rnp->qsmask = 0; rnp->qsmaskinit = 0; rnp->grplo = j * cpustride; rnp->grphi = (j + 1) * cpustride - 1; if (rnp->grphi >= nr_cpu_ids) rnp->grphi = nr_cpu_ids - 1; if (i == 0) { rnp->grpnum = 0; rnp->grpmask = 0; rnp->parent = NULL; } else { rnp->grpnum = j % levelspread[i - 1]; rnp->grpmask = BIT(rnp->grpnum); rnp->parent = rcu_state.level[i - 1] + j / levelspread[i - 1]; } rnp->level = i; INIT_LIST_HEAD(&rnp->blkd_tasks); rcu_init_one_nocb(rnp); init_waitqueue_head(&rnp->exp_wq[0]); init_waitqueue_head(&rnp->exp_wq[1]); init_waitqueue_head(&rnp->exp_wq[2]); init_waitqueue_head(&rnp->exp_wq[3]); spin_lock_init(&rnp->exp_lock); mutex_init(&rnp->kthread_mutex); raw_spin_lock_init(&rnp->exp_poll_lock); rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED; INIT_WORK(&rnp->exp_poll_wq, sync_rcu_do_polled_gp); } }
init_swait_queue_head(&rcu_state.gp_wq); init_swait_queue_head(&rcu_state.expedited_wq); rnp = rcu_first_leaf_node(); for_each_possible_cpu(i) { while (i > rnp->grphi) rnp++; per_cpu_ptr(&rcu_data, i)->mynode = rnp; per_cpu_ptr(&rcu_data, i)->barrier_head.next = &per_cpu_ptr(&rcu_data, i)->barrier_head; rcu_boot_init_percpu_data(i); }}
/* * Force priority from the kernel command-line into range. */static void __init sanitize_kthread_prio(void){ int kthread_prio_in = kthread_prio;
if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 2 && IS_BUILTIN(CONFIG_RCU_TORTURE_TEST)) kthread_prio = 2; else if (IS_ENABLED(CONFIG_RCU_BOOST) && kthread_prio < 1) kthread_prio = 1; else if (kthread_prio < 0) kthread_prio = 0; else if (kthread_prio > 99) kthread_prio = 99;
if (kthread_prio != kthread_prio_in) pr_alert("%s: Limited prio to %d from %d\n", __func__, kthread_prio, kthread_prio_in);}
/* * Compute the rcu_node tree geometry from kernel parameters. This cannot * replace the definitions in tree.h because those are needed to size * the ->node array in the rcu_state structure. */void rcu_init_geometry(void){ ulong d; int i; static unsigned long old_nr_cpu_ids; int rcu_capacity[RCU_NUM_LVLS]; static bool initialized;
if (initialized) { /* * Warn if setup_nr_cpu_ids() had not yet been invoked, * unless nr_cpus_ids == NR_CPUS, in which case who cares? */ WARN_ON_ONCE(old_nr_cpu_ids != nr_cpu_ids); return; }
old_nr_cpu_ids = nr_cpu_ids; initialized = true;
/* * Initialize any unspecified boot parameters. * The default values of jiffies_till_first_fqs and * jiffies_till_next_fqs are set to the RCU_JIFFIES_TILL_FORCE_QS * value, which is a function of HZ, then adding one for each * RCU_JIFFIES_FQS_DIV CPUs that might be on the system. */ d = RCU_JIFFIES_TILL_FORCE_QS + nr_cpu_ids / RCU_JIFFIES_FQS_DIV; if (jiffies_till_first_fqs == ULONG_MAX) jiffies_till_first_fqs = d; if (jiffies_till_next_fqs == ULONG_MAX) jiffies_till_next_fqs = d; adjust_jiffies_till_sched_qs();
/* If the compile-time values are accurate, just leave. */ if (rcu_fanout_leaf == RCU_FANOUT_LEAF && nr_cpu_ids == NR_CPUS) return; pr_info("Adjusting geometry for rcu_fanout_leaf=%d, nr_cpu_ids=%u\n", rcu_fanout_leaf, nr_cpu_ids);
/* * The boot-time rcu_fanout_leaf parameter must be at least two * and cannot exceed the number of bits in the rcu_node masks. * Complain and fall back to the compile-time values if this * limit is exceeded. */ if (rcu_fanout_leaf < 2 || rcu_fanout_leaf > BITS_PER_LONG) { rcu_fanout_leaf = RCU_FANOUT_LEAF; WARN_ON(1); return; }
/* * Compute number of nodes that can be handled an rcu_node tree * with the given number of levels. */ rcu_capacity[0] = rcu_fanout_leaf; for (i = 1; i < RCU_NUM_LVLS; i++) rcu_capacity[i] = rcu_capacity[i - 1] * RCU_FANOUT;
/* * The tree must be able to accommodate the configured number of CPUs. * If this limit is exceeded, fall back to the compile-time values. */ if (nr_cpu_ids > rcu_capacity[RCU_NUM_LVLS - 1]) { rcu_fanout_leaf = RCU_FANOUT_LEAF; WARN_ON(1); return; }
/* Calculate the number of levels in the tree. */ for (i = 0; nr_cpu_ids > rcu_capacity[i]; i++) { } rcu_num_lvls = i + 1;
/* Calculate the number of rcu_nodes at each level of the tree. */ for (i = 0; i < rcu_num_lvls; i++) { int cap = rcu_capacity[(rcu_num_lvls - 1) - i]; num_rcu_lvl[i] = DIV_ROUND_UP(nr_cpu_ids, cap); }
/* Calculate the total number of rcu_node structures. */ rcu_num_nodes = 0; for (i = 0; i < rcu_num_lvls; i++) rcu_num_nodes += num_rcu_lvl[i];}
/* * Dump out the structure of the rcu_node combining tree associated * with the rcu_state structure. */static void __init rcu_dump_rcu_node_tree(void){ int level = 0; struct rcu_node *rnp;
pr_info("rcu_node tree layout dump\n"); pr_info(" "); rcu_for_each_node_breadth_first(rnp) { if (rnp->level != level) { pr_cont("\n"); pr_info(" "); level = rnp->level; } pr_cont("%d:%d ^%d ", rnp->grplo, rnp->grphi, rnp->grpnum); } pr_cont("\n");}
struct workqueue_struct *rcu_gp_wq;
void __init rcu_init(void){ int cpu = smp_processor_id();
rcu_early_boot_tests();
rcu_bootup_announce(); sanitize_kthread_prio(); rcu_init_geometry(); rcu_init_one(); if (dump_tree) rcu_dump_rcu_node_tree(); if (use_softirq) open_softirq(RCU_SOFTIRQ, rcu_core_si);
/* * We don't need protection against CPU-hotplug here because * this is called early in boot, before either interrupts * or the scheduler are operational. */ pm_notifier(rcu_pm_notify, 0); WARN_ON(num_online_cpus() > 1); // Only one CPU this early in boot. rcutree_prepare_cpu(cpu); rcutree_report_cpu_starting(cpu); rcutree_online_cpu(cpu);
/* Create workqueue for Tree SRCU and for expedited GPs. */ rcu_gp_wq = alloc_workqueue("rcu_gp", WQ_MEM_RECLAIM | WQ_PERCPU, 0); WARN_ON(!rcu_gp_wq);
sync_wq = alloc_workqueue("sync_wq", WQ_MEM_RECLAIM | WQ_UNBOUND, 0); WARN_ON(!sync_wq);
/* Fill in default value for rcutree.qovld boot parameter. */ /* -After- the rcu_node ->lock fields are initialized! */ if (qovld < 0) qovld_calc = DEFAULT_RCU_QOVLD_MULT * qhimark; else qovld_calc = qovld;
// Kick-start in case any polled grace periods started early. (void)start_poll_synchronize_rcu_expedited();
rcu_test_sync_prims();
tasks_cblist_init_generic();}
#include "tree_stall.h"#include "tree_exp.h"#include "tree_nocb.h"#include "tree_plugin.h"