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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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#include <linux/console.h>#include <linux/lockdep.h>
static void rcu_exp_handler(void *unused);static int rcu_print_task_exp_stall(struct rcu_node *rnp);static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp);
/* * Record the start of an expedited grace period. */static void rcu_exp_gp_seq_start(void){ rcu_seq_start(&rcu_state.expedited_sequence); rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_exp_snap);}
/* * Return the value that the expedited-grace-period counter will have * at the end of the current grace period. */static __maybe_unused unsigned long rcu_exp_gp_seq_endval(void){ return rcu_seq_endval(&rcu_state.expedited_sequence);}
/* * Record the end of an expedited grace period. */static void rcu_exp_gp_seq_end(void){ rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_exp_snap); rcu_seq_end(&rcu_state.expedited_sequence); smp_mb(); /* Ensure that consecutive grace periods serialize. */}
/* * Take a snapshot of the expedited-grace-period counter, which is the * earliest value that will indicate that a full grace period has * elapsed since the current time. */static unsigned long rcu_exp_gp_seq_snap(void){ unsigned long s;
smp_mb(); /* Caller's modifications seen first by other CPUs. */ s = rcu_seq_snap(&rcu_state.expedited_sequence); trace_rcu_exp_grace_period(rcu_state.name, s, TPS("snap")); return s;}
/* * Given a counter snapshot from rcu_exp_gp_seq_snap(), return true * if a full expedited grace period has elapsed since that snapshot * was taken. */static bool rcu_exp_gp_seq_done(unsigned long s){ return rcu_seq_done(&rcu_state.expedited_sequence, s);}
/* * Reset the ->expmaskinit values in the rcu_node tree to reflect any * recent CPU-online activity. Note that these masks are not cleared * when CPUs go offline, so they reflect the union of all CPUs that have * ever been online. This means that this function normally takes its * no-work-to-do fastpath. */static void sync_exp_reset_tree_hotplug(void){ bool done; unsigned long flags; unsigned long mask; unsigned long oldmask; int ncpus = smp_load_acquire(&rcu_state.ncpus); /* Order vs. locking. */ struct rcu_node *rnp; struct rcu_node *rnp_up;
/* If no new CPUs onlined since last time, nothing to do. */ if (likely(ncpus == rcu_state.ncpus_snap)) return; rcu_state.ncpus_snap = ncpus;
/* * Each pass through the following loop propagates newly onlined * CPUs for the current rcu_node structure up the rcu_node tree. */ rcu_for_each_leaf_node(rnp) { raw_spin_lock_irqsave_rcu_node(rnp, flags); if (rnp->expmaskinit == rnp->expmaskinitnext) { raw_spin_unlock_irqrestore_rcu_node(rnp, flags); continue; /* No new CPUs, nothing to do. */ }
/* Update this node's mask, track old value for propagation. */ oldmask = rnp->expmaskinit; rnp->expmaskinit = rnp->expmaskinitnext; raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
/* If was already nonzero, nothing to propagate. */ if (oldmask) continue;
/* Propagate the new CPU up the tree. */ mask = rnp->grpmask; rnp_up = rnp->parent; done = false; while (rnp_up) { raw_spin_lock_irqsave_rcu_node(rnp_up, flags); if (rnp_up->expmaskinit) done = true; rnp_up->expmaskinit |= mask; raw_spin_unlock_irqrestore_rcu_node(rnp_up, flags); if (done) break; mask = rnp_up->grpmask; rnp_up = rnp_up->parent; } }}
/* * Reset the ->expmask values in the rcu_node tree in preparation for * a new expedited grace period. */static void __maybe_unused sync_exp_reset_tree(void){ unsigned long flags; struct rcu_node *rnp;
sync_exp_reset_tree_hotplug(); rcu_for_each_node_breadth_first(rnp) { raw_spin_lock_irqsave_rcu_node(rnp, flags); WARN_ON_ONCE(rnp->expmask); WRITE_ONCE(rnp->expmask, rnp->expmaskinit); /* * Need to wait for any blocked tasks as well. Note that * additional blocking tasks will also block the expedited GP * until such time as the ->expmask bits are cleared. */ if (rcu_is_leaf_node(rnp) && rcu_preempt_has_tasks(rnp)) WRITE_ONCE(rnp->exp_tasks, rnp->blkd_tasks.next); raw_spin_unlock_irqrestore_rcu_node(rnp, flags); }}
/* * Return non-zero if there is no RCU expedited grace period in progress * for the specified rcu_node structure, in other words, if all CPUs and * tasks covered by the specified rcu_node structure have done their bit * for the current expedited grace period. */static bool sync_rcu_exp_done(struct rcu_node *rnp){ raw_lockdep_assert_held_rcu_node(rnp); return READ_ONCE(rnp->exp_tasks) == NULL && READ_ONCE(rnp->expmask) == 0;}
/* * Like sync_rcu_exp_done(), but where the caller does not hold the * rcu_node's ->lock. */static bool sync_rcu_exp_done_unlocked(struct rcu_node *rnp){ unsigned long flags; bool ret;
raw_spin_lock_irqsave_rcu_node(rnp, flags); ret = sync_rcu_exp_done(rnp); raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
return ret;}
/* * Report the exit from RCU read-side critical section for the last task * that queued itself during or before the current expedited preemptible-RCU * grace period. This event is reported either to the rcu_node structure on * which the task was queued or to one of that rcu_node structure's ancestors, * recursively up the tree. (Calm down, calm down, we do the recursion * iteratively!) */static void __rcu_report_exp_rnp(struct rcu_node *rnp, bool wake, unsigned long flags) __releases(rnp->lock){ unsigned long mask;
raw_lockdep_assert_held_rcu_node(rnp); for (;;) { if (!sync_rcu_exp_done(rnp)) { if (!rnp->expmask) rcu_initiate_boost(rnp, flags); else raw_spin_unlock_irqrestore_rcu_node(rnp, flags); break; } if (rnp->parent == NULL) { raw_spin_unlock_irqrestore_rcu_node(rnp, flags); if (wake) swake_up_one(&rcu_state.expedited_wq);
break; } mask = rnp->grpmask; raw_spin_unlock_rcu_node(rnp); /* irqs remain disabled */ rnp = rnp->parent; raw_spin_lock_rcu_node(rnp); /* irqs already disabled */ WARN_ON_ONCE(!(rnp->expmask & mask)); WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask); }}
/* * Report expedited quiescent state for specified node. This is a * lock-acquisition wrapper function for __rcu_report_exp_rnp(). */static void __maybe_unused rcu_report_exp_rnp(struct rcu_node *rnp, bool wake){ unsigned long flags;
raw_spin_lock_irqsave_rcu_node(rnp, flags); __rcu_report_exp_rnp(rnp, wake, flags);}
/* * Report expedited quiescent state for multiple CPUs, all covered by the * specified leaf rcu_node structure, which is acquired by the caller. */static void rcu_report_exp_cpu_mult(struct rcu_node *rnp, unsigned long flags, unsigned long mask_in, bool wake) __releases(rnp->lock){ int cpu; unsigned long mask; struct rcu_data *rdp;
raw_lockdep_assert_held_rcu_node(rnp); if (!(rnp->expmask & mask_in)) { raw_spin_unlock_irqrestore_rcu_node(rnp, flags); return; } mask = mask_in & rnp->expmask; WRITE_ONCE(rnp->expmask, rnp->expmask & ~mask); for_each_leaf_node_cpu_mask(rnp, cpu, mask) { rdp = per_cpu_ptr(&rcu_data, cpu); if (!IS_ENABLED(CONFIG_NO_HZ_FULL) || !rdp->rcu_forced_tick_exp) continue; rdp->rcu_forced_tick_exp = false; tick_dep_clear_cpu(cpu, TICK_DEP_BIT_RCU_EXP); } __rcu_report_exp_rnp(rnp, wake, flags); /* Releases rnp->lock. */}
/* * Report expedited quiescent state for specified rcu_data (CPU). */static void rcu_report_exp_rdp(struct rcu_data *rdp){ unsigned long flags; struct rcu_node *rnp = rdp->mynode;
raw_spin_lock_irqsave_rcu_node(rnp, flags); WRITE_ONCE(rdp->cpu_no_qs.b.exp, false); ASSERT_EXCLUSIVE_WRITER(rdp->cpu_no_qs.b.exp); rcu_report_exp_cpu_mult(rnp, flags, rdp->grpmask, true);}
/* Common code for work-done checking. */static bool sync_exp_work_done(unsigned long s){ if (rcu_exp_gp_seq_done(s)) { trace_rcu_exp_grace_period(rcu_state.name, s, TPS("done")); /* * Order GP completion with preceding accesses. Order also GP * completion with post GP update side accesses. Pairs with * rcu_seq_end(). */ smp_mb(); return true; } return false;}
/* * Funnel-lock acquisition for expedited grace periods. Returns true * if some other task completed an expedited grace period that this task * can piggy-back on, and with no mutex held. Otherwise, returns false * with the mutex held, indicating that the caller must actually do the * expedited grace period. */static bool exp_funnel_lock(unsigned long s){ struct rcu_data *rdp = per_cpu_ptr(&rcu_data, raw_smp_processor_id()); struct rcu_node *rnp = rdp->mynode; struct rcu_node *rnp_root = rcu_get_root();
/* Low-contention fastpath. */ if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s) && (rnp == rnp_root || ULONG_CMP_LT(READ_ONCE(rnp_root->exp_seq_rq), s)) && mutex_trylock(&rcu_state.exp_mutex)) goto fastpath;
/* * Each pass through the following loop works its way up * the rcu_node tree, returning if others have done the work or * otherwise falls through to acquire ->exp_mutex. The mapping * from CPU to rcu_node structure can be inexact, as it is just * promoting locality and is not strictly needed for correctness. */ for (; rnp != NULL; rnp = rnp->parent) { if (sync_exp_work_done(s)) return true;
/* Work not done, either wait here or go up. */ spin_lock(&rnp->exp_lock); if (ULONG_CMP_GE(rnp->exp_seq_rq, s)) {
/* Someone else doing GP, so wait for them. */ spin_unlock(&rnp->exp_lock); trace_rcu_exp_funnel_lock(rcu_state.name, rnp->level, rnp->grplo, rnp->grphi, TPS("wait")); wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3], sync_exp_work_done(s)); return true; } WRITE_ONCE(rnp->exp_seq_rq, s); /* Followers can wait on us. */ spin_unlock(&rnp->exp_lock); trace_rcu_exp_funnel_lock(rcu_state.name, rnp->level, rnp->grplo, rnp->grphi, TPS("nxtlvl")); } mutex_lock(&rcu_state.exp_mutex);fastpath: if (sync_exp_work_done(s)) { mutex_unlock(&rcu_state.exp_mutex); return true; } rcu_exp_gp_seq_start(); trace_rcu_exp_grace_period(rcu_state.name, s, TPS("start")); return false;}
/* * Select the CPUs within the specified rcu_node that the upcoming * expedited grace period needs to wait for. */static void __sync_rcu_exp_select_node_cpus(struct rcu_exp_work *rewp){ int cpu; unsigned long flags; unsigned long mask_ofl_test; unsigned long mask_ofl_ipi; int ret; struct rcu_node *rnp = container_of(rewp, struct rcu_node, rew);
raw_spin_lock_irqsave_rcu_node(rnp, flags);
/* Each pass checks a CPU for identity, offline, and idle. */ mask_ofl_test = 0; for_each_leaf_node_cpu_mask(rnp, cpu, rnp->expmask) { struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); unsigned long mask = rdp->grpmask; int snap;
if (raw_smp_processor_id() == cpu || !(rnp->qsmaskinitnext & mask)) { mask_ofl_test |= mask; } else { /* * 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, relayed by kworkers * locking and even further by smp_mb__after_unlock_lock() * barriers chained all the way throughout the rnp locking * tree since sync_exp_reset_tree() 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. */ snap = ct_rcu_watching_cpu_acquire(cpu); if (rcu_watching_snap_in_eqs(snap)) mask_ofl_test |= mask; else rdp->exp_watching_snap = snap; } } mask_ofl_ipi = rnp->expmask & ~mask_ofl_test;
raw_spin_unlock_irqrestore_rcu_node(rnp, flags);
/* IPI the remaining CPUs for expedited quiescent state. */ for_each_leaf_node_cpu_mask(rnp, cpu, mask_ofl_ipi) { struct rcu_data *rdp = per_cpu_ptr(&rcu_data, cpu); unsigned long mask = rdp->grpmask;
retry_ipi: if (rcu_watching_snap_stopped_since(rdp, rdp->exp_watching_snap)) { mask_ofl_test |= mask; continue; } if (get_cpu() == cpu) { mask_ofl_test |= mask; put_cpu(); continue; } ret = smp_call_function_single(cpu, rcu_exp_handler, NULL, 0); put_cpu(); /* The CPU will report the QS in response to the IPI. */ if (!ret) continue;
/* Failed, raced with CPU hotplug operation. */ raw_spin_lock_irqsave_rcu_node(rnp, flags); if ((rnp->qsmaskinitnext & mask) && (rnp->expmask & mask)) { /* Online, so delay for a bit and try again. */ raw_spin_unlock_irqrestore_rcu_node(rnp, flags); trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("selectofl")); schedule_timeout_idle(1); goto retry_ipi; } /* CPU really is offline, so we must report its QS. */ if (rnp->expmask & mask) mask_ofl_test |= mask; raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } /* Report quiescent states for those that went offline. */ if (mask_ofl_test) { raw_spin_lock_irqsave_rcu_node(rnp, flags); rcu_report_exp_cpu_mult(rnp, flags, mask_ofl_test, false); }}
static void rcu_exp_sel_wait_wake(unsigned long s);
static void sync_rcu_exp_select_node_cpus(struct kthread_work *wp){ struct rcu_exp_work *rewp = container_of(wp, struct rcu_exp_work, rew_work);
__sync_rcu_exp_select_node_cpus(rewp);}
static inline bool rcu_exp_worker_started(void){ return !!READ_ONCE(rcu_exp_gp_kworker);}
static inline bool rcu_exp_par_worker_started(struct rcu_node *rnp){ return !!READ_ONCE(rnp->exp_kworker);}
static inline void sync_rcu_exp_select_cpus_queue_work(struct rcu_node *rnp){ kthread_init_work(&rnp->rew.rew_work, sync_rcu_exp_select_node_cpus); /* * Use rcu_exp_par_gp_kworker, because flushing a work item from * another work item on the same kthread worker can result in * deadlock. */ kthread_queue_work(READ_ONCE(rnp->exp_kworker), &rnp->rew.rew_work);}
static inline void sync_rcu_exp_select_cpus_flush_work(struct rcu_node *rnp){ kthread_flush_work(&rnp->rew.rew_work);}
/* * Work-queue handler to drive an expedited grace period forward. */static void wait_rcu_exp_gp(struct kthread_work *wp){ struct rcu_exp_work *rewp;
rewp = container_of(wp, struct rcu_exp_work, rew_work); rcu_exp_sel_wait_wake(rewp->rew_s);}
static inline void synchronize_rcu_expedited_queue_work(struct rcu_exp_work *rew){ kthread_init_work(&rew->rew_work, wait_rcu_exp_gp); kthread_queue_work(rcu_exp_gp_kworker, &rew->rew_work);}
/* * Select the nodes that the upcoming expedited grace period needs * to wait for. */static void sync_rcu_exp_select_cpus(void){ struct rcu_node *rnp;
trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("reset")); sync_exp_reset_tree(); trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("select"));
/* Schedule work for each leaf rcu_node structure. */ rcu_for_each_leaf_node(rnp) { rnp->exp_need_flush = false; if (!READ_ONCE(rnp->expmask)) continue; /* Avoid early boot non-existent wq. */ if (!rcu_exp_par_worker_started(rnp) || rcu_scheduler_active != RCU_SCHEDULER_RUNNING || rcu_is_last_leaf_node(rnp)) { /* No worker started yet or last leaf, do direct call. */ sync_rcu_exp_select_node_cpus(&rnp->rew.rew_work); continue; } sync_rcu_exp_select_cpus_queue_work(rnp); rnp->exp_need_flush = true; }
/* Wait for jobs (if any) to complete. */ rcu_for_each_leaf_node(rnp) if (rnp->exp_need_flush) sync_rcu_exp_select_cpus_flush_work(rnp);}
/* * Wait for the expedited grace period to elapse, within time limit. * If the time limit is exceeded without the grace period elapsing, * return false, otherwise return true. */static bool synchronize_rcu_expedited_wait_once(long tlimit){ int t; struct rcu_node *rnp_root = rcu_get_root();
t = swait_event_timeout_exclusive(rcu_state.expedited_wq, sync_rcu_exp_done_unlocked(rnp_root), tlimit); // Workqueues should not be signaled. if (t > 0 || sync_rcu_exp_done_unlocked(rnp_root)) return true; WARN_ON(t < 0); /* workqueues should not be signaled. */ return false;}
/* * Print out an expedited RCU CPU stall warning message. */static void synchronize_rcu_expedited_stall(unsigned long jiffies_start, unsigned long j){ int cpu; unsigned long mask; int ndetected; struct rcu_node *rnp; struct rcu_node *rnp_root = rcu_get_root();
if (READ_ONCE(csd_lock_suppress_rcu_stall) && csd_lock_is_stuck()) { pr_err("INFO: %s detected expedited stalls, but suppressed full report due to a stuck CSD-lock.\n", rcu_state.name); return; } pr_err("INFO: %s detected expedited stalls on CPUs/tasks: {", rcu_state.name); ndetected = 0; rcu_for_each_leaf_node(rnp) { ndetected += rcu_print_task_exp_stall(rnp); for_each_leaf_node_possible_cpu(rnp, cpu) { struct rcu_data *rdp;
mask = leaf_node_cpu_bit(rnp, cpu); if (!(READ_ONCE(rnp->expmask) & mask)) continue; ndetected++; rdp = per_cpu_ptr(&rcu_data, cpu); pr_cont(" %d-%c%c%c%c", cpu, "O."[!!cpu_online(cpu)], "o."[!!(rdp->grpmask & rnp->expmaskinit)], "N."[!!(rdp->grpmask & rnp->expmaskinitnext)], "D."[!!data_race(rdp->cpu_no_qs.b.exp)]); } } pr_cont(" } %lu jiffies s: %lu root: %#lx/%c\n", j - jiffies_start, rcu_state.expedited_sequence, data_race(rnp_root->expmask), ".T"[!!data_race(rnp_root->exp_tasks)]); if (!ndetected) { // This is invoked from the grace-period worker, so // a new grace period cannot have started. And if this // worker were stalled, we would not get here. ;-) pr_err("INFO: Expedited stall ended before state dump start\n"); } else { pr_err("blocking rcu_node structures (internal RCU debug):"); rcu_for_each_node_breadth_first(rnp) { if (rnp == rnp_root) continue; /* printed unconditionally */ if (sync_rcu_exp_done_unlocked(rnp)) continue; pr_cont(" l=%u:%d-%d:%#lx/%c", rnp->level, rnp->grplo, rnp->grphi, data_race(rnp->expmask), ".T"[!!data_race(rnp->exp_tasks)]); } pr_cont("\n"); } rcu_for_each_leaf_node(rnp) { for_each_leaf_node_possible_cpu(rnp, cpu) { mask = leaf_node_cpu_bit(rnp, cpu); if (!(READ_ONCE(rnp->expmask) & mask)) continue; dump_cpu_task(cpu); } rcu_exp_print_detail_task_stall_rnp(rnp); }}
/* * Wait for the expedited grace period to elapse, issuing any needed * RCU CPU stall warnings along the way. */static void synchronize_rcu_expedited_wait(void){ int cpu; unsigned long j; unsigned long jiffies_stall; unsigned long jiffies_start; unsigned long mask; struct rcu_data *rdp; struct rcu_node *rnp; unsigned long flags;
trace_rcu_exp_grace_period(rcu_state.name, rcu_exp_gp_seq_endval(), TPS("startwait")); jiffies_stall = rcu_exp_jiffies_till_stall_check(); jiffies_start = jiffies; if (tick_nohz_full_enabled() && rcu_inkernel_boot_has_ended()) { if (synchronize_rcu_expedited_wait_once(1)) return; rcu_for_each_leaf_node(rnp) { raw_spin_lock_irqsave_rcu_node(rnp, flags); mask = READ_ONCE(rnp->expmask); for_each_leaf_node_cpu_mask(rnp, cpu, mask) { rdp = per_cpu_ptr(&rcu_data, cpu); if (rdp->rcu_forced_tick_exp) continue; rdp->rcu_forced_tick_exp = true; if (cpu_online(cpu)) tick_dep_set_cpu(cpu, TICK_DEP_BIT_RCU_EXP); } raw_spin_unlock_irqrestore_rcu_node(rnp, flags); } j = READ_ONCE(jiffies_till_first_fqs); if (synchronize_rcu_expedited_wait_once(j + HZ)) return; }
for (;;) { unsigned long j;
if (synchronize_rcu_expedited_wait_once(jiffies_stall)) return; if (rcu_stall_is_suppressed()) continue;
nbcon_cpu_emergency_enter();
j = jiffies; rcu_stall_notifier_call_chain(RCU_STALL_NOTIFY_EXP, (void *)(j - jiffies_start)); trace_rcu_stall_warning(rcu_state.name, TPS("ExpeditedStall")); synchronize_rcu_expedited_stall(jiffies_start, j); jiffies_stall = 3 * rcu_exp_jiffies_till_stall_check() + 3;
nbcon_cpu_emergency_exit();
panic_on_rcu_stall(); }}
/* * Wait for the current expedited grace period to complete, and then * wake up everyone who piggybacked on the just-completed expedited * grace period. Also update all the ->exp_seq_rq counters as needed * in order to avoid counter-wrap problems. */static void rcu_exp_wait_wake(unsigned long s){ struct rcu_node *rnp;
synchronize_rcu_expedited_wait();
// Switch over to wakeup mode, allowing the next GP to proceed. // End the previous grace period only after acquiring the mutex // to ensure that only one GP runs concurrently with wakeups. mutex_lock(&rcu_state.exp_wake_mutex); rcu_exp_gp_seq_end(); trace_rcu_exp_grace_period(rcu_state.name, s, TPS("end"));
rcu_for_each_node_breadth_first(rnp) { if (ULONG_CMP_LT(READ_ONCE(rnp->exp_seq_rq), s)) { spin_lock(&rnp->exp_lock); /* Recheck, avoid hang in case someone just arrived. */ if (ULONG_CMP_LT(rnp->exp_seq_rq, s)) WRITE_ONCE(rnp->exp_seq_rq, s); spin_unlock(&rnp->exp_lock); } smp_mb(); /* All above changes before wakeup. */ wake_up_all(&rnp->exp_wq[rcu_seq_ctr(s) & 0x3]); } trace_rcu_exp_grace_period(rcu_state.name, s, TPS("endwake")); mutex_unlock(&rcu_state.exp_wake_mutex);}
/* * Common code to drive an expedited grace period forward, used by * workqueues and mid-boot-time tasks. */static void rcu_exp_sel_wait_wake(unsigned long s){ /* Initialize the rcu_node tree in preparation for the wait. */ sync_rcu_exp_select_cpus();
/* Wait and clean up, including waking everyone. */ rcu_exp_wait_wake(s);}
/* Request an expedited quiescent state. */static void rcu_exp_need_qs(void){ lockdep_assert_irqs_disabled(); ASSERT_EXCLUSIVE_WRITER_SCOPED(*this_cpu_ptr(&rcu_data.cpu_no_qs.b.exp)); __this_cpu_write(rcu_data.cpu_no_qs.b.exp, true); /* Store .exp before .rcu_urgent_qs. */ smp_store_release(this_cpu_ptr(&rcu_data.rcu_urgent_qs), true); set_need_resched_current();}
#ifdef CONFIG_PREEMPT_RCU
/* * Remote handler for smp_call_function_single(). If there is an * RCU read-side critical section in effect, request that the * next rcu_read_unlock() record the quiescent state up the * ->expmask fields in the rcu_node tree. Otherwise, immediately * report the quiescent state. */static void rcu_exp_handler(void *unused){ int depth = rcu_preempt_depth(); unsigned long flags; struct rcu_data *rdp = this_cpu_ptr(&rcu_data); struct rcu_node *rnp = rdp->mynode; struct task_struct *t = current;
/* * WARN if the CPU is unexpectedly already looking for a * QS or has already reported one. */ ASSERT_EXCLUSIVE_WRITER_SCOPED(rdp->cpu_no_qs.b.exp); if (WARN_ON_ONCE(!(READ_ONCE(rnp->expmask) & rdp->grpmask) || READ_ONCE(rdp->cpu_no_qs.b.exp))) return;
/* * Second, the common case of not being in an RCU read-side * critical section. If also enabled or idle, immediately * report the quiescent state, otherwise defer. */ if (!depth) { if (!(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK)) || rcu_is_cpu_rrupt_from_idle()) rcu_report_exp_rdp(rdp); else rcu_exp_need_qs(); return; }
/* * Third, the less-common case of being in an RCU read-side * critical section. In this case we can count on a future * rcu_read_unlock(). However, this rcu_read_unlock() might * execute on some other CPU, but in that case there will be * a future context switch. Either way, if the expedited * grace period is still waiting on this CPU, set ->deferred_qs * so that the eventual quiescent state will be reported. * Note that there is a large group of race conditions that * can have caused this quiescent state to already have been * reported, so we really do need to check ->expmask. */ if (depth > 0) { raw_spin_lock_irqsave_rcu_node(rnp, flags); if (rnp->expmask & rdp->grpmask) { WRITE_ONCE(rdp->cpu_no_qs.b.exp, true); t->rcu_read_unlock_special.b.exp_hint = true; } raw_spin_unlock_irqrestore_rcu_node(rnp, flags); return; }
// Fourth and finally, negative nesting depth should not happen. WARN_ON_ONCE(1);}
/* * Scan the current list of tasks blocked within RCU read-side critical * sections, printing out the tid of each that is blocking the current * expedited grace period. */static int rcu_print_task_exp_stall(struct rcu_node *rnp){ unsigned long flags; int ndetected = 0; struct task_struct *t;
raw_spin_lock_irqsave_rcu_node(rnp, flags); if (!rnp->exp_tasks) { raw_spin_unlock_irqrestore_rcu_node(rnp, flags); return 0; } t = list_entry(rnp->exp_tasks->prev, struct task_struct, rcu_node_entry); list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { pr_cont(" P%d", t->pid); ndetected++; } raw_spin_unlock_irqrestore_rcu_node(rnp, flags); return ndetected;}
/* * Scan the current list of tasks blocked within RCU read-side critical * sections, dumping the stack of each that is blocking the current * expedited grace period. */static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp){ unsigned long flags; struct task_struct *t;
if (!rcu_exp_stall_task_details) return; raw_spin_lock_irqsave_rcu_node(rnp, flags); if (!READ_ONCE(rnp->exp_tasks)) { raw_spin_unlock_irqrestore_rcu_node(rnp, flags); return; } t = list_entry(rnp->exp_tasks->prev, struct task_struct, rcu_node_entry); list_for_each_entry_continue(t, &rnp->blkd_tasks, rcu_node_entry) { /* * We could be printing a lot while holding a spinlock. * Avoid triggering hard lockup. */ touch_nmi_watchdog(); sched_show_task(t); } raw_spin_unlock_irqrestore_rcu_node(rnp, flags);}
#else /* #ifdef CONFIG_PREEMPT_RCU */
/* Invoked on each online non-idle CPU for expedited quiescent state. */static void rcu_exp_handler(void *unused){ struct rcu_data *rdp = this_cpu_ptr(&rcu_data); struct rcu_node *rnp = rdp->mynode; bool preempt_bh_enabled = !(preempt_count() & (PREEMPT_MASK | SOFTIRQ_MASK));
ASSERT_EXCLUSIVE_WRITER_SCOPED(rdp->cpu_no_qs.b.exp); if (!(READ_ONCE(rnp->expmask) & rdp->grpmask) || __this_cpu_read(rcu_data.cpu_no_qs.b.exp)) return; if (rcu_is_cpu_rrupt_from_idle() || (IS_ENABLED(CONFIG_PREEMPT_COUNT) && preempt_bh_enabled)) { rcu_report_exp_rdp(this_cpu_ptr(&rcu_data)); return; } rcu_exp_need_qs();}
/* * Because preemptible RCU does not exist, we never have to check for * tasks blocked within RCU read-side critical sections that are * blocking the current expedited grace period. */static int rcu_print_task_exp_stall(struct rcu_node *rnp){ return 0;}
/* * Because preemptible RCU does not exist, we never have to print out * tasks blocked within RCU read-side critical sections that are blocking * the current expedited grace period. */static void rcu_exp_print_detail_task_stall_rnp(struct rcu_node *rnp){}
#endif /* #else #ifdef CONFIG_PREEMPT_RCU */
/** * synchronize_rcu_expedited - Brute-force RCU grace period * * Wait for an RCU grace period, but expedite it. The basic idea is to * IPI all non-idle non-nohz online CPUs. The IPI handler checks whether * the CPU is in an RCU critical section, and if so, it sets a flag that * causes the outermost rcu_read_unlock() to report the quiescent state * for RCU-preempt or asks the scheduler for help for RCU-sched. On the * other hand, if the CPU is not in an RCU read-side critical section, * the IPI handler reports the quiescent state immediately. * * Although this is a great improvement over previous expedited * implementations, it is still unfriendly to real-time workloads, so is * thus not recommended for any sort of common-case code. In fact, if * you are using synchronize_rcu_expedited() in a loop, please restructure * your code to batch your updates, and then use a single synchronize_rcu() * instead. * * This has the same semantics as (but is more brutal than) synchronize_rcu(). */void synchronize_rcu_expedited(void){ unsigned long flags; struct rcu_exp_work rew; struct rcu_node *rnp; unsigned long s;
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_expedited() in RCU read-side critical section");
/* Is the state is such that the call is a grace period? */ if (rcu_blocking_is_gp()) { // Note well that this code runs with !PREEMPT && !SMP. // In addition, all code that advances grace periods runs // at process level. Therefore, this expedited GP overlaps // with other expedited GPs only by being fully nested within // them, which allows reuse of ->gp_seq_polled_exp_snap. rcu_poll_gp_seq_start_unlocked(&rcu_state.gp_seq_polled_exp_snap); rcu_poll_gp_seq_end_unlocked(&rcu_state.gp_seq_polled_exp_snap);
local_irq_save(flags); WARN_ON_ONCE(num_online_cpus() > 1); rcu_state.expedited_sequence += (1 << RCU_SEQ_CTR_SHIFT); local_irq_restore(flags); return; // Context allows vacuous grace periods. }
/* If expedited grace periods are prohibited, fall back to normal. */ if (rcu_gp_is_normal()) { synchronize_rcu_normal(); return; }
/* Take a snapshot of the sequence number. */ s = rcu_exp_gp_seq_snap(); if (exp_funnel_lock(s)) return; /* Someone else did our work for us. */
/* Ensure that load happens before action based on it. */ if (unlikely((rcu_scheduler_active == RCU_SCHEDULER_INIT) || !rcu_exp_worker_started())) { /* Direct call during scheduler init and early_initcalls(). */ rcu_exp_sel_wait_wake(s); } else { /* Marshall arguments & schedule the expedited grace period. */ rew.rew_s = s; synchronize_rcu_expedited_queue_work(&rew); }
/* Wait for expedited grace period to complete. */ rnp = rcu_get_root(); wait_event(rnp->exp_wq[rcu_seq_ctr(s) & 0x3], sync_exp_work_done(s));
/* Let the next expedited grace period start. */ mutex_unlock(&rcu_state.exp_mutex);}EXPORT_SYMBOL_GPL(synchronize_rcu_expedited);
/* * Ensure that start_poll_synchronize_rcu_expedited() has the expedited * RCU grace periods that it needs. */static void sync_rcu_do_polled_gp(struct work_struct *wp){ unsigned long flags; int i = 0; struct rcu_node *rnp = container_of(wp, struct rcu_node, exp_poll_wq); unsigned long s;
raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags); s = rnp->exp_seq_poll_rq; rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED; raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags); if (s == RCU_GET_STATE_COMPLETED) return; while (!poll_state_synchronize_rcu(s)) { synchronize_rcu_expedited(); if (i == 10 || i == 20) pr_info("%s: i = %d s = %lx gp_seq_polled = %lx\n", __func__, i, s, READ_ONCE(rcu_state.gp_seq_polled)); i++; } raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags); s = rnp->exp_seq_poll_rq; if (poll_state_synchronize_rcu(s)) rnp->exp_seq_poll_rq = RCU_GET_STATE_COMPLETED; raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);}
/** * start_poll_synchronize_rcu_expedited - Snapshot current RCU state and start expedited grace period * * Returns a cookie to pass to a call to cond_synchronize_rcu(), * cond_synchronize_rcu_expedited(), or poll_state_synchronize_rcu(), * allowing them to determine whether or not any sort of grace period has * elapsed in the meantime. If the needed expedited grace period is not * already slated to start, initiates that grace period. */unsigned long start_poll_synchronize_rcu_expedited(void){ unsigned long flags; struct rcu_data *rdp; struct rcu_node *rnp; unsigned long s;
s = get_state_synchronize_rcu(); rdp = per_cpu_ptr(&rcu_data, raw_smp_processor_id()); rnp = rdp->mynode; if (rcu_init_invoked()) raw_spin_lock_irqsave(&rnp->exp_poll_lock, flags); if (!poll_state_synchronize_rcu(s)) { if (rcu_init_invoked()) { rnp->exp_seq_poll_rq = s; queue_work(rcu_gp_wq, &rnp->exp_poll_wq); } } if (rcu_init_invoked()) raw_spin_unlock_irqrestore(&rnp->exp_poll_lock, flags);
return s;}EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_expedited);
/** * start_poll_synchronize_rcu_expedited_full - Take a full snapshot and start expedited grace period * @rgosp: Place to put snapshot of 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. * If the needed expedited grace period is not already slated to start, * initiates that grace period. */void start_poll_synchronize_rcu_expedited_full(struct rcu_gp_oldstate *rgosp){ get_state_synchronize_rcu_full(rgosp); (void)start_poll_synchronize_rcu_expedited();}EXPORT_SYMBOL_GPL(start_poll_synchronize_rcu_expedited_full);
/** * cond_synchronize_rcu_expedited - Conditionally wait for an expedited RCU grace period * * @oldstate: value from get_state_synchronize_rcu(), start_poll_synchronize_rcu(), or start_poll_synchronize_rcu_expedited() * * If any type of full RCU grace period has elapsed since the earlier * call to get_state_synchronize_rcu(), start_poll_synchronize_rcu(), * or start_poll_synchronize_rcu_expedited(), just return. Otherwise, * invoke synchronize_rcu_expedited() 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_expedited(unsigned long oldstate){ if (!poll_state_synchronize_rcu(oldstate)) synchronize_rcu_expedited();}EXPORT_SYMBOL_GPL(cond_synchronize_rcu_expedited);
/** * cond_synchronize_rcu_expedited_full - Conditionally wait for an expedited 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_expedited() * 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_expedited_full(struct rcu_gp_oldstate *rgosp){ if (!poll_state_synchronize_rcu_full(rgosp)) synchronize_rcu_expedited();}EXPORT_SYMBOL_GPL(cond_synchronize_rcu_expedited_full);