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Linux kernel mirror (for testing) git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138139140141142143144145146147148149150151152153154155156157158159160161162163164165166167168169170171172173174175176177178179180181182183184185186187188189190191192193194195196197198199200201202203204205206207208209210211212213214215216217218219220221222223224225226227228229230231232233234235236237238239240241242243244245246247248249250251252253254255256257258259260261262263264265266267268269270271272273274275276277278279280281282283284285286287288289290291292293294295296297298299300301302303304305306307308309310311312313314315316317318319320321322323324325326327328329330331332333334// SPDX-License-Identifier: GPL-2.0+/* * Sleepable Read-Copy Update mechanism for mutual exclusion, * tiny version for non-preemptible single-CPU use. * * Copyright (C) IBM Corporation, 2017 * * Author: Paul McKenney <paulmck@linux.ibm.com> */
#include <linux/export.h>#include <linux/irq_work.h>#include <linux/mutex.h>#include <linux/preempt.h>#include <linux/rcupdate_wait.h>#include <linux/sched.h>#include <linux/delay.h>#include <linux/srcu.h>
#include <linux/rcu_node_tree.h>#include "rcu_segcblist.h"#include "rcu.h"
#ifndef CONFIG_TREE_RCUint rcu_scheduler_active __read_mostly;#else // #ifndef CONFIG_TREE_RCUextern int rcu_scheduler_active;#endif // #else // #ifndef CONFIG_TREE_RCUstatic LIST_HEAD(srcu_boot_list);static bool srcu_init_done;
static int init_srcu_struct_fields(struct srcu_struct *ssp){ ssp->srcu_lock_nesting[0] = 0; ssp->srcu_lock_nesting[1] = 0; init_swait_queue_head(&ssp->srcu_wq); ssp->srcu_cb_head = NULL; ssp->srcu_cb_tail = &ssp->srcu_cb_head; ssp->srcu_gp_running = false; ssp->srcu_gp_waiting = false; ssp->srcu_idx = 0; ssp->srcu_idx_max = 0; INIT_WORK(&ssp->srcu_work, srcu_drive_gp); INIT_LIST_HEAD(&ssp->srcu_work.entry); init_irq_work(&ssp->srcu_irq_work, srcu_tiny_irq_work); return 0;}
#ifdef CONFIG_DEBUG_LOCK_ALLOC
int __init_srcu_struct(struct srcu_struct *ssp, const char *name, struct lock_class_key *key){ /* Don't re-initialize a lock while it is held. */ debug_check_no_locks_freed((void *)ssp, sizeof(*ssp)); lockdep_init_map(&ssp->dep_map, name, key, 0); return init_srcu_struct_fields(ssp);}EXPORT_SYMBOL_GPL(__init_srcu_struct);
#else /* #ifdef CONFIG_DEBUG_LOCK_ALLOC */
/* * init_srcu_struct - initialize a sleep-RCU structure * @ssp: structure to initialize. * * Must invoke this on a given srcu_struct before passing that srcu_struct * to any other function. Each srcu_struct represents a separate domain * of SRCU protection. */int init_srcu_struct(struct srcu_struct *ssp){ return init_srcu_struct_fields(ssp);}EXPORT_SYMBOL_GPL(init_srcu_struct);
#endif /* #else #ifdef CONFIG_DEBUG_LOCK_ALLOC */
/* * cleanup_srcu_struct - deconstruct a sleep-RCU structure * @ssp: structure to clean up. * * Must invoke this after you are finished using a given srcu_struct that * was initialized via init_srcu_struct(), else you leak memory. */void cleanup_srcu_struct(struct srcu_struct *ssp){ WARN_ON(ssp->srcu_lock_nesting[0] || ssp->srcu_lock_nesting[1]); irq_work_sync(&ssp->srcu_irq_work); flush_work(&ssp->srcu_work); WARN_ON(ssp->srcu_gp_running); WARN_ON(ssp->srcu_gp_waiting); WARN_ON(ssp->srcu_cb_head); WARN_ON(&ssp->srcu_cb_head != ssp->srcu_cb_tail); WARN_ON(ssp->srcu_idx != ssp->srcu_idx_max); WARN_ON(ssp->srcu_idx & 0x1);}EXPORT_SYMBOL_GPL(cleanup_srcu_struct);
/* * Removes the count for the old reader from the appropriate element of * the srcu_struct. */void __srcu_read_unlock(struct srcu_struct *ssp, int idx){ int newval;
preempt_disable(); // Needed for PREEMPT_LAZY newval = READ_ONCE(ssp->srcu_lock_nesting[idx]) - 1; WRITE_ONCE(ssp->srcu_lock_nesting[idx], newval); preempt_enable(); if (!newval && READ_ONCE(ssp->srcu_gp_waiting) && in_task() && !irqs_disabled()) swake_up_one(&ssp->srcu_wq);}EXPORT_SYMBOL_GPL(__srcu_read_unlock);
/* * Workqueue handler to drive one grace period and invoke any callbacks * that become ready as a result. Single-CPU operation and preemption * disabling mean that we get away with murder on synchronization. ;-) */void srcu_drive_gp(struct work_struct *wp){ int idx; struct rcu_head *lh; struct rcu_head *rhp; struct srcu_struct *ssp;
ssp = container_of(wp, struct srcu_struct, srcu_work); preempt_disable(); // Needed for PREEMPT_LAZY if (ssp->srcu_gp_running || ULONG_CMP_GE(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max))) { preempt_enable(); return; /* Already running or nothing to do. */ }
/* Remove recently arrived callbacks and wait for readers. */ WRITE_ONCE(ssp->srcu_gp_running, true); local_irq_disable(); lh = ssp->srcu_cb_head; ssp->srcu_cb_head = NULL; ssp->srcu_cb_tail = &ssp->srcu_cb_head; local_irq_enable(); idx = (ssp->srcu_idx & 0x2) / 2; WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); WRITE_ONCE(ssp->srcu_gp_waiting, true); /* srcu_read_unlock() wakes! */ preempt_enable(); do { // Deadlock issues prevent __srcu_read_unlock() from // doing an unconditional wakeup, so polling is required. swait_event_timeout_exclusive(ssp->srcu_wq, !READ_ONCE(ssp->srcu_lock_nesting[idx]), HZ / 10); } while (READ_ONCE(ssp->srcu_lock_nesting[idx])); preempt_disable(); // Needed for PREEMPT_LAZY WRITE_ONCE(ssp->srcu_gp_waiting, false); /* srcu_read_unlock() cheap. */ WRITE_ONCE(ssp->srcu_idx, ssp->srcu_idx + 1); preempt_enable();
/* Invoke the callbacks we removed above. */ while (lh) { rhp = lh; lh = lh->next; debug_rcu_head_callback(rhp); local_bh_disable(); rhp->func(rhp); local_bh_enable(); }
/* * Enable rescheduling, and if there are more callbacks, * reschedule ourselves. This can race with a call_srcu() * at interrupt level, but the ->srcu_gp_running checks will * straighten that out. */ preempt_disable(); // Needed for PREEMPT_LAZY WRITE_ONCE(ssp->srcu_gp_running, false); idx = ULONG_CMP_LT(ssp->srcu_idx, READ_ONCE(ssp->srcu_idx_max)); preempt_enable(); if (idx) schedule_work(&ssp->srcu_work);}EXPORT_SYMBOL_GPL(srcu_drive_gp);
/* * Use an irq_work to defer schedule_work() to avoid acquiring the workqueue * pool->lock while the caller might hold scheduler locks, causing lockdep * splats due to workqueue_init() doing a wakeup. */void srcu_tiny_irq_work(struct irq_work *irq_work){ struct srcu_struct *ssp;
ssp = container_of(irq_work, struct srcu_struct, srcu_irq_work); schedule_work(&ssp->srcu_work);}EXPORT_SYMBOL_GPL(srcu_tiny_irq_work);
static void srcu_gp_start_if_needed(struct srcu_struct *ssp){ unsigned long cookie;
lockdep_assert_preemption_disabled(); // Needed for PREEMPT_LAZY cookie = get_state_synchronize_srcu(ssp); if (ULONG_CMP_GE(READ_ONCE(ssp->srcu_idx_max), cookie)) { return; } WRITE_ONCE(ssp->srcu_idx_max, cookie); if (!READ_ONCE(ssp->srcu_gp_running)) { if (likely(srcu_init_done)) irq_work_queue(&ssp->srcu_irq_work); else if (list_empty(&ssp->srcu_work.entry)) list_add(&ssp->srcu_work.entry, &srcu_boot_list); }}
/* * Enqueue an SRCU callback on the specified srcu_struct structure, * initiating grace-period processing if it is not already running. */void call_srcu(struct srcu_struct *ssp, struct rcu_head *rhp, rcu_callback_t func){ unsigned long flags;
rhp->func = func; rhp->next = NULL; preempt_disable(); // Needed for PREEMPT_LAZY local_irq_save(flags); *ssp->srcu_cb_tail = rhp; ssp->srcu_cb_tail = &rhp->next; local_irq_restore(flags); srcu_gp_start_if_needed(ssp); preempt_enable();}EXPORT_SYMBOL_GPL(call_srcu);
/* * synchronize_srcu - wait for prior SRCU read-side critical-section completion */void synchronize_srcu(struct srcu_struct *ssp){ struct rcu_synchronize rs;
srcu_lock_sync(&ssp->dep_map);
RCU_LOCKDEP_WARN(lockdep_is_held(ssp) || lock_is_held(&rcu_bh_lock_map) || lock_is_held(&rcu_lock_map) || lock_is_held(&rcu_sched_lock_map), "Illegal synchronize_srcu() in same-type SRCU (or in RCU) read-side critical section");
if (rcu_scheduler_active == RCU_SCHEDULER_INACTIVE) return;
might_sleep(); init_rcu_head_on_stack(&rs.head); init_completion(&rs.completion); call_srcu(ssp, &rs.head, wakeme_after_rcu); wait_for_completion(&rs.completion); destroy_rcu_head_on_stack(&rs.head);}EXPORT_SYMBOL_GPL(synchronize_srcu);
/* * get_state_synchronize_srcu - Provide an end-of-grace-period cookie */unsigned long get_state_synchronize_srcu(struct srcu_struct *ssp){ unsigned long ret;
barrier(); ret = (READ_ONCE(ssp->srcu_idx) + 3) & ~0x1; barrier(); return ret;}EXPORT_SYMBOL_GPL(get_state_synchronize_srcu);
/* * start_poll_synchronize_srcu - Provide cookie and start grace period * * The difference between this and get_state_synchronize_srcu() is that * this function ensures that the poll_state_synchronize_srcu() will * eventually return the value true. */unsigned long start_poll_synchronize_srcu(struct srcu_struct *ssp){ unsigned long ret;
preempt_disable(); // Needed for PREEMPT_LAZY ret = get_state_synchronize_srcu(ssp); srcu_gp_start_if_needed(ssp); preempt_enable(); return ret;}EXPORT_SYMBOL_GPL(start_poll_synchronize_srcu);
/* * poll_state_synchronize_srcu - Has cookie's grace period ended? */bool poll_state_synchronize_srcu(struct srcu_struct *ssp, unsigned long cookie){ unsigned long cur_s = READ_ONCE(ssp->srcu_idx);
barrier(); return cookie == SRCU_GET_STATE_COMPLETED || ULONG_CMP_GE(cur_s, cookie) || ULONG_CMP_LT(cur_s, cookie - 3);}EXPORT_SYMBOL_GPL(poll_state_synchronize_srcu);
#ifndef CONFIG_TREE_RCU/* Lockdep diagnostics. */void __init rcu_scheduler_starting(void){ rcu_scheduler_active = RCU_SCHEDULER_RUNNING;}#endif // #ifndef CONFIG_TREE_RCU
/* * Queue work for srcu_struct structures with early boot callbacks. * The work won't actually execute until the workqueue initialization * phase that takes place after the scheduler starts. */void __init srcu_init(void){ struct srcu_struct *ssp;
srcu_init_done = true; while (!list_empty(&srcu_boot_list)) { ssp = list_first_entry(&srcu_boot_list, struct srcu_struct, srcu_work.entry); list_del_init(&ssp->srcu_work.entry); schedule_work(&ssp->srcu_work); }}