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/* * Read-Copy Update mechanism for mutual exclusion, the Bloatwatch edition. * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2 of the License, or * (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; if not, you can access it online at * http://www.gnu.org/licenses/gpl-2.0.html. * * Copyright IBM Corporation, 2008 * * Author: Paul E. McKenney <paulmck@linux.vnet.ibm.com> * * For detailed explanation of Read-Copy Update mechanism see - * Documentation/RCU */ #include <linux/completion.h> #include <linux/interrupt.h> #include <linux/notifier.h> #include <linux/rcupdate.h> #include <linux/kernel.h> #include <linux/export.h> #include <linux/mutex.h> #include <linux/sched.h> #include <linux/types.h> #include <linux/init.h> #include <linux/time.h> #include <linux/cpu.h> #include <linux/prefetch.h> #include <linux/trace_events.h> #include "rcu.h" /* Forward declarations for tiny_plugin.h. */ struct rcu_ctrlblk; static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp); static void rcu_process_callbacks(struct softirq_action *unused); static void __call_rcu(struct rcu_head *head, rcu_callback_t func, struct rcu_ctrlblk *rcp); #include "tiny_plugin.h" #if defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) /* * Test whether RCU thinks that the current CPU is idle. */ bool notrace __rcu_is_watching(void) { return true; } EXPORT_SYMBOL(__rcu_is_watching); #endif /* defined(CONFIG_DEBUG_LOCK_ALLOC) || defined(CONFIG_RCU_TRACE) */ /* * Helper function for rcu_sched_qs() and rcu_bh_qs(). * Also irqs are disabled to avoid confusion due to interrupt handlers * invoking call_rcu(). */ static int rcu_qsctr_help(struct rcu_ctrlblk *rcp) { RCU_TRACE(reset_cpu_stall_ticks(rcp)); if (rcp->donetail != rcp->curtail) { rcp->donetail = rcp->curtail; return 1; } return 0; } /* * Record an rcu quiescent state. And an rcu_bh quiescent state while we * are at it, given that any rcu quiescent state is also an rcu_bh * quiescent state. Use "+" instead of "||" to defeat short circuiting. */ void rcu_sched_qs(void) { unsigned long flags; local_irq_save(flags); if (rcu_qsctr_help(&rcu_sched_ctrlblk) + rcu_qsctr_help(&rcu_bh_ctrlblk)) raise_softirq(RCU_SOFTIRQ); local_irq_restore(flags); } /* * Record an rcu_bh quiescent state. */ void rcu_bh_qs(void) { unsigned long flags; local_irq_save(flags); if (rcu_qsctr_help(&rcu_bh_ctrlblk)) raise_softirq(RCU_SOFTIRQ); local_irq_restore(flags); } /* * Check to see if the scheduling-clock interrupt came from an extended * quiescent state, and, if so, tell RCU about it. This function must * be called from hardirq context. It is normally called from the * scheduling-clock interrupt. */ void rcu_check_callbacks(int user) { RCU_TRACE(check_cpu_stalls()); if (user) rcu_sched_qs(); else if (!in_softirq()) rcu_bh_qs(); if (user) rcu_note_voluntary_context_switch(current); } /* * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure * whose grace period has elapsed. */ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp) { const char *rn = NULL; struct rcu_head *next, *list; unsigned long flags; RCU_TRACE(int cb_count = 0); /* Move the ready-to-invoke callbacks to a local list. */ local_irq_save(flags); if (rcp->donetail == &rcp->rcucblist) { /* No callbacks ready, so just leave. */ local_irq_restore(flags); return; } RCU_TRACE(trace_rcu_batch_start(rcp->name, 0, rcp->qlen, -1)); list = rcp->rcucblist; rcp->rcucblist = *rcp->donetail; *rcp->donetail = NULL; if (rcp->curtail == rcp->donetail) rcp->curtail = &rcp->rcucblist; rcp->donetail = &rcp->rcucblist; local_irq_restore(flags); /* Invoke the callbacks on the local list. */ RCU_TRACE(rn = rcp->name); while (list) { next = list->next; prefetch(next); debug_rcu_head_unqueue(list); local_bh_disable(); __rcu_reclaim(rn, list); local_bh_enable(); list = next; RCU_TRACE(cb_count++); } RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count)); RCU_TRACE(trace_rcu_batch_end(rcp->name, cb_count, 0, need_resched(), is_idle_task(current), false)); } static __latent_entropy void rcu_process_callbacks(struct softirq_action *unused) { __rcu_process_callbacks(&rcu_sched_ctrlblk); __rcu_process_callbacks(&rcu_bh_ctrlblk); } /* * Wait for a grace period to elapse. But it is illegal to invoke * synchronize_sched() from within an RCU read-side critical section. * Therefore, any legal call to synchronize_sched() is a quiescent * state, and so on a UP system, synchronize_sched() need do nothing. * Ditto for synchronize_rcu_bh(). (But Lai Jiangshan points out the * benefits of doing might_sleep() to reduce latency.) * * Cool, huh? (Due to Josh Triplett.) * * But we want to make this a static inline later. The cond_resched() * currently makes this problematic. */ void synchronize_sched(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 synchronize_sched() in RCU read-side critical section"); cond_resched(); } EXPORT_SYMBOL_GPL(synchronize_sched); /* * Helper function for call_rcu() and call_rcu_bh(). */ static void __call_rcu(struct rcu_head *head, rcu_callback_t func, struct rcu_ctrlblk *rcp) { unsigned long flags; debug_rcu_head_queue(head); head->func = func; head->next = NULL; local_irq_save(flags); *rcp->curtail = head; rcp->curtail = &head->next; RCU_TRACE(rcp->qlen++); local_irq_restore(flags); if (unlikely(is_idle_task(current))) { /* force scheduling for rcu_sched_qs() */ resched_cpu(0); } } /* * Post an RCU callback to be invoked after the end of an RCU-sched grace * period. But since we have but one CPU, that would be after any * quiescent state. */ void call_rcu_sched(struct rcu_head *head, rcu_callback_t func) { __call_rcu(head, func, &rcu_sched_ctrlblk); } EXPORT_SYMBOL_GPL(call_rcu_sched); /* * Post an RCU bottom-half callback to be invoked after any subsequent * quiescent state. */ void call_rcu_bh(struct rcu_head *head, rcu_callback_t func) { __call_rcu(head, func, &rcu_bh_ctrlblk); } EXPORT_SYMBOL_GPL(call_rcu_bh); void __init rcu_init(void) { open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); RCU_TRACE(reset_cpu_stall_ticks(&rcu_sched_ctrlblk)); RCU_TRACE(reset_cpu_stall_ticks(&rcu_bh_ctrlblk)); rcu_early_boot_tests(); }
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