/* * 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, write to the Free Software * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. * * 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/moduleparam.h> #include <linux/completion.h> #include <linux/interrupt.h> #include <linux/notifier.h> #include <linux/rcupdate.h> #include <linux/kernel.h> #include <linux/module.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> /* Controls for rcu_kthread() kthread, replacing RCU_SOFTIRQ used previously. */ static struct task_struct *rcu_kthread_task; static DECLARE_WAIT_QUEUE_HEAD(rcu_kthread_wq); static unsigned long have_rcu_kthread_work; static void invoke_rcu_kthread(void); /* Forward declarations for rcutiny_plugin.h. */ struct rcu_ctrlblk; static void rcu_process_callbacks(struct rcu_ctrlblk *rcp); static int rcu_kthread(void *arg); static void __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), struct rcu_ctrlblk *rcp); #include "rcutiny_plugin.h" #ifdef CONFIG_NO_HZ static long rcu_dynticks_nesting = 1; /* * Enter dynticks-idle mode, which is an extended quiescent state * if we have fully entered that mode (i.e., if the new value of * dynticks_nesting is zero). */ void rcu_enter_nohz(void) { if (--rcu_dynticks_nesting == 0) rcu_sched_qs(0); /* implies rcu_bh_qsctr_inc(0) */ } /* * Exit dynticks-idle mode, so that we are no longer in an extended * quiescent state. */ void rcu_exit_nohz(void) { rcu_dynticks_nesting++; } #endif /* #ifdef CONFIG_NO_HZ */ /* * Helper function for rcu_qsctr_inc() and rcu_bh_qsctr_inc(). * Also disable irqs to avoid confusion due to interrupt handlers * invoking call_rcu(). */ static int rcu_qsctr_help(struct rcu_ctrlblk *rcp) { unsigned long flags; local_irq_save(flags); if (rcp->rcucblist != NULL && rcp->donetail != rcp->curtail) { rcp->donetail = rcp->curtail; local_irq_restore(flags); return 1; } local_irq_restore(flags); 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(int cpu) { if (rcu_qsctr_help(&rcu_sched_ctrlblk) + rcu_qsctr_help(&rcu_bh_ctrlblk)) invoke_rcu_kthread(); } /* * Record an rcu_bh quiescent state. */ void rcu_bh_qs(int cpu) { if (rcu_qsctr_help(&rcu_bh_ctrlblk)) invoke_rcu_kthread(); } /* * Check to see if the scheduling-clock interrupt came from an extended * quiescent state, and, if so, tell RCU about it. */ void rcu_check_callbacks(int cpu, int user) { if (user || (idle_cpu(cpu) && !in_softirq() && hardirq_count() <= (1 << HARDIRQ_SHIFT))) rcu_sched_qs(cpu); else if (!in_softirq()) rcu_bh_qs(cpu); rcu_preempt_check_callbacks(); } /* * Invoke the RCU callbacks on the specified rcu_ctrlkblk structure * whose grace period has elapsed. */ static void rcu_process_callbacks(struct rcu_ctrlblk *rcp) { struct rcu_head *next, *list; unsigned long flags; RCU_TRACE(int cb_count = 0); /* If no RCU callbacks ready to invoke, just return. */ if (&rcp->rcucblist == rcp->donetail) return; /* Move the ready-to-invoke callbacks to a local list. */ local_irq_save(flags); list = rcp->rcucblist; rcp->rcucblist = *rcp->donetail; *rcp->donetail = NULL; if (rcp->curtail == rcp->donetail) rcp->curtail = &rcp->rcucblist; rcu_preempt_remove_callbacks(rcp); rcp->donetail = &rcp->rcucblist; local_irq_restore(flags); /* Invoke the callbacks on the local list. */ while (list) { next = list->next; prefetch(next); debug_rcu_head_unqueue(list); local_bh_disable(); list->func(list); local_bh_enable(); list = next; RCU_TRACE(cb_count++); } RCU_TRACE(rcu_trace_sub_qlen(rcp, cb_count)); } /* * This kthread invokes RCU callbacks whose grace periods have * elapsed. It is awakened as needed, and takes the place of the * RCU_SOFTIRQ that was used previously for this purpose. * This is a kthread, but it is never stopped, at least not until * the system goes down. */ static int rcu_kthread(void *arg) { unsigned long work; unsigned long morework; unsigned long flags; for (;;) { wait_event_interruptible(rcu_kthread_wq, have_rcu_kthread_work != 0); morework = rcu_boost(); local_irq_save(flags); work = have_rcu_kthread_work; have_rcu_kthread_work = morework; local_irq_restore(flags); if (work) { rcu_process_callbacks(&rcu_sched_ctrlblk); rcu_process_callbacks(&rcu_bh_ctrlblk); rcu_preempt_process_callbacks(); } schedule_timeout_interruptible(1); /* Leave CPU for others. */ } return 0; /* Not reached, but needed to shut gcc up. */ } /* * Wake up rcu_kthread() to process callbacks now eligible for invocation * or to boost readers. */ static void invoke_rcu_kthread(void) { unsigned long flags; local_irq_save(flags); have_rcu_kthread_work = 1; wake_up(&rcu_kthread_wq); local_irq_restore(flags); } /* * 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) { cond_resched(); } EXPORT_SYMBOL_GPL(synchronize_sched); /* * Helper function for call_rcu() and call_rcu_bh(). */ static void __call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu), 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); } /* * 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, void (*func)(struct rcu_head *rcu)) { __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, void (*func)(struct rcu_head *rcu)) { __call_rcu(head, func, &rcu_bh_ctrlblk); } EXPORT_SYMBOL_GPL(call_rcu_bh); void rcu_barrier_bh(void) { struct rcu_synchronize rcu; init_rcu_head_on_stack(&rcu.head); init_completion(&rcu.completion); /* Will wake me after RCU finished. */ call_rcu_bh(&rcu.head, wakeme_after_rcu); /* Wait for it. */ wait_for_completion(&rcu.completion); destroy_rcu_head_on_stack(&rcu.head); } EXPORT_SYMBOL_GPL(rcu_barrier_bh); void rcu_barrier_sched(void) { struct rcu_synchronize rcu; init_rcu_head_on_stack(&rcu.head); init_completion(&rcu.completion); /* Will wake me after RCU finished. */ call_rcu_sched(&rcu.head, wakeme_after_rcu); /* Wait for it. */ wait_for_completion(&rcu.completion); destroy_rcu_head_on_stack(&rcu.head); } EXPORT_SYMBOL_GPL(rcu_barrier_sched); /* * Spawn the kthread that invokes RCU callbacks. */ static int __init rcu_spawn_kthreads(void) { struct sched_param sp; rcu_kthread_task = kthread_run(rcu_kthread, NULL, "rcu_kthread"); sp.sched_priority = RCU_BOOST_PRIO; sched_setscheduler_nocheck(rcu_kthread_task, SCHED_FIFO, &sp); return 0; } early_initcall(rcu_spawn_kthreads);