/* * 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> /* Global control variables for rcupdate callback mechanism. */ struct rcu_ctrlblk { struct rcu_head *rcucblist; /* List of pending callbacks (CBs). */ struct rcu_head **donetail; /* ->next pointer of last "done" CB. */ struct rcu_head **curtail; /* ->next pointer of last CB. */ }; /* Definition for rcupdate control block. */ static struct rcu_ctrlblk rcu_ctrlblk = { .donetail = &rcu_ctrlblk.rcucblist, .curtail = &rcu_ctrlblk.rcucblist, }; static struct rcu_ctrlblk rcu_bh_ctrlblk = { .donetail = &rcu_bh_ctrlblk.rcucblist, .curtail = &rcu_bh_ctrlblk.rcucblist, }; #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_ctrlblk) + rcu_qsctr_help(&rcu_bh_ctrlblk)) raise_softirq(RCU_SOFTIRQ); } /* * Record an rcu_bh quiescent state. */ void rcu_bh_qs(int cpu) { if (rcu_qsctr_help(&rcu_bh_ctrlblk)) raise_softirq(RCU_SOFTIRQ); } /* * 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); } /* * Helper function for rcu_process_callbacks() that operates on the * specified rcu_ctrlkblk structure. */ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp) { struct rcu_head *next, *list; unsigned long flags; /* 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; rcp->donetail = &rcp->rcucblist; local_irq_restore(flags); /* Invoke the callbacks on the local list. */ while (list) { next = list->next; prefetch(next); list->func(list); list = next; } } /* * Invoke any callbacks whose grace period has completed. */ static void rcu_process_callbacks(struct softirq_action *unused) { __rcu_process_callbacks(&rcu_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. */ void synchronize_sched(void) { cond_resched(); } EXPORT_SYMBOL_GPL(synchronize_sched); void synchronize_rcu_bh(void) { synchronize_sched(); } EXPORT_SYMBOL_GPL(synchronize_rcu_bh); /* * 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; head->func = func; head->next = NULL; local_irq_save(flags); *rcp->curtail = head; rcp->curtail = &head->next; local_irq_restore(flags); } /* * Post an RCU callback to be invoked after the end of an RCU grace * period. But since we have but one CPU, that would be after any * quiescent state. */ void call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) { __call_rcu(head, func, &rcu_ctrlblk); } EXPORT_SYMBOL_GPL(call_rcu); /* * 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(void) { struct rcu_synchronize rcu; init_completion(&rcu.completion); /* Will wake me after RCU finished. */ call_rcu(&rcu.head, wakeme_after_rcu); /* Wait for it. */ wait_for_completion(&rcu.completion); } EXPORT_SYMBOL_GPL(rcu_barrier); void rcu_barrier_bh(void) { struct rcu_synchronize rcu; 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); } EXPORT_SYMBOL_GPL(rcu_barrier_bh); void rcu_barrier_sched(void) { struct rcu_synchronize rcu; 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); } EXPORT_SYMBOL_GPL(rcu_barrier_sched); void __init rcu_init(void) { open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); }