/* * Read-Copy Update mechanism for mutual exclusion * * 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 (C) IBM Corporation, 2001 * * Authors: Dipankar Sarma <dipankar@in.ibm.com> * Manfred Spraul <manfred@colorfullife.com> * * Based on the original work by Paul McKenney <paulmck@us.ibm.com> * and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen. * Papers: * http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf * http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001) * * For detailed explanation of Read-Copy Update mechanism see - * http://lse.sourceforge.net/locking/rcupdate.html * */ #include <linux/types.h> #include <linux/kernel.h> #include <linux/init.h> #include <linux/spinlock.h> #include <linux/smp.h> #include <linux/interrupt.h> #include <linux/sched.h> #include <asm/atomic.h> #include <linux/bitops.h> #include <linux/module.h> #include <linux/completion.h> #include <linux/moduleparam.h> #include <linux/percpu.h> #include <linux/notifier.h> #include <linux/rcupdate.h> #include <linux/rcuref.h> #include <linux/cpu.h> /* Definition for rcupdate control block. */ struct rcu_ctrlblk rcu_ctrlblk = { .cur = -300, .completed = -300 }; struct rcu_ctrlblk rcu_bh_ctrlblk = { .cur = -300, .completed = -300 }; /* Bookkeeping of the progress of the grace period */ struct rcu_state { spinlock_t lock; /* Guard this struct and writes to rcu_ctrlblk */ cpumask_t cpumask; /* CPUs that need to switch in order */ /* for current batch to proceed. */ }; static struct rcu_state rcu_state ____cacheline_maxaligned_in_smp = {.lock = SPIN_LOCK_UNLOCKED, .cpumask = CPU_MASK_NONE }; static struct rcu_state rcu_bh_state ____cacheline_maxaligned_in_smp = {.lock = SPIN_LOCK_UNLOCKED, .cpumask = CPU_MASK_NONE }; DEFINE_PER_CPU(struct rcu_data, rcu_data) = { 0L }; DEFINE_PER_CPU(struct rcu_data, rcu_bh_data) = { 0L }; /* Fake initialization required by compiler */ static DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL}; static int maxbatch = 10000; #ifndef __HAVE_ARCH_CMPXCHG /* * We use an array of spinlocks for the rcurefs -- similar to ones in sparc * 32 bit atomic_t implementations, and a hash function similar to that * for our refcounting needs. * Can't help multiprocessors which donot have cmpxchg :( */ spinlock_t __rcuref_hash[RCUREF_HASH_SIZE] = { [0 ... (RCUREF_HASH_SIZE-1)] = SPIN_LOCK_UNLOCKED }; #endif /** * call_rcu - Queue an RCU callback for invocation after a grace period. * @head: structure to be used for queueing the RCU updates. * @func: actual update function to be invoked after the grace period * * The update function will be invoked some time after a full grace * period elapses, in other words after all currently executing RCU * read-side critical sections have completed. RCU read-side critical * sections are delimited by rcu_read_lock() and rcu_read_unlock(), * and may be nested. */ void fastcall call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) { unsigned long flags; struct rcu_data *rdp; head->func = func; head->next = NULL; local_irq_save(flags); rdp = &__get_cpu_var(rcu_data); *rdp->nxttail = head; rdp->nxttail = &head->next; if (unlikely(++rdp->count > 10000)) set_need_resched(); local_irq_restore(flags); } /** * call_rcu_bh - Queue an RCU for invocation after a quicker grace period. * @head: structure to be used for queueing the RCU updates. * @func: actual update function to be invoked after the grace period * * The update function will be invoked some time after a full grace * period elapses, in other words after all currently executing RCU * read-side critical sections have completed. call_rcu_bh() assumes * that the read-side critical sections end on completion of a softirq * handler. This means that read-side critical sections in process * context must not be interrupted by softirqs. This interface is to be * used when most of the read-side critical sections are in softirq context. * RCU read-side critical sections are delimited by rcu_read_lock() and * rcu_read_unlock(), * if in interrupt context or rcu_read_lock_bh() * and rcu_read_unlock_bh(), if in process context. These may be nested. */ void fastcall call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) { unsigned long flags; struct rcu_data *rdp; head->func = func; head->next = NULL; local_irq_save(flags); rdp = &__get_cpu_var(rcu_bh_data); *rdp->nxttail = head; rdp->nxttail = &head->next; rdp->count++; /* * Should we directly call rcu_do_batch() here ? * if (unlikely(rdp->count > 10000)) * rcu_do_batch(rdp); */ local_irq_restore(flags); } /* * Return the number of RCU batches processed thus far. Useful * for debug and statistics. */ long rcu_batches_completed(void) { return rcu_ctrlblk.completed; } /* * Invoke the completed RCU callbacks. They are expected to be in * a per-cpu list. */ static void rcu_do_batch(struct rcu_data *rdp) { struct rcu_head *next, *list; int count = 0; list = rdp->donelist; while (list) { next = rdp->donelist = list->next; list->func(list); list = next; rdp->count--; if (++count >= maxbatch) break; } if (!rdp->donelist) rdp->donetail = &rdp->donelist; else tasklet_schedule(&per_cpu(rcu_tasklet, rdp->cpu)); } /* * Grace period handling: * The grace period handling consists out of two steps: * - A new grace period is started. * This is done by rcu_start_batch. The start is not broadcasted to * all cpus, they must pick this up by comparing rcp->cur with * rdp->quiescbatch. All cpus are recorded in the * rcu_state.cpumask bitmap. * - All cpus must go through a quiescent state. * Since the start of the grace period is not broadcasted, at least two * calls to rcu_check_quiescent_state are required: * The first call just notices that a new grace period is running. The * following calls check if there was a quiescent state since the beginning * of the grace period. If so, it updates rcu_state.cpumask. If * the bitmap is empty, then the grace period is completed. * rcu_check_quiescent_state calls rcu_start_batch(0) to start the next grace * period (if necessary). */ /* * Register a new batch of callbacks, and start it up if there is currently no * active batch and the batch to be registered has not already occurred. * Caller must hold rcu_state.lock. */ static void rcu_start_batch(struct rcu_ctrlblk *rcp, struct rcu_state *rsp, int next_pending) { if (next_pending) rcp->next_pending = 1; if (rcp->next_pending && rcp->completed == rcp->cur) { /* Can't change, since spin lock held. */ cpus_andnot(rsp->cpumask, cpu_online_map, nohz_cpu_mask); rcp->next_pending = 0; /* next_pending == 0 must be visible in __rcu_process_callbacks() * before it can see new value of cur. */ smp_wmb(); rcp->cur++; } } /* * cpu went through a quiescent state since the beginning of the grace period. * Clear it from the cpu mask and complete the grace period if it was the last * cpu. Start another grace period if someone has further entries pending */ static void cpu_quiet(int cpu, struct rcu_ctrlblk *rcp, struct rcu_state *rsp) { cpu_clear(cpu, rsp->cpumask); if (cpus_empty(rsp->cpumask)) { /* batch completed ! */ rcp->completed = rcp->cur; rcu_start_batch(rcp, rsp, 0); } } /* * Check if the cpu has gone through a quiescent state (say context * switch). If so and if it already hasn't done so in this RCU * quiescent cycle, then indicate that it has done so. */ static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp, struct rcu_state *rsp, struct rcu_data *rdp) { if (rdp->quiescbatch != rcp->cur) { /* start new grace period: */ rdp->qs_pending = 1; rdp->passed_quiesc = 0; rdp->quiescbatch = rcp->cur; return; } /* Grace period already completed for this cpu? * qs_pending is checked instead of the actual bitmap to avoid * cacheline trashing. */ if (!rdp->qs_pending) return; /* * Was there a quiescent state since the beginning of the grace * period? If no, then exit and wait for the next call. */ if (!rdp->passed_quiesc) return; rdp->qs_pending = 0; spin_lock(&rsp->lock); /* * rdp->quiescbatch/rcp->cur and the cpu bitmap can come out of sync * during cpu startup. Ignore the quiescent state. */ if (likely(rdp->quiescbatch == rcp->cur)) cpu_quiet(rdp->cpu, rcp, rsp); spin_unlock(&rsp->lock); } #ifdef CONFIG_HOTPLUG_CPU /* warning! helper for rcu_offline_cpu. do not use elsewhere without reviewing * locking requirements, the list it's pulling from has to belong to a cpu * which is dead and hence not processing interrupts. */ static void rcu_move_batch(struct rcu_data *this_rdp, struct rcu_head *list, struct rcu_head **tail) { local_irq_disable(); *this_rdp->nxttail = list; if (list) this_rdp->nxttail = tail; local_irq_enable(); } static void __rcu_offline_cpu(struct rcu_data *this_rdp, struct rcu_ctrlblk *rcp, struct rcu_state *rsp, struct rcu_data *rdp) { /* if the cpu going offline owns the grace period * we can block indefinitely waiting for it, so flush * it here */ spin_lock_bh(&rsp->lock); if (rcp->cur != rcp->completed) cpu_quiet(rdp->cpu, rcp, rsp); spin_unlock_bh(&rsp->lock); rcu_move_batch(this_rdp, rdp->curlist, rdp->curtail); rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail); } static void rcu_offline_cpu(int cpu) { struct rcu_data *this_rdp = &get_cpu_var(rcu_data); struct rcu_data *this_bh_rdp = &get_cpu_var(rcu_bh_data); __rcu_offline_cpu(this_rdp, &rcu_ctrlblk, &rcu_state, &per_cpu(rcu_data, cpu)); __rcu_offline_cpu(this_bh_rdp, &rcu_bh_ctrlblk, &rcu_bh_state, &per_cpu(rcu_bh_data, cpu)); put_cpu_var(rcu_data); put_cpu_var(rcu_bh_data); tasklet_kill_immediate(&per_cpu(rcu_tasklet, cpu), cpu); } #else static void rcu_offline_cpu(int cpu) { } #endif /* * This does the RCU processing work from tasklet context. */ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp, struct rcu_state *rsp, struct rcu_data *rdp) { if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch)) { *rdp->donetail = rdp->curlist; rdp->donetail = rdp->curtail; rdp->curlist = NULL; rdp->curtail = &rdp->curlist; } local_irq_disable(); if (rdp->nxtlist && !rdp->curlist) { rdp->curlist = rdp->nxtlist; rdp->curtail = rdp->nxttail; rdp->nxtlist = NULL; rdp->nxttail = &rdp->nxtlist; local_irq_enable(); /* * start the next batch of callbacks */ /* determine batch number */ rdp->batch = rcp->cur + 1; /* see the comment and corresponding wmb() in * the rcu_start_batch() */ smp_rmb(); if (!rcp->next_pending) { /* and start it/schedule start if it's a new batch */ spin_lock(&rsp->lock); rcu_start_batch(rcp, rsp, 1); spin_unlock(&rsp->lock); } } else { local_irq_enable(); } rcu_check_quiescent_state(rcp, rsp, rdp); if (rdp->donelist) rcu_do_batch(rdp); } static void rcu_process_callbacks(unsigned long unused) { __rcu_process_callbacks(&rcu_ctrlblk, &rcu_state, &__get_cpu_var(rcu_data)); __rcu_process_callbacks(&rcu_bh_ctrlblk, &rcu_bh_state, &__get_cpu_var(rcu_bh_data)); } void rcu_check_callbacks(int cpu, int user) { if (user || (idle_cpu(cpu) && !in_softirq() && hardirq_count() <= (1 << HARDIRQ_SHIFT))) { rcu_qsctr_inc(cpu); rcu_bh_qsctr_inc(cpu); } else if (!in_softirq()) rcu_bh_qsctr_inc(cpu); tasklet_schedule(&per_cpu(rcu_tasklet, cpu)); } static void rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp, struct rcu_data *rdp) { memset(rdp, 0, sizeof(*rdp)); rdp->curtail = &rdp->curlist; rdp->nxttail = &rdp->nxtlist; rdp->donetail = &rdp->donelist; rdp->quiescbatch = rcp->completed; rdp->qs_pending = 0; rdp->cpu = cpu; } static void __devinit rcu_online_cpu(int cpu) { struct rcu_data *rdp = &per_cpu(rcu_data, cpu); struct rcu_data *bh_rdp = &per_cpu(rcu_bh_data, cpu); rcu_init_percpu_data(cpu, &rcu_ctrlblk, rdp); rcu_init_percpu_data(cpu, &rcu_bh_ctrlblk, bh_rdp); tasklet_init(&per_cpu(rcu_tasklet, cpu), rcu_process_callbacks, 0UL); } static int __devinit rcu_cpu_notify(struct notifier_block *self, unsigned long action, void *hcpu) { long cpu = (long)hcpu; switch (action) { case CPU_UP_PREPARE: rcu_online_cpu(cpu); break; case CPU_DEAD: rcu_offline_cpu(cpu); break; default: break; } return NOTIFY_OK; } static struct notifier_block __devinitdata rcu_nb = { .notifier_call = rcu_cpu_notify, }; /* * Initializes rcu mechanism. Assumed to be called early. * That is before local timer(SMP) or jiffie timer (uniproc) is setup. * Note that rcu_qsctr and friends are implicitly * initialized due to the choice of ``0'' for RCU_CTR_INVALID. */ void __init rcu_init(void) { rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE, (void *)(long)smp_processor_id()); /* Register notifier for non-boot CPUs */ register_cpu_notifier(&rcu_nb); } struct rcu_synchronize { struct rcu_head head; struct completion completion; }; /* Because of FASTCALL declaration of complete, we use this wrapper */ static void wakeme_after_rcu(struct rcu_head *head) { struct rcu_synchronize *rcu; rcu = container_of(head, struct rcu_synchronize, head); complete(&rcu->completion); } /** * synchronize_rcu - wait until a grace period has elapsed. * * Control will return to the caller some time after a full grace * period has elapsed, in other words after all currently executing RCU * read-side critical sections have completed. RCU read-side critical * sections are delimited by rcu_read_lock() and rcu_read_unlock(), * and may be nested. * * If your read-side code is not protected by rcu_read_lock(), do -not- * use synchronize_rcu(). */ void synchronize_rcu(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); } /* * Deprecated, use synchronize_rcu() or synchronize_sched() instead. */ void synchronize_kernel(void) { synchronize_rcu(); } module_param(maxbatch, int, 0); EXPORT_SYMBOL_GPL(rcu_batches_completed); EXPORT_SYMBOL(call_rcu); /* WARNING: GPL-only in April 2006. */ EXPORT_SYMBOL(call_rcu_bh); /* WARNING: GPL-only in April 2006. */ EXPORT_SYMBOL_GPL(synchronize_rcu); EXPORT_SYMBOL(synchronize_kernel); /* WARNING: GPL-only in April 2006. */