/* * 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 IBM Corporation, 2001 * * Authors: Dipankar Sarma * Manfred Spraul * * Based on the original work by Paul McKenney * 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 - * Documentation/RCU * */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #ifdef CONFIG_DEBUG_LOCK_ALLOC static struct lock_class_key rcu_lock_key; struct lockdep_map rcu_lock_map = STATIC_LOCKDEP_MAP_INIT("rcu_read_lock", &rcu_lock_key); EXPORT_SYMBOL_GPL(rcu_lock_map); #endif /* Definition for rcupdate control block. */ static struct rcu_ctrlblk rcu_ctrlblk = { .cur = -300, .completed = -300, .pending = -300, .lock = __SPIN_LOCK_UNLOCKED(&rcu_ctrlblk.lock), .cpumask = CPU_BITS_NONE, }; static struct rcu_ctrlblk rcu_bh_ctrlblk = { .cur = -300, .completed = -300, .pending = -300, .lock = __SPIN_LOCK_UNLOCKED(&rcu_bh_ctrlblk.lock), .cpumask = CPU_BITS_NONE, }; static DEFINE_PER_CPU(struct rcu_data, rcu_data); static DEFINE_PER_CPU(struct rcu_data, rcu_bh_data); /* * Increment the quiescent state counter. * The counter is a bit degenerated: We do not need to know * how many quiescent states passed, just if there was at least * one since the start of the grace period. Thus just a flag. */ void rcu_qsctr_inc(int cpu) { struct rcu_data *rdp = &per_cpu(rcu_data, cpu); rdp->passed_quiesc = 1; } void rcu_bh_qsctr_inc(int cpu) { struct rcu_data *rdp = &per_cpu(rcu_bh_data, cpu); rdp->passed_quiesc = 1; } static int blimit = 10; static int qhimark = 10000; static int qlowmark = 100; #ifdef CONFIG_SMP static void force_quiescent_state(struct rcu_data *rdp, struct rcu_ctrlblk *rcp) { int cpu; unsigned long flags; set_need_resched(); spin_lock_irqsave(&rcp->lock, flags); if (unlikely(!rcp->signaled)) { rcp->signaled = 1; /* * Don't send IPI to itself. With irqs disabled, * rdp->cpu is the current cpu. * * cpu_online_mask is updated by the _cpu_down() * using __stop_machine(). Since we're in irqs disabled * section, __stop_machine() is not exectuting, hence * the cpu_online_mask is stable. * * However, a cpu might have been offlined _just_ before * we disabled irqs while entering here. * And rcu subsystem might not yet have handled the CPU_DEAD * notification, leading to the offlined cpu's bit * being set in the rcp->cpumask. * * Hence cpumask = (rcp->cpumask & cpu_online_mask) to prevent * sending smp_reschedule() to an offlined CPU. */ for_each_cpu_and(cpu, to_cpumask(rcp->cpumask), cpu_online_mask) { if (cpu != rdp->cpu) smp_send_reschedule(cpu); } } spin_unlock_irqrestore(&rcp->lock, flags); } #else static inline void force_quiescent_state(struct rcu_data *rdp, struct rcu_ctrlblk *rcp) { set_need_resched(); } #endif static void __call_rcu(struct rcu_head *head, struct rcu_ctrlblk *rcp, struct rcu_data *rdp) { long batch; head->next = NULL; smp_mb(); /* Read of rcu->cur must happen after any change by caller. */ /* * Determine the batch number of this callback. * * Using ACCESS_ONCE to avoid the following error when gcc eliminates * local variable "batch" and emits codes like this: * 1) rdp->batch = rcp->cur + 1 # gets old value * ...... * 2)rcu_batch_after(rcp->cur + 1, rdp->batch) # gets new value * then [*nxttail[0], *nxttail[1]) may contain callbacks * that batch# = rdp->batch, see the comment of struct rcu_data. */ batch = ACCESS_ONCE(rcp->cur) + 1; if (rdp->nxtlist && rcu_batch_after(batch, rdp->batch)) { /* process callbacks */ rdp->nxttail[0] = rdp->nxttail[1]; rdp->nxttail[1] = rdp->nxttail[2]; if (rcu_batch_after(batch - 1, rdp->batch)) rdp->nxttail[0] = rdp->nxttail[2]; } rdp->batch = batch; *rdp->nxttail[2] = head; rdp->nxttail[2] = &head->next; if (unlikely(++rdp->qlen > qhimark)) { rdp->blimit = INT_MAX; force_quiescent_state(rdp, &rcu_ctrlblk); } } #ifdef CONFIG_RCU_CPU_STALL_DETECTOR static void record_gp_stall_check_time(struct rcu_ctrlblk *rcp) { rcp->gp_start = jiffies; rcp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_CHECK; } static void print_other_cpu_stall(struct rcu_ctrlblk *rcp) { int cpu; long delta; unsigned long flags; /* Only let one CPU complain about others per time interval. */ spin_lock_irqsave(&rcp->lock, flags); delta = jiffies - rcp->jiffies_stall; if (delta < 2 || rcp->cur != rcp->completed) { spin_unlock_irqrestore(&rcp->lock, flags); return; } rcp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_RECHECK; spin_unlock_irqrestore(&rcp->lock, flags); /* OK, time to rat on our buddy... */ printk(KERN_ERR "INFO: RCU detected CPU stalls:"); for_each_possible_cpu(cpu) { if (cpumask_test_cpu(cpu, to_cpumask(rcp->cpumask))) printk(" %d", cpu); } printk(" (detected by %d, t=%ld jiffies)\n", smp_processor_id(), (long)(jiffies - rcp->gp_start)); } static void print_cpu_stall(struct rcu_ctrlblk *rcp) { unsigned long flags; printk(KERN_ERR "INFO: RCU detected CPU %d stall (t=%lu/%lu jiffies)\n", smp_processor_id(), jiffies, jiffies - rcp->gp_start); dump_stack(); spin_lock_irqsave(&rcp->lock, flags); if ((long)(jiffies - rcp->jiffies_stall) >= 0) rcp->jiffies_stall = jiffies + RCU_SECONDS_TILL_STALL_RECHECK; spin_unlock_irqrestore(&rcp->lock, flags); set_need_resched(); /* kick ourselves to get things going. */ } static void check_cpu_stall(struct rcu_ctrlblk *rcp) { long delta; delta = jiffies - rcp->jiffies_stall; if (cpumask_test_cpu(smp_processor_id(), to_cpumask(rcp->cpumask)) && delta >= 0) { /* We haven't checked in, so go dump stack. */ print_cpu_stall(rcp); } else if (rcp->cur != rcp->completed && delta >= 2) { /* They had two seconds to dump stack, so complain. */ print_other_cpu_stall(rcp); } } #else /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ static void record_gp_stall_check_time(struct rcu_ctrlblk *rcp) { } static inline void check_cpu_stall(struct rcu_ctrlblk *rcp) { } #endif /* #else #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ /** * 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 call_rcu(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) { unsigned long flags; head->func = func; local_irq_save(flags); __call_rcu(head, &rcu_ctrlblk, &__get_cpu_var(rcu_data)); local_irq_restore(flags); } EXPORT_SYMBOL_GPL(call_rcu); /** * 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 call_rcu_bh(struct rcu_head *head, void (*func)(struct rcu_head *rcu)) { unsigned long flags; head->func = func; local_irq_save(flags); __call_rcu(head, &rcu_bh_ctrlblk, &__get_cpu_var(rcu_bh_data)); local_irq_restore(flags); } EXPORT_SYMBOL_GPL(call_rcu_bh); /* * Return the number of RCU batches processed thus far. Useful * for debug and statistics. */ long rcu_batches_completed(void) { return rcu_ctrlblk.completed; } EXPORT_SYMBOL_GPL(rcu_batches_completed); /* * Return the number of RCU batches processed thus far. Useful * for debug and statistics. */ long rcu_batches_completed_bh(void) { return rcu_bh_ctrlblk.completed; } EXPORT_SYMBOL_GPL(rcu_batches_completed_bh); /* Raises the softirq for processing rcu_callbacks. */ static inline void raise_rcu_softirq(void) { raise_softirq(RCU_SOFTIRQ); } /* * Invoke the completed RCU callbacks. They are expected to be in * a per-cpu list. */ static void rcu_do_batch(struct rcu_data *rdp) { unsigned long flags; struct rcu_head *next, *list; int count = 0; list = rdp->donelist; while (list) { next = list->next; prefetch(next); list->func(list); list = next; if (++count >= rdp->blimit) break; } rdp->donelist = list; local_irq_save(flags); rdp->qlen -= count; local_irq_restore(flags); if (rdp->blimit == INT_MAX && rdp->qlen <= qlowmark) rdp->blimit = blimit; if (!rdp->donelist) rdp->donetail = &rdp->donelist; else raise_rcu_softirq(); } /* * 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_ctrlblk.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_ctrlblk.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_ctrlblk.lock. */ static void rcu_start_batch(struct rcu_ctrlblk *rcp) { if (rcp->cur != rcp->pending && rcp->completed == rcp->cur) { rcp->cur++; record_gp_stall_check_time(rcp); /* * Accessing nohz_cpu_mask before incrementing rcp->cur needs a * Barrier Otherwise it can cause tickless idle CPUs to be * included in rcp->cpumask, which will extend graceperiods * unnecessarily. */ smp_mb(); cpumask_andnot(to_cpumask(rcp->cpumask), cpu_online_mask, nohz_cpu_mask); rcp->signaled = 0; } } /* * 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) { cpumask_clear_cpu(cpu, to_cpumask(rcp->cpumask)); if (cpumask_empty(to_cpumask(rcp->cpumask))) { /* batch completed ! */ rcp->completed = rcp->cur; rcu_start_batch(rcp); } } /* * 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_data *rdp) { unsigned long flags; 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_irqsave(&rcp->lock, flags); /* * 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); spin_unlock_irqrestore(&rcp->lock, flags); } #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, long batch) { unsigned long flags; if (list) { local_irq_save(flags); this_rdp->batch = batch; *this_rdp->nxttail[2] = list; this_rdp->nxttail[2] = tail; local_irq_restore(flags); } } static void __rcu_offline_cpu(struct rcu_data *this_rdp, struct rcu_ctrlblk *rcp, struct rcu_data *rdp) { unsigned long flags; /* * if the cpu going offline owns the grace period * we can block indefinitely waiting for it, so flush * it here */ spin_lock_irqsave(&rcp->lock, flags); if (rcp->cur != rcp->completed) cpu_quiet(rdp->cpu, rcp); rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail, rcp->cur + 1); rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail[2], rcp->cur + 1); spin_unlock(&rcp->lock); this_rdp->qlen += rdp->qlen; local_irq_restore(flags); } 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, &per_cpu(rcu_data, cpu)); __rcu_offline_cpu(this_bh_rdp, &rcu_bh_ctrlblk, &per_cpu(rcu_bh_data, cpu)); put_cpu_var(rcu_data); put_cpu_var(rcu_bh_data); } #else static void rcu_offline_cpu(int cpu) { } #endif /* * This does the RCU processing work from softirq context. */ static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp, struct rcu_data *rdp) { unsigned long flags; long completed_snap; if (rdp->nxtlist) { local_irq_save(flags); completed_snap = ACCESS_ONCE(rcp->completed); /* * move the other grace-period-completed entries to * [rdp->nxtlist, *rdp->nxttail[0]) temporarily */ if (!rcu_batch_before(completed_snap, rdp->batch)) rdp->nxttail[0] = rdp->nxttail[1] = rdp->nxttail[2]; else if (!rcu_batch_before(completed_snap, rdp->batch - 1)) rdp->nxttail[0] = rdp->nxttail[1]; /* * the grace period for entries in * [rdp->nxtlist, *rdp->nxttail[0]) has completed and * move these entries to donelist */ if (rdp->nxttail[0] != &rdp->nxtlist) { *rdp->donetail = rdp->nxtlist; rdp->donetail = rdp->nxttail[0]; rdp->nxtlist = *rdp->nxttail[0]; *rdp->donetail = NULL; if (rdp->nxttail[1] == rdp->nxttail[0]) rdp->nxttail[1] = &rdp->nxtlist; if (rdp->nxttail[2] == rdp->nxttail[0]) rdp->nxttail[2] = &rdp->nxtlist; rdp->nxttail[0] = &rdp->nxtlist; } local_irq_restore(flags); if (rcu_batch_after(rdp->batch, rcp->pending)) { unsigned long flags2; /* and start it/schedule start if it's a new batch */ spin_lock_irqsave(&rcp->lock, flags2); if (rcu_batch_after(rdp->batch, rcp->pending)) { rcp->pending = rdp->batch; rcu_start_batch(rcp); } spin_unlock_irqrestore(&rcp->lock, flags2); } } rcu_check_quiescent_state(rcp, rdp); if (rdp->donelist) rcu_do_batch(rdp); } static void rcu_process_callbacks(struct softirq_action *unused) { /* * Memory references from any prior RCU read-side critical sections * executed by the interrupted code must be see before any RCU * grace-period manupulations below. */ smp_mb(); /* See above block comment. */ __rcu_process_callbacks(&rcu_ctrlblk, &__get_cpu_var(rcu_data)); __rcu_process_callbacks(&rcu_bh_ctrlblk, &__get_cpu_var(rcu_bh_data)); /* * Memory references from any later RCU read-side critical sections * executed by the interrupted code must be see after any RCU * grace-period manupulations above. */ smp_mb(); /* See above block comment. */ } static int __rcu_pending(struct rcu_ctrlblk *rcp, struct rcu_data *rdp) { /* Check for CPU stalls, if enabled. */ check_cpu_stall(rcp); if (rdp->nxtlist) { long completed_snap = ACCESS_ONCE(rcp->completed); /* * This cpu has pending rcu entries and the grace period * for them has completed. */ if (!rcu_batch_before(completed_snap, rdp->batch)) return 1; if (!rcu_batch_before(completed_snap, rdp->batch - 1) && rdp->nxttail[0] != rdp->nxttail[1]) return 1; if (rdp->nxttail[0] != &rdp->nxtlist) return 1; /* * This cpu has pending rcu entries and the new batch * for then hasn't been started nor scheduled start */ if (rcu_batch_after(rdp->batch, rcp->pending)) return 1; } /* This cpu has finished callbacks to invoke */ if (rdp->donelist) return 1; /* The rcu core waits for a quiescent state from the cpu */ if (rdp->quiescbatch != rcp->cur || rdp->qs_pending) return 1; /* nothing to do */ return 0; } /* * Check to see if there is any immediate RCU-related work to be done * by the current CPU, returning 1 if so. This function is part of the * RCU implementation; it is -not- an exported member of the RCU API. */ int rcu_pending(int cpu) { return __rcu_pending(&rcu_ctrlblk, &per_cpu(rcu_data, cpu)) || __rcu_pending(&rcu_bh_ctrlblk, &per_cpu(rcu_bh_data, cpu)); } /* * Check to see if any future RCU-related work will need to be done * by the current CPU, even if none need be done immediately, returning * 1 if so. This function is part of the RCU implementation; it is -not- * an exported member of the RCU API. */ int rcu_needs_cpu(int cpu) { struct rcu_data *rdp = &per_cpu(rcu_data, cpu); struct rcu_data *rdp_bh = &per_cpu(rcu_bh_data, cpu); return !!rdp->nxtlist || !!rdp_bh->nxtlist || rcu_pending(cpu); } /* * Top-level function driving RCU grace-period detection, normally * invoked from the scheduler-clock interrupt. This function simply * increments counters that are read only from softirq by this same * CPU, so there are no memory barriers required. */ void rcu_check_callbacks(int cpu, int user) { if (user || (idle_cpu(cpu) && rcu_scheduler_active && !in_softirq() && hardirq_count() <= (1 << HARDIRQ_SHIFT))) { /* * Get here if this CPU took its interrupt from user * mode or from the idle loop, and if this is not a * nested interrupt. In this case, the CPU is in * a quiescent state, so count it. * * Also do a memory barrier. This is needed to handle * the case where writes from a preempt-disable section * of code get reordered into schedule() by this CPU's * write buffer. The memory barrier makes sure that * the rcu_qsctr_inc() and rcu_bh_qsctr_inc() are see * by other CPUs to happen after any such write. */ smp_mb(); /* See above block comment. */ rcu_qsctr_inc(cpu); rcu_bh_qsctr_inc(cpu); } else if (!in_softirq()) { /* * Get here if this CPU did not take its interrupt from * softirq, in other words, if it is not interrupting * a rcu_bh read-side critical section. This is an _bh * critical section, so count it. The memory barrier * is needed for the same reason as is the above one. */ smp_mb(); /* See above block comment. */ rcu_bh_qsctr_inc(cpu); } raise_rcu_softirq(); } static void __cpuinit rcu_init_percpu_data(int cpu, struct rcu_ctrlblk *rcp, struct rcu_data *rdp) { unsigned long flags; spin_lock_irqsave(&rcp->lock, flags); memset(rdp, 0, sizeof(*rdp)); rdp->nxttail[0] = rdp->nxttail[1] = rdp->nxttail[2] = &rdp->nxtlist; rdp->donetail = &rdp->donelist; rdp->quiescbatch = rcp->completed; rdp->qs_pending = 0; rdp->cpu = cpu; rdp->blimit = blimit; spin_unlock_irqrestore(&rcp->lock, flags); } static void __cpuinit 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); open_softirq(RCU_SOFTIRQ, rcu_process_callbacks); } static int __cpuinit rcu_cpu_notify(struct notifier_block *self, unsigned long action, void *hcpu) { long cpu = (long)hcpu; switch (action) { case CPU_UP_PREPARE: case CPU_UP_PREPARE_FROZEN: rcu_online_cpu(cpu); break; case CPU_DEAD: case CPU_DEAD_FROZEN: rcu_offline_cpu(cpu); break; default: break; } return NOTIFY_OK; } static struct notifier_block __cpuinitdata 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) { #ifdef CONFIG_RCU_CPU_STALL_DETECTOR printk(KERN_INFO "RCU-based detection of stalled CPUs is enabled.\n"); #endif /* #ifdef CONFIG_RCU_CPU_STALL_DETECTOR */ rcu_cpu_notify(&rcu_nb, CPU_UP_PREPARE, (void *)(long)smp_processor_id()); /* Register notifier for non-boot CPUs */ register_cpu_notifier(&rcu_nb); } module_param(blimit, int, 0); module_param(qhimark, int, 0); module_param(qlowmark, int, 0);