litmus-rt.git - The LITMUS^RT kernel.

The LITMUS^RT kernel.

Bjoern Brandenburg

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	Commit message (Expand)	Author	Age
*	Linux-2.6.12-rc2v2.6.12-rc2	Linus Torvalds	2005-04-16

/* * 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/rcupdate.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/cpu.h> #include <linux/mutex.h> /* Definition for rcupdate control block. */ static struct rcu_ctrlblk rcu_ctrlblk = { .cur = -300, .completed = -300, .lock = __SPIN_LOCK_UNLOCKED(&rcu_ctrlblk.lock), .cpumask = CPU_MASK_NONE, }; static struct rcu_ctrlblk rcu_bh_ctrlblk = { .cur = -300, .completed = -300, .lock = __SPIN_LOCK_UNLOCKED(&rcu_bh_ctrlblk.lock), .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 blimit = 10; static int qhimark = 10000; static int qlowmark = 100; static atomic_t rcu_barrier_cpu_count; static DEFINE_MUTEX(rcu_barrier_mutex); static struct completion rcu_barrier_completion; #ifdef CONFIG_SMP static void force_quiescent_state(struct rcu_data *rdp, struct rcu_ctrlblk *rcp) { int cpu; cpumask_t cpumask; set_need_resched(); if (unlikely(!rcp->signaled)) { rcp->signaled = 1; /* * Don't send IPI to itself. With irqs disabled, * rdp->cpu is the current cpu. */ cpumask = rcp->cpumask; cpu_clear(rdp->cpu, cpumask); for_each_cpu_mask(cpu, cpumask) smp_send_reschedule(cpu); } } #else static inline void force_quiescent_state(struct rcu_data *rdp, struct rcu_ctrlblk *rcp) { set_need_resched(); } #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->qlen > qhimark)) { rdp->blimit = INT_MAX; force_quiescent_state(rdp, &rcu_ctrlblk); } 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; if (unlikely(++rdp->qlen > qhimark)) { rdp->blimit = INT_MAX; force_quiescent_state(rdp, &rcu_bh_ctrlblk); } 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; } /* * 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; } static void rcu_barrier_callback(struct rcu_head *notused) { if (atomic_dec_and_test(&rcu_barrier_cpu_count)) complete(&rcu_barrier_completion); } /* * Called with preemption disabled, and from cross-cpu IRQ context. */ static void rcu_barrier_func(void *notused) { int cpu = smp_processor_id(); struct rcu_data *rdp = &per_cpu(rcu_data, cpu); struct rcu_head *head; head = &rdp->barrier; atomic_inc(&rcu_barrier_cpu_count); call_rcu(head, rcu_barrier_callback); } /** * rcu_barrier - Wait until all the in-flight RCUs are complete. */ void rcu_barrier(void) { BUG_ON(in_interrupt()); /* Take cpucontrol mutex to protect against CPU hotplug */ mutex_lock(&rcu_barrier_mutex); init_completion(&rcu_barrier_completion); atomic_set(&rcu_barrier_cpu_count, 0); on_each_cpu(rcu_barrier_func, NULL, 0, 1); wait_for_completion(&rcu_barrier_completion); mutex_unlock(&rcu_barrier_mutex); } EXPORT_SYMBOL_GPL(rcu_barrier); /* * 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 = list->next; prefetch(next); list->func(list); list = next; if (++count >= rdp->blimit) break; } rdp->donelist = list; local_irq_disable(); rdp->qlen -= count; local_irq_enable(); if (rdp->blimit == INT_MAX && rdp->qlen <= qlowmark) rdp->blimit = blimit; 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_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->next_pending && rcp->completed == rcp->cur) { 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++; /* * 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(); cpus_andnot(rcp->cpumask, cpu_online_map, 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) { cpu_clear(cpu, rcp->cpumask); if (cpus_empty(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) { 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(&rcp->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); spin_unlock(&rcp->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_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(&rcp->lock); if (rcp->cur != rcp->completed) cpu_quiet(rdp->cpu, rcp); spin_unlock_bh(&rcp->lock); rcu_move_batch(this_rdp, rdp->curlist, rdp->curtail); rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail); rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail); } 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); 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_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; } if (rdp->nxtlist && !rdp->curlist) { local_irq_disable(); 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;