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![Oleg Nesterov](/assets/img/avatar_default.png)
Kill a hard-to-calculate 'rsinterval' boot parameter and per-cpu rcu_data.last_rs_qlen. Instead, it adds adds a flag rcu_ctrlblk.signaled, which records the fact that one of CPUs has sent a resched IPI since the last rcu_start_batch(). Roughly speaking, we need two rcu_start_batch()s in order to move callbacks from ->nxtlist to ->donelist. This means that when ->qlen exceeds qhimark and continues to grow, we should send a resched IPI, and then do it again after we gone through a quiescent state. On the other hand, if it was already sent, we don't need to do it again when another CPU detects overflow of the queue. Signed-off-by: Oleg Nesterov <oleg@tv-sign.ru> Acked-by: Paul E. McKenney <paulmck@us.ibm.com> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
633 lines
17 KiB
C
633 lines
17 KiB
C
/*
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* Read-Copy Update mechanism for mutual exclusion
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2 of the License, or
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* (at your option) any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; if not, write to the Free Software
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* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
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*
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* Copyright (C) IBM Corporation, 2001
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*
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* Authors: Dipankar Sarma <dipankar@in.ibm.com>
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* Manfred Spraul <manfred@colorfullife.com>
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*
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* Based on the original work by Paul McKenney <paulmck@us.ibm.com>
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* and inputs from Rusty Russell, Andrea Arcangeli and Andi Kleen.
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* Papers:
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* http://www.rdrop.com/users/paulmck/paper/rclockpdcsproof.pdf
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* http://lse.sourceforge.net/locking/rclock_OLS.2001.05.01c.sc.pdf (OLS2001)
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*
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* For detailed explanation of Read-Copy Update mechanism see -
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* http://lse.sourceforge.net/locking/rcupdate.html
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*
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*/
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#include <linux/types.h>
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#include <linux/kernel.h>
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#include <linux/init.h>
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#include <linux/spinlock.h>
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#include <linux/smp.h>
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#include <linux/rcupdate.h>
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#include <linux/interrupt.h>
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#include <linux/sched.h>
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#include <asm/atomic.h>
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#include <linux/bitops.h>
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#include <linux/module.h>
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#include <linux/completion.h>
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#include <linux/moduleparam.h>
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#include <linux/percpu.h>
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#include <linux/notifier.h>
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#include <linux/rcupdate.h>
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#include <linux/cpu.h>
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#include <linux/mutex.h>
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/* Definition for rcupdate control block. */
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static struct rcu_ctrlblk rcu_ctrlblk = {
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.cur = -300,
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.completed = -300,
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.lock = __SPIN_LOCK_UNLOCKED(&rcu_ctrlblk.lock),
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.cpumask = CPU_MASK_NONE,
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};
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static struct rcu_ctrlblk rcu_bh_ctrlblk = {
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.cur = -300,
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.completed = -300,
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.lock = __SPIN_LOCK_UNLOCKED(&rcu_bh_ctrlblk.lock),
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.cpumask = CPU_MASK_NONE,
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};
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DEFINE_PER_CPU(struct rcu_data, rcu_data) = { 0L };
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DEFINE_PER_CPU(struct rcu_data, rcu_bh_data) = { 0L };
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/* Fake initialization required by compiler */
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static DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL};
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static int blimit = 10;
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static int qhimark = 10000;
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static int qlowmark = 100;
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static atomic_t rcu_barrier_cpu_count;
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static DEFINE_MUTEX(rcu_barrier_mutex);
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static struct completion rcu_barrier_completion;
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#ifdef CONFIG_SMP
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static void force_quiescent_state(struct rcu_data *rdp,
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struct rcu_ctrlblk *rcp)
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{
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int cpu;
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cpumask_t cpumask;
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set_need_resched();
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if (unlikely(!rcp->signaled)) {
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rcp->signaled = 1;
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/*
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* Don't send IPI to itself. With irqs disabled,
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* rdp->cpu is the current cpu.
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*/
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cpumask = rcp->cpumask;
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cpu_clear(rdp->cpu, cpumask);
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for_each_cpu_mask(cpu, cpumask)
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smp_send_reschedule(cpu);
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}
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}
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#else
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static inline void force_quiescent_state(struct rcu_data *rdp,
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struct rcu_ctrlblk *rcp)
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{
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set_need_resched();
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}
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#endif
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/**
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* call_rcu - Queue an RCU callback for invocation after a grace period.
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* @head: structure to be used for queueing the RCU updates.
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* @func: actual update function to be invoked after the grace period
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*
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* The update function will be invoked some time after a full grace
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* period elapses, in other words after all currently executing RCU
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* read-side critical sections have completed. RCU read-side critical
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* sections are delimited by rcu_read_lock() and rcu_read_unlock(),
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* and may be nested.
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*/
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void fastcall call_rcu(struct rcu_head *head,
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void (*func)(struct rcu_head *rcu))
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{
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unsigned long flags;
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struct rcu_data *rdp;
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head->func = func;
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head->next = NULL;
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local_irq_save(flags);
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rdp = &__get_cpu_var(rcu_data);
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*rdp->nxttail = head;
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rdp->nxttail = &head->next;
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if (unlikely(++rdp->qlen > qhimark)) {
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rdp->blimit = INT_MAX;
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force_quiescent_state(rdp, &rcu_ctrlblk);
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}
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local_irq_restore(flags);
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}
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/**
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* call_rcu_bh - Queue an RCU for invocation after a quicker grace period.
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* @head: structure to be used for queueing the RCU updates.
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* @func: actual update function to be invoked after the grace period
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*
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* The update function will be invoked some time after a full grace
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* period elapses, in other words after all currently executing RCU
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* read-side critical sections have completed. call_rcu_bh() assumes
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* that the read-side critical sections end on completion of a softirq
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* handler. This means that read-side critical sections in process
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* context must not be interrupted by softirqs. This interface is to be
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* used when most of the read-side critical sections are in softirq context.
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* RCU read-side critical sections are delimited by rcu_read_lock() and
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* rcu_read_unlock(), * if in interrupt context or rcu_read_lock_bh()
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* and rcu_read_unlock_bh(), if in process context. These may be nested.
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*/
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void fastcall call_rcu_bh(struct rcu_head *head,
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void (*func)(struct rcu_head *rcu))
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{
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unsigned long flags;
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struct rcu_data *rdp;
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head->func = func;
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head->next = NULL;
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local_irq_save(flags);
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rdp = &__get_cpu_var(rcu_bh_data);
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*rdp->nxttail = head;
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rdp->nxttail = &head->next;
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if (unlikely(++rdp->qlen > qhimark)) {
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rdp->blimit = INT_MAX;
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force_quiescent_state(rdp, &rcu_bh_ctrlblk);
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}
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local_irq_restore(flags);
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}
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/*
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* Return the number of RCU batches processed thus far. Useful
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* for debug and statistics.
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*/
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long rcu_batches_completed(void)
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{
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return rcu_ctrlblk.completed;
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}
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/*
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* Return the number of RCU batches processed thus far. Useful
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* for debug and statistics.
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*/
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long rcu_batches_completed_bh(void)
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{
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return rcu_bh_ctrlblk.completed;
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}
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static void rcu_barrier_callback(struct rcu_head *notused)
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{
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if (atomic_dec_and_test(&rcu_barrier_cpu_count))
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complete(&rcu_barrier_completion);
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}
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/*
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* Called with preemption disabled, and from cross-cpu IRQ context.
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*/
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static void rcu_barrier_func(void *notused)
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{
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int cpu = smp_processor_id();
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struct rcu_data *rdp = &per_cpu(rcu_data, cpu);
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struct rcu_head *head;
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head = &rdp->barrier;
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atomic_inc(&rcu_barrier_cpu_count);
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call_rcu(head, rcu_barrier_callback);
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}
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/**
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* rcu_barrier - Wait until all the in-flight RCUs are complete.
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*/
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void rcu_barrier(void)
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{
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BUG_ON(in_interrupt());
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/* Take cpucontrol mutex to protect against CPU hotplug */
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mutex_lock(&rcu_barrier_mutex);
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init_completion(&rcu_barrier_completion);
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atomic_set(&rcu_barrier_cpu_count, 0);
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on_each_cpu(rcu_barrier_func, NULL, 0, 1);
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wait_for_completion(&rcu_barrier_completion);
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mutex_unlock(&rcu_barrier_mutex);
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}
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EXPORT_SYMBOL_GPL(rcu_barrier);
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/*
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* Invoke the completed RCU callbacks. They are expected to be in
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* a per-cpu list.
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*/
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static void rcu_do_batch(struct rcu_data *rdp)
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{
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struct rcu_head *next, *list;
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int count = 0;
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list = rdp->donelist;
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while (list) {
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next = rdp->donelist = list->next;
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list->func(list);
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list = next;
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if (++count >= rdp->blimit)
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break;
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}
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local_irq_disable();
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rdp->qlen -= count;
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local_irq_enable();
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if (rdp->blimit == INT_MAX && rdp->qlen <= qlowmark)
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rdp->blimit = blimit;
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if (!rdp->donelist)
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rdp->donetail = &rdp->donelist;
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else
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tasklet_schedule(&per_cpu(rcu_tasklet, rdp->cpu));
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}
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/*
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* Grace period handling:
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* The grace period handling consists out of two steps:
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* - A new grace period is started.
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* This is done by rcu_start_batch. The start is not broadcasted to
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* all cpus, they must pick this up by comparing rcp->cur with
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* rdp->quiescbatch. All cpus are recorded in the
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* rcu_ctrlblk.cpumask bitmap.
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* - All cpus must go through a quiescent state.
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* Since the start of the grace period is not broadcasted, at least two
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* calls to rcu_check_quiescent_state are required:
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* The first call just notices that a new grace period is running. The
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* following calls check if there was a quiescent state since the beginning
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* of the grace period. If so, it updates rcu_ctrlblk.cpumask. If
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* the bitmap is empty, then the grace period is completed.
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* rcu_check_quiescent_state calls rcu_start_batch(0) to start the next grace
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* period (if necessary).
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*/
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/*
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* Register a new batch of callbacks, and start it up if there is currently no
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* active batch and the batch to be registered has not already occurred.
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* Caller must hold rcu_ctrlblk.lock.
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*/
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static void rcu_start_batch(struct rcu_ctrlblk *rcp)
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{
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if (rcp->next_pending &&
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rcp->completed == rcp->cur) {
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rcp->next_pending = 0;
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/*
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* next_pending == 0 must be visible in
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* __rcu_process_callbacks() before it can see new value of cur.
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*/
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smp_wmb();
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rcp->cur++;
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/*
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* Accessing nohz_cpu_mask before incrementing rcp->cur needs a
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* Barrier Otherwise it can cause tickless idle CPUs to be
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* included in rcp->cpumask, which will extend graceperiods
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* unnecessarily.
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*/
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smp_mb();
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cpus_andnot(rcp->cpumask, cpu_online_map, nohz_cpu_mask);
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rcp->signaled = 0;
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}
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}
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/*
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* cpu went through a quiescent state since the beginning of the grace period.
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* Clear it from the cpu mask and complete the grace period if it was the last
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* cpu. Start another grace period if someone has further entries pending
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*/
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static void cpu_quiet(int cpu, struct rcu_ctrlblk *rcp)
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{
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cpu_clear(cpu, rcp->cpumask);
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if (cpus_empty(rcp->cpumask)) {
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/* batch completed ! */
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rcp->completed = rcp->cur;
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rcu_start_batch(rcp);
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}
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}
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/*
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* Check if the cpu has gone through a quiescent state (say context
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* switch). If so and if it already hasn't done so in this RCU
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* quiescent cycle, then indicate that it has done so.
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*/
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static void rcu_check_quiescent_state(struct rcu_ctrlblk *rcp,
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struct rcu_data *rdp)
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{
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if (rdp->quiescbatch != rcp->cur) {
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/* start new grace period: */
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rdp->qs_pending = 1;
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rdp->passed_quiesc = 0;
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rdp->quiescbatch = rcp->cur;
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return;
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}
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/* Grace period already completed for this cpu?
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* qs_pending is checked instead of the actual bitmap to avoid
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* cacheline trashing.
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*/
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if (!rdp->qs_pending)
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return;
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/*
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* Was there a quiescent state since the beginning of the grace
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* period? If no, then exit and wait for the next call.
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*/
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if (!rdp->passed_quiesc)
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return;
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rdp->qs_pending = 0;
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spin_lock(&rcp->lock);
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/*
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* rdp->quiescbatch/rcp->cur and the cpu bitmap can come out of sync
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* during cpu startup. Ignore the quiescent state.
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*/
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if (likely(rdp->quiescbatch == rcp->cur))
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cpu_quiet(rdp->cpu, rcp);
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spin_unlock(&rcp->lock);
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}
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#ifdef CONFIG_HOTPLUG_CPU
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/* warning! helper for rcu_offline_cpu. do not use elsewhere without reviewing
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* locking requirements, the list it's pulling from has to belong to a cpu
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* which is dead and hence not processing interrupts.
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*/
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static void rcu_move_batch(struct rcu_data *this_rdp, struct rcu_head *list,
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struct rcu_head **tail)
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{
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local_irq_disable();
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*this_rdp->nxttail = list;
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if (list)
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this_rdp->nxttail = tail;
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local_irq_enable();
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}
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static void __rcu_offline_cpu(struct rcu_data *this_rdp,
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struct rcu_ctrlblk *rcp, struct rcu_data *rdp)
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{
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/* if the cpu going offline owns the grace period
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* we can block indefinitely waiting for it, so flush
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* it here
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*/
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spin_lock_bh(&rcp->lock);
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if (rcp->cur != rcp->completed)
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cpu_quiet(rdp->cpu, rcp);
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spin_unlock_bh(&rcp->lock);
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rcu_move_batch(this_rdp, rdp->curlist, rdp->curtail);
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rcu_move_batch(this_rdp, rdp->nxtlist, rdp->nxttail);
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rcu_move_batch(this_rdp, rdp->donelist, rdp->donetail);
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}
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static void rcu_offline_cpu(int cpu)
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{
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struct rcu_data *this_rdp = &get_cpu_var(rcu_data);
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struct rcu_data *this_bh_rdp = &get_cpu_var(rcu_bh_data);
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__rcu_offline_cpu(this_rdp, &rcu_ctrlblk,
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&per_cpu(rcu_data, cpu));
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__rcu_offline_cpu(this_bh_rdp, &rcu_bh_ctrlblk,
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&per_cpu(rcu_bh_data, cpu));
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put_cpu_var(rcu_data);
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put_cpu_var(rcu_bh_data);
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tasklet_kill_immediate(&per_cpu(rcu_tasklet, cpu), cpu);
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}
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#else
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static void rcu_offline_cpu(int cpu)
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{
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}
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#endif
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/*
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* This does the RCU processing work from tasklet context.
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*/
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static void __rcu_process_callbacks(struct rcu_ctrlblk *rcp,
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struct rcu_data *rdp)
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{
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if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch)) {
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*rdp->donetail = rdp->curlist;
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rdp->donetail = rdp->curtail;
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rdp->curlist = NULL;
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rdp->curtail = &rdp->curlist;
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}
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if (rdp->nxtlist && !rdp->curlist) {
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local_irq_disable();
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rdp->curlist = rdp->nxtlist;
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rdp->curtail = rdp->nxttail;
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rdp->nxtlist = NULL;
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rdp->nxttail = &rdp->nxtlist;
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local_irq_enable();
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/*
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* start the next batch of callbacks
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*/
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/* determine batch number */
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rdp->batch = rcp->cur + 1;
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/* see the comment and corresponding wmb() in
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* the rcu_start_batch()
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*/
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smp_rmb();
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if (!rcp->next_pending) {
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/* and start it/schedule start if it's a new batch */
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spin_lock(&rcp->lock);
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rcp->next_pending = 1;
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rcu_start_batch(rcp);
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spin_unlock(&rcp->lock);
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}
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}
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rcu_check_quiescent_state(rcp, rdp);
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if (rdp->donelist)
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rcu_do_batch(rdp);
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}
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static void rcu_process_callbacks(unsigned long unused)
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{
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__rcu_process_callbacks(&rcu_ctrlblk, &__get_cpu_var(rcu_data));
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__rcu_process_callbacks(&rcu_bh_ctrlblk, &__get_cpu_var(rcu_bh_data));
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}
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static int __rcu_pending(struct rcu_ctrlblk *rcp, struct rcu_data *rdp)
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{
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/* This cpu has pending rcu entries and the grace period
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* for them has completed.
|
|
*/
|
|
if (rdp->curlist && !rcu_batch_before(rcp->completed, rdp->batch))
|
|
return 1;
|
|
|
|
/* This cpu has no pending entries, but there are new entries */
|
|
if (!rdp->curlist && rdp->nxtlist)
|
|
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->curlist || !!rdp_bh->curlist || rcu_pending(cpu));
|
|
}
|
|
|
|
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;
|
|
rdp->blimit = blimit;
|
|
}
|
|
|
|
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 __cpuinit 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 __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)
|
|
{
|
|
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);
|
|
}
|
|
|
|
module_param(blimit, int, 0);
|
|
module_param(qhimark, int, 0);
|
|
module_param(qlowmark, int, 0);
|
|
EXPORT_SYMBOL_GPL(rcu_batches_completed);
|
|
EXPORT_SYMBOL_GPL(rcu_batches_completed_bh);
|
|
EXPORT_SYMBOL_GPL(call_rcu);
|
|
EXPORT_SYMBOL_GPL(call_rcu_bh);
|
|
EXPORT_SYMBOL_GPL(synchronize_rcu);
|