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7053ea1a34
There is a race between stop_two_cpus, and the global stop_cpus. It is possible for two CPUs to get their stopper functions queued "backwards" from one another, resulting in the stopper threads getting stuck, and the system hanging. This can happen because queuing up stoppers is not synchronized. This patch adds synchronization between stop_cpus (a rare operation), and stop_two_cpus. Reported-and-Tested-by: Prarit Bhargava <prarit@redhat.com> Signed-off-by: Rik van Riel <riel@redhat.com> Signed-off-by: Peter Zijlstra <peterz@infradead.org> Acked-by: Mel Gorman <mgorman@suse.de> Link: http://lkml.kernel.org/r/20131101104146.03d1e043@annuminas.surriel.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
648 lines
17 KiB
C
648 lines
17 KiB
C
/*
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* kernel/stop_machine.c
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*
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* Copyright (C) 2008, 2005 IBM Corporation.
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* Copyright (C) 2008, 2005 Rusty Russell rusty@rustcorp.com.au
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* Copyright (C) 2010 SUSE Linux Products GmbH
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* Copyright (C) 2010 Tejun Heo <tj@kernel.org>
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*
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* This file is released under the GPLv2 and any later version.
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*/
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#include <linux/completion.h>
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#include <linux/cpu.h>
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#include <linux/init.h>
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#include <linux/kthread.h>
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#include <linux/export.h>
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#include <linux/percpu.h>
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#include <linux/sched.h>
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#include <linux/stop_machine.h>
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#include <linux/interrupt.h>
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#include <linux/kallsyms.h>
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#include <linux/smpboot.h>
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#include <linux/atomic.h>
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#include <linux/lglock.h>
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/*
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* Structure to determine completion condition and record errors. May
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* be shared by works on different cpus.
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*/
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struct cpu_stop_done {
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atomic_t nr_todo; /* nr left to execute */
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bool executed; /* actually executed? */
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int ret; /* collected return value */
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struct completion completion; /* fired if nr_todo reaches 0 */
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};
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/* the actual stopper, one per every possible cpu, enabled on online cpus */
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struct cpu_stopper {
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spinlock_t lock;
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bool enabled; /* is this stopper enabled? */
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struct list_head works; /* list of pending works */
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};
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static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
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static DEFINE_PER_CPU(struct task_struct *, cpu_stopper_task);
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static bool stop_machine_initialized = false;
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/*
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* Avoids a race between stop_two_cpus and global stop_cpus, where
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* the stoppers could get queued up in reverse order, leading to
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* system deadlock. Using an lglock means stop_two_cpus remains
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* relatively cheap.
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*/
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DEFINE_STATIC_LGLOCK(stop_cpus_lock);
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static void cpu_stop_init_done(struct cpu_stop_done *done, unsigned int nr_todo)
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{
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memset(done, 0, sizeof(*done));
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atomic_set(&done->nr_todo, nr_todo);
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init_completion(&done->completion);
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}
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/* signal completion unless @done is NULL */
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static void cpu_stop_signal_done(struct cpu_stop_done *done, bool executed)
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{
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if (done) {
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if (executed)
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done->executed = true;
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if (atomic_dec_and_test(&done->nr_todo))
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complete(&done->completion);
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}
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}
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/* queue @work to @stopper. if offline, @work is completed immediately */
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static void cpu_stop_queue_work(unsigned int cpu, struct cpu_stop_work *work)
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{
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struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
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struct task_struct *p = per_cpu(cpu_stopper_task, cpu);
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unsigned long flags;
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spin_lock_irqsave(&stopper->lock, flags);
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if (stopper->enabled) {
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list_add_tail(&work->list, &stopper->works);
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wake_up_process(p);
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} else
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cpu_stop_signal_done(work->done, false);
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spin_unlock_irqrestore(&stopper->lock, flags);
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}
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/**
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* stop_one_cpu - stop a cpu
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* @cpu: cpu to stop
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* @fn: function to execute
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* @arg: argument to @fn
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*
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* Execute @fn(@arg) on @cpu. @fn is run in a process context with
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* the highest priority preempting any task on the cpu and
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* monopolizing it. This function returns after the execution is
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* complete.
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*
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* This function doesn't guarantee @cpu stays online till @fn
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* completes. If @cpu goes down in the middle, execution may happen
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* partially or fully on different cpus. @fn should either be ready
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* for that or the caller should ensure that @cpu stays online until
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* this function completes.
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*
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* CONTEXT:
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* Might sleep.
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*
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* RETURNS:
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* -ENOENT if @fn(@arg) was not executed because @cpu was offline;
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* otherwise, the return value of @fn.
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*/
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int stop_one_cpu(unsigned int cpu, cpu_stop_fn_t fn, void *arg)
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{
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struct cpu_stop_done done;
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struct cpu_stop_work work = { .fn = fn, .arg = arg, .done = &done };
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cpu_stop_init_done(&done, 1);
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cpu_stop_queue_work(cpu, &work);
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wait_for_completion(&done.completion);
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return done.executed ? done.ret : -ENOENT;
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}
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/* This controls the threads on each CPU. */
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enum multi_stop_state {
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/* Dummy starting state for thread. */
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MULTI_STOP_NONE,
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/* Awaiting everyone to be scheduled. */
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MULTI_STOP_PREPARE,
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/* Disable interrupts. */
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MULTI_STOP_DISABLE_IRQ,
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/* Run the function */
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MULTI_STOP_RUN,
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/* Exit */
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MULTI_STOP_EXIT,
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};
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struct multi_stop_data {
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int (*fn)(void *);
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void *data;
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/* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
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unsigned int num_threads;
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const struct cpumask *active_cpus;
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enum multi_stop_state state;
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atomic_t thread_ack;
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};
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static void set_state(struct multi_stop_data *msdata,
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enum multi_stop_state newstate)
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{
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/* Reset ack counter. */
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atomic_set(&msdata->thread_ack, msdata->num_threads);
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smp_wmb();
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msdata->state = newstate;
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}
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/* Last one to ack a state moves to the next state. */
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static void ack_state(struct multi_stop_data *msdata)
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{
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if (atomic_dec_and_test(&msdata->thread_ack))
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set_state(msdata, msdata->state + 1);
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}
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/* This is the cpu_stop function which stops the CPU. */
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static int multi_cpu_stop(void *data)
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{
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struct multi_stop_data *msdata = data;
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enum multi_stop_state curstate = MULTI_STOP_NONE;
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int cpu = smp_processor_id(), err = 0;
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unsigned long flags;
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bool is_active;
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/*
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* When called from stop_machine_from_inactive_cpu(), irq might
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* already be disabled. Save the state and restore it on exit.
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*/
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local_save_flags(flags);
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if (!msdata->active_cpus)
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is_active = cpu == cpumask_first(cpu_online_mask);
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else
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is_active = cpumask_test_cpu(cpu, msdata->active_cpus);
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/* Simple state machine */
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do {
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/* Chill out and ensure we re-read multi_stop_state. */
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cpu_relax();
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if (msdata->state != curstate) {
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curstate = msdata->state;
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switch (curstate) {
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case MULTI_STOP_DISABLE_IRQ:
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local_irq_disable();
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hard_irq_disable();
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break;
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case MULTI_STOP_RUN:
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if (is_active)
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err = msdata->fn(msdata->data);
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break;
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default:
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break;
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}
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ack_state(msdata);
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}
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} while (curstate != MULTI_STOP_EXIT);
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local_irq_restore(flags);
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return err;
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}
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struct irq_cpu_stop_queue_work_info {
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int cpu1;
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int cpu2;
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struct cpu_stop_work *work1;
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struct cpu_stop_work *work2;
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};
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/*
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* This function is always run with irqs and preemption disabled.
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* This guarantees that both work1 and work2 get queued, before
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* our local migrate thread gets the chance to preempt us.
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*/
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static void irq_cpu_stop_queue_work(void *arg)
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{
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struct irq_cpu_stop_queue_work_info *info = arg;
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cpu_stop_queue_work(info->cpu1, info->work1);
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cpu_stop_queue_work(info->cpu2, info->work2);
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}
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/**
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* stop_two_cpus - stops two cpus
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* @cpu1: the cpu to stop
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* @cpu2: the other cpu to stop
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* @fn: function to execute
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* @arg: argument to @fn
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*
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* Stops both the current and specified CPU and runs @fn on one of them.
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*
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* returns when both are completed.
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*/
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int stop_two_cpus(unsigned int cpu1, unsigned int cpu2, cpu_stop_fn_t fn, void *arg)
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{
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struct cpu_stop_done done;
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struct cpu_stop_work work1, work2;
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struct irq_cpu_stop_queue_work_info call_args;
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struct multi_stop_data msdata;
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preempt_disable();
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msdata = (struct multi_stop_data){
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.fn = fn,
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.data = arg,
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.num_threads = 2,
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.active_cpus = cpumask_of(cpu1),
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};
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work1 = work2 = (struct cpu_stop_work){
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.fn = multi_cpu_stop,
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.arg = &msdata,
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.done = &done
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};
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call_args = (struct irq_cpu_stop_queue_work_info){
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.cpu1 = cpu1,
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.cpu2 = cpu2,
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.work1 = &work1,
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.work2 = &work2,
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};
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cpu_stop_init_done(&done, 2);
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set_state(&msdata, MULTI_STOP_PREPARE);
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/*
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* If we observe both CPUs active we know _cpu_down() cannot yet have
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* queued its stop_machine works and therefore ours will get executed
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* first. Or its not either one of our CPUs that's getting unplugged,
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* in which case we don't care.
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*
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* This relies on the stopper workqueues to be FIFO.
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*/
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if (!cpu_active(cpu1) || !cpu_active(cpu2)) {
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preempt_enable();
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return -ENOENT;
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}
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lg_local_lock(&stop_cpus_lock);
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/*
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* Queuing needs to be done by the lowest numbered CPU, to ensure
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* that works are always queued in the same order on every CPU.
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* This prevents deadlocks.
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*/
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smp_call_function_single(min(cpu1, cpu2),
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&irq_cpu_stop_queue_work,
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&call_args, 0);
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lg_local_unlock(&stop_cpus_lock);
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preempt_enable();
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wait_for_completion(&done.completion);
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return done.executed ? done.ret : -ENOENT;
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}
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/**
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* stop_one_cpu_nowait - stop a cpu but don't wait for completion
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* @cpu: cpu to stop
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* @fn: function to execute
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* @arg: argument to @fn
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*
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* Similar to stop_one_cpu() but doesn't wait for completion. The
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* caller is responsible for ensuring @work_buf is currently unused
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* and will remain untouched until stopper starts executing @fn.
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*
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* CONTEXT:
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* Don't care.
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*/
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void stop_one_cpu_nowait(unsigned int cpu, cpu_stop_fn_t fn, void *arg,
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struct cpu_stop_work *work_buf)
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{
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*work_buf = (struct cpu_stop_work){ .fn = fn, .arg = arg, };
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cpu_stop_queue_work(cpu, work_buf);
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}
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/* static data for stop_cpus */
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static DEFINE_MUTEX(stop_cpus_mutex);
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static DEFINE_PER_CPU(struct cpu_stop_work, stop_cpus_work);
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static void queue_stop_cpus_work(const struct cpumask *cpumask,
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cpu_stop_fn_t fn, void *arg,
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struct cpu_stop_done *done)
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{
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struct cpu_stop_work *work;
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unsigned int cpu;
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/* initialize works and done */
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for_each_cpu(cpu, cpumask) {
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work = &per_cpu(stop_cpus_work, cpu);
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work->fn = fn;
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work->arg = arg;
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work->done = done;
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}
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/*
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* Disable preemption while queueing to avoid getting
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* preempted by a stopper which might wait for other stoppers
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* to enter @fn which can lead to deadlock.
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*/
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lg_global_lock(&stop_cpus_lock);
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for_each_cpu(cpu, cpumask)
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cpu_stop_queue_work(cpu, &per_cpu(stop_cpus_work, cpu));
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lg_global_unlock(&stop_cpus_lock);
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}
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static int __stop_cpus(const struct cpumask *cpumask,
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cpu_stop_fn_t fn, void *arg)
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{
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struct cpu_stop_done done;
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cpu_stop_init_done(&done, cpumask_weight(cpumask));
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queue_stop_cpus_work(cpumask, fn, arg, &done);
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wait_for_completion(&done.completion);
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return done.executed ? done.ret : -ENOENT;
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}
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/**
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* stop_cpus - stop multiple cpus
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* @cpumask: cpus to stop
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* @fn: function to execute
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* @arg: argument to @fn
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*
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* Execute @fn(@arg) on online cpus in @cpumask. On each target cpu,
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* @fn is run in a process context with the highest priority
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* preempting any task on the cpu and monopolizing it. This function
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* returns after all executions are complete.
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*
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* This function doesn't guarantee the cpus in @cpumask stay online
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* till @fn completes. If some cpus go down in the middle, execution
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* on the cpu may happen partially or fully on different cpus. @fn
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* should either be ready for that or the caller should ensure that
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* the cpus stay online until this function completes.
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*
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* All stop_cpus() calls are serialized making it safe for @fn to wait
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* for all cpus to start executing it.
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*
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* CONTEXT:
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* Might sleep.
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*
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* RETURNS:
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* -ENOENT if @fn(@arg) was not executed at all because all cpus in
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* @cpumask were offline; otherwise, 0 if all executions of @fn
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* returned 0, any non zero return value if any returned non zero.
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*/
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int stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
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{
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int ret;
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/* static works are used, process one request at a time */
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mutex_lock(&stop_cpus_mutex);
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ret = __stop_cpus(cpumask, fn, arg);
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mutex_unlock(&stop_cpus_mutex);
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return ret;
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}
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/**
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* try_stop_cpus - try to stop multiple cpus
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* @cpumask: cpus to stop
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* @fn: function to execute
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* @arg: argument to @fn
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*
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* Identical to stop_cpus() except that it fails with -EAGAIN if
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* someone else is already using the facility.
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*
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* CONTEXT:
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* Might sleep.
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*
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* RETURNS:
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* -EAGAIN if someone else is already stopping cpus, -ENOENT if
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* @fn(@arg) was not executed at all because all cpus in @cpumask were
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* offline; otherwise, 0 if all executions of @fn returned 0, any non
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* zero return value if any returned non zero.
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*/
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int try_stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
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{
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int ret;
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/* static works are used, process one request at a time */
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if (!mutex_trylock(&stop_cpus_mutex))
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return -EAGAIN;
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ret = __stop_cpus(cpumask, fn, arg);
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mutex_unlock(&stop_cpus_mutex);
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return ret;
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}
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static int cpu_stop_should_run(unsigned int cpu)
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{
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struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
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unsigned long flags;
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int run;
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spin_lock_irqsave(&stopper->lock, flags);
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run = !list_empty(&stopper->works);
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spin_unlock_irqrestore(&stopper->lock, flags);
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return run;
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}
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static void cpu_stopper_thread(unsigned int cpu)
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{
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struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
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struct cpu_stop_work *work;
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int ret;
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repeat:
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work = NULL;
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spin_lock_irq(&stopper->lock);
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if (!list_empty(&stopper->works)) {
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work = list_first_entry(&stopper->works,
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struct cpu_stop_work, list);
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list_del_init(&work->list);
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}
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spin_unlock_irq(&stopper->lock);
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if (work) {
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cpu_stop_fn_t fn = work->fn;
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void *arg = work->arg;
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struct cpu_stop_done *done = work->done;
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char ksym_buf[KSYM_NAME_LEN] __maybe_unused;
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/* cpu stop callbacks are not allowed to sleep */
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preempt_disable();
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ret = fn(arg);
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if (ret)
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done->ret = ret;
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/* restore preemption and check it's still balanced */
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preempt_enable();
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WARN_ONCE(preempt_count(),
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"cpu_stop: %s(%p) leaked preempt count\n",
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kallsyms_lookup((unsigned long)fn, NULL, NULL, NULL,
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ksym_buf), arg);
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cpu_stop_signal_done(done, true);
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goto repeat;
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}
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}
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extern void sched_set_stop_task(int cpu, struct task_struct *stop);
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static void cpu_stop_create(unsigned int cpu)
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{
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sched_set_stop_task(cpu, per_cpu(cpu_stopper_task, cpu));
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}
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static void cpu_stop_park(unsigned int cpu)
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{
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struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
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struct cpu_stop_work *work;
|
|
unsigned long flags;
|
|
|
|
/* drain remaining works */
|
|
spin_lock_irqsave(&stopper->lock, flags);
|
|
list_for_each_entry(work, &stopper->works, list)
|
|
cpu_stop_signal_done(work->done, false);
|
|
stopper->enabled = false;
|
|
spin_unlock_irqrestore(&stopper->lock, flags);
|
|
}
|
|
|
|
static void cpu_stop_unpark(unsigned int cpu)
|
|
{
|
|
struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
|
|
|
|
spin_lock_irq(&stopper->lock);
|
|
stopper->enabled = true;
|
|
spin_unlock_irq(&stopper->lock);
|
|
}
|
|
|
|
static struct smp_hotplug_thread cpu_stop_threads = {
|
|
.store = &cpu_stopper_task,
|
|
.thread_should_run = cpu_stop_should_run,
|
|
.thread_fn = cpu_stopper_thread,
|
|
.thread_comm = "migration/%u",
|
|
.create = cpu_stop_create,
|
|
.setup = cpu_stop_unpark,
|
|
.park = cpu_stop_park,
|
|
.pre_unpark = cpu_stop_unpark,
|
|
.selfparking = true,
|
|
};
|
|
|
|
static int __init cpu_stop_init(void)
|
|
{
|
|
unsigned int cpu;
|
|
|
|
for_each_possible_cpu(cpu) {
|
|
struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
|
|
|
|
spin_lock_init(&stopper->lock);
|
|
INIT_LIST_HEAD(&stopper->works);
|
|
}
|
|
|
|
BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
|
|
stop_machine_initialized = true;
|
|
return 0;
|
|
}
|
|
early_initcall(cpu_stop_init);
|
|
|
|
#ifdef CONFIG_STOP_MACHINE
|
|
|
|
int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
|
|
{
|
|
struct multi_stop_data msdata = {
|
|
.fn = fn,
|
|
.data = data,
|
|
.num_threads = num_online_cpus(),
|
|
.active_cpus = cpus,
|
|
};
|
|
|
|
if (!stop_machine_initialized) {
|
|
/*
|
|
* Handle the case where stop_machine() is called
|
|
* early in boot before stop_machine() has been
|
|
* initialized.
|
|
*/
|
|
unsigned long flags;
|
|
int ret;
|
|
|
|
WARN_ON_ONCE(msdata.num_threads != 1);
|
|
|
|
local_irq_save(flags);
|
|
hard_irq_disable();
|
|
ret = (*fn)(data);
|
|
local_irq_restore(flags);
|
|
|
|
return ret;
|
|
}
|
|
|
|
/* Set the initial state and stop all online cpus. */
|
|
set_state(&msdata, MULTI_STOP_PREPARE);
|
|
return stop_cpus(cpu_online_mask, multi_cpu_stop, &msdata);
|
|
}
|
|
|
|
int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
|
|
{
|
|
int ret;
|
|
|
|
/* No CPUs can come up or down during this. */
|
|
get_online_cpus();
|
|
ret = __stop_machine(fn, data, cpus);
|
|
put_online_cpus();
|
|
return ret;
|
|
}
|
|
EXPORT_SYMBOL_GPL(stop_machine);
|
|
|
|
/**
|
|
* stop_machine_from_inactive_cpu - stop_machine() from inactive CPU
|
|
* @fn: the function to run
|
|
* @data: the data ptr for the @fn()
|
|
* @cpus: the cpus to run the @fn() on (NULL = any online cpu)
|
|
*
|
|
* This is identical to stop_machine() but can be called from a CPU which
|
|
* is not active. The local CPU is in the process of hotplug (so no other
|
|
* CPU hotplug can start) and not marked active and doesn't have enough
|
|
* context to sleep.
|
|
*
|
|
* This function provides stop_machine() functionality for such state by
|
|
* using busy-wait for synchronization and executing @fn directly for local
|
|
* CPU.
|
|
*
|
|
* CONTEXT:
|
|
* Local CPU is inactive. Temporarily stops all active CPUs.
|
|
*
|
|
* RETURNS:
|
|
* 0 if all executions of @fn returned 0, any non zero return value if any
|
|
* returned non zero.
|
|
*/
|
|
int stop_machine_from_inactive_cpu(int (*fn)(void *), void *data,
|
|
const struct cpumask *cpus)
|
|
{
|
|
struct multi_stop_data msdata = { .fn = fn, .data = data,
|
|
.active_cpus = cpus };
|
|
struct cpu_stop_done done;
|
|
int ret;
|
|
|
|
/* Local CPU must be inactive and CPU hotplug in progress. */
|
|
BUG_ON(cpu_active(raw_smp_processor_id()));
|
|
msdata.num_threads = num_active_cpus() + 1; /* +1 for local */
|
|
|
|
/* No proper task established and can't sleep - busy wait for lock. */
|
|
while (!mutex_trylock(&stop_cpus_mutex))
|
|
cpu_relax();
|
|
|
|
/* Schedule work on other CPUs and execute directly for local CPU */
|
|
set_state(&msdata, MULTI_STOP_PREPARE);
|
|
cpu_stop_init_done(&done, num_active_cpus());
|
|
queue_stop_cpus_work(cpu_active_mask, multi_cpu_stop, &msdata,
|
|
&done);
|
|
ret = multi_cpu_stop(&msdata);
|
|
|
|
/* Busy wait for completion. */
|
|
while (!completion_done(&done.completion))
|
|
cpu_relax();
|
|
|
|
mutex_unlock(&stop_cpus_mutex);
|
|
return ret ?: done.ret;
|
|
}
|
|
|
|
#endif /* CONFIG_STOP_MACHINE */
|