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![Tejun Heo](/assets/img/avatar_default.png)
Implement a simplistic per-cpu maximum priority cpu monopolization mechanism. A non-sleeping callback can be scheduled to run on one or multiple cpus with maximum priority monopolozing those cpus. This is primarily to replace and unify RT workqueue usage in stop_machine and scheduler migration_thread which currently is serving multiple purposes. Four functions are provided - stop_one_cpu(), stop_one_cpu_nowait(), stop_cpus() and try_stop_cpus(). This is to allow clean sharing of resources among stop_cpu and all the migration thread users. One stopper thread per cpu is created which is currently named "stopper/CPU". This will eventually replace the migration thread and take on its name. * This facility was originally named cpuhog and lived in separate files but Peter Zijlstra nacked the name and thus got renamed to cpu_stop and moved into stop_machine.c. * Better reporting of preemption leak as per Peter's suggestion. Signed-off-by: Tejun Heo <tj@kernel.org> Acked-by: Peter Zijlstra <peterz@infradead.org> Cc: Oleg Nesterov <oleg@redhat.com> Cc: Dimitri Sivanich <sivanich@sgi.com>
561 lines
14 KiB
C
561 lines
14 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/module.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 <asm/atomic.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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struct list_head works; /* list of pending works */
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struct task_struct *thread; /* stopper thread */
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bool enabled; /* is this stopper enabled? */
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};
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static DEFINE_PER_CPU(struct cpu_stopper, cpu_stopper);
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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(struct cpu_stopper *stopper,
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struct cpu_stop_work *work)
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{
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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(stopper->thread);
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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(&per_cpu(cpu_stopper, 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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/**
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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(&per_cpu(cpu_stopper, 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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int __stop_cpus(const struct cpumask *cpumask, cpu_stop_fn_t fn, void *arg)
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{
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struct cpu_stop_work *work;
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struct cpu_stop_done done;
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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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cpu_stop_init_done(&done, cpumask_weight(cpumask));
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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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preempt_disable();
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for_each_cpu(cpu, cpumask)
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cpu_stop_queue_work(&per_cpu(cpu_stopper, cpu),
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&per_cpu(stop_cpus_work, cpu));
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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_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_stopper_thread(void *data)
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{
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struct cpu_stopper *stopper = data;
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struct cpu_stop_work *work;
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int ret;
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repeat:
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set_current_state(TASK_INTERRUPTIBLE); /* mb paired w/ kthread_stop */
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if (kthread_should_stop()) {
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__set_current_state(TASK_RUNNING);
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return 0;
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}
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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];
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__set_current_state(TASK_RUNNING);
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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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} else
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schedule();
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goto repeat;
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}
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/* manage stopper for a cpu, mostly lifted from sched migration thread mgmt */
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static int __cpuinit cpu_stop_cpu_callback(struct notifier_block *nfb,
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unsigned long action, void *hcpu)
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{
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struct sched_param param = { .sched_priority = MAX_RT_PRIO - 1 };
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unsigned int cpu = (unsigned long)hcpu;
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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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struct task_struct *p;
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switch (action & ~CPU_TASKS_FROZEN) {
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case CPU_UP_PREPARE:
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BUG_ON(stopper->thread || stopper->enabled ||
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!list_empty(&stopper->works));
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p = kthread_create(cpu_stopper_thread, stopper, "stopper/%d",
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cpu);
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if (IS_ERR(p))
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return NOTIFY_BAD;
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sched_setscheduler_nocheck(p, SCHED_FIFO, ¶m);
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get_task_struct(p);
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stopper->thread = p;
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break;
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case CPU_ONLINE:
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kthread_bind(stopper->thread, cpu);
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/* strictly unnecessary, as first user will wake it */
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wake_up_process(stopper->thread);
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/* mark enabled */
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spin_lock_irq(&stopper->lock);
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stopper->enabled = true;
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spin_unlock_irq(&stopper->lock);
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break;
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#ifdef CONFIG_HOTPLUG_CPU
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case CPU_UP_CANCELED:
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case CPU_DEAD:
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/* kill the stopper */
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kthread_stop(stopper->thread);
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/* drain remaining works */
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spin_lock_irq(&stopper->lock);
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list_for_each_entry(work, &stopper->works, list)
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cpu_stop_signal_done(work->done, false);
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stopper->enabled = false;
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spin_unlock_irq(&stopper->lock);
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/* release the stopper */
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put_task_struct(stopper->thread);
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stopper->thread = NULL;
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break;
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#endif
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}
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return NOTIFY_OK;
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}
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/*
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* Give it a higher priority so that cpu stopper is available to other
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* cpu notifiers. It currently shares the same priority as sched
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* migration_notifier.
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*/
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static struct notifier_block __cpuinitdata cpu_stop_cpu_notifier = {
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.notifier_call = cpu_stop_cpu_callback,
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.priority = 10,
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};
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static int __init cpu_stop_init(void)
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{
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void *bcpu = (void *)(long)smp_processor_id();
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unsigned int cpu;
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int err;
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for_each_possible_cpu(cpu) {
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struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
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spin_lock_init(&stopper->lock);
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INIT_LIST_HEAD(&stopper->works);
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}
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/* start one for the boot cpu */
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err = cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_UP_PREPARE,
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bcpu);
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BUG_ON(err == NOTIFY_BAD);
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cpu_stop_cpu_callback(&cpu_stop_cpu_notifier, CPU_ONLINE, bcpu);
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register_cpu_notifier(&cpu_stop_cpu_notifier);
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return 0;
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}
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early_initcall(cpu_stop_init);
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/* This controls the threads on each CPU. */
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enum stopmachine_state {
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/* Dummy starting state for thread. */
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STOPMACHINE_NONE,
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/* Awaiting everyone to be scheduled. */
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STOPMACHINE_PREPARE,
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/* Disable interrupts. */
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STOPMACHINE_DISABLE_IRQ,
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/* Run the function */
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STOPMACHINE_RUN,
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/* Exit */
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STOPMACHINE_EXIT,
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};
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static enum stopmachine_state state;
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struct stop_machine_data {
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int (*fn)(void *);
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void *data;
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int fnret;
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};
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/* Like num_online_cpus(), but hotplug cpu uses us, so we need this. */
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static unsigned int num_threads;
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static atomic_t thread_ack;
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static DEFINE_MUTEX(lock);
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/* setup_lock protects refcount, stop_machine_wq and stop_machine_work. */
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static DEFINE_MUTEX(setup_lock);
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/* Users of stop_machine. */
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static int refcount;
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static struct workqueue_struct *stop_machine_wq;
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static struct stop_machine_data active, idle;
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static const struct cpumask *active_cpus;
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static void __percpu *stop_machine_work;
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static void set_state(enum stopmachine_state newstate)
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{
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/* Reset ack counter. */
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atomic_set(&thread_ack, num_threads);
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smp_wmb();
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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(void)
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{
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if (atomic_dec_and_test(&thread_ack))
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set_state(state + 1);
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}
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/* This is the actual function which stops the CPU. It runs
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* in the context of a dedicated stopmachine workqueue. */
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static void stop_cpu(struct work_struct *unused)
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{
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enum stopmachine_state curstate = STOPMACHINE_NONE;
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struct stop_machine_data *smdata = &idle;
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int cpu = smp_processor_id();
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int err;
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if (!active_cpus) {
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if (cpu == cpumask_first(cpu_online_mask))
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smdata = &active;
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} else {
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if (cpumask_test_cpu(cpu, active_cpus))
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smdata = &active;
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}
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/* Simple state machine */
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do {
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/* Chill out and ensure we re-read stopmachine_state. */
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cpu_relax();
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if (state != curstate) {
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curstate = state;
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switch (curstate) {
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case STOPMACHINE_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 STOPMACHINE_RUN:
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/* On multiple CPUs only a single error code
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* is needed to tell that something failed. */
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err = smdata->fn(smdata->data);
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if (err)
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smdata->fnret = err;
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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();
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}
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} while (curstate != STOPMACHINE_EXIT);
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local_irq_enable();
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}
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/* Callback for CPUs which aren't supposed to do anything. */
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static int chill(void *unused)
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{
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return 0;
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}
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int stop_machine_create(void)
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{
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mutex_lock(&setup_lock);
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if (refcount)
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goto done;
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stop_machine_wq = create_rt_workqueue("kstop");
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if (!stop_machine_wq)
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goto err_out;
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stop_machine_work = alloc_percpu(struct work_struct);
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if (!stop_machine_work)
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goto err_out;
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done:
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refcount++;
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mutex_unlock(&setup_lock);
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return 0;
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err_out:
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if (stop_machine_wq)
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destroy_workqueue(stop_machine_wq);
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mutex_unlock(&setup_lock);
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return -ENOMEM;
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}
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EXPORT_SYMBOL_GPL(stop_machine_create);
|
|
|
|
void stop_machine_destroy(void)
|
|
{
|
|
mutex_lock(&setup_lock);
|
|
refcount--;
|
|
if (refcount)
|
|
goto done;
|
|
destroy_workqueue(stop_machine_wq);
|
|
free_percpu(stop_machine_work);
|
|
done:
|
|
mutex_unlock(&setup_lock);
|
|
}
|
|
EXPORT_SYMBOL_GPL(stop_machine_destroy);
|
|
|
|
int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
|
|
{
|
|
struct work_struct *sm_work;
|
|
int i, ret;
|
|
|
|
/* Set up initial state. */
|
|
mutex_lock(&lock);
|
|
num_threads = num_online_cpus();
|
|
active_cpus = cpus;
|
|
active.fn = fn;
|
|
active.data = data;
|
|
active.fnret = 0;
|
|
idle.fn = chill;
|
|
idle.data = NULL;
|
|
|
|
set_state(STOPMACHINE_PREPARE);
|
|
|
|
/* Schedule the stop_cpu work on all cpus: hold this CPU so one
|
|
* doesn't hit this CPU until we're ready. */
|
|
get_cpu();
|
|
for_each_online_cpu(i) {
|
|
sm_work = per_cpu_ptr(stop_machine_work, i);
|
|
INIT_WORK(sm_work, stop_cpu);
|
|
queue_work_on(i, stop_machine_wq, sm_work);
|
|
}
|
|
/* This will release the thread on our CPU. */
|
|
put_cpu();
|
|
flush_workqueue(stop_machine_wq);
|
|
ret = active.fnret;
|
|
mutex_unlock(&lock);
|
|
return ret;
|
|
}
|
|
|
|
int stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
|
|
{
|
|
int ret;
|
|
|
|
ret = stop_machine_create();
|
|
if (ret)
|
|
return ret;
|
|
/* No CPUs can come up or down during this. */
|
|
get_online_cpus();
|
|
ret = __stop_machine(fn, data, cpus);
|
|
put_online_cpus();
|
|
stop_machine_destroy();
|
|
return ret;
|
|
}
|
|
EXPORT_SYMBOL_GPL(stop_machine);
|