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![Thomas Gleixner](/assets/img/avatar_default.png)
commit 14e568e78
(stop_machine: Use smpboot threads) introduced the
following regression:
Before this commit the stopper enabled bit was set in the online
notifier.
CPU0 CPU1
cpu_up
cpu online
hotplug_notifier(ONLINE)
stopper(CPU1)->enabled = true;
...
stop_machine()
The conversion to smpboot threads moved the enablement to the wakeup
path of the parked thread. The majority of users seem to have the
following working order:
CPU0 CPU1
cpu_up
cpu online
unpark_threads()
wakeup(stopper[CPU1])
....
stopper thread runs
stopper(CPU1)->enabled = true;
stop_machine()
But Konrad and Sander have observed:
CPU0 CPU1
cpu_up
cpu online
unpark_threads()
wakeup(stopper[CPU1])
....
stop_machine()
stopper thread runs
stopper(CPU1)->enabled = true;
Now the stop machinery kicks CPU0 into the stop loop, where it gets
stuck forever because the queue code saw stopper(CPU1)->enabled ==
false, so CPU0 waits for CPU1 to enter stomp_machine, but the CPU1
stopper work got discarded due to enabled == false.
Add a pre_unpark function to the smpboot thread descriptor and call it
before waking the thread.
This fixes the problem at hand, but the stop_machine code should be
more robust. The stopper->enabled flag smells fishy at best.
Thanks to Konrad for going through a loop of debug patches and
providing the information to decode this issue.
Reported-and-tested-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Reported-and-tested-by: Sander Eikelenboom <linux@eikelenboom.it>
Cc: Srivatsa S. Bhat <srivatsa.bhat@linux.vnet.ibm.com>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Link: http://lkml.kernel.org/r/alpine.LFD.2.02.1302261843240.22263@ionos
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
544 lines
15 KiB
C
544 lines
15 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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/*
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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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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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/**
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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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preempt_disable();
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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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preempt_enable();
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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;
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unsigned long flags;
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/* drain remaining works */
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spin_lock_irqsave(&stopper->lock, flags);
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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_irqrestore(&stopper->lock, flags);
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}
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static void cpu_stop_unpark(unsigned int cpu)
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{
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struct cpu_stopper *stopper = &per_cpu(cpu_stopper, cpu);
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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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}
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static struct smp_hotplug_thread cpu_stop_threads = {
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.store = &cpu_stopper_task,
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.thread_should_run = cpu_stop_should_run,
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.thread_fn = cpu_stopper_thread,
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.thread_comm = "migration/%u",
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.create = cpu_stop_create,
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.setup = cpu_stop_unpark,
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.park = cpu_stop_park,
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.pre_unpark = cpu_stop_unpark,
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.selfparking = true,
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};
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static int __init cpu_stop_init(void)
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{
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unsigned int cpu;
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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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BUG_ON(smpboot_register_percpu_thread(&cpu_stop_threads));
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stop_machine_initialized = true;
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return 0;
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}
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early_initcall(cpu_stop_init);
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#ifdef CONFIG_STOP_MACHINE
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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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struct stop_machine_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 stopmachine_state state;
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atomic_t thread_ack;
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};
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static void set_state(struct stop_machine_data *smdata,
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enum stopmachine_state newstate)
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{
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/* Reset ack counter. */
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atomic_set(&smdata->thread_ack, smdata->num_threads);
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smp_wmb();
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smdata->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 stop_machine_data *smdata)
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{
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if (atomic_dec_and_test(&smdata->thread_ack))
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set_state(smdata, smdata->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 stop_machine_cpu_stop(void *data)
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{
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struct stop_machine_data *smdata = data;
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enum stopmachine_state curstate = STOPMACHINE_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 (!smdata->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, smdata->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 stopmachine_state. */
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cpu_relax();
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if (smdata->state != curstate) {
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curstate = smdata->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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if (is_active)
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err = smdata->fn(smdata->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(smdata);
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}
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} while (curstate != STOPMACHINE_EXIT);
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local_irq_restore(flags);
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return err;
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}
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int __stop_machine(int (*fn)(void *), void *data, const struct cpumask *cpus)
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{
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struct stop_machine_data smdata = { .fn = fn, .data = data,
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.num_threads = num_online_cpus(),
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.active_cpus = cpus };
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if (!stop_machine_initialized) {
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/*
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* Handle the case where stop_machine() is called
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* early in boot before stop_machine() has been
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* initialized.
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*/
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unsigned long flags;
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int ret;
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WARN_ON_ONCE(smdata.num_threads != 1);
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local_irq_save(flags);
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hard_irq_disable();
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ret = (*fn)(data);
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local_irq_restore(flags);
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return ret;
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}
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/* Set the initial state and stop all online cpus. */
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set_state(&smdata, STOPMACHINE_PREPARE);
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return stop_cpus(cpu_online_mask, stop_machine_cpu_stop, &smdata);
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}
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|
|
|
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();
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|
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 stop_machine_data smdata = { .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()));
|
|
smdata.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(&smdata, STOPMACHINE_PREPARE);
|
|
cpu_stop_init_done(&done, num_active_cpus());
|
|
queue_stop_cpus_work(cpu_active_mask, stop_machine_cpu_stop, &smdata,
|
|
&done);
|
|
ret = stop_machine_cpu_stop(&smdata);
|
|
|
|
/* Busy wait for completion. */
|
|
while (!completion_done(&done.completion))
|
|
cpu_relax();
|
|
|
|
mutex_unlock(&stop_cpus_mutex);
|
|
return ret ?: done.ret;
|
|
}
|
|
|
|
#endif /* CONFIG_STOP_MACHINE */
|