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workqueue: fix race condition in schedule_on_each_cpu()

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Commit 65a6446434 ("HWPOISON: Allow
schedule_on_each_cpu() from keventd") which allows schedule_on_each_cpu()
to be called from keventd added a race condition.  schedule_on_each_cpu()
may race with cpu hotplug and end up executing the function twice on a
cpu.

Fix it by moving direct execution into the section protected with
get/put_online_cpus().  While at it, update code such that direct
execution is done after works have been scheduled for all other cpus and
drop unnecessary cpu != orig test from flush loop.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>
Acked-by: Oleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Tejun Heo 2009-11-17 14:06:20 -08:00 committed by Linus Torvalds
parent e13193319d
commit 9398180097
1 changed files with 16 additions and 18 deletions
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34
kernel/workqueue.c
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@ -692,31 +692,29 @@ int schedule_on_each_cpu(work_func_t func)
if (!works)
return -ENOMEM;
/*
* when running in keventd don't schedule a work item on itself.
* Can just call directly because the work queue is already bound.
* This also is faster.
* Make this a generic parameter for other workqueues?
*/
if (current_is_keventd()) {
orig = raw_smp_processor_id();
INIT_WORK(per_cpu_ptr(works, orig), func);
func(per_cpu_ptr(works, orig));
}
get_online_cpus();
/*
* When running in keventd don't schedule a work item on
* itself. Can just call directly because the work queue is
* already bound. This also is faster.
*/
if (current_is_keventd())
orig = raw_smp_processor_id();
for_each_online_cpu(cpu) {
struct work_struct *work = per_cpu_ptr(works, cpu);
if (cpu == orig)
continue;
INIT_WORK(work, func);
schedule_work_on(cpu, work);
}
for_each_online_cpu(cpu) {
if (cpu != orig)
flush_work(per_cpu_ptr(works, cpu));
schedule_work_on(cpu, work);
}
if (orig >= 0)
func(per_cpu_ptr(works, orig));
for_each_online_cpu(cpu)
flush_work(per_cpu_ptr(works, cpu));
put_online_cpus();
free_percpu(works);
return 0;