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Commit 93981800 authored by Tejun Heo's avatar Tejun Heo Committed by Linus Torvalds
Browse files

workqueue: fix race condition in schedule_on_each_cpu() 



Commit 65a64464 ("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: default avatarTejun Heo <tj@kernel.org>
Cc: Andi Kleen <ak@linux.intel.com>
Acked-by: default avatarOleg Nesterov <oleg@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent e1319331

kernel/workqueue.c

+13 −15
Original line number Diff line number Diff line
@@ -692,31 +692,29 @@ int schedule_on_each_cpu(work_func_t func) 
	if (!works)

		return -ENOMEM;



	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.

	 * Make this a generic parameter for other workqueues?

	 * 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()) {

	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();

	for_each_online_cpu(cpu) {

		struct work_struct *work = per_cpu_ptr(works, cpu);



		if (cpu == orig)

			continue;

		INIT_WORK(work, func);

		if (cpu != orig)

			schedule_work_on(cpu, work);

	}

	for_each_online_cpu(cpu) {

		if (cpu != orig)

	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;