Commit 23657bb1 authored by Tejun Heo's avatar Tejun Heo
Browse files

workqueue: add missing wmb() in clear_work_data() 



Any operation which clears PENDING should be preceded by a wmb to
guarantee that the next PENDING owner sees all the changes made before
PENDING release.

There are only two places where PENDING is cleared -
set_work_cpu_and_clear_pending() and clear_work_data().  The caller of
the former already does smp_wmb() but the latter doesn't have any.

Move the wmb above set_work_cpu_and_clear_pending() into it and add
one to clear_work_data().

There hasn't been any report related to this issue, and, given how
clear_work_data() is used, it is extremely unlikely to have caused any
actual problems on any architecture.

Signed-off-by: default avatarTejun Heo <tj@kernel.org>
Cc: Oleg Nesterov <oleg@redhat.com>
parent 1265057f

kernel/workqueue.c

+12 −7
Original line number Diff line number Diff line
@@ -570,11 +570,19 @@ static void set_work_cwq(struct work_struct *work, 
static void set_work_cpu_and_clear_pending(struct work_struct *work,

					   unsigned int cpu)

{

	/*

	 * The following wmb is paired with the implied mb in

	 * test_and_set_bit(PENDING) and ensures all updates to @work made

	 * here are visible to and precede any updates by the next PENDING

	 * owner.

	 */

	smp_wmb();

	set_work_data(work, (unsigned long)cpu << WORK_OFFQ_CPU_SHIFT, 0);

}



static void clear_work_data(struct work_struct *work)

{

	smp_wmb();	/* see set_work_cpu_and_clear_pending() */

	set_work_data(work, WORK_STRUCT_NO_CPU, 0);

}
@@ -2182,14 +2190,11 @@ __acquires(&gcwq->lock) 
		wake_up_worker(pool);



	/*

	 * Record the last CPU and clear PENDING.  The following wmb is

	 * paired with the implied mb in test_and_set_bit(PENDING) and

	 * ensures all updates to @work made here are visible to and

	 * precede any updates by the next PENDING owner.  Also, clear

	 * PENDING inside @gcwq->lock so that PENDING and queued state

	 * changes happen together while IRQ is disabled.

	 * Record the last CPU and clear PENDING which should be the last

	 * update to @work.  Also, do this inside @gcwq->lock so that

	 * PENDING and queued state changes happen together while IRQ is

	 * disabled.

	 */

	smp_wmb();

	set_work_cpu_and_clear_pending(work, gcwq->cpu);



	spin_unlock_irq(&gcwq->lock);

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