tree af06187bebae44b48ca8e68a639a4ddc6b0a3509
parent 0d7614f09c1ebdbaa1599a5aba7593f147bf96ee
author Lai Jiangshan <laijs@cn.fujitsu.com> 1346516899 +0800
committer Tejun Heo <tj@kernel.org> 1346803485 -0700

workqueue: UNBOUND -> REBIND morphing in rebind_workers() should be atomic

The compiler may compile the following code into TWO write/modify
instructions.

	worker->flags &= ~WORKER_UNBOUND;
	worker->flags |= WORKER_REBIND;

so the other CPU may temporarily see worker->flags which doesn't have
either WORKER_UNBOUND or WORKER_REBIND set and perform local wakeup
prematurely.

Fix it by using single explicit assignment via ACCESS_ONCE().

Because idle workers have another WORKER_NOT_RUNNING flag, this bug
doesn't exist for them; however, update it to use the same pattern for
consistency.

tj: Applied the change to idle workers too and updated comments and
    patch description a bit.

Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: stable@vger.kernel.org