On Fri, 2012-09-21 at 10:07 -0700, [email protected] wrote: > The patch below does not apply to the 3.5-stable tree. > If someone wants it applied there, or to any other stable or longterm > tree, then please email the backport, including the original git commit > id to <[email protected]>. [...]
Tejun Heo already provided a backported version, attached. Ben. -- Ben Hutchings Once a job is fouled up, anything done to improve it makes it worse.
From: Lai Jiangshan <[email protected]> Date: Sun, 2 Sep 2012 00:28:19 +0800 Subject: workqueue: UNBOUND -> REBIND morphing in rebind_workers() should be atomic commit 96e65306b81351b656835c15931d1d237b252f27 upstream. 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. stable: Idle worker rebinding doesn't apply for -stable and WORKER_UNBOUND used to be WORKER_ROGUE. Updated accordingly. Signed-off-by: Lai Jiangshan <[email protected]> Signed-off-by: Tejun Heo <[email protected]> --- kernel/workqueue.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 9a3128d..d7eb05a 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -3441,14 +3441,17 @@ static int __cpuinit trustee_thread(void *__gcwq) for_each_busy_worker(worker, i, pos, gcwq) { struct work_struct *rebind_work = &worker->rebind_work; + unsigned long worker_flags = worker->flags; /* * Rebind_work may race with future cpu hotplug * operations. Use a separate flag to mark that - * rebinding is scheduled. + * rebinding is scheduled. The morphing should + * be atomic. */ - worker->flags |= WORKER_REBIND; - worker->flags &= ~WORKER_ROGUE; + worker_flags |= WORKER_REBIND; + worker_flags &= ~WORKER_ROGUE; + ACCESS_ONCE(worker->flags) = worker_flags; /* queue rebind_work, wq doesn't matter, use the default one */ if (test_and_set_bit(WORK_STRUCT_PENDING_BIT,
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