From: Lai Jiangshan Date: Sat, 1 Sep 2012 16:28:19 +0000 (+0800) Subject: workqueue: UNBOUND -> REBIND morphing in rebind_workers() should be atomic X-Git-Tag: firefly_0821_release~7541^2~637 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=bc713e264ea9badd399aa34f208154a64e4e1b3b;p=firefly-linux-kernel-4.4.55.git 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. Signed-off-by: Lai Jiangshan Signed-off-by: Tejun Heo Signed-off-by: Greg Kroah-Hartman --- diff --git a/kernel/workqueue.c b/kernel/workqueue.c index ebd96393ae52..00c0bad50609 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -3412,14 +3412,17 @@ 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,