Messages in this thread Patch in this message | | | Date | Tue, 4 Sep 2012 16:58:12 -0700 | From | Tejun Heo <> | Subject | [PATCH -stable] workqueue: UNBOUND -> REBIND morphing in rebind_workers() should be atomic |
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From: Lai Jiangshan <laijs@cn.fujitsu.com>
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 <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org> Cc: stable@vger.kernel.org --- 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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