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author | Lai Jiangshan <laijs@cn.fujitsu.com> | 2012-09-02 00:28:19 +0800 |
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committer | Ben Hutchings <ben@decadent.org.uk> | 2012-09-19 15:04:58 +0100 |
commit | f152c392a7715862818fb671cbd5e0b2545aedae (patch) | |
tree | 2b70726d6ba9730d54dab7a1efe35ce1d5a56ab0 /kernel/workqueue.c | |
parent | e8bf333a7a14bd2fa1d091794a168d3ed570457d (diff) | |
download | linux-stable-f152c392a7715862818fb671cbd5e0b2545aedae.tar.gz linux-stable-f152c392a7715862818fb671cbd5e0b2545aedae.tar.bz2 linux-stable-f152c392a7715862818fb671cbd5e0b2545aedae.zip |
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 <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Diffstat (limited to 'kernel/workqueue.c')
-rw-r--r-- | kernel/workqueue.c | 9 |
1 files changed, 6 insertions, 3 deletions
diff --git a/kernel/workqueue.c b/kernel/workqueue.c index a650bee67859..979d4ded6360 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -3437,14 +3437,17 @@ 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, |