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| author | Lai Jiangshan <laijs@cn.fujitsu.com> | 2012-09-02 00:28:19 +0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2012-10-02 10:30:33 -0700 |
| commit | 6adebb0e1d4820435e0c6739b0de20a196cc20d5 (patch) | |
| tree | 2e572784e0ddf58832e1cc9aba859e365834f5a5 /kernel/workqueue.c | |
| parent | 956b165f9e89e37aff44d615321d1e3166589701 (diff) | |
| download | lwn-6adebb0e1d4820435e0c6739b0de20a196cc20d5.tar.gz lwn-6adebb0e1d4820435e0c6739b0de20a196cc20d5.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.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.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 f483dd0bc9c9..7584322349c1 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -3433,14 +3433,17 @@ 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, |