Messages in this thread Patch in this message | | | From | Luis Henriques <> | Subject | [PATCH 3.5 22/62] workqueue: ensure @task is valid across kthread_stop() | Date | Wed, 5 Mar 2014 14:36:26 +0000 |
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3.5.7.32 -stable review patch. If anyone has any objections, please let me know.
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From: Lai Jiangshan <laijs@cn.fujitsu.com>
commit 5bdfff96c69a4d5ab9c49e60abf9e070ecd2acbb upstream.
When a kworker should die, the kworkre is notified through WORKER_DIE flag instead of kthread_should_stop(). This, IIRC, is primarily to keep the test synchronized inside worker_pool lock. WORKER_DIE is first set while holding pool->lock, the lock is dropped and kthread_stop() is called.
Unfortunately, this means that there's a slight chance that the target kworker may see WORKER_DIE before kthread_stop() finishes and exits and frees the target task before or during kthread_stop().
Fix it by pinning the target task before setting WORKER_DIE and putting it after kthread_stop() is done.
tj: Improved patch description and comment. Moved pinning above WORKER_DIE for better signify what it's protecting.
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org> [ luis: backported to 3.5: adjusted context ] Signed-off-by: Luis Henriques <luis.henriques@canonical.com> --- kernel/workqueue.c | 7 +++++++ 1 file changed, 7 insertions(+)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 89743ae..d19727f 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -1472,12 +1472,19 @@ static void destroy_worker(struct worker *worker) if (worker->flags & WORKER_IDLE) gcwq->nr_idle--; + /* + * Once WORKER_DIE is set, the kworker may destroy itself at any + * point. Pin to ensure the task stays until we're done with it. + */ + get_task_struct(worker->task); + list_del_init(&worker->entry); worker->flags |= WORKER_DIE; spin_unlock_irq(&gcwq->lock); kthread_stop(worker->task); + put_task_struct(worker->task); kfree(worker); spin_lock_irq(&gcwq->lock); -- 1.9.0
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