From c37145e29e4cd71a5aff0e2bb5837e821d538c16 Mon Sep 17 00:00:00 2001 From: Lai Jiangshan Date: Sat, 15 Feb 2014 22:02:28 +0800 Subject: workqueue: ensure @task is valid across kthread_stop() 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 Signed-off-by: Tejun Heo Signed-off-by: Ben Hutchings --- kernel/workqueue.c | 7 +++++++ 1 file changed, 7 insertions(+) (limited to 'kernel') diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 0bc9ff0f8e8b..563820c59d54 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -1474,12 +1474,19 @@ 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); -- cgit v1.2.3