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Subject[PATCH 3.8 39/81] workqueue: ensure @task is valid across kthread_stop()
Date -stable review patch.  If anyone has any objections, please let me know.


From: Lai Jiangshan <>

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: Kamal Mostafa <>
kernel/workqueue.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 338b3bd..1fd7e24 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1902,12 +1902,19 @@ static void destroy_worker(struct worker *worker)
if (worker->flags & WORKER_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);
worker->flags |= WORKER_DIE;


+ put_task_struct(worker->task);


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