This is a note to let you know that I've just added the patch titled
workqueue: ensure @task is valid across kthread_stop()
to the 3.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
workqueue-ensure-task-is-valid-across-kthread_stop.patch
and it can be found in the queue-3.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 5bdfff96c69a4d5ab9c49e60abf9e070ecd2acbb Mon Sep 17 00:00:00 2001
From: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
Date: Sat, 15 Feb 2014 22:02:28 +0800
Subject: workqueue: ensure @task is valid across kthread_stop()
From: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
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@xxxxxxxxxxxxxx>
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
kernel/workqueue.c | 7 +++++++
1 file changed, 7 insertions(+)
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1469,12 +1469,19 @@ static void destroy_worker(struct 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);
Patches currently in stable-queue which might be from laijs@xxxxxxxxxxxxxx are
queue-3.4/workqueue-ensure-task-is-valid-across-kthread_stop.patch
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