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authorLai Jiangshan <laijs@cn.fujitsu.com>2014-02-15 22:02:28 +0800
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-03-06 21:30:11 -0800
commit4403be9e25c9d9b82f881cec4fe9a126de02fb9b (patch)
tree003364a5eaccc9fb936ad70b578e41fe69494d12
parent755ac7af96bdc50bf65254ac3699e0279a342440 (diff)
downloadlinux-linaro-stable-4403be9e25c9d9b82f881cec4fe9a126de02fb9b.tar.gz
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 <laijs@cn.fujitsu.com> Signed-off-by: Tejun Heo <tj@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--kernel/workqueue.c7
1 files changed, 7 insertions, 0 deletions
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 68086a34b8ef..db7a6ac7c0a8 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1823,6 +1823,12 @@ static void destroy_worker(struct worker *worker)
if (worker->flags & WORKER_IDLE)
pool->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;
@@ -1831,6 +1837,7 @@ static void destroy_worker(struct worker *worker)
spin_unlock_irq(&pool->lock);
kthread_stop(worker->task);
+ put_task_struct(worker->task);
kfree(worker);
spin_lock_irq(&pool->lock);