workqueue: ensure @task is valid across kthread_stop()
authorLai Jiangshan <laijs@cn.fujitsu.com>
Sat, 15 Feb 2014 14:02:28 +0000 (22:02 +0800)
committerTejun Heo <tj@kernel.org>
Tue, 18 Feb 2014 21:35:20 +0000 (16:35 -0500)
commit5bdfff96c69a4d5ab9c49e60abf9e070ecd2acbb
treedab862c9f8694478b58adf92d3e1c87ba5a24a44
parentfada94ee64e6e18793b1db60fb8278d2eddbf922
workqueue: ensure @task is valid across kthread_stop()

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.

CC: stable@vger.kernel.org
Signed-off-by: Lai Jiangshan <laijs@cn.fujitsu.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
kernel/workqueue.c