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authorLai Jiangshan <laijs@cn.fujitsu.com>2014-04-18 11:04:16 -0400
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-06-07 13:25:37 -0700
commitaac8b37ffaa2bacc0430aa7b45c7d3aad22209fc (patch)
treeb2061b8c2c2ca16ac58ca648ba27c51bcd1adb2a
parent55a3dfcc84ab3dc82708d93cd0bca4a0aad7715c (diff)
downloadlinux-linaro-stable-aac8b37ffaa2bacc0430aa7b45c7d3aad22209fc.tar.gz
workqueue: fix a possible race condition between rescuer and pwq-release
commit 77668c8b559e4fe2acf2a0749c7c83cde49a5025 upstream. There is a race condition between rescuer_thread() and pwq_unbound_release_workfn(). Even after a pwq is scheduled for rescue, the associated work items may be consumed by any worker. If all of them are consumed before the rescuer gets to them and the pwq's base ref was put due to attribute change, the pwq may be released while still being linked on @wq->maydays list making the rescuer dereference already freed pwq later. Make send_mayday() pin the target pwq until the rescuer is done with it. tj: Updated comment and patch description. 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.c12
1 files changed, 12 insertions, 0 deletions
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 45c24d723448..2288293a314e 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -1881,6 +1881,12 @@ static void send_mayday(struct work_struct *work)
/* mayday mayday mayday */
if (list_empty(&pwq->mayday_node)) {
+ /*
+ * If @pwq is for an unbound wq, its base ref may be put at
+ * any time due to an attribute change. Pin @pwq until the
+ * rescuer is done with it.
+ */
+ get_pwq(pwq);
list_add_tail(&pwq->mayday_node, &wq->maydays);
wake_up_process(wq->rescuer->task);
}
@@ -2403,6 +2409,12 @@ repeat:
process_scheduled_works(rescuer);
/*
+ * Put the reference grabbed by send_mayday(). @pool won't
+ * go away while we're holding its lock.
+ */
+ put_pwq(pwq);
+
+ /*
* Leave this pool. If keep_working() is %true, notify a
* regular worker; otherwise, we end up with 0 concurrency
* and stalling the execution.