From 4ce48b37bfedc2bc11e61eae76784887e88b922c Mon Sep 17 00:00:00 2001 From: Tejun Heo Date: Fri, 2 Jul 2010 10:03:51 +0200 Subject: [PATCH] workqueue: fix race condition in flush_workqueue() When one flusher is cascading to the next flusher, it first sets wq->first_flusher to the next one and sets up the next flush cycle. If there's nothing to do for the next cycle, it clears wq->flush_flusher and proceeds to the one after that. If the woken up flusher checks wq->first_flusher before it gets cleared, it will incorrectly assume the role of the first flusher, which triggers BUG_ON() sanity check. Fix it by checking wq->first_flusher again after grabbing the mutex. Signed-off-by: Tejun Heo --- kernel/workqueue.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 558733801ac0..b59c946433f4 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -2138,6 +2138,10 @@ void flush_workqueue(struct workqueue_struct *wq) mutex_lock(&wq->flush_mutex); + /* we might have raced, check again with mutex held */ + if (wq->first_flusher != &this_flusher) + goto out_unlock; + wq->first_flusher = NULL; BUG_ON(!list_empty(&this_flusher.list));