tree 0829ba93c3bb5f586bacd11c3f21711b3de04da2
parent cb444766996395d4370bcc17ec895dd4e13ceb72
author Tejun Heo <tj@kernel.org> 1278057831 +0200
committer Tejun Heo <tj@kernel.org> 1278057831 +0200

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 <tj@kernel.org>