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authorTejun Heo <tj@kernel.org>2010-07-02 04:03:51 -0400
committerTejun Heo <tj@kernel.org>2010-07-02 04:03:51 -0400
commit4ce48b37bfedc2bc11e61eae76784887e88b922c (patch)
tree0829ba93c3bb5f586bacd11c3f21711b3de04da2 /kernel/workqueue.c
parentcb444766996395d4370bcc17ec895dd4e13ceb72 (diff)
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>
Diffstat (limited to 'kernel/workqueue.c')
-rw-r--r--kernel/workqueue.c4
1 files changed, 4 insertions, 0 deletions
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)
2138 2138
2139 mutex_lock(&wq->flush_mutex); 2139 mutex_lock(&wq->flush_mutex);
2140 2140
2141 /* we might have raced, check again with mutex held */
2142 if (wq->first_flusher != &this_flusher)
2143 goto out_unlock;
2144
2141 wq->first_flusher = NULL; 2145 wq->first_flusher = NULL;
2142 2146
2143 BUG_ON(!list_empty(&this_flusher.list)); 2147 BUG_ON(!list_empty(&this_flusher.list));