Author: Oleg Nesterov <[EMAIL PROTECTED]>
AuthorDate: Tue Jul 17 04:03:55 2007 -0700
Committer: Linus Torvalds <[EMAIL PROTECTED]>
CommitDate: Tue Jul 17 10:23:03 2007 -0700
destroy_workqueue() can livelock
Pointed out by Michal Schmidt <[EMAIL PROTECTED]>.
The bug was introduced in 2.6.22 by me.
cleanup_workqueue_thread() does flush_cpu_workqueue(cwq) in a loop until
->worklist becomes empty. This is live-lockable, a re-niced caller can get
CPU after wake_up() and insert a new barrier before the lower-priority
cwq->thread has a chance to clear ->current_work.
Change cleanup_workqueue_thread() to do flush_cpu_workqueue(cwq) only once.
We can rely on the fact that run_workqueue() won't return until it flushes
all works. So it is safe to call kthread_stop() after that, the "should
stop" request won't be noticed until run_workqueue() returns.
Signed-off-by: Oleg Nesterov <[EMAIL PROTECTED]>
Cc: Michal Schmidt <[EMAIL PROTECTED]>
Cc: Srivatsa Vaddagiri <[EMAIL PROTECTED]>
Cc: <[EMAIL PROTECTED]>
Signed-off-by: Andrew Morton <[EMAIL PROTECTED]>
Signed-off-by: Linus Torvalds <[EMAIL PROTECTED]>
kernel/workqueue.c | 11 +++++------
1 files changed, 5 insertions(+), 6 deletions(-)
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 1935302..58e5c15 100644
@@ -752,18 +752,17 @@ static void cleanup_workqueue_thread(struct
cpu_workqueue_struct *cwq, int cpu)
if (cwq->thread == NULL)
- * If the caller is CPU_DEAD the single flush_cpu_workqueue()
- * is not enough, a concurrent flush_workqueue() can insert a
- * barrier after us.
+ * If the caller is CPU_DEAD and cwq->worklist was not empty,
+ * a concurrent flush_workqueue() can insert a barrier after us.
+ * However, in that case run_workqueue() won't return and check
+ * kthread_should_stop() until it flushes all work_struct's.
* When ->worklist becomes empty it is safe to exit because no
* more work_structs can be queued on this cwq: flush_workqueue
* checks list_empty(), and a "normal" queue_work() can't use
* a dead CPU.
- while (flush_cpu_workqueue(cwq))
cwq->thread = NULL;
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