Messages in this thread | | | Date | Thu, 19 Apr 2012 11:10:41 -0700 | From | Stephen Boyd <> | Subject | Re: [PATCH 1/2] workqueue: Catch more locking problems with flush_work() |
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On 04/19/12 08:28, Tejun Heo wrote: > On Wed, Apr 18, 2012 at 08:25:57PM -0700, Stephen Boyd wrote: >> @@ -2513,8 +2513,11 @@ bool flush_work(struct work_struct *work) >> wait_for_completion(&barr.done); >> destroy_work_on_stack(&barr.work); >> return true; >> - } else >> + } else { >> + lock_map_acquire(&work->lockdep_map); >> + lock_map_release(&work->lockdep_map); >> return false; > We don't have this annotation when start_flush_work() succeeds either, > right? IOW, would lockdep trigger when an actual deadlock happens?
I believe it does although I haven't tested it.
> If not, why not add the acquire/release() before flush_work() does > anything? >
I was worried about causing false positive lockdep warnings in the case that start_flush_work() succeeds and returns true. In that case, lockdep is told about the cwq lockdep map:
static bool start_flush_work(struct work_struct *work, struct wq_barrier *barr, bool wait_executing) {
.....
if (cwq->wq->saved_max_active == 1 || cwq->wq->flags & WQ_RESCUER) lock_map_acquire(&cwq->wq->lockdep_map); else lock_map_acquire_read(&cwq->wq->lockdep_map);
and so if we acquired the work->lockdep_map before the cwq->wq->lockdep_map we would get a warning about ABBA between these two lockdep maps. At least that is what I'm lead to believe when I look at what process_one_work() is doing. Please correct me if I'm wrong.
-- Sent by an employee of the Qualcomm Innovation Center, Inc. The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
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