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SubjectRe: [PATCH 1/2] workqueue: Catch more locking problems with flush_work()
On 4/20/2012 12:18 AM, Yong Zhang wrote:
> On Thu, Apr 19, 2012 at 11:26:47PM -0700, Stephen Boyd wrote:
>> complain in the case where the work is not queued. That case is not a
>> false positive. We will get a lockdep warning if the work is running
> IIRC, flush_work() is just a nop when a work is not queued nor running.

Agreed, but it's better to always print a lockdep warning instead of
only when the deadlock is going to occur.

>> (when start_flush_work() returns true) solely with the
>> lock_map_acquire() on cwq->wq->lockdep_map.
> Yeah, that is the point we use lockdep to detect deadlock for workqueue.
> But when looking at start_flush_work(), for some case
> !(cwq->wq->saved_max_active == 1 || cwq->wq->flags & WQ_RESCUER),
> lock_map_acquire_read() is called, but recursive read is not added to
> the chain list. So when lock_map_acquire_read(&cwq->wq->lockdep_map)
> is called, deadlock will not be detected. I hope you don't hit that
> special case.

Hmm. Originally I had what you suggested in my patch but I left it out
because I wasn't sure if it would cause false positives. Do you see any
possibility for false positives? I'll add it back in if not.

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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