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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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