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    SubjectRe: net/bluetooth: workqueue destruction WARNING in hci_unregister_dev
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    Hello,

    On 03/18/2016, 09:52 PM, Tejun Heo wrote:
    > On Thu, Mar 17, 2016 at 01:00:13PM +0100, Jiri Slaby wrote:
    >>>> I have not done that yet, but today, I see:
    >>>> destroy_workqueue: name='req_hci0' pwq=ffff88002f590300
    >>>> wq->dfl_pwq=ffff88002f591e00 pwq->refcnt=2 pwq->nr_active=0 delayed_works:
    >>>> pwq 12: cpus=0-1 node=0 flags=0x4 nice=-20 active=0/1
    >>>> in-flight: 18568:wq_barrier_func
    >>>
    >>> So, this means that there's flush_work() racing against workqueue
    >>> destruction, which can't be safe. :(
    >>
    >> But I cannot trigger the WARN_ONs in the attached patch, so I am
    >> confused how this can happen :(. (While I am still seeing the destroy
    >> WARNINGs.)
    >
    > So, no operations should be in progress when destroy_workqueue() is
    > called. If somebody was flushing a work item, the flush call must
    > have returned before destroy_workqueue() was invoked, which doesn't
    > seem to be the case here. Can you trigger BUG_ON() or sysrq-t when
    > the above triggers? There must be a task which is flushing a work
    > item there and it shouldn't be difficult to pinpoint what's going on
    > from it.

    The output of sysrq-t is here (> 200k), but I cannot see anything
    suspicious in it:
    http://www.fi.muni.cz/~xslaby/sklad/panics/jctl.txt

    This is what the code does now:
    + if ((pwq != wq->dfl_pwq) && (pwq->refcnt > 1)) {
    + pr_info("%s: name='%s' pwq=%p wq->dfl_pwq=%p
    pwq->refcnt=%d pwq->nr_active=%d delayed_works:",
    + __func__, wq->name, pwq,
    wq->dfl_pwq,
    + pwq->refcnt, pwq->nr_active);
    +
    + show_pwq(pwq);
    +
    + mutex_unlock(&wq->mutex);
    + show_state();
    + show_workqueue_state();
    + WARN_ON(1);
    + return;
    + }

    thanks,
    --
    js
    suse labs

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