From mboxrd@z Thu Jan  1 00:00:00 1970
From: Jiri Slaby <jslaby-AlSwsSmVLrQ@public.gmane.org>
Subject: Re: net/bluetooth: workqueue destruction WARNING in
 hci_unregister_dev
Date: Tue, 13 Sep 2016 20:14:40 +0200
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Cc: Marcel Holtmann <marcel-kz+m5ild9QBg9hUCZPvPmw@public.gmane.org>,
        Gustavo Padovan <gustavo-THi1TnShQwVAfugRpC6u6w@public.gmane.org>,
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        "David S. Miller" <davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org>,
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        Takashi Iwai <tiwai-IBi9RG/b67k@public.gmane.org>
To: Tejun Heo <tj-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Dmitry Vyukov <dvyukov-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org>
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On 09/13/2016, 05:35 PM, Tejun Heo wrote:
> Hello,
> 
> On Sat, Sep 10, 2016 at 11:33:48AM +0200, Dmitry Vyukov wrote:
>> Hit the WARNING with the patch. It showed "Showing busy workqueues and
>> worker pools:" after the WARNING, but then no queue info. Was it
>> already destroyed and removed from the list?...
> 
> Hmm...  It either means that the work item which was in flight when
> WARN_ON() ran finished by the time the debug printout got to it or
> that it's something unrelated to busy work items.
> 
>> [ 198.113838] WARNING: CPU: 2 PID: 26691 at kernel/workqueue.c:4042
>> destroy_workqueue+0x17b/0x630
> 
> I don't seem to have the same source code that you have.  Which exact
> WARN_ON() is this?

I assume Dmitry sees the same what I am still seeing, so I reported this
some time ago:
https://lkml.org/lkml/2016/3/21/492

This warning is trigerred there and still occurs with "HEAD":
  (pwq != wq->dfl_pwq) && (pwq->refcnt > 1)
and the state dump is in the log empty too:
destroy_workqueue: name='hci0' pwq=ffff88006b5c8f00
wq->dfl_pwq=ffff88006b5c9b00 pwq->refcnt=2 pwq->nr_active=0 delayed_works:
  pwq 13:
 cpus=2-3 node=1 flags=0x4 nice=-20 active=0/1
    in-flight: 2669:wq_barrier_func

thanks,
-- 
js
suse labs