netdev - Re: net/bluetooth: workqueue destruction WARNING in hci_unregister

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Date:   Tue, 13 Sep 2016 20:14:40 +0200
From:   Jiri Slaby <jslaby@...e.cz>
To:     Tejun Heo <tj@...nel.org>, Dmitry Vyukov <dvyukov@...gle.com>
Cc:     Marcel Holtmann <marcel@...tmann.org>,
        Gustavo Padovan <gustavo@...ovan.org>,
        Johan Hedberg <johan.hedberg@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        linux-bluetooth <linux-bluetooth@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller <syzkaller@...glegroups.com>,
        Kostya Serebryany <kcc@...gle.com>,
        Alexander Potapenko <glider@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Takashi Iwai <tiwai@...e.com>
Subject: Re: net/bluetooth: workqueue destruction WARNING in
 hci_unregister_dev

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