linux-kernel - Re: net/bluetooth: workqueue destruction WARNING in hci_unregister

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Date:	Thu, 17 Mar 2016 13:00:13 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	Tejun Heo <tj@...nel.org>
Cc:	Dmitry Vyukov <dvyukov@...gle.com>,
	Marcel Holtmann <marcel@...tmann.org>,
	Gustavo Padovan <gustavo@...ovan.org>,
	Johan Hedberg <johan.hedberg@...il.com>,
	"David S. Miller" <davem@...emloft.net>,
	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>,
	Sasha Levin <sasha.levin@...cle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Takashi Iwai <tiwai@...e.com>
Subject: Re: net/bluetooth: workqueue destruction WARNING in
 hci_unregister_dev

Hello,

On 03/11/2016, 06:12 PM, Tejun Heo wrote:
> On Thu, Mar 03, 2016 at 10:12:01AM +0100, Jiri Slaby wrote:
>> On 03/02/2016, 04:45 PM, Tejun Heo wrote:
>>> On Fri, Feb 19, 2016 at 01:10:00PM +0100, Jiri Slaby wrote:
>>>>> 1. didn't help, the problem persists. So I haven't applied the patch from 2.
>>>>
>>>> FWIW I dumped more info about the wq:
>>>> wq->name='hci0' pwq=ffff8800390d7600 wq->dfl_pwq=ffff8800390d5200
>>>> pwq->refcnt=2 pwq->nr_active=0 delayed_works: <nothing>
>>>
>>> Can you please print out the same info for all pwq's during shutdown?
>>> It looks like we're leaking pwq refcnt but I can't spot a place where
>>> that could happen on an empty pwq.
>>
>> 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.)

BTW. what did you mean by dumping the states at shutdown? Is it still
relevant?

thanks,
-- 
js
suse labs

View attachment "vhci_debug.patch" of type "text/x-patch" (7550 bytes)