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

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Date:	Fri, 11 Mar 2016 12:12:05 -0500
From:	Tejun Heo <tj@...nel.org>
To:	Jiri Slaby <jslaby@...e.cz>
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,

Sorry about the delay.

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. :(

Thanks.

-- 
tejun