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Subject: Re: [linux-next / tty] possible circular locking dependency detected
From: Vegard Nossum <vegard.nossum@oracle.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Cc: Jiri Slaby <jslaby@suse.com>, linux-kernel@vger.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
References: <20170522073943.GA469@jagdpanzerIV.localdomain>
 <20170522102454.GA30331@kroah.com>
 <50cc6717-c709-873c-b434-07da13365977@oracle.com>
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Date: Mon, 29 May 2017 12:43:39 +0200
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On 05/22/17 12:27, Vegard Nossum wrote:
> On 05/22/17 12:24, Greg Kroah-Hartman wrote:
>> On Mon, May 22, 2017 at 04:39:43PM +0900, Sergey Senozhatsky wrote:
>>> Hello,
>>>
>>> [ 1274.378287] ======================================================
>>> [ 1274.378289] WARNING: possible circular locking dependency detected
>>> [ 1274.378290] 4.12.0-rc1-next-20170522-dbg-00007-gc09b2ab28b74-dirty 
>>> #1317 Not tainted
>>> [ 1274.378291] ------------------------------------------------------
>>> [ 1274.378293] kworker/u8:5/111 is trying to acquire lock:
>>> [ 1274.378294]  (&buf->lock){+.+...}, at: [<ffffffff812f2831>] 
>>> tty_buffer_flush+0x34/0x88
>>> [ 1274.378300]
>>>                 but task is already holding lock:
>>> [ 1274.378301]  (&o_tty->termios_rwsem/1){++++..}, at: 
>>> [<ffffffff812ee5c7>] isig+0x47/0xd2
>>> [ 1274.378307]
>>>                 which lock already depends on the new lock.
>>>
> 
>> Any hint as to what you were doing when this happened?
>>
>> Does this also show up in 4.11?
> 
> It's my patch "tty: fix port buffer locking" :-/
> 
> At a glance, looks related to pty taking the lock on the other side in a
> different order. I'll have a closer look.

I can reproduce the lockdep report locally on v4.12-rc3. Looking at it now.


Vegard