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Date: Sat, 3 Jun 2017 18:34:20 +0900
From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: Vegard Nossum <vegard.nossum@oracle.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        Jiri Slaby <jslaby@suse.com>, linux-kernel@vger.kernel.org,
        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Subject: Re: [linux-next / tty] possible circular locking dependency detected
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On Mon, May 29, 2017 at 12:43:39PM +0200, Vegard Nossum wrote:
> 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.

Any ideas?  Or should I just revert the original patch?

thanks,

greg k-h