linux-kernel - Re: tty: possible deadlock in tty_buffer

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Message-ID: <1496857168.2779.0.camel@sandisk.com>
Date:   Wed, 7 Jun 2017 17:39:30 +0000
From:   Bart Van Assche <Bart.VanAssche@...disk.com>
To:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     "jslaby@...e.com" <jslaby@...e.com>,
        "andreyknvl@...gle.com" <andreyknvl@...gle.com>,
        "kcc@...gle.com" <kcc@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dvyukov@...gle.com" <dvyukov@...gle.com>,
        "syzkaller@...glegroups.com" <syzkaller@...glegroups.com>
Subject: Re: tty: possible deadlock in tty_buffer_flush

On Wed, 2017-06-07 at 10:50 +0200, gregkh@...uxfoundation.org wrote:
> On Wed, Jun 07, 2017 at 12:42:12AM +0000, Bart Van Assche wrote:
> > On Mon, 2017-05-29 at 17:19 +0200, Andrey Konovalov wrote:
> > > I've got the following error report while fuzzing the kernel with syzkaller.
> > > 
> > > On commit 5ed02dbb497422bf225783f46e6eadd237d23d6b (4.12-rc3).
> > > 
> > > ======================================================
> > > WARNING: possible circular locking dependency detected
> > > 4.12.0-rc3+ #369 Not tainted
> > > ------------------------------------------------------
> > > kworker/u9:1/31 is trying to acquire lock:
> > >  (&buf->lock){+.+...}, at: [<ffffffff823dd42b>]
> > > tty_buffer_flush+0xbb/0x3b0 drivers/tty/tty_buffer.c:221
> > > 
> > > but task is already holding lock:
> > >  (&o_tty->termios_rwsem/1){++++..}, at: [<ffffffff823cd5d1>]
> > > isig+0xa1/0x4d0 drivers/tty/n_tty.c:1100
> > > 
> > > which lock already depends on the new lock.
> > 
> > Hello Andrey,
> > 
> > I also see this warning but during regular boot (without running syzkaller).
> > Do you perhaps have the time to bisect this?
> 
> Should be fixed in 4.12-rc4, right?

That's right.

Thanks!

Bart.