From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S932966AbcATMrr (ORCPT <rfc822;w@1wt.eu>);
	Wed, 20 Jan 2016 07:47:47 -0500
Received: from mail-wm0-f47.google.com ([74.125.82.47]:37129 "EHLO
	mail-wm0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751039AbcATMrn (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Wed, 20 Jan 2016 07:47:43 -0500
Subject: Re: tty: deadlock between n_tracerouter_receivebuf and flush_to_ldisc
To: Dmitry Vyukov <dvyukov@google.com>,
        J Freyensee <james_p_freyensee@linux.intel.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        LKML <linux-kernel@vger.kernel.org>
References: <CACT4Y+Z3or-Tb=COdS0iMhKSy_+ECs7QGnreLCPdDttUmnc-Cw@mail.gmail.com>
Cc: Eric Dumazet <edumazet@google.com>,
        Alexander Potapenko <glider@google.com>,
        Kostya Serebryany <kcc@google.com>,
        syzkaller <syzkaller@googlegroups.com>,
        Sasha Levin <sasha.levin@oracle.com>,
        Peter Zijlstra <peterz@infradead.org>
From: Jiri Slaby <jslaby@suse.cz>
Message-ID: <569F81EC.4070602@suse.cz>
Date: Wed, 20 Jan 2016 13:47:40 +0100
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101
 Thunderbird/38.5.1
MIME-Version: 1.0
In-Reply-To: <CACT4Y+Z3or-Tb=COdS0iMhKSy_+ECs7QGnreLCPdDttUmnc-Cw@mail.gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On 12/30/2015, 11:44 AM, Dmitry Vyukov wrote:
> the existing dependency chain (in reverse order) is:
> 
> -> #3 (&buf->lock){+.+...}:
>        [<ffffffff813f0acf>] lock_acquire+0x19f/0x3c0
> kernel/locking/lockdep.c:3585
>        [<     inline     >] __raw_spin_lock_irqsave
> include/linux/spinlock_api_smp.h:112
>        [<ffffffff85c8e790>] _raw_spin_lock_irqsave+0x50/0x70
> kernel/locking/spinlock.c:159
>        [<ffffffff82b8c050>] tty_get_pgrp+0x20/0x80 drivers/tty/tty_io.c:2502

But at this line, there is &tty->ctrl_lock, not &buf->lock. I am
confused now :/.
spin_lock_irqsave(&tty->ctrl_lock, flags);

>        [<ffffffff82b9a09a>] __isig+0x1a/0x50 drivers/tty/n_tty.c:1112
>        [<ffffffff82b9c16e>] isig+0xae/0x2c0 drivers/tty/n_tty.c:1131
>        [<ffffffff82b9ef02>] n_tty_receive_signal_char+0x22/0xf0
> drivers/tty/n_tty.c:1243
>        [<ffffffff82ba4958>] n_tty_receive_char_special+0x1278/0x2bf0
> drivers/tty/n_tty.c:1289
>        [<     inline     >] n_tty_receive_buf_fast drivers/tty/n_tty.c:1613
>        [<     inline     >] __receive_buf drivers/tty/n_tty.c:1647
>        [<ffffffff82ba7ca6>] n_tty_receive_buf_common+0x19d6/0x2450
> drivers/tty/n_tty.c:1745
>        [<ffffffff82ba8753>] n_tty_receive_buf2+0x33/0x40
> drivers/tty/n_tty.c:1780
>        [<     inline     >] receive_buf drivers/tty/tty_buffer.c:450
>        [<ffffffff82bafa6f>] flush_to_ldisc+0x3bf/0x7f0
> drivers/tty/tty_buffer.c:517
>        [<ffffffff8133833c>] process_one_work+0x76c/0x13e0
> kernel/workqueue.c:2030
>        [<ffffffff81339093>] worker_thread+0xe3/0xe90 kernel/workqueue.c:2162
>        [<ffffffff8134b63f>] kthread+0x23f/0x2d0 drivers/block/aoe/aoecmd.c:1303
>        [<ffffffff85c8eeef>] ret_from_fork+0x3f/0x70
> arch/x86/entry/entry_64.S:468


-- 
js
suse labs