Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761924AbZLLLDO (ORCPT ); Sat, 12 Dec 2009 06:03:14 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756258AbZLLLDO (ORCPT ); Sat, 12 Dec 2009 06:03:14 -0500 Received: from earthlight.etchedpixels.co.uk ([81.2.110.250]:60869 "EHLO www.etchedpixels.co.uk" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1756041AbZLLLDN (ORCPT ); Sat, 12 Dec 2009 06:03:13 -0500 Date: Sat, 12 Dec 2009 11:02:40 +0000 From: Alan Cox To: Andrew Morton Cc: Ingo Molnar , Greg KH , Thomas Gleixner , Peter Zijlstra , Linus Torvalds , linux-kernel@vger.kernel.org Subject: Re: [GIT PATCH] TTY patches for 2.6.33-git Message-ID: <20091212110240.194760cc@lxorguk.ukuu.org.uk> In-Reply-To: <20091212013927.58d386d1.akpm@linux-foundation.org> References: <20091211232805.GA10652@kroah.com> <20091212084611.GA28266@elte.hu> <20091212013927.58d386d1.akpm@linux-foundation.org> X-Mailer: Claws Mail 3.7.3 (GTK+ 2.16.6; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1833 Lines: 53 > The do_tty_hangup()->tty_fasync() path takes the locks in the > file_list_lock()->lock_kernel() direction whereas most other code takes > them in the other direction, which cannot be good. But I'm not sure Thats a bug - the BKL does want to be taken first (and will sleep/yield/drop) > Have a trace. I'm actually wondering if perhaps there's a missing > unlock_kernel() somewhere else, and the tty code is just the victim of > that. It's introduced by the BKL shuffle. Try the following commit 1f61f07a985c7e8cfc20ad8fcced2f3d226bd0dc Author: Alan Cox Date: Sat Dec 12 10:32:36 2009 +0000 tty: Fix the AB-BA locking bug introduced in the BKL split The fasync path takes the BKL (it probably doesn't need to in fact) but this causes lock inversions and deadlocks so we can't do that. Leave the BKL over that bit for the moment. Identified by AKPM. Signed-off-by: Alan Cox diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c index 684f0e0..f15df40 100644 --- a/drivers/char/tty_io.c +++ b/drivers/char/tty_io.c @@ -516,7 +516,6 @@ static void do_tty_hangup(struct work_struct *work) /* inuse_filps is protected by the single kernel lock */ lock_kernel(); check_tty_count(tty, "do_tty_hangup"); - unlock_kernel(); file_list_lock(); /* This breaks for file handles being sent over AF_UNIX sockets ? */ @@ -531,7 +530,6 @@ static void do_tty_hangup(struct work_struct *work) } file_list_unlock(); - lock_kernel(); tty_ldisc_hangup(tty); read_lock(&tasklist_lock); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/