From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755303AbYLCAbv (ORCPT ); Tue, 2 Dec 2008 19:31:51 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753438AbYLCAbm (ORCPT ); Tue, 2 Dec 2008 19:31:42 -0500 Received: from smtp1.linux-foundation.org ([140.211.169.13]:59036 "EHLO smtp1.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754003AbYLCAbm (ORCPT ); Tue, 2 Dec 2008 19:31:42 -0500 Date: Tue, 2 Dec 2008 16:30:55 -0800 From: Andrew Morton To: Michael Buesch Cc: philb@gnu.org, carsten@sol.wohnheim.uni-ulm.de, renau@acm.org, tim@cyberelk.demon.co.uk, linux-kernel@vger.kernel.org Subject: Re: [PATCH] IEEE1284: Use del_timer_sync in parport_wait_event Message-Id: <20081202163055.e80e0b81.akpm@linux-foundation.org> In-Reply-To: <200811302120.49766.mb@bu3sch.de> References: <200811302120.49766.mb@bu3sch.de> X-Mailer: Sylpheed version 2.2.4 (GTK+ 2.8.20; i486-pc-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 On Sun, 30 Nov 2008 21:20:49 +0100 Michael Buesch wrote: > Use del_timer_sync() instead of del_timer() to make sure > the timer won't be running when we return from parport_wait_event(), > because this would crash due to destruction of timer_list. > > Signed-off-by: Michael Buesch > > --- > > This is completely untested and just based on a code review. > Just think about the following sequence of events: > add_timer. > down_interruptible is interrupted by a signal. > We enter the timer callback handler on another CPU. > del_timer, but the timer callback is still running. > Return from parport_wait_even, which destroys the automatic variable "timer" > while the callback is running on another CPU. > Yes, I agree. > =================================================================== > --- linux-2.6.orig/drivers/parport/ieee1284.c 2008-10-24 21:08:12.000000000 +0200 > +++ linux-2.6/drivers/parport/ieee1284.c 2008-11-30 21:09:25.000000000 +0100 > @@ -84,7 +84,7 @@ int parport_wait_event (struct parport * > > add_timer (&timer); > ret = down_interruptible (&port->physport->ieee1284.irq); > - if (!del_timer (&timer) && !ret) > + if (!del_timer_sync (&timer) && !ret) > /* Timed out. */ > ret = 1; Please fix checkpatch errors when altering code. This function is already a mismash of correct and incorrect styles - we might as well increase the correctness density. What we really want in this function is down_interruptible_timeout(). afaict we have all the infrastructure in place to implement that, but nobody has typed static noinline int __sched __down_interruptible_timeout(struct semaphore *sem, long jiffies) { return __down_common(sem, TASK_INTERRUPTIBLE, jiffies); } and then tested it. Or convert the whole thing to mutexes and write mutex_lock_interruptible_timeout() :)