Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756079Ab3EGXMv (ORCPT ); Tue, 7 May 2013 19:12:51 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:55789 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750881Ab3EGXMu (ORCPT ); Tue, 7 May 2013 19:12:50 -0400 Date: Tue, 7 May 2013 16:12:48 -0700 From: Andrew Morton To: Daniel Vetter Cc: Imre Deak , "Paul E. McKenney" , David Howells , Dave Jones , Jens Axboe , Lukas Czerner , Linux Kernel Mailing List Subject: Re: [PATCH] wait: fix false timeouts when using wait_event_timeout() Message-Id: <20130507161248.aedfde86659ae45cc5390bc4@linux-foundation.org> In-Reply-To: References: <1367485129-4423-1-git-send-email-imre.deak@intel.com> X-Mailer: Sylpheed 3.2.0beta5 (GTK+ 2.24.10; x86_64-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 Content-Length: 1571 Lines: 32 On Thu, 2 May 2013 11:36:56 +0200 Daniel Vetter wrote: > On Thu, May 2, 2013 at 10:58 AM, Imre Deak wrote: > > Many callers of the wait_event_timeout() and > > wait_event_interruptible_timeout() expect that the return value will be > > positive if the specified condition becomes true before the timeout > > elapses. However, at the moment this isn't guaranteed. If the wake-up > > handler is delayed enough, the time remaining until timeout will be > > calculated as 0 - and passed back as a return value - even if the > > condition became true before the timeout has passed. > > > > Fix this by returning at least 1 if the condition becomes true. This > > semantic is in line with what wait_for_condition_timeout() does; see > > commit bb10ed09 - "sched: fix wait_for_completion_timeout() spurious > > failure under heavy load". > > > > Signed-off-by: Imre Deak > > We have 3 instances of this bug in drm/i915. One case even where we > switch between the interruptible and not interruptible > wait_event_timeout variants, foolishly presuming they have the same > semantics. I very much like this. Let's think about scheduling this fix. Are any of the bugs which we expect this patch fixes serious enough to warrant merging it into 3.10? And -stable? -- 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/