Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753701Ab3EHJty (ORCPT ); Wed, 8 May 2013 05:49:54 -0400 Received: from mga14.intel.com ([143.182.124.37]:32775 "EHLO mga14.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751950Ab3EHJtx (ORCPT ); Wed, 8 May 2013 05:49:53 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.87,632,1363158000"; d="scan'208";a="299314269" Message-ID: <1368006588.16616.5.camel@intelbox> Subject: Re: [PATCH] wait: fix false timeouts when using wait_event_timeout() From: Imre Deak Reply-To: imre.deak@intel.com To: Andrew Morton Cc: Daniel Vetter , "Paul E. McKenney" , David Howells , Dave Jones , Jens Axboe , Lukas Czerner , Linux Kernel Mailing List Date: Wed, 08 May 2013 12:49:48 +0300 In-Reply-To: <20130507161248.aedfde86659ae45cc5390bc4@linux-foundation.org> References: <1367485129-4423-1-git-send-email-imre.deak@intel.com> <20130507161248.aedfde86659ae45cc5390bc4@linux-foundation.org> Organization: Intel Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.6.2-0ubuntu0.1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1857 Lines: 42 On Tue, 2013-05-07 at 16:12 -0700, Andrew Morton wrote: > 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? There is at least [1], but I'm sure there is more similar reports about i915. I'd vote for -stable at least. --Imre [1] https://bugs.freedesktop.org/show_bug.cgi?id=64133 -- 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/