From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755404AbXI3HVW (ORCPT ); Sun, 30 Sep 2007 03:21:22 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753429AbXI3HVP (ORCPT ); Sun, 30 Sep 2007 03:21:15 -0400 Received: from mx2.mail.elte.hu ([157.181.151.9]:45370 "EHLO mx2.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753401AbXI3HVO (ORCPT ); Sun, 30 Sep 2007 03:21:14 -0400 Date: Sun, 30 Sep 2007 09:20:56 +0200 From: Ingo Molnar To: Jan Luebbe Cc: linux-kernel@vger.kernel.org, torvalds@linux-foundation.org Subject: Re: [PATCH] fix console change race exposed by CFS Message-ID: <20070930072056.GA18108@elte.hu> References: <1191084471.24185.11.camel@polaris> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <1191084471.24185.11.camel@polaris> User-Agent: Mutt/1.5.14 (2007-02-12) X-ELTE-VirusStatus: clean X-ELTE-SpamScore: -1.5 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=-1.5 required=5.9 tests=BAYES_00 autolearn=no SpamAssassin version=3.1.7-deb -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org * Jan Luebbe wrote: > From: Jan Lübbe > > The new behaviour of CFS exposes a race which occurs if a switch is > requested when vt_mode.mode is VT_PROCESS. > > The process with vc->vt_pid is signaled before vc->vt_newvt is set. This > causes the switch to fail when triggered by the monitoing process > because the target is still -1. > > Signed-off-by: Jan Lübbe nifty! I'm wondering what the symptoms of this bug were - how did you notice it? Also, i'm wondering how you managed to debug this - looks quite hard to trigger this race, right? Acked-by: Ingo Molnar Ingo