From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759535AbZBTROz (ORCPT ); Fri, 20 Feb 2009 12:14:55 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754434AbZBTROm (ORCPT ); Fri, 20 Feb 2009 12:14:42 -0500 Received: from mx3.mail.elte.hu ([157.181.1.138]:58186 "EHLO mx3.mail.elte.hu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755018AbZBTROl (ORCPT ); Fri, 20 Feb 2009 12:14:41 -0500 Date: Fri, 20 Feb 2009 18:14:27 +0100 From: Ingo Molnar To: "Paul E. McKenney" Cc: Vegard Nossum , stable@kernel.org, Andrew Morton , Nick Piggin , Pekka Enberg , linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm: fix lazy vmap purging (use-after-free error) Message-ID: <20090220171427.GE24538@elte.hu> References: <20090220134121.GA19575@damson.getinternet.no> <20090220135000.GA9616@elte.hu> <20090220140157.GA12799@elte.hu> <19f34abd0902200651k7e86aebay5398ef5ac0578561@mail.gmail.com> <20090220154619.GC6960@linux.vnet.ibm.com> <20090220160409.GB11294@elte.hu> <20090220164441.GG6960@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20090220164441.GG6960@linux.vnet.ibm.com> User-Agent: Mutt/1.5.18 (2008-05-17) 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=3.2.3 -1.5 BAYES_00 BODY: Bayesian spam probability is 0 to 1% [score: 0.0000] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org * Paul E. McKenney wrote: > > > So, what flavor of RCU were you using? > > > > well, even in preemptible RCU the grace period should be > > extended as long as we are non-preempt (which we are here), > > correct? > > Given Classic RCU, you are quite correct. With preemptable > RCU, if there are no readers, and if irqs are enabled, the > grace period could end within the spinlock's critical section. > Of course, the spinlock would need to be held for an > improbably long time -- many milliseconds. ah. But we _can_ get unlucky there and get into multiple-milliseconds of blockage: for example if some heavy interrupt source or softirq processes stuff for many milliseconds. So it's a real fix needed both for mainline and for 2.6.28. And kudos to kmemcheck ;-) Ingo