From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756915AbZKRK0J (ORCPT ); Wed, 18 Nov 2009 05:26:09 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756621AbZKRK0J (ORCPT ); Wed, 18 Nov 2009 05:26:09 -0500 Received: from casper.infradead.org ([85.118.1.10]:54407 "EHLO casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756503AbZKRK0I (ORCPT ); Wed, 18 Nov 2009 05:26:08 -0500 Subject: Re: [PATCH 1/2] lockdep: Include recursive read-locks dependencies in the tree From: Peter Zijlstra To: Frederic Weisbecker Cc: Ingo Molnar , LKML , Thomas Gleixner , Ming Lei , Gautham R Shenoy In-Reply-To: <1258506398-5151-2-git-send-email-fweisbec@gmail.com> References: <1258506398-5151-1-git-send-email-fweisbec@gmail.com> <1258506398-5151-2-git-send-email-fweisbec@gmail.com> Content-Type: text/plain; charset="UTF-8" Date: Wed, 18 Nov 2009 11:26:05 +0100 Message-ID: <1258539965.3918.194.camel@laptop> Mime-Version: 1.0 X-Mailer: Evolution 2.28.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2009-11-18 at 02:06 +0100, Frederic Weisbecker wrote: > Currently, recursive read locks are checked in two ways: > > - walk through the locks held by the current task and check possible > deadlock. > > - if the recursive read lock is not already present in the lock held > by the current task, check its dependencies against the tree. > > But this recursive read lock will never be added to the tree of > dependencies. It means that the following sequence: > > A = rwlock (Ar: taken as read recursive, Aw: taken as write) > B = normal lock > > Ar -> B > B -> Aw > > won't ever be detected as a lock inversion. > This patch fixes it by inserting the recursive read locks into the > tree of dependencies and enhancing the circular checks (check the > class and the read attribute collision). There were some very funny corner cases with IRQ state vs recursive locks, I don't seen any of that mentioned here. Bot ego and I poked at it at various times, but neither of us managed to actually finish it due to getting distracted with other bits I guess. http://programming.kicks-ass.net/kernel-patches/cpu-hotplug/ http://lkml.org/lkml/2009/5/11/203