From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756872Ab1HEP3A (ORCPT ); Fri, 5 Aug 2011 11:29:00 -0400 Received: from mail-ey0-f174.google.com ([209.85.215.174]:56123 "EHLO mail-ey0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753643Ab1HEP27 (ORCPT ); Fri, 5 Aug 2011 11:28:59 -0400 Date: Fri, 5 Aug 2011 18:27:55 +0300 From: Sergey Senozhatsky To: Peter Zijlstra Cc: Ingo Molnar , Thomas Gleixner , Andrew Morton , linux-kernel@vger.kernel.org, KAMEZAWA Hiroyuki , linux-mm@kvack.org Subject: Re: select_task_rq_fair: WARNING: at kernel/lockdep.c match_held_lock Message-ID: <20110805152755.GA4148@swordfish.minsk.epam.com> References: <20110804141306.GA3536@swordfish.minsk.epam.com> <1312470358.16729.25.camel@twins> <20110804153752.GA3562@swordfish.minsk.epam.com> <1312472867.16729.38.camel@twins> <20110804155347.GB3562@swordfish.minsk.epam.com> <1312547780.28695.1.camel@twins> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1312547780.28695.1.camel@twins> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (08/05/11 14:36), Peter Zijlstra wrote: > The below is what I've come up with. > Hello, I think that should work. Will test, anyway. Thanks, Sergey > --- > Subject: lockdep: Fix wrong assumption in match_held_lock > From: Peter Zijlstra > Date: Fri Aug 05 14:26:17 CEST 2011 > > match_held_lock() was assuming it was being called on a lock class > that had already seen usage. > > This condition was true for bug-free code using lockdep_assert_held(), > since you're in fact holding the lock when calling it. However the > assumption fails the moment you assume the assertion can fail, which > is the whole point of having the assertion in the first place. > > Anyway, now that there's more lockdep_is_held() users, notably > __rcu_dereference_check(), its much easier to trigger this since we > test for a number of locks and we only need to hold any one of them to > be good. > > Reported-by: Sergey Senozhatsky > Signed-off-by: Peter Zijlstra > --- > kernel/lockdep.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > Index: linux-2.6/kernel/lockdep.c > =================================================================== > --- linux-2.6.orig/kernel/lockdep.c > +++ linux-2.6/kernel/lockdep.c > @@ -3111,7 +3111,13 @@ static int match_held_lock(struct held_l > if (!class) > class = look_up_lock_class(lock, 0); > > - if (DEBUG_LOCKS_WARN_ON(!class)) > + /* > + * If look_up_lock_class() failed to find a class, we're trying > + * to test if we hold a lock that has never yet been acquired. > + * Clearly if the lock hasn't been acquired _ever_, we're not > + * holding it either, so report failure. > + */ > + if (!class) > return 0; > > if (DEBUG_LOCKS_WARN_ON(!hlock->nest_lock)) >