Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751253AbaALU6Z (ORCPT ); Sun, 12 Jan 2014 15:58:25 -0500 Received: from merlin.infradead.org ([205.233.59.134]:39109 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750962AbaALU6X (ORCPT ); Sun, 12 Jan 2014 15:58:23 -0500 Date: Sun, 12 Jan 2014 21:58:14 +0100 From: Peter Zijlstra To: Oleg Nesterov Cc: linux-kernel@vger.kernel.org, Ingo Molnar , Thomas Gleixner , Steven Rostedt , Paul McKenney , Linus Torvalds Subject: Re: check && lockdep_no_validate (Was: lockdep: Introduce wait-type checks) Message-ID: <20140112205814.GP7572@laptop.programming.kicks-ass.net> References: <20140109111516.GE7572@laptop.programming.kicks-ass.net> <20140109163120.GA8038@redhat.com> <20140109170823.GF7572@laptop.programming.kicks-ass.net> <20140109175448.GA17673@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20140109175448.GA17673@redhat.com> User-Agent: Mutt/1.5.21 (2012-12-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Jan 09, 2014 at 06:54:48PM +0100, Oleg Nesterov wrote: > But this connects to lockdep_no_validate. Not sure I understand what > this class should actually do, but consider this code: > > DEFINE_MUTEX(m1); > DEFINE_MUTEX(m2); > DEFINE_MUTEX(mx); > > void lockdep_should_complain(void) > { > lockdep_set_novalidate_class(&mx); > > // m1 -> mx -> m2 > mutex_lock(&m1); > mutex_lock(&mx); > mutex_lock(&m2); > mutex_unlock(&m2); > mutex_unlock(&mx); > mutex_unlock(&m1); > > > // m2 -> m1 ; should trigger the warning > mutex_lock(&m2); > mutex_lock(&m1); > mutex_unlock(&m1); > mutex_unlock(&m2); > } > > lockdep doesn't not detect the trivial possible deadlock. > > The patch below seems to work but most probably it is not right, and > I forgot everything (not too much) I knew about lockdep internals. > > Oleg. > > --- a/kernel/locking/lockdep.c > +++ b/kernel/locking/lockdep.c > @@ -1939,7 +1939,8 @@ check_prevs_add(struct task_struct *curr, struct held_lock *next) > * Only non-recursive-read entries get new dependencies > * added: > */ > - if (hlock->read != 2) { > + if (hlock->read != 2 && > + hlock->instance->key != &__lockdep_no_validate__) { > if (!check_prev_add(curr, hlock, next, > distance, trylock_loop)) > return 0; > Hmm, you are quite right indeed; although I would write it like: if (hlock->read != 2 && hlock->check == 2) because the __lockdep_no_validate__ thing forces the ->check value to 1. -- 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/