From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753453AbdARM3z (ORCPT ); Wed, 18 Jan 2017 07:29:55 -0500 Received: from bombadil.infradead.org ([198.137.202.9]:35066 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751256AbdARM3y (ORCPT ); Wed, 18 Jan 2017 07:29:54 -0500 Date: Wed, 18 Jan 2017 13:07:57 +0100 From: Peter Zijlstra To: Byungchul Park Cc: Boqun Feng , mingo@kernel.org, tglx@linutronix.de, walken@google.com, kirill@shutemov.name, linux-kernel@vger.kernel.org, linux-mm@kvack.org, iamjoonsoo.kim@lge.com, akpm@linux-foundation.org, npiggin@gmail.com Subject: Re: [PATCH v4 15/15] lockdep: Crossrelease feature documentation Message-ID: <20170118120757.GD6515@twins.programming.kicks-ass.net> References: <1481260331-360-1-git-send-email-byungchul.park@lge.com> <1481260331-360-16-git-send-email-byungchul.park@lge.com> <20170118064230.GF15084@tardis.cn.ibm.com> <20170118105346.GL3326@X58A-UD3R> <20170118110317.GC6515@twins.programming.kicks-ass.net> <20170118115428.GM3326@X58A-UD3R> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170118115428.GM3326@X58A-UD3R> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jan 18, 2017 at 08:54:28PM +0900, Byungchul Park wrote: > On Wed, Jan 18, 2017 at 12:03:17PM +0100, Peter Zijlstra wrote: > > On Wed, Jan 18, 2017 at 07:53:47PM +0900, Byungchul Park wrote: > > > On Wed, Jan 18, 2017 at 02:42:30PM +0800, Boqun Feng wrote: > > > > On Fri, Dec 09, 2016 at 02:12:11PM +0900, Byungchul Park wrote: > > > > [...] > > > > > +Example 1: > > > > > + > > > > > + CONTEXT X CONTEXT Y > > > > > + --------- --------- > > > > > + mutext_lock A > > > > > + lock_page B > > > > > + lock_page B > > > > > + mutext_lock A /* DEADLOCK */ > > > > > > > > s/mutext_lock/mutex_lock > > > > > > Thank you. > > > > > > > > +Example 3: > > > > > + > > > > > + CONTEXT X CONTEXT Y > > > > > + --------- --------- > > > > > + mutex_lock A > > > > > + mutex_lock A > > > > > + mutex_unlock A > > > > > + wait_for_complete B /* DEADLOCK */ > > > > > > > > I think this part better be: > > > > > > > > CONTEXT X CONTEXT Y > > > > --------- --------- > > > > mutex_lock A > > > > mutex_lock A > > > > wait_for_complete B /* DEADLOCK */ > > > > mutex_unlock A > > > > > > > > , right? Because Y triggers DEADLOCK before X could run mutex_unlock(). > > > > > > There's no different between two examples. > > > > There is.. > > > > > No matter which one is chosen, mutex_lock A in CONTEXT X cannot be passed. > > > > But your version shows it does mutex_unlock() before CONTEXT Y does > > wait_for_completion(). > > > > The thing about these diagrams is that both columns are assumed to have > > the same timeline. > > X cannot acquire mutex A because Y already acquired it. > > In order words, all statements below mutex_lock A in X cannot run. But your timeline shows it does, which is the error that Boqun pointed out.