Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751371AbdH3Hl2 (ORCPT ); Wed, 30 Aug 2017 03:41:28 -0400 Received: from LGEAMRELO12.lge.com ([156.147.23.52]:39045 "EHLO lgeamrelo12.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751302AbdH3Hl1 (ORCPT ); Wed, 30 Aug 2017 03:41:27 -0400 X-Original-SENDERIP: 156.147.1.125 X-Original-MAILFROM: byungchul.park@lge.com X-Original-SENDERIP: 10.177.222.33 X-Original-MAILFROM: byungchul.park@lge.com Date: Wed, 30 Aug 2017 16:41:17 +0900 From: Byungchul Park To: Peter Zijlstra Cc: mingo@kernel.org, tj@kernel.org, boqun.feng@gmail.com, david@fromorbit.com, johannes@sipsolutions.net, oleg@redhat.com, linux-kernel@vger.kernel.org, kernel-team@lge.com Subject: Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Message-ID: <20170830074117.GG3240@X58A-UD3R> References: <20170823115843.662056844@infradead.org> <20170823121432.990701317@infradead.org> <20170824021840.GC6772@X58A-UD3R> <20170824140240.t4imrpvussebfimm@hirez.programming.kicks-ass.net> <20170825011114.GA3858@X58A-UD3R> <20170829085939.ggmb6xiohw67micb@hirez.programming.kicks-ass.net> <20170830020953.GE3240@X58A-UD3R> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170830020953.GE3240@X58A-UD3R> 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 Content-Length: 2346 Lines: 49 On Wed, Aug 30, 2017 at 11:09:53AM +0900, Byungchul Park wrote: > On Tue, Aug 29, 2017 at 10:59:39AM +0200, Peter Zijlstra wrote: > > Subject: lockdep: Untangle xhlock history save/restore from task independence > > > > Where XHLOCK_{SOFT,HARD} are save/restore points in the xhlocks[] to > > ensure the temporal IRQ events don't interact with task state, the > > XHLOCK_PROC is a fundament different beast that just happens to share > > the interface. > > > > The purpose of XHLOCK_PROC is to annotate independent execution inside > > one task. For example workqueues, each work should appear to run in its > > own 'pristine' 'task'. > > > > Remove XHLOCK_PROC in favour of its own interface to avoid confusion. > > Much better to me than the patch you did previously, but, see blow. > > > Signed-off-by: Peter Zijlstra (Intel) > > --- > > diff --git a/kernel/workqueue.c b/kernel/workqueue.c > > index c0331891dec1..ab3c0dc8c7ed 100644 > > --- a/kernel/workqueue.c > > +++ b/kernel/workqueue.c > > @@ -2107,14 +2107,14 @@ __acquires(&pool->lock) > > * Which would create W1->C->W1 dependencies, even though there is no > > * actual deadlock possible. There are two solutions, using a > > * read-recursive acquire on the work(queue) 'locks', but this will then > > - * hit the lockdep limitation on recursive locks, or simly discard > > + * hit the lockdep limitation on recursive locks, or simply discard > > * these locks. > > * > > * AFAICT there is no possible deadlock scenario between the > > * flush_work() and complete() primitives (except for single-threaded > > * workqueues), so hiding them isn't a problem. > > */ > > - crossrelease_hist_start(XHLOCK_PROC, true); > > + lockdep_invariant_state(true); > > This is what I am always curious about. It would be ok if you agree with > removing this work-around after fixing acquire things in wq. But, you > keep to say this is essencial. > > You should focus on what dependencies actually are, than saparating > contexts unnecessarily. Of course, we have to do it for each work, _BUT_ > not between outside of work and each work since there might be > dependencies between them certainly. You have never answered it. I'm curious about your answer. If you can't, I think you have to revert all your patches. All yours are wrong.