Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751325AbdIEHIg (ORCPT ); Tue, 5 Sep 2017 03:08:36 -0400 Received: from merlin.infradead.org ([205.233.59.134]:49002 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750810AbdIEHIf (ORCPT ); Tue, 5 Sep 2017 03:08:35 -0400 Date: Tue, 5 Sep 2017 09:08:25 +0200 From: Peter Zijlstra To: Byungchul Park Cc: Byungchul Park , Ingo Molnar , Tejun Heo , Boqun Feng , david@fromorbit.com, Johannes Berg , oleg@redhat.com, "linux-kernel@vger.kernel.org" , kernel-team@lge.com Subject: Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation Message-ID: <20170905070825.tovfkqvxpwosh5oa@hirez.programming.kicks-ass.net> References: <20170831083453.5tfjofzk7idthsof@hirez.programming.kicks-ass.net> <20170901020512.GK3240@X58A-UD3R> <20170901094747.iv6s532ccuuzpry2@hirez.programming.kicks-ass.net> <20170901101629.GL3240@X58A-UD3R> <20170901123856.p2trpebau57yxftc@hirez.programming.kicks-ass.net> <20170901163852.ckslrgldsalqmg3c@hirez.programming.kicks-ass.net> <20170904013031.GM3240@X58A-UD3R> <20170904114248.kls4jv2ggsv46mli@hirez.programming.kicks-ass.net> <20170905003844.GO3240@X58A-UD3R> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170905003844.GO3240@X58A-UD3R> User-Agent: NeoMutt/20170609 (1.8.3) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2990 Lines: 85 On Tue, Sep 05, 2017 at 09:38:45AM +0900, Byungchul Park wrote: > On Mon, Sep 04, 2017 at 01:42:48PM +0200, Peter Zijlstra wrote: > > On Mon, Sep 04, 2017 at 10:30:32AM +0900, Byungchul Park wrote: > > > On Fri, Sep 01, 2017 at 06:38:52PM +0200, Peter Zijlstra wrote: > > > > And get tangled up with the workqueue annotation again, no thanks. > > > > Having the first few works see the thread setup isn't worth it. > > > > > > > > And your work_id annotation had the same problem. > > > > > > I keep asking you for an example because I really understand you. > > > > > > Fix my problematic example with your patches, > > > > > > or, > > > > > > Show me a problematic scenario with my original code, you expect. > > > > > > Whatever, it would be helpful to understand you. > > > > I _really_ don't understand what you're worried about. Is it the kthread > > create and workqueue init or the pool->lock that is released/acquired in > > process_one_work()? > > s/in process_one_work()/in all worker code including setup code/ > > Original code was already designed to handle real dependencies well. But > you invalidated it _w/o_ any reason, that's why I don't agree with your > patches. The reasons: - it avoids the interaction with the workqueue annotation - it makes each work consistent - its not different from what you did with work_id: https://lkml.kernel.org/r/1489479542-27030-6-git-send-email-byungchul.park@lge.com crossrelease_work_start() vs same_context_xhlock() { if (xhlock->work_id == curr->workid) ... } > Your patches only do avoiding the wq issue now we focus on. > > Look at: > > worker thread another context > ------------- --------------- > wait_for_completion() > | > | (1) > v > +---------+ > | Work A | (2) > +---------+ > | > | (3) > v > +---------+ > | Work B | (4) > +---------+ > | > | (5) > v > +---------+ > | Work C | (6) > +---------+ > | > v > > We have to consider whole context of the worker to build dependencies > with a crosslock e.g. wait_for_commplete(). > > Only thing we have to care here is to make all works e.g. (2), (4) and > (6) independent, because workqueue does _concurrency control_. As I said > last year at the very beginning, for works not applied the control e.g. > max_active == 1, we don't need that isolation. I said, it's a future work. > > It would have been much easier to communicate with each other if you > *tried* to understand my examples like now or you *tried* to give me one > example at least. You didn't even *try*. Only thing I want to ask you > for is to *try* to understand my opinions on conflicts. > > Now, understand what I intended? Still unsufficient? So you worry about max_active==1 ? Or you worry about pool->lock or about the thread setup? I'm still not sure.