From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
        id S1751785AbdIEIaf (ORCPT <rfc822;w@1wt.eu>);
        Tue, 5 Sep 2017 04:30:35 -0400
Received: from LGEAMRELO11.lge.com ([156.147.23.51]:36971 "EHLO
        lgeamrelo11.lge.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1751495AbdIEIab (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Tue, 5 Sep 2017 04:30:31 -0400
X-Original-SENDERIP: 156.147.1.151
X-Original-MAILFROM: byungchul.park@lge.com
X-Original-SENDERIP: 10.177.222.33
X-Original-MAILFROM: byungchul.park@lge.com
Date: Tue, 5 Sep 2017 17:30:23 +0900
From: Byungchul Park <byungchul.park@lge.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Byungchul Park <max.byungchul.park@gmail.com>,
        Ingo Molnar <mingo@kernel.org>, Tejun Heo <tj@kernel.org>,
        Boqun Feng <boqun.feng@gmail.com>, david@fromorbit.com,
        Johannes Berg <johannes@sipsolutions.net>, oleg@redhat.com,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        kernel-team@lge.com
Subject: Re: [PATCH 4/4] lockdep: Fix workqueue crossrelease annotation
Message-ID: <20170905083023.GU3240@X58A-UD3R>
References: <20170901020512.GK3240@X58A-UD3R>
 <20170901094747.iv6s532ccuuzpry2@hirez.programming.kicks-ass.net>
 <20170901101629.GL3240@X58A-UD3R>
 <20170901123856.p2trpebau57yxftc@hirez.programming.kicks-ass.net>
 <CANrsvRMc4QXnRFpYY1m7X+WU52WrC7HvvhbvAUqTWQTx2Py6bQ@mail.gmail.com>
 <20170901163852.ckslrgldsalqmg3c@hirez.programming.kicks-ass.net>
 <20170904013031.GM3240@X58A-UD3R>
 <20170904114248.kls4jv2ggsv46mli@hirez.programming.kicks-ass.net>
 <20170905003844.GO3240@X58A-UD3R>
 <20170905070825.tovfkqvxpwosh5oa@hirez.programming.kicks-ass.net>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20170905070825.tovfkqvxpwosh5oa@hirez.programming.kicks-ass.net>
User-Agent: Mutt/1.5.21 (2010-09-15)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Tue, Sep 05, 2017 at 09:08:25AM +0200, Peter Zijlstra wrote:
> > 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.

It's close to the letter. Precisely, I worry about (1), (3), (5) and so
on, since they certainly create dependencies with crosslocks e.g.
completion in my example.