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 S1751828AbdIAJsA (ORCPT <rfc822;w@1wt.eu>);
        Fri, 1 Sep 2017 05:48:00 -0400
Received: from merlin.infradead.org ([205.233.59.134]:52708 "EHLO
        merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
        with ESMTP id S1751676AbdIAJr7 (ORCPT
        <rfc822;linux-kernel@vger.kernel.org>);
        Fri, 1 Sep 2017 05:47:59 -0400
Date: Fri, 1 Sep 2017 11:47:47 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Byungchul Park <byungchul.park@lge.com>
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: <20170901094747.iv6s532ccuuzpry2@hirez.programming.kicks-ass.net>
References: <20170830074117.GG3240@X58A-UD3R>
 <20170830085333.GM32112@worktop.programming.kicks-ass.net>
 <004601d3216e$a3702030$ea506090$@lge.com>
 <20170830091223.xxnh3podtcumlabm@hirez.programming.kicks-ass.net>
 <004701d32171$ce57d4c0$6b077e40$@lge.com>
 <20170830112546.GH3240@X58A-UD3R>
 <20170831080442.5vdgoaijzmrc776x@hirez.programming.kicks-ass.net>
 <20170831081501.GJ3240@X58A-UD3R>
 <20170831083453.5tfjofzk7idthsof@hirez.programming.kicks-ass.net>
 <20170901020512.GK3240@X58A-UD3R>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20170901020512.GK3240@X58A-UD3R>
User-Agent: NeoMutt/20170609 (1.8.3)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

On Fri, Sep 01, 2017 at 11:05:12AM +0900, Byungchul Park wrote:
> On Thu, Aug 31, 2017 at 10:34:53AM +0200, Peter Zijlstra wrote:
> > On Thu, Aug 31, 2017 at 05:15:01PM +0900, Byungchul Park wrote:
> > > It's not important. Ok, check the following, instead:
> > > 
> > > context X                 context Y
> > > ---------                 ---------
> > >                           wait_for_completion(C)
> > > acquire(A)
> > > release(A)
> > > process_one_work()
> > >    acquire(B)
> > >    release(B)
> > >    work->fn()
> > >       complete(C)
> > > 
> > > We don't need to lose C->A and C->B dependencies unnecessarily.
> > 
> > I really can't be arsed about them. Its really only the first few works
> > that will retain that dependency anyway, even if you were to retain
> > them.
> 
> Wrong.
> 
> Every 'work' doing complete() for different classes of completion
> variable suffers from losing valuable dependencies, every time, not
> first few ones.

The moment you overrun the history array its gone. So yes, only the
first few works will ever see them