Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1758610AbcDHP6P (ORCPT <rfc822;w@1wt.eu>);
	Fri, 8 Apr 2016 11:58:15 -0400
Received: from mail-ob0-f175.google.com ([209.85.214.175]:33119 "EHLO
	mail-ob0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1754035AbcDHP6N (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Fri, 8 Apr 2016 11:58:13 -0400
MIME-Version: 1.0
In-Reply-To: <20160408110232.GP3448@twins.programming.kicks-ass.net>
References: <20151027235635.16059.11630.stgit@pjt-glaptop.roam.corp.google.com>
 <CALCETrW=3bZyC9d5tUoESEsNt-rc-uhNhZpgEgeSC8W4FAVYkg@mail.gmail.com>
 <20160407120254.GY3448@twins.programming.kicks-ass.net> <CALCETrV0vcYcnBrs0axykJD=_BM28wKWVMG6bMzK8zh8R3m5fg@mail.gmail.com>
 <20160407152432.GZ3448@twins.programming.kicks-ass.net> <CALCETrU5ZL6Jajc=9up-j86vY_Xtt-gTFjdQE0sB0d=d-CJZ6A@mail.gmail.com>
 <20160407155312.GA3448@twins.programming.kicks-ass.net> <CALCETrVGo1Di3qamxx1NAFUSN_o=-HnYRDpeVp7zrQEBwe5u-g@mail.gmail.com>
 <20160407201156.GC3448@twins.programming.kicks-ass.net> <CALCETrXVReuuGGKW6EOV7tFFaK9RbwWxYvKdpUdvU=MpDaOtsQ@mail.gmail.com>
 <20160408110232.GP3448@twins.programming.kicks-ass.net>
From: Andy Lutomirski <luto@amacapital.net>
Date: Fri, 8 Apr 2016 08:57:53 -0700
Message-ID: <CALCETrWwNSjr0aRTPB3QrLNXztqwOBPWmNGggEJ+W+nxbLDaDA@mail.gmail.com>
Subject: Re: [RFC PATCH 0/3] restartable sequences v2: fast user-space percpu
 critical sections
To: Peter Zijlstra <peterz@infradead.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Ingo Molnar <mingo@redhat.com>, Paul Turner <commonly@gmail.com>,
        Chris Lameter <cl@linux.com>, Andi Kleen <andi@firstfloor.org>,
        Josh Triplett <josh@joshtriplett.org>,
        Dave Watson <davejwatson@fb.com>,
        Linux API <linux-api@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Andrew Hunter <ahh@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>
Content-Type: text/plain; charset=UTF-8
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org
Content-Length: 725
Lines: 19

On Apr 8, 2016 4:04 AM, "Peter Zijlstra" <peterz@infradead.org> wrote:
>
> On Thu, Apr 07, 2016 at 03:05:26PM -0700, Andy Lutomirski wrote:
>
> > It doesn't, which is what I like about my variant.  If the thread
> > accesses the protected data structure, though, it should bump the
> > sequence count, which will cause the first thread to about when it
> > gets scheduled in.
>
> Nope it won't, because that first thread is right at the commit
> instruction, nothing will stop it from executing that store and clobbing
> what we just wrote.
>

I don't think so.  I write an event number.  You commit because you
didn't notice.  I haven't loaded yet from the value you wrote when you
committed, so nothing goes wrong.

--Andy