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 S1751930AbaJSBso (ORCPT <rfc822;w@1wt.eu>);
	Sat, 18 Oct 2014 21:48:44 -0400
Received: from casper.infradead.org ([85.118.1.10]:38458 "EHLO
	casper.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1751907AbaJSBsn (ORCPT
	<rfc822;linux-kernel@vger.kernel.org>);
	Sat, 18 Oct 2014 21:48:43 -0400
User-Agent: K-9 Mail for Android
In-Reply-To: <1413663590.17869.14.camel@linux-t7sj.site>
References: <1413563929-2664-1-git-send-email-catalin.marinas@arm.com> <5442C045.2040909@linux.intel.com> <1413663590.17869.14.camel@linux-t7sj.site>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Content-Type: text/plain;
 charset=UTF-8
Subject: Re: [PATCH] futex: Ensure get_futex_key_refs() always implies a barrier
From: Darren Hart <dvhart@infradead.org>
Date: Sat, 18 Oct 2014 13:25:07 -0700
To: Davidlohr Bueso <dave@stgolabs.net>, Darren Hart <dvhart@linux.intel.com>
CC: Catalin Marinas <catalin.marinas@arm.com>, linux-kernel@vger.kernel.org,
        Matteo Franchin <Matteo.Franchin@arm.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Peter Zijlstra <peterz@infradead.org>, Ingo Molnar <mingo@kernel.org>,
        "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Mike Galbraith <umgwanakikbuti@gmail.com>
Message-ID: <6F818AE2-0865-420A-B568-44A6BA934235@infradead.org>
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org



On October 18, 2014 3:19:50 PM CDT, Davidlohr Bueso <dave@stgolabs.net> wrote:
>On Sat, 2014-10-18 at 14:32 -0500, Darren Hart wrote:
>> Which is not incomplete (lacking the explicit smp_mb()) added by this
>> patch. Perhaps the MB implementation of get_futex_key_refs() need not
>be
>> explicitly enumerated here?
>
>Agreed, how about this:
>
>diff --git a/kernel/futex.c b/kernel/futex.c
>index 21f7e41..7a0805a 100644
>--- a/kernel/futex.c
>+++ b/kernel/futex.c
>@@ -143,9 +143,8 @@
>  *
>* Where (A) orders the waiters increment and the futex value read
>through
>* atomic operations (see hb_waiters_inc) and where (B) orders the write
>- * to futex and the waiters read -- this is done by the barriers in
>- * get_futex_key_refs(), through either ihold or atomic_inc, depending
>on the
>- * futex type.
>+ * to futex and the waiters read -- this is done by the barriers for
>both
>+ * shared and private futexes in get_futex_key_refs().

Works for me.

-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.