From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755321AbcI2P63 (ORCPT ); Thu, 29 Sep 2016 11:58:29 -0400 Received: from merlin.infradead.org ([205.233.59.134]:47716 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751710AbcI2P6X (ORCPT ); Thu, 29 Sep 2016 11:58:23 -0400 Date: Thu, 29 Sep 2016 17:58:17 +0200 From: Peter Zijlstra To: "Paul E. McKenney" Cc: linux-kernel@vger.kernel.org, mingo@kernel.org, dhowells@redhat.com, will.deacon@arm.com, stern@rowland.harvard.edu Subject: Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability Message-ID: <20160929155817.GB5016@twins.programming.kicks-ass.net> References: <20160929155401.GA5097@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20160929155401.GA5097@linux.vnet.ibm.com> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Sep 29, 2016 at 08:54:01AM -0700, Paul E. McKenney wrote: > If two processes are related by a RELEASE+ACQUIRE pair, ordering can be > broken if a third process overwrites the value written by the RELEASE > operation before the ACQUIRE operation has a chance of reading it. > This commit therefore updates the documentation to call this vulnerability > out explicitly. > > Reported-by: Alan Stern > Signed-off-by: Paul E. McKenney > + However, please note that a chain of RELEASE+ACQUIRE pairs may be > + broken by a store by another thread that overwrites the RELEASE > + operation's store before the ACQUIRE operation's read. This is the powerpc lwsync quirk, right? Where the barrier disappears when it looses the store. Or is there more to it? Its not entirely clear from the Changelog, which I feel should describe the reason for the behaviour.