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Date: Fri, 30 Sep 2016 10:53:34 +0200
From: Peter Zijlstra <peterz@infradead.org>
To: Alan Stern <stern@rowland.harvard.edu>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
        Will Deacon <will.deacon@arm.com>, linux-kernel@vger.kernel.org,
        mingo@kernel.org, dhowells@redhat.com
Subject: Re: [PATCH locking/Documentation 1/2] Add note of release-acquire
 store vulnerability
Message-ID: <20160930085334.GE5016@twins.programming.kicks-ass.net>
References: <20160929191858.GD14933@linux.vnet.ibm.com>
 <Pine.LNX.4.44L0.1609291527490.1387-100000@iolanthe.rowland.org>
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On Thu, Sep 29, 2016 at 03:36:38PM -0400, Alan Stern wrote:
> > > If you execute P0 and P1 concurrently and one store of each 'wins' the
> > > LWSYNC of either is null and void, and therefore P2 is unordered and can
> > > observe r2==0.
> 
> Not so.  lwsync instructions cannot be "voided".

I distinctly remember there being a case (smp_wmb()) where the lwsync
would disappear if the store was lost.