linux-kernel - Re: [PATCH locking/Documentation 1/2] Add note of release-acquire store vulnerability

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Message-ID: <20160930125113.GY5012@twins.programming.kicks-ass.net>
Date:   Fri, 30 Sep 2016 14:51:13 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Cc:     Will Deacon <will.deacon@....com>, linux-kernel@...r.kernel.org,
        mingo@...nel.org, dhowells@...hat.com, stern@...land.harvard.edu
Subject: Re: [PATCH locking/Documentation 1/2] Add note of release-acquire
 store vulnerability

On Fri, Sep 30, 2016 at 05:14:03AM -0700, Paul E. McKenney wrote:
> PowerPC does not "obscure" stores, so both stores really are there and
> the lwsync really has effect on all CPUs.  From what I understand, even
> CPUs that do obscure stores only do so in the case of repeated stores
> by the same CPU to the same variable, and the above litmus test doesn't
> have this.
> 
> So all the stores happen, and each CPU's stores are at least locally
> ordered.

OK, when I'm not sure I ever understood the case where smp_wmb() went
wonky on PPC, sadly I cannot now find the email where you mentioned
that :/