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

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Date:   Fri, 30 Sep 2016 14:45:42 +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 05:17:21AM -0700, Paul E. McKenney wrote:
> On Fri, Sep 30, 2016 at 12:25:16PM +0200, Peter Zijlstra wrote:

> > So its a pretty dumb thing to do in any case (and yes the kernel does
> > this). Its also entirely expected in my book, that if you generate
> > conflicting writes on a release, ordering is out the window.
> > 
> > Why do we need to call this out? Who in his right mind would want to do
> > this and expect anything other than wreckage?
> > 
> > Not that we're not having too much 'fun' discussing this,.. but I do
> > wonder why we need to call this out.
> 
> You lost me on this one...  If no one does this, sure, we can leave it out.
> But if some part of the kernel does rely on this, we should call it out as
> forbidden.  And fix the kernel, of course.

Well, the kernel does this, but doesn't rely on ordering. Do "git grep
zap_locks". Its disgusting, can (and does) fail and generally is a sign
of badly broken code (printk is all that).

> Or am I missing your point?

My point was, its obvious crack, anybody doing this needs to have his
head examined. Then again, maybe we should just say that :-)