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

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Message-Id: <20160930131000.GQ14933@linux.vnet.ibm.com>
Date:   Fri, 30 Sep 2016 06:10:00 -0700
From:   "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 02:45:42PM +0200, Peter Zijlstra wrote:
> 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 :-)

I do find that as I get older, emphatically stating the obvious becomes
an increasingly large fraction of my role, so agreed.  ;-)

							Thanx, Paul