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

From: Peter Zijlstra
Date: Fri Sep 30 2016 - 08:45:59 EST

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 :-)