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

Paul E. McKenney
2016-09-30T13:10:12Z

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