[BUG] completely bonkers use of set_need_resched + VM_FAULT_NOPAGE

[Thomas Gleixner]

On Thu, 12 Sep 2013, Daniel Vetter wrote:

> On Thu, Sep 12, 2013 at 9:58 PM, Thomas Gleixner <tglx at linutronix.de> wrote:
> >
> >> On Thu, Sep 12, 2013 at 6:22 PM, Peter Zijlstra <peterz at infradead.org> wrote:
> >> > If 'sane' userspace is never supposed to do this, then only insane
> >> > userspace is going to hurt from this and that's a GOOD (tm) thing,
> >> > right? ;-)
> >>
> >> Afaik sane userspace doesn't hit the _deadlock_ (or lifelock if we
> >> have the set_need_resched in there). drm/i915 is a bit different since
> >> we have just one lock, and so the same design would actually deadlock
> >> even for sane userspace. But hitting contention there and yielding is
> >> somewhat expected. Obviously shouldn't happen too often since it'll
> >> hurt performance, with either blocking or the yield spinning loop.
> >
> > So this is actually a non priviledged DoS interface, right?
> 
> I think for ttm drivers it's just execbuf being exploitable. But on
> drm/i915 we've
> had the same issue with the pwrite/pread ioctls, so a simple
> glBufferData(glMap) kind of recursion from gl clients blew the kernel
> to pieces ...

And the only answer you folks came up with is set_need_resched() and
yield()? Oh well....

Thanks,

	tglx