[BUG] completely bonkers use of set_need_resched + VM_FAULT_NOPAGE

Thomas Gleixner tglx at linutronix.de
Thu Sep 12 12:58:05 PDT 2013

On Thu, 12 Sep 2013, Daniel Vetter 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?



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