[BUG] completely bonkers use of set_need_resched + VM_FAULT_NOPAGE

Daniel Vetter daniel.vetter at ffwll.ch
Thu Sep 12 13:04:03 PDT 2013

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 ...
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch

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