linux-kernel - Re: [BUG] completely bonkers use of set_need_resched + VM_FAULT

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Message-ID: <alpine.DEB.2.02.1309122157300.4089@ionos.tec.linutronix.de>
Date:	Thu, 12 Sep 2013 21:58:05 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Daniel Vetter <daniel.vetter@...ll.ch>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Dave Airlie <airlied@...ux.ie>,
	Maarten Lankhorst <maarten.lankhorst@...onical.com>,
	Thomas Hellstrom <thellstrom@...are.com>,
	intel-gfx <intel-gfx@...ts.freedesktop.org>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [BUG] completely bonkers use of set_need_resched +
 VM_FAULT_NOPAGE

On Thu, 12 Sep 2013, Daniel Vetter wrote:

> On Thu, Sep 12, 2013 at 6:22 PM, Peter Zijlstra <peterz@...radead.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?

Thanks,

	tglx
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