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

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Message-ID: <CAKMK7uGsgYOtKQrCoq26RV9a_8na14sbpanUxM2_3EBwz-3vVw@mail.gmail.com>
Date:	Thu, 12 Sep 2013 21:52:23 +0200
From:	Daniel Vetter <daniel.vetter@...ll.ch>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	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>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [BUG] completely bonkers use of set_need_resched + VM_FAULT_NOPAGE

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