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From: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
To: Chris Wilson <chris@chris-wilson.co.uk>, intel-gfx@lists.freedesktop.org
Cc: Daniel Vetter <daniel.vetter@intel.com>
Subject: Re: [PATCH] drm/i915: Embrace the race in busy-ioctl
Date: Mon, 15 Aug 2016 15:48:15 +0300	[thread overview]
Message-ID: <1471265295.10724.13.camel@linux.intel.com> (raw)
In-Reply-To: <1471024321-1583-1-git-send-email-chris@chris-wilson.co.uk>

On pe, 2016-08-12 at 18:52 +0100, Chris Wilson wrote:
> Daniel Vetter proposed a new challenge to the serialisation inside the
> busy-ioctl that exposed a flaw that could result in us reporting the
> wrong engine as being busy. If the request is reallocated as we test
> its busyness and then reassigned to this object by another thread, we
> would not notice that the test itself was incorrect.
> 
> We are faced with a choice of using __i915_gem_active_get_request_rcu()
> to first acquire a reference to the request preventing the race, or to
> acknowledge the race and accept the limitations upon the accuracy of the
> busy flags. Note that we guarantee that we never falsely report the
> object as idle (providing userspace itself doesn't race), and so the
> most important use of the busy-ioctl and its guarantees are fulfilled.
> 

If Daniel acks the userspace change,

Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

Regards, Joonas
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation
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  parent reply	other threads:[~2016-08-15 12:48 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-08-12 17:52 [PATCH] drm/i915: Embrace the race in busy-ioctl Chris Wilson
2016-08-13  5:23 ` ✗ Ro.CI.BAT: failure for " Patchwork
2016-08-15 12:48 ` Joonas Lahtinen [this message]
2016-08-15 13:06 ` [PATCH] " Mika Kuoppala

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