[Intel-gfx] [PATCH] drm/i915: Check the timeout passed to i915_wait_request

[Jani Nikula]

On Thu, 26 Nov 2015, Chris Wilson <chris at chris-wilson.co.uk> wrote:
> On Thu, Nov 26, 2015 at 03:49:00PM +0100, Daniel Vetter wrote:
>> On Thu, Nov 26, 2015 at 01:31:42PM +0000, Chris Wilson wrote:
>> > We have relied upon the sole caller (wait_ioctl) validating the timeout
>> > argument. However, when waiting for multiple requests I forgot to ensure
>> > that the timeout was still positive on the later requests. This is more
>> > simply done inside __i915_wait_request.
>> > 
>> > Fixes regression introduced in
>> > commit b47161858ba13c9c7e03333132230d66e008dd55
>> > Author: Chris Wilson <chris at chris-wilson.co.uk>
>> > Date:   Mon Apr 27 13:41:17 2015 +0100
>> > 
>> >     drm/i915: Implement inter-engine read-read optimisations
>> > 
>> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
>> > Cc: Lionel Landwerlin <lionel.g.landwerlin at linux.intel.com>
>> > Cc: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>> > Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
>> > Cc: stable at vger.kernel.org
>> 
>> Commit message should explain what the actual problem is - we add 1 jiffy
>> of delay for each wait_request, potentially waiting quite a bit longer
>> than what userspace asked for.
>> 
>> And not sure this really justifies for cc: stable, since all the wait
>> syscalls reserve the right to wait longer. Of course we should fix it,
>> just to keep validating this possible.
>
> Dropping stable is fine, that was just a knee jerk reaction to finding a
> regression. The impact is 1 jiffie for each extra active ring for a
> wait_ioctl with a timeout -- I don't think anyone has noticed.

Pushed to drm-intel-fixes with some random copy-paste added about the 1
jiffy. Thanks for the patch and review.

BR,
Jani.


-- 
Jani Nikula, Intel Open Source Technology Center