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

[Chris Wilson]

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.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre