[Intel-gfx] [PATCH] drm/i915: Fix RPS pointer passed from wait_ioctl to i915_wait_request

[Daniel Vetter]

On Thu, Dec 03, 2015 at 09:25:37PM +0000, Chris Wilson wrote:
> On Wed, Dec 02, 2015 at 09:13:46AM +0000, Chris Wilson wrote:
> > In commit 2e1b873072dfe3bbcc158a9c21acde1ab0d36c55 [v4.2]
> > Author: Chris Wilson <chris at chris-wilson.co.uk>
> > Date:   Mon Apr 27 13:41:22 2015 +0100
> > 
> >     drm/i915: Convert RPS tracking to a intel_rps_client struct
> > 
> > we converted the __i915_wait_request() to take a new intel_rps_client
> > struct (rather than having to pass fake drm_i915_file_private structs).
> > However, due to use of passing a void pointer, I didn't spot one
> > callsite in wait-ioctl was passing the wrong pointer.
> > 
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> > Cc: Daniel Vetter <daniel.vetter at ffwll.ch>
> > Cc: stable at vger.kernel.org
> 
> Fwiw, the impact of this bug is zero. Along the rps path, we always
> first call list_empty(rps) which when we pass in the wrong pointer
> always evaluates to false and we return early and never chase the
> invalid pointers.
> 
> The user visible impact is then wait-ioctl doesn't get the same
> waitboosting as the other interfaces (set-domain, throttle), which is a
> performance concern for the *very* few users of the wait interface.
> There is also a libdrm_intel patch to use the wait-ioctl for
> drm_intel_bo_wait_rendering() if anyone feels inclined to review
> libdrm_intel patches.

I added this to the commit message and figured it's not 100% justified for
-fixes. So applied to dinq.

Thanks, Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch