[Intel-gfx] [PATCH 22/22] drm/i915: Export our request as a dma-buf fence on the reservation object

[Chris Wilson]

On Thu, Jul 28, 2016 at 12:32:42PM +0200, Daniel Vetter wrote:
> On Wed, Jul 27, 2016 at 12:15:00PM +0100, Chris Wilson wrote:
> > If the GEM objects being rendered with in this request have been
> > exported via dma-buf to a third party, hook ourselves into the dma-buf
> > reservation object so that the third party can serialise with our
> > rendering via the dma-buf fences.
> > 
> > Testcase: igt/prime_busy
> > Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> 
> Style nit: I prefer ww_mutex_lock(&resv->lock, NULL); over
> mutex_lock(&resv->lock.base). The former makes it clear it's a ww mutex,
> but we don't bother with the multi-lock dance. The latter needles around
> in implemenation details, which it really shouldn't. Please change.

Passing NULL as ww_acquite_ctx is illegal.

> The other wonky bit is that changing reservations on multiple objects
> without the full ww mutex dance is deadlock-risky. But only when you both
> add and wait/stall on fences.

Note that it is only so when trying to lock multiple objects simultaneously,
which we do not require.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre