On 05/03/2020 13:48, Chris Wilson wrote:

Requests within a timeline are ordered by that timeline, so awaiting for the start of a request within the timeline is a no-op. This used to work by falling out of the mutex_trylock() as the signaler and waiter had the same timeline and not returning an error.

Fixes: 6a79d848403d ("drm/i915: Lock signaler timeline while navigating") Signed-off-by: Chris Wilson chris@chris-wilson.co.uk Cc: Tvrtko Ursulin tvrtko.ursulin@linux.intel.com Cc: stable@vger.kernel.org # v5.5+

---

drivers/gpu/drm/i915/i915_request.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c index 46dae33c1a20..ca5361eb1f0b 100644 --- a/drivers/gpu/drm/i915/i915_request.c +++ b/drivers/gpu/drm/i915/i915_request.c @@ -837,8 +837,8 @@ i915_request_await_start(struct i915_request *rq, struct i915_request *signal) struct dma_fence *fence; int err;

• GEM_BUG_ON(i915_request_timeline(rq) ==

•    rcu_access_pointer(signal->timeline));
  

• if (i915_request_timeline(rq) == rcu_access_pointer(signal->timeline))

• return 0;
  

if (i915_request_started(signal)) return 0;

Reviewed-by: Tvrtko Ursulin tvrtko.ursulin@intel.com

Regards,

Tvrtko