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@xxxxxxxxxxxxxxxxxx>
Cc: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx> # v5.5+
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Link: https://patchwork.freedesktop.org/patch/msgid/20200305134822.2750496-1-chris@xxxxxxxxxxxxxxxxxx
(cherry picked from commit ab7a69020fb5d5c7ba19fba60f62fd6f9ca9f779)
---
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 6c387fa1a8547..1213009f31fbe 100644
--- a/drivers/gpu/drm/i915/i915_request.c
+++ b/drivers/gpu/drm/i915/i915_request.c
@@ -830,8 +830,8 @@ 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;
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