Quoting Chris Wilson (2019-06-17 09:40:44)
> Though we pin the context first before taking the pm wakeref, during
> retire we need to unpin before dropping the pm wakeref (breaking the
> "natural" onion). During the unpin, we may need to attach a cleanup
> operation on to the engine wakeref, ergo we want to keep the engine
> awake until after the unpin.
>
> Fixes: ce476c80b8bf ("drm/i915: Keep contexts pinned until after the next
> kernel context switch")
> Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
> Cc: Mika Kuoppala <mika.kuopp...@linux.intel.com>
> ---
> drivers/gpu/drm/i915/i915_request.c | 3 ++-
> 1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_request.c
> b/drivers/gpu/drm/i915/i915_request.c
> index 9819483d1b5d..8d952bc03d5c 100644
> --- a/drivers/gpu/drm/i915/i915_request.c
> +++ b/drivers/gpu/drm/i915/i915_request.c
> @@ -250,8 +250,9 @@ static bool i915_request_retire(struct i915_request *rq)
>
> local_irq_enable();
>
> - intel_context_exit(rq->hw_context);
> + /* Onion reversed to keep engine alive until after unpinning */
> intel_context_unpin(rq->hw_context);
> + intel_context_exit(rq->hw_context);
The alternative is to keep the onion unwind here and to add the engine
wakerefs into the barriers. Hmm.
That seems like it should be more foolproof, perhaps?
-Chris
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