Re: [Intel-gfx] [PATCH] drm/i915: Mark the removal of the i915_request from the sched.link

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 20/01/2020 17:57, Chris Wilson wrote:
> Keep the rq->fence.flags consistent with the status of the
> rq->sched.link, and clear the associated bits when decoupling the link
> on retirement (as we may wish to inspect those flags independent of
> other state).
> 
> Fixes: 32ff621fd744 ("drm/i915/gt: Allow temporary suspension of inflight requests")
> References: https://gitlab.freedesktop.org/drm/intel/issues/997
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> ---
>   drivers/gpu/drm/i915/i915_request.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c
> index 9ed0d3bc7249..78a5f5d3c070 100644
> --- a/drivers/gpu/drm/i915/i915_request.c
> +++ b/drivers/gpu/drm/i915/i915_request.c
> @@ -221,6 +221,8 @@ static void remove_from_engine(struct i915_request *rq)
>   		locked = engine;
>   	}
>   	list_del_init(&rq->sched.link);
> +	clear_bit(I915_FENCE_FLAG_PQUEUE, &rq->fence.flags);

This one I think can not be set in retirement. Or there is a path?

[comes back after writing the comment below]

Race between completion to hold puts the request on hold, then request 
completes just as it is un-held? It needs retire to happen at the right 
time, driven by ...? Is this it?

> +	clear_bit(I915_FENCE_FLAG_HOLD, &rq->fence.flags);

This one I think indeed can race with completion.

Regards,

Tvrtko

>   	spin_unlock_irq(&locked->active.lock);
>   }
>   
> 
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