Re: [Intel-gfx] [PATCH 2/2] drm/i915/guc: Look for a guilty context when an engine reset fails

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

On 29/11/2022 21:12, John.C.Harrison@Intel.com wrote:
> From: John Harrison <John.C.Harrison@Intel.com>
> 
> Engine resets are supposed to never happen. But in the case when one

Engine resets or engine reset failures? Hopefully the latter.

> does (due to unknwon reasons that normally come down to a missing
> w/a), it is useful to get as much information out of the system as
> possible. Given that the GuC effectively dies on such a situation, it
> is not possible to get a guilty context notification back. So do a
> manual search instead. Given that GuC is dead, this is safe because
> GuC won't be changing the engine state asynchronously.
> 
> Signed-off-by: John Harrison <John.C.Harrison@Intel.com>
> ---
>   drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 15 ++++++++++++++-
>   1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> index 0a42f1807f52c..c82730804a1c4 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> @@ -4751,11 +4751,24 @@ static void reset_fail_worker_func(struct work_struct *w)
>   	guc->submission_state.reset_fail_mask = 0;
>   	spin_unlock_irqrestore(&guc->submission_state.lock, flags);
>   
> -	if (likely(reset_fail_mask))
> +	if (likely(reset_fail_mask)) {
> +		struct intel_engine_cs *engine;
> +		enum intel_engine_id id;
> +
> +		/*
> +		 * GuC is toast at this point - it dead loops after sending the failed
> +		 * reset notification. So need to manually determine the guilty context.
> +		 * Note that it should be safe/reliable to do this here because the GuC
> +		 * is toast and will not be scheduling behind the KMD's back.
> +		 */
> +		for_each_engine_masked(engine, gt, reset_fail_mask, id)
> +			intel_guc_find_hung_context(engine);
> +
>   		intel_gt_handle_error(gt, reset_fail_mask,
>   				      I915_ERROR_CAPTURE,
>   				      "GuC failed to reset engine mask=0x%x\n",
>   				      reset_fail_mask);

If GuC is defined by ABI contract to be dead, should the flow be 
attempting to do a full GPU reset here, or maybe it happens somewhere 
else as a consequence anyway? (In which case is the engine reset here 
even needed?)

Regards,

Tvrtko

> +	}
>   }
>   
>   int intel_guc_engine_failure_process_msg(struct intel_guc *guc,