[Intel-gfx] [PATCH 04/27] drm/i915/guc: Don't drop ce->guc_active.lock when unwinding context

[Daniele Ceraolo Spurio]

On 8/18/2021 11:16 PM, Matthew Brost wrote:
> Don't drop ce->guc_active.lock when unwinding a context after reset.
> At one point we had to drop this because of a lock inversion but that is
> no longer the case. It is much safer to hold the lock so let's do that.
>
> Fixes: eb5e7da736f3 ("drm/i915/guc: Reset implementation for new GuC interface")
> Signed-off-by: Matthew Brost <matthew.brost at intel.com>
> Cc: <stable at vger.kernel.org>

Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio at intel.com>

Do we have a trybot of this series with GuC enabled? I've checked the 
functions called in the previously unlocked chunk and didn't spot 
anything requiring the lock to be dropped, but I'd feel safer if we had 
lockdep results as well.

Daniele

> ---
>   drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 4 ----
>   1 file changed, 4 deletions(-)
>
> 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 9ca0ba4ea85a..e4a099f8f820 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> @@ -812,8 +812,6 @@ __unwind_incomplete_requests(struct intel_context *ce)
>   			continue;
>   
>   		list_del_init(&rq->sched.link);
> -		spin_unlock(&ce->guc_active.lock);
> -
>   		__i915_request_unsubmit(rq);
>   
>   		/* Push the request back into the queue for later resubmission. */
> @@ -826,8 +824,6 @@ __unwind_incomplete_requests(struct intel_context *ce)
>   
>   		list_add(&rq->sched.link, pl);
>   		set_bit(I915_FENCE_FLAG_PQUEUE, &rq->fence.flags);
> -
> -		spin_lock(&ce->guc_active.lock);
>   	}
>   	spin_unlock(&ce->guc_active.lock);
>   	spin_unlock_irqrestore(&sched_engine->lock, flags);