[PATCH 08/22] drm/i915/guc: Don't enable scheduling on a banned context, guc_id invalid, not registered

[Daniel Vetter]

On Mon, Aug 16, 2021 at 06:51:25AM -0700, Matthew Brost wrote:
> When unblocking a context, do not enable scheduling if the context is
> banned, guc_id invalid, or not registered.
> 
> Fixes: 62eaf0ae217d ("drm/i915/guc: Support request cancellation")
> Signed-off-by: Matthew Brost <matthew.brost at intel.com>
> Cc: <stable at vger.kernel.org>
> ---
>  drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> 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 c3b7bf7319dd..353899634fa8 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> @@ -1579,6 +1579,9 @@ static void guc_context_unblock(struct intel_context *ce)
>  	spin_lock_irqsave(&ce->guc_state.lock, flags);
>  
>  	if (unlikely(submission_disabled(guc) ||
> +		     intel_context_is_banned(ce) ||
> +		     context_guc_id_invalid(ce) ||
> +		     !lrc_desc_registered(guc, ce->guc_id) ||
>  		     !intel_context_is_pinned(ce) ||
>  		     context_pending_disable(ce) ||
>  		     context_blocked(ce) > 1)) {

I think this entire if condition here is screaming that our intel_context
state machinery for guc is way too complex, and on the wrong side of
incomprehensible.

Also some of these check state outside of the context, and we don't seem
to hold spinlocks for those, or anything else.

I general I have no idea which of these are defensive programming and
cannot ever happen, and which actually can happen. There's for sure way
too many races going on given that this is all context-local stuff.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch