[PATCH v2] drm/i915/guc: Flush ct receive tasklet during reset preparation

[Rodrigo Vivi]

On Mon, Nov 04, 2024 at 01:41:03PM -0800, Zhanjun Dong wrote:
> GuC to host communication is interrupt driven, the handling has 3
> parts: interrupt context, tasklet and request queue worker.
> During GuC reset prepare, interrupt is disabled before destroy
> contexts steps start. The IRQ and worker are flushed to finish
> any outstanding in-progress message handling. But, the tasklet
> flush is missing, it might causes 2 race conditions:
> 1. Tasklet runs after IRQ flushed, add request to queue after worker
> flush started, causes unexpected G2H message request processing,
> meanwhile, reset prepare code already get the context destroyed.
> This will causes error reported about bad context state.
> (https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/11349 and
> https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/12303)
> 2. Tasklet runs after intel_guc_submission_reset_prepare,
> ct_try_receive_message start to run, while intel_uc_reset_prepare
> already finished guc sanitize and set ct->enable to false. This will
> causes warning on incorrect ct->enable state.
> (https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/12439)
> 
> Add the missing tasklet flush to flush all 3 parts.
> 

Tvrtko, Zhanjun has later found out that this patch deserves a fixes
and cc-stable tags.
I wonder if it would be possible to manually pick this to drm-intel-fixes
and while at it add:

Fixes: eb5e7da736f3 ("drm/i915/guc: Reset implementation for new GuC interface")
Cc: stable at vger.kernel.org # v6.1+

Thoughts on the inclusion of the tags while cherry-picking for the fixes?
If okay, could you please do this since you are in charge of this round of the
drm-fixes?

The merged commit is: b939a08bc378 ("drm/i915/guc: Flush ct receive tasklet during reset preparation")

Thanks,
Rodrigo.

> Signed-off-by: Zhanjun Dong <zhanjun.dong at intel.com>
> Reviewed-by: Alan Previn <alan.previn.teres.alexis at intel.com>
> ---
>  drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 4 ++++
>  1 file changed, 4 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 9ede6f240d79..353a9167c9a4 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> @@ -1688,6 +1688,10 @@ void intel_guc_submission_reset_prepare(struct intel_guc *guc)
>  	spin_lock_irq(guc_to_gt(guc)->irq_lock);
>  	spin_unlock_irq(guc_to_gt(guc)->irq_lock);
>  
> +	/* Flush tasklet */
> +	tasklet_disable(&guc->ct.receive_tasklet);
> +	tasklet_enable(&guc->ct.receive_tasklet);
> +
>  	guc_flush_submissions(guc);
>  	guc_flush_destroyed_contexts(guc);
>  	flush_work(&guc->ct.requests.worker);
> -- 
> 2.34.1
>