Re: [Intel-gfx] [PATCH] drm/i915/guc: Cancel GuC engine busyness worker synchronously

["Dixit, Ashutosh" <ashutosh.dixit@intel.com>]

On Fri, 26 Aug 2022 17:21:35 -0700, Umesh Nerlige Ramappa wrote:
>
> The worker is canceled in gt_park path, but earlier it was assumed that
> gt_park path cannot sleep and the cancel is asynchronous. This caused a
> race with suspend flow where the worker runs after suspend and causes an
> unclaimed register access warning. Cancel the worker synchronously since
> the gt_park is indeed allowed to sleep.

Indeed, __gt_park already calls cancel_work_sync and synchronize_irq which
can sleep:

Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>

> v2: Fix author name and sign-off mismatch
>
> Signed-off-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
> Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/4419
> Fixes: 77cdd054dd2c ("drm/i915/pmu: Connect engine busyness stats from GuC to pmu")
> ---
>  drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c | 7 ++++++-
>  1 file changed, 6 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 0d56b615bf78..e6275380b253 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> @@ -1438,7 +1438,12 @@ void intel_guc_busyness_park(struct intel_gt *gt)
>	if (!guc_submission_initialized(guc))
>		return;
>
> -	cancel_delayed_work(&guc->timestamp.work);
> +	/*
> +	 * There is a race with suspend flow where the worker runs after suspend
> +	 * and causes an unclaimed register access warning. Cancel the worker
> +	 * synchronously here.
> +	 */
> +	cancel_delayed_work_sync(&guc->timestamp.work);
>
>	/*
>	 * Before parking, we should sample engine busyness stats if we need to.
> --
> 2.25.1
>