Re: [PATCH] drm/i915: Mark intel_wakeref_get() as a sleeper

[Mika Kuoppala <mika.kuoppala@linux.intel.com>]

Chris Wilson <chris@chris-wilson.co.uk> writes:

> Assume that intel_wakereg_get() may take the mutex, and perform other
> sleeping actions in the course of its callbacks and so use might_sleep()
> to ensure that all callers abide. Anything that cannot sleep has to use
> e.g. intel_wakeref_get_if_active() to guarantee its avoidance of the
> non-atomic paths.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>

> ---
>  drivers/gpu/drm/i915/gt/intel_gt_pm.h           |  5 +++++
>  drivers/gpu/drm/i915/gt/intel_lrc.c             |  2 +-
>  .../gpu/drm/i915/gt/uc/intel_guc_submission.c   |  2 +-
>  drivers/gpu/drm/i915/intel_wakeref.h            | 17 +++++++++++++++--
>  4 files changed, 22 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/gt/intel_gt_pm.h b/drivers/gpu/drm/i915/gt/intel_gt_pm.h
> index 990efc27a4e4..4a9e48c12bd4 100644
> --- a/drivers/gpu/drm/i915/gt/intel_gt_pm.h
> +++ b/drivers/gpu/drm/i915/gt/intel_gt_pm.h
> @@ -22,6 +22,11 @@ static inline void intel_gt_pm_get(struct intel_gt *gt)
>  	intel_wakeref_get(&gt->wakeref);
>  }
>  
> +static inline void __intel_gt_pm_get(struct intel_gt *gt)
> +{
> +	__intel_wakeref_get(&gt->wakeref);
> +}
> +
>  static inline bool intel_gt_pm_get_if_awake(struct intel_gt *gt)
>  {
>  	return intel_wakeref_get_if_active(&gt->wakeref);
> diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c
> index b65bc06855b0..516306ebc839 100644
> --- a/drivers/gpu/drm/i915/gt/intel_lrc.c
> +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
> @@ -1121,7 +1121,7 @@ __execlists_schedule_in(struct i915_request *rq)
>  		BUILD_BUG_ON(NUM_CONTEXT_TAG > GEN12_MAX_CONTEXT_HW_ID);
>  	}
>  
> -	intel_gt_pm_get(engine->gt);
> +	__intel_gt_pm_get(engine->gt);
>  	execlists_context_status_change(rq, INTEL_CONTEXT_SCHEDULE_IN);
>  	intel_engine_context_in(engine);
>  
> 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 dcccbd640809..6f94af7ad1de 100644
> --- a/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> +++ b/drivers/gpu/drm/i915/gt/uc/intel_guc_submission.c
> @@ -529,7 +529,7 @@ static struct i915_request *schedule_in(struct i915_request *rq, int idx)
>  	 * required if we generalise the inflight tracking.
>  	 */
>  
> -	intel_gt_pm_get(rq->engine->gt);
> +	__intel_gt_pm_get(rq->engine->gt);
>  	return i915_request_get(rq);
>  }
>  
> diff --git a/drivers/gpu/drm/i915/intel_wakeref.h b/drivers/gpu/drm/i915/intel_wakeref.h
> index da6e8fd506e6..3897bfea72d9 100644
> --- a/drivers/gpu/drm/i915/intel_wakeref.h
> +++ b/drivers/gpu/drm/i915/intel_wakeref.h
> @@ -59,9 +59,7 @@ void __intel_wakeref_put_last(struct intel_wakeref *wf, unsigned long flags);
>  
>  /**
>   * intel_wakeref_get: Acquire the wakeref
> - * @i915: the drm_i915_private device
>   * @wf: the wakeref
> - * @fn: callback for acquired the wakeref, called only on first acquire.
>   *
>   * Acquire a hold on the wakeref. The first user to do so, will acquire
>   * the runtime pm wakeref and then call the @fn underneath the wakeref
> @@ -76,12 +74,27 @@ void __intel_wakeref_put_last(struct intel_wakeref *wf, unsigned long flags);
>  static inline int
>  intel_wakeref_get(struct intel_wakeref *wf)
>  {
> +	might_sleep();
>  	if (unlikely(!atomic_inc_not_zero(&wf->count)))
>  		return __intel_wakeref_get_first(wf);
>  
>  	return 0;
>  }
>  
> +/**
> + * __intel_wakeref_get: Acquire the wakeref, again
> + * @wf: the wakeref
> + *
> + * Increment the wakeref counter, but only valid if it is already held by
> + * the caller.
> + */
> +static inline void
> +__intel_wakeref_get(struct intel_wakeref *wf)
> +{
> +	INTEL_WAKEREF_BUG_ON(!atomic_read(&wf->count));
> +	atomic_inc(&wf->count);
> +}
> +
>  /**
>   * intel_wakeref_get_if_in_use: Acquire the wakeref
>   * @wf: the wakeref
> -- 
> 2.24.0
>
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