Re: [PATCH 1/2] drm/i915: Wrap the protected active RCU dereference in a helper

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Aug 08, 2016 at 08:28:47AM +0100, Chris Wilson wrote:
> As we do the lockdep protected RCU lookup in a couple of places,
> refactor that code to a common helper i915_gem_active_raw()..
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_gem_request.h | 21 +++++++++++++++++----
>  1 file changed, 17 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_request.h b/drivers/gpu/drm/i915/i915_gem_request.h
> index 3496e28785e7..6dd01cbf4895 100644
> --- a/drivers/gpu/drm/i915/i915_gem_request.h
> +++ b/drivers/gpu/drm/i915/i915_gem_request.h
> @@ -360,6 +360,21 @@ __i915_gem_active_peek(const struct i915_gem_active *active)
>  }
>  
>  /**
> + * i915_gem_active_raw - return the active request
> + * @active - the active tracker
> + *
> + * i915_gem_active_raw() returns the current request being tracked, or NULL.
> + * It does not obtain a reference on the request for the caller, so the caller
> + * must hold struct_mutex.
> + */
> +static inline struct drm_i915_gem_request *
> +i915_gem_active_raw(const struct i915_gem_active *active, struct mutex *mutex)

There's a rcu_dereference_raw helper which doesn't bother with any lockdep
checking. A bit confusing naming, otoh I couldn't come up with something
better.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

> +{
> +	return rcu_dereference_protected(active->request,
> +					 lockdep_is_held(mutex));
> +}
> +
> +/**
>   * i915_gem_active_peek - report the active request being monitored
>   * @active - the active tracker
>   *
> @@ -372,8 +387,7 @@ i915_gem_active_peek(const struct i915_gem_active *active, struct mutex *mutex)
>  {
>  	struct drm_i915_gem_request *request;
>  
> -	request = rcu_dereference_protected(active->request,
> -					    lockdep_is_held(mutex));
> +	request = i915_gem_active_raw(active, mutex);
>  	if (!request || i915_gem_request_completed(request))
>  		return NULL;
>  
> @@ -635,8 +649,7 @@ i915_gem_active_retire(struct i915_gem_active *active,
>  	struct drm_i915_gem_request *request;
>  	int ret;
>  
> -	request = rcu_dereference_protected(active->request,
> -					    lockdep_is_held(mutex));
> +	request = i915_gem_active_raw(active, mutex);
>  	if (!request)
>  		return 0;
>  
> -- 
> 2.8.1
> 
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> Intel-gfx@lists.freedesktop.org
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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