[Intel-gfx] [PATCH 1/3] drm/i915: Remove struct_mutex for destroying framebuffers

[Joonas Lahtinen]

On ke, 2017-02-15 at 10:59 +0000, Chris Wilson wrote:
> We do not need to hold struct_mutex for destroying drm_i915_gem_objects
> any longer, and with a little care taken over tracking
> obj->framebuffer_references, we can relinquish BKL locking around the
> destroy of intel_framebuffer.
> 
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>

<SNIP>

> @@ -14266,14 +14266,14 @@ static void intel_setup_outputs(struct drm_i915_private *dev_priv)
>  
>  static void intel_user_framebuffer_destroy(struct drm_framebuffer *fb)
>  {
> -	struct drm_device *dev = fb->dev;
>  	struct intel_framebuffer *intel_fb = to_intel_framebuffer(fb);
>  
>  	drm_framebuffer_cleanup(fb);
> -	mutex_lock(&dev->struct_mutex);
> -	WARN_ON(!intel_fb->obj->framebuffer_references--);
> +
> +	WARN_ON(atomic_read(&intel_fb->obj->framebuffer_references) == 0);
> +	atomic_dec(&intel_fb->obj->framebuffer_references);

Umm isn't the point of atomicity that you do this in one step?

Regards, Joonas
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation