Re: [PATCH] drm/i915: Remove locking for get-caching query

[Daniel Vetter <daniel@ffwll.ch>]

On Thu, May 07, 2015 at 12:14:55PM +0100, Chris Wilson wrote:
> Reading a single value from the object, the locking only provides futile
> protection against userspace races. The locking is useless so remove it.
> 
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_gem.c | 17 ++++-------------
>  1 file changed, 4 insertions(+), 13 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
> index 2b2b74dbb446..d071d0af2a6c 100644
> --- a/drivers/gpu/drm/i915/i915_gem.c
> +++ b/drivers/gpu/drm/i915/i915_gem.c
> @@ -3983,17 +3983,10 @@ int i915_gem_get_caching_ioctl(struct drm_device *dev, void *data,
>  {
>  	struct drm_i915_gem_caching *args = data;
>  	struct drm_i915_gem_object *obj;
> -	int ret;
> -
> -	ret = i915_mutex_lock_interruptible(dev);
> -	if (ret)
> -		return ret;
>  
>  	obj = to_intel_bo(drm_gem_object_lookup(dev, file, args->handle));
> -	if (&obj->base == NULL) {
> -		ret = -ENOENT;
> -		goto unlock;
> -	}
> +	if (&obj->base == NULL)
> +		return -ENOENT;
>  
>  	switch (obj->cache_level) {

Wrap this in ACCESS_ONCE, just for documentation purpose? Can do while
applying if you ack.
-Daniel

>  	case I915_CACHE_LLC:
> @@ -4010,10 +4003,8 @@ int i915_gem_get_caching_ioctl(struct drm_device *dev, void *data,
>  		break;
>  	}
>  
> -	drm_gem_object_unreference(&obj->base);
> -unlock:
> -	mutex_unlock(&dev->struct_mutex);
> -	return ret;
> +	drm_gem_object_unreference_unlocked(&obj->base);
> +	return 0;
>  }
>  
>  int i915_gem_set_caching_ioctl(struct drm_device *dev, void *data,
> -- 
> 2.1.4
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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