[Intel-gfx] [PATCH 1/6] drm/i915: Remove misleading comment in request_alloc

[Chris Wilson]

On Thu, May 18, 2017 at 03:59:39PM +0200, Michał Winiarski wrote:
> Passing NULL ctx to request_alloc would lead to null-ptr-deref.
> Let's replace the comment with GEM_BUG_ON.
> 
> Signed-off-by: Michał Winiarski <michal.winiarski at intel.com>
> ---
>  drivers/gpu/drm/i915/i915_gem_request.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
> index 1ccf252..1352d3c 100644
> --- a/drivers/gpu/drm/i915/i915_gem_request.c
> +++ b/drivers/gpu/drm/i915/i915_gem_request.c
> @@ -538,9 +538,6 @@ submit_notify(struct i915_sw_fence *fence, enum i915_sw_fence_notify state)
>   *
>   * @engine: engine that we wish to issue the request on.
>   * @ctx: context that the request will be associated with.
> - *       This can be NULL if the request is not directly related to
> - *       any specific user context, in which case this function will
> - *       choose an appropriate context to use.
>   *
>   * Returns a pointer to the allocated request if successful,
>   * or an error code if not.
> @@ -554,6 +551,7 @@ i915_gem_request_alloc(struct intel_engine_cs *engine,
>  	struct intel_ring *ring;
>  	int ret;
>  
> +	GEM_BUG_ON(!ctx);

We try not to use BUG_ON for NULL pointer protection, as the NULL
pointer GPF is often enough to pinpoint the error. NULL function
pointers tend to be the exception.

>  	lockdep_assert_held(&dev_priv->drm.struct_mutex);
>  
>  	/* ABI: Before userspace accesses the GPU (e.g. execbuffer), report
> -- 
> 2.9.4
> 
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-- 
Chris Wilson, Intel Open Source Technology Centre