[Intel-gfx] [PATCH 08/19] drm/i915: Add a relay backed debugfs interface for capturing GuC logs

[Chris Wilson]

On Fri, Aug 19, 2016 at 02:13:07PM +0530, akash.goel at intel.com wrote:
>  static void *guc_get_write_buffer(struct intel_guc *guc)
>  {
> -	return NULL;
> +	/* FIXME: Cover the check under a lock ? */
> +	if (!guc->log.relay_chan)
> +		return NULL;
> +
> +	/* Just get the base address of a new sub buffer and copy data into it
> +	 * ourselves. NULL will be returned in no-overwrite mode, if all sub
> +	 * buffers are full. Could have used the relay_write() to indirectly
> +	 * copy the data, but that would have been bit convoluted, as we need to
> +	 * write to only certain locations inside a sub buffer which cannot be
> +	 * done without using relay_reserve() along with relay_write(). So its
> +	 * better to use relay_reserve() alone.
> +	 */
> +	return relay_reserve(guc->log.relay_chan, 0);
>  }

You have to chase through the code a long way to check whether or not
the allocation is correct.

Please do consider adding a check such as

	GEM_BUG_ON(guc->log.relay_chan->size < guc->log.vma->size);
(near the allocation)

	GEM_BUG_ON(write_offset + buffer_size > guc->log.relay_chan->size);
(before the memcpy, or whatever is appropriate).

Just to leave some clues to the reader as to what is going on.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre