drm/ttm: Be consistent on ttm_bo_init() failures

Call destroy() on _all_ ttm_bo_init() failures, and make sure that
behavior is documented in the function description.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/ttm/ttm_bo.c

@@ -1144,6 +1144,10 @@ int ttm_bo_init(struct ttm_bo_device *bdev,
 	num_pages = (size + PAGE_SIZE - 1) >> PAGE_SHIFT;
 	if (num_pages == 0) {
 		printk(KERN_ERR TTM_PFX "Illegal buffer object size.\n");
+		if (destroy)
+			(*destroy)(bo);
+		else
+			kfree(bo);
 		return -EINVAL;
 	}
 	bo->destroy = destroy;

include/drm/ttm/ttm_bo_api.h

@@ -432,6 +432,10 @@ extern void ttm_bo_synccpu_write_release(struct ttm_buffer_object *bo);
  * together with the @destroy function,
  * enables driver-specific objects derived from a ttm_buffer_object.
  * On successful return, the object kref and list_kref are set to 1.
+ * If a failure occurs, the function will call the @destroy function, or
+ * kfree() if @destroy is NULL. Thus, after a failure, dereferencing @bo is
+ * illegal and will likely cause memory corruption.
+ *
  * Returns
  * -ENOMEM: Out of memory.
  * -EINVAL: Invalid placement flags.