[PATCH] drm: Declare that create drm_mm nodes with size 0 is illegal

[Chris Wilson]

At a higher level, all objects are created with definite size i.e. 0 is
illegal. In forthcoming patches, this assumption is dependent upon in
the drm_mm range manager, i.e. trying to create a drm_mm node with size
0 will have undefined behaviour. Add a couple of WARNs upon creating the
drm_mm node to prevent later bugs.

Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
---
 drivers/gpu/drm/drm_mm.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/gpu/drm/drm_mm.c b/drivers/gpu/drm/drm_mm.c
index cb39f45d6a16..e8c15795386d 100644
--- a/drivers/gpu/drm/drm_mm.c
+++ b/drivers/gpu/drm/drm_mm.c
@@ -185,6 +185,9 @@ int drm_mm_reserve_node(struct drm_mm *mm, struct drm_mm_node *node)
 
 	BUG_ON(node == NULL);
 
+	if (WARN_ON(node->size == 0))
+		return -EINVAL;
+
 	end = node->start + node->size;
 
 	/* Find the relevant hole to add our node to */
@@ -239,6 +242,9 @@ int drm_mm_insert_node_generic(struct drm_mm *mm, struct drm_mm_node *node,
 {
 	struct drm_mm_node *hole_node;
 
+	if (WARN_ON(size == 0))
+		return -EINVAL;
+
 	hole_node = drm_mm_search_free_generic(mm, size, alignment,
 					       color, sflags);
 	if (!hole_node)
@@ -340,6 +346,9 @@ int drm_mm_insert_node_in_range_generic(struct drm_mm *mm, struct drm_mm_node *n
 {
 	struct drm_mm_node *hole_node;
 
+	if (WARN_ON(size == 0))
+		return -EINVAL;
+
 	hole_node = drm_mm_search_free_in_range_generic(mm,
 							size, alignment, color,
 							start, end, sflags);
-- 
2.8.1