drm/nouveau/core/mm: fill in holes with "allocated" nodes

The allocation algorithm doesn't expect there to be holes in the mm, which
causes its alignment/cutoff calculations to choke (and go negative) when
encountering the last chunk of a block before a hole.

The least expensive solution is to simply fill in any holes with nodes
that are pre-marked as being allocated.
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drivers/gpu/drm/nouveau/core/core/mm.c

@@ -116,7 +116,7 @@ nouveau_mm_head(struct nouveau_mm *mm, u8 type, u32 size_max, u32 size_min,
 	u32 splitoff;
 	u32 s, e;
 
-	BUG_ON(type == NVKM_MM_TYPE_NONE);
+	BUG_ON(type == NVKM_MM_TYPE_NONE || type == NVKM_MM_TYPE_HOLE);
 
 	list_for_each_entry(this, &mm->free, fl_entry) {
 		e = this->offset + this->length;
@@ -182,7 +182,7 @@ nouveau_mm_tail(struct nouveau_mm *mm, u8 type, u32 size_max, u32 size_min,
 	struct nouveau_mm_node *prev, *this, *next;
 	u32 mask = align - 1;
 
-	BUG_ON(type == NVKM_MM_TYPE_NONE);
+	BUG_ON(type == NVKM_MM_TYPE_NONE || type == NVKM_MM_TYPE_HOLE);
 
 	list_for_each_entry_reverse(this, &mm->free, fl_entry) {
 		u32 e = this->offset + this->length;
@@ -227,9 +227,21 @@ nouveau_mm_tail(struct nouveau_mm *mm, u8 type, u32 size_max, u32 size_min,
 int
 nouveau_mm_init(struct nouveau_mm *mm, u32 offset, u32 length, u32 block)
 {
-	struct nouveau_mm_node *node;
+	struct nouveau_mm_node *node, *prev;
+	u32 next;
 
 	if (nouveau_mm_initialised(mm)) {
+		prev = list_last_entry(&mm->nodes, typeof(*node), nl_entry);
+		next = prev->offset + prev->length;
+		if (next != offset) {
+			BUG_ON(next > offset);
+			if (!(node = kzalloc(sizeof(*node), GFP_KERNEL)))
+				return -ENOMEM;
+			node->type   = NVKM_MM_TYPE_HOLE;
+			node->offset = next;
+			node->length = offset - next;
+			list_add_tail(&node->nl_entry, &mm->nodes);
+		}
 		BUG_ON(block != mm->block_size);
 	} else {
 		INIT_LIST_HEAD(&mm->nodes);
@@ -264,11 +276,13 @@ nouveau_mm_fini(struct nouveau_mm *mm)
 		return 0;
 
 	list_for_each_entry(node, &mm->nodes, nl_entry) {
+		if (node->type != NVKM_MM_TYPE_HOLE) {
 			if (++nodes > mm->heap_nodes) {
 				nouveau_mm_dump(mm, "mm not clean!");
 				return -EBUSY;
 			}
 		}
+	}
 
 	list_for_each_entry_safe(node, temp, &mm->nodes, nl_entry) {
 		list_del(&node->nl_entry);

drivers/gpu/drm/nouveau/core/include/core/mm.h

@@ -7,6 +7,7 @@ struct nouveau_mm_node {
 	struct list_head rl_entry;
 
 #define NVKM_MM_TYPE_NONE 0x00
+#define NVKM_MM_TYPE_HOLE 0xff
 	u8  type;
 	u32 offset;
 	u32 length;