mm/vmalloc: simplify augment_tree_propagate_check()

This function is for debug purpose only.  Currently it uses recursion for
tree traversal, checking an augmented value of each node to find out if it
is valid or not.

The recursion can corrupt the stack because the tree can be huge if
synthetic tests are applied.  To prevent it, navigate the tree from bottom
to upper levels using a regular list instead, because nodes are linked
among each other also.  It is faster and without recursion.
Signed-off-by: NUladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20200527205054.1696-2-urezki@gmail.comSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/vmalloc.c

@@ -633,43 +633,17 @@ unlink_va(struct vmap_area *va, struct rb_root *root)
 
 #if DEBUG_AUGMENT_PROPAGATE_CHECK
 static void
-augment_tree_propagate_check(struct rb_node *n)
+augment_tree_propagate_check(void)
 {
 	struct vmap_area *va;
-	struct rb_node *node;
-	unsigned long size;
-	bool found = false;
-
-	if (n == NULL)
-		return;
-
-	va = rb_entry(n, struct vmap_area, rb_node);
-	size = va->subtree_max_size;
-	node = n;
-
-	while (node) {
-		va = rb_entry(node, struct vmap_area, rb_node);
-
-		if (get_subtree_max_size(node->rb_left) == size) {
-			node = node->rb_left;
-		} else {
-			if (va_size(va) == size) {
-				found = true;
-				break;
-			}
+	unsigned long computed_size;
 
-			node = node->rb_right;
-		}
-	}
-
-	if (!found) {
-		va = rb_entry(n, struct vmap_area, rb_node);
-		pr_emerg("tree is corrupted: %lu, %lu\n",
-			va_size(va), va->subtree_max_size);
+	list_for_each_entry(va, &free_vmap_area_list, list) {
+		computed_size = compute_subtree_max_size(va);
+		if (computed_size != va->subtree_max_size)
+			pr_emerg("tree is corrupted: %lu, %lu\n",
+				va_size(va), va->subtree_max_size);
 	}
-
-	augment_tree_propagate_check(n->rb_left);
-	augment_tree_propagate_check(n->rb_right);
 }
 #endif
 
@@ -724,7 +698,7 @@ augment_tree_propagate_from(struct vmap_area *va)
 	}
 
 #if DEBUG_AUGMENT_PROPAGATE_CHECK
-	augment_tree_propagate_check(free_vmap_area_root.rb_node);
+	augment_tree_propagate_check();
 #endif
 }