mm/vmap: add DEBUG_AUGMENT_PROPAGATE_CHECK macro

This macro adds some debug code to check that the augment tree is
maintained correctly, meaning that every node contains valid
subtree_max_size value.

By default this option is set to 0 and not active.  It requires
recompilation of the kernel to activate it.  Set to 1, compile the
kernel.

[urezki@gmail.com: v4]
  Link: http://lkml.kernel.org/r/20190406183508.25273-3-urezki@gmail.com
Link: http://lkml.kernel.org/r/20190402162531.10888-3-urezki@gmail.com
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Roman Gushchin <guro@fb.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Joel Fernandes <joelaf@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@sonymobile.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Tejun Heo <tj@kernel.org>
Cc: Thomas Garnier <thgarnie@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index f8f61ff..aac34c2 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -325,6 +325,8 @@
 
 /*** Global kva allocator ***/
 
+#define DEBUG_AUGMENT_PROPAGATE_CHECK 0
+
 #define VM_LAZY_FREE	0x02
 #define VM_VM_AREA	0x04
 
@@ -539,6 +541,48 @@
 	}
 }
 
+#if DEBUG_AUGMENT_PROPAGATE_CHECK
+static void
+augment_tree_propagate_check(struct rb_node *n)
+{
+	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;
+			}
+
+			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);
+	}
+
+	augment_tree_propagate_check(n->rb_left);
+	augment_tree_propagate_check(n->rb_right);
+}
+#endif
+
 /*
  * This function populates subtree_max_size from bottom to upper
  * levels starting from VA point. The propagation must be done
@@ -588,6 +632,10 @@
 		va->subtree_max_size = new_va_sub_max_size;
 		node = rb_parent(&va->rb_node);
 	}
+
+#if DEBUG_AUGMENT_PROPAGATE_CHECK
+	augment_tree_propagate_check(free_vmap_area_root.rb_node);
+#endif
 }
 
 static void