linux-kernel - [PATCH 2/3] mm/vmalloc: simplify augment_tree_propagate

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Date:   Wed, 27 May 2020 22:50:53 +0200
From:   "Uladzislau Rezki (Sony)" <urezki@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>,
        Uladzislau Rezki <urezki@...il.com>,
        Hillf Danton <hdanton@...a.com>,
        Michal Hocko <mhocko@...e.com>,
        Matthew Wilcox <willy@...radead.org>,
        Oleksiy Avramchenko <oleksiy.avramchenko@...ymobile.com>,
        Steven Rostedt <rostedt@...dmis.org>
Subject: [PATCH 2/3] mm/vmalloc: simplify augment_tree_propagate_check() func.

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: Uladzislau Rezki (Sony) <urezki@...il.com>
---
 mm/vmalloc.c | 42 ++++++++----------------------------------
 1 file changed, 8 insertions(+), 34 deletions(-)

diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index a875eef1e2c2..62d48f5e7105 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -589,43 +589,17 @@ 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
 
@@ -680,7 +654,7 @@ 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
 }
 
-- 
2.20.1