[PATCH 2/3] tracing/stat: simplify rbtree freeing code

[Li Zefan <lizf@cn.fujitsu.com>]

When closing a trace_stat file, we destroy the rbtree constructed during
file open, but there is memory leak that the root node is not freed:

static struct rb_node *release_next(struct rb_node *node)
{
	...
	else {
		if (!parent)		<-- here we leak @node
			return NULL;
	...
}

This patch keeps removing root node until the tree is empty. We regress
from O(n) to O(nlogn), but since both open() and read() are O(nlogn) and
it's a slow path, this change won't affect scalibility.

[ Impact: fix memory leak when closing a trace_stat file ]

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
 kernel/trace/trace_stat.c |   39 +++++----------------------------------
 1 files changed, 5 insertions(+), 34 deletions(-)

diff --git a/kernel/trace/trace_stat.c b/kernel/trace/trace_stat.c
index 6efbcb4..ed18701 100644
--- a/kernel/trace/trace_stat.c
+++ b/kernel/trace/trace_stat.c
@@ -42,47 +42,18 @@ static DEFINE_MUTEX(all_stat_sessions_mutex);
 /* The root directory for all stat files */
 static struct dentry		*stat_dir;
 
-/*
- * Iterate through the rbtree using a post order traversal path
- * to release the next node.
- * It won't necessary release one at each iteration
- * but it will at least advance closer to the next one
- * to be released.
- */
-static struct rb_node *release_next(struct rb_node *node)
+static void reset_stat_session(struct stat_session *session)
 {
 	struct stat_node *snode;
-	struct rb_node *parent = rb_parent(node);
-
-	if (node->rb_left)
-		return node->rb_left;
-	else if (node->rb_right)
-		return node->rb_right;
-	else {
-		if (!parent)
-			return NULL;
-		if (parent->rb_left == node)
-			parent->rb_left = NULL;
-		else
-			parent->rb_right = NULL;
+	struct rb_root *sroot = &session->stat_root;
 
-		snode = container_of(node, struct stat_node, node);
+	while (!RB_EMPTY_ROOT(sroot)) {
+		snode = rb_entry(sroot->rb_node, struct stat_node, node);
+		rb_erase(&snode->node, sroot);
 		kfree(snode);
-
-		return parent;
 	}
 }
 
-static void reset_stat_session(struct stat_session *session)
-{
-	struct rb_node *node = session->stat_root.rb_node;
-
-	while (node)
-		node = release_next(node);
-
-	session->stat_root = RB_ROOT;
-}
-
 static void destroy_session(struct stat_session *session)
 {
 	debugfs_remove(session->file);
-- 
1.5.4.rc3