[PATCH] kernfs: fix a subdir count leak

[PATCH] kernfs: fix a subdir count leak

[Jianyu Zhan]

Currently kernfs_link_sibling() increates parent->dir.subdirs before
adding the node into parent's chidren rb tree.

Because it is possible that kernfs_link_sibling() couldn't find
a suitable slot and bail out, this leads to a mismatch between
elevated subdir count with actual children node numbers.

This patches fix this problem, by moving the subdir accouting
after the actual addtion happening.

Signed-off-by: Jianyu Zhan <nasa4836@gmail.com>
---
 fs/kernfs/dir.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/fs/kernfs/dir.c b/fs/kernfs/dir.c
index 78f3403..ac127cd 100644
--- a/fs/kernfs/dir.c
+++ b/fs/kernfs/dir.c
@@ -232,9 +232,6 @@ static int kernfs_link_sibling(struct kernfs_node *kn)
 	struct rb_node **node = &kn->parent->dir.children.rb_node;
 	struct rb_node *parent = NULL;
 
-	if (kernfs_type(kn) == KERNFS_DIR)
-		kn->parent->dir.subdirs++;
-
 	while (*node) {
 		struct kernfs_node *pos;
 		int result;
@@ -249,9 +246,15 @@ static int kernfs_link_sibling(struct kernfs_node *kn)
 		else
 			return -EEXIST;
 	}
+
 	/* add new node and rebalance the tree */
 	rb_link_node(&kn->rb, parent, node);
 	rb_insert_color(&kn->rb, &kn->parent->dir.children);
+
+	/* successfully added, account subdir number */
+	if (kernfs_type(kn) == KERNFS_DIR)
+		kn->parent->dir.subdirs++;
+
 	return 0;
 }
 
-- 
1.9.0.GIT

Re: [PATCH] kernfs: fix a subdir count leak

[Tejun Heo]

On Thu, Apr 17, 2014 at 05:52:10PM +0800, Jianyu Zhan wrote:
> Currently kernfs_link_sibling() increates parent->dir.subdirs before
> adding the node into parent's chidren rb tree.
> 
> Because it is possible that kernfs_link_sibling() couldn't find
> a suitable slot and bail out, this leads to a mismatch between
> elevated subdir count with actual children node numbers.
> 
> This patches fix this problem, by moving the subdir accouting
> after the actual addtion happening.
> 
> Signed-off-by: Jianyu Zhan <nasa4836@gmail.com>

Acked-by: Tejun Heo <tj@kernel.org>

Thanks.

-- 
tejun