sysfs: fix namespace refcnt leak

As mount() and kill_sb() is not a one-to-one match, we shoudn't get
ns refcnt unconditionally in sysfs_mount(), and instead we should
get the refcnt only when kernfs_mount() allocated a new superblock.

v2:
- Changed the name of the new argument, suggested by Tejun.
- Made the argument optional, suggested by Tejun.

v3:
- Make the new argument as second-to-last arg, suggested by Tejun.

Signed-off-by: Li Zefan <lizefan@huawei.com>
Acked-by: Tejun Heo <tj@kernel.org>
 ---
 fs/kernfs/mount.c      | 8 +++++++-
 fs/sysfs/mount.c       | 5 +++--
 include/linux/kernfs.h | 9 +++++----
 3 files changed, 15 insertions(+), 7 deletions(-)
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 5 insertions, 4 deletions

diff --git a/include/linux/kernfs.h b/include/linux/kernfs.h
index 5be9f0228a3b..d267623c28cf 100644
--- a/include/linux/kernfs.h
+++ b/include/linux/kernfs.h
@@ -249,7 +249,8 @@ void kernfs_notify(struct kernfs_node *kn);
 
 const void *kernfs_super_ns(struct super_block *sb);
 struct dentry *kernfs_mount_ns(struct file_system_type *fs_type, int flags,
-			       struct kernfs_root *root, const void *ns);
+			       struct kernfs_root *root, bool *new_sb_created,
+			       const void *ns);
 void kernfs_kill_sb(struct super_block *sb);
 
 void kernfs_init(void);
@@ -317,7 +318,7 @@ static inline const void *kernfs_super_ns(struct super_block *sb)
 
 static inline struct dentry *
 kernfs_mount_ns(struct file_system_type *fs_type, int flags,
-		struct kernfs_root *root, const void *ns)
+		struct kernfs_root *root, bool *new_sb_created, const void *ns)
 { return ERR_PTR(-ENOSYS); }
 
 static inline void kernfs_kill_sb(struct super_block *sb) { }
@@ -368,9 +369,9 @@ static inline int kernfs_remove_by_name(struct kernfs_node *parent,
 
 static inline struct dentry *
 kernfs_mount(struct file_system_type *fs_type, int flags,
-	     struct kernfs_root *root)
+	     struct kernfs_root *root, bool *new_sb_created)
 {
-	return kernfs_mount_ns(fs_type, flags, root, NULL);
+	return kernfs_mount_ns(fs_type, flags, root, new_sb_created, NULL);
 }
 
 #endif	/* __LINUX_KERNFS_H */