[PATCH] fat: fix parent link count when replacing a sibling directory

[Hungyu Lin <dennylin0707@gmail.com>]

vfat_rename() and do_msdos_rename() adjust parent link counts only when
updating the dotdot entry for a move between different parents. Replacing
an existing empty directory in the same parent also removes a
subdirectory, but leaves the parent's link count unchanged.

For example, renaming one of two sibling directories over the other
leaves the parent with four links instead of three. stat and ls report
the stale count, and find -links 3 does not match the parent.

Drop the parent's link count for this case after the source entry has
been removed successfully. Leave cross-parent renames, regular files
and the existing error paths unchanged.

Signed-off-by: Hungyu Lin <dennylin0707@gmail.com>
---
 fs/fat/namei_msdos.c | 2 ++
 fs/fat/namei_vfat.c  | 2 ++
 2 files changed, 4 insertions(+)

diff --git a/fs/fat/namei_msdos.c b/fs/fat/namei_msdos.c
index c7500c2859e0..570dd75dd275 100644
--- a/fs/fat/namei_msdos.c
+++ b/fs/fat/namei_msdos.c
@@ -565,6 +565,8 @@ static int do_msdos_rename(struct inode *old_dir, unsigned char *old_name,
 		(void)sync_inode_metadata(old_dir, 1);
 
 	if (new_inode) {
+		if (is_dir && old_dir == new_dir)
+			drop_nlink(old_dir);
 		drop_nlink(new_inode);
 		if (is_dir)
 			drop_nlink(new_inode);
diff --git a/fs/fat/namei_vfat.c b/fs/fat/namei_vfat.c
index ff7652bf0410..d7e2df5bf7e5 100644
--- a/fs/fat/namei_vfat.c
+++ b/fs/fat/namei_vfat.c
@@ -1011,6 +1011,8 @@ static int vfat_rename(struct inode *old_dir, struct dentry *old_dentry,
 	vfat_update_dir_metadata(old_dir, &ts);
 
 	if (new_inode) {
+		if (is_dir && old_dir == new_dir)
+			drop_nlink(old_dir);
 		drop_nlink(new_inode);
 		if (is_dir)
 			drop_nlink(new_inode);
-- 
2.43.0