f2fs: Avoid reading renamed directory if parent does not change

The VFS will not be locking moved directory if its parent does not
change.  Change f2fs rename code to avoid reading renamed directory if
its parent does not change.  Having it uninlined while we are reading
it would cause trouble and we won't be able to rely upon ->i_rwsem
on the directory being renamed in cases that do not alter its parent.
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/f2fs/namei.c

@@ -963,6 +963,7 @@ static int f2fs_rename(struct mnt_idmap *idmap, struct inode *old_dir,
 	struct f2fs_dir_entry *old_dir_entry = NULL;
 	struct f2fs_dir_entry *old_entry;
 	struct f2fs_dir_entry *new_entry;
+	bool old_is_dir = S_ISDIR(old_inode->i_mode);
 	int err;
 
 	if (unlikely(f2fs_cp_error(sbi)))
@@ -1017,7 +1018,7 @@ static int f2fs_rename(struct mnt_idmap *idmap, struct inode *old_dir,
 		goto out;
 	}
 
-	if (S_ISDIR(old_inode->i_mode)) {
+	if (old_is_dir && old_dir != new_dir) {
 		old_dir_entry = f2fs_parent_dir(old_inode, &old_dir_page);
 		if (!old_dir_entry) {
 			if (IS_ERR(old_dir_page))
@@ -1029,7 +1030,7 @@ static int f2fs_rename(struct mnt_idmap *idmap, struct inode *old_dir,
 	if (new_inode) {
 
 		err = -ENOTEMPTY;
-		if (old_dir_entry && !f2fs_empty_dir(new_inode))
+		if (old_is_dir && !f2fs_empty_dir(new_inode))
 			goto out_dir;
 
 		err = -ENOENT;
@@ -1054,7 +1055,7 @@ static int f2fs_rename(struct mnt_idmap *idmap, struct inode *old_dir,
 
 		inode_set_ctime_current(new_inode);
 		f2fs_down_write(&F2FS_I(new_inode)->i_sem);
-		if (old_dir_entry)
+		if (old_is_dir)
 			f2fs_i_links_write(new_inode, false);
 		f2fs_i_links_write(new_inode, false);
 		f2fs_up_write(&F2FS_I(new_inode)->i_sem);
@@ -1074,12 +1075,12 @@ static int f2fs_rename(struct mnt_idmap *idmap, struct inode *old_dir,
 			goto out_dir;
 		}
 
-		if (old_dir_entry)
+		if (old_is_dir)
 			f2fs_i_links_write(new_dir, true);
 	}
 
 	f2fs_down_write(&F2FS_I(old_inode)->i_sem);
-	if (!old_dir_entry || whiteout)
+	if (!old_is_dir || whiteout)
 		file_lost_pino(old_inode);
 	else
 		/* adjust dir's i_pino to pass fsck check */
@@ -1105,8 +1106,8 @@ static int f2fs_rename(struct mnt_idmap *idmap, struct inode *old_dir,
 		iput(whiteout);
 	}
 
-	if (old_dir_entry) {
-		if (old_dir != new_dir && !whiteout)
+	if (old_is_dir) {
+		if (old_dir_entry && !whiteout)
 			f2fs_set_link(old_inode, old_dir_entry,
 						old_dir_page, new_dir);
 		else