ext4: fix bogus warning in ext4_update_dx_flag()

The idea of the warning in ext4_update_dx_flag() is that we should warn
when we are clearing EXT4_INODE_INDEX on a filesystem with metadata
checksums enabled since after clearing the flag, checksums for internal
htree nodes will become invalid. So there's no need to warn (or actually
do anything) when EXT4_INODE_INDEX is not set.

Link: https://lore.kernel.org/r/20201118153032.17281-1-jack@suse.cz
Fixes: 48a34311 ("ext4: fix checksum errors with indexed dirs")
Reported-by: Eric Biggers <ebiggers@kernel.org>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@kernel.org

fs/ext4/ext4.h

@@ -2695,7 +2695,8 @@ void ext4_insert_dentry(struct inode *inode,
 			struct ext4_filename *fname);
 static inline void ext4_update_dx_flag(struct inode *inode)
 {
-	if (!ext4_has_feature_dir_index(inode->i_sb)) {
+	if (!ext4_has_feature_dir_index(inode->i_sb) &&
+	    ext4_test_inode_flag(inode, EXT4_INODE_INDEX)) {
 		/* ext4_iget() should have caught this... */
 		WARN_ON_ONCE(ext4_has_feature_metadata_csum(inode->i_sb));
 		ext4_clear_inode_flag(inode, EXT4_INODE_INDEX);