ext4: Replace open coded mdata csum feature to helper function

Besides the fact that this replacement improves code readability
it also protects from errors caused direct EXT4_S(sb)->s_es manipulation
which may result attempt to use uninitialized  csum machinery.

#Testcase_BEGIN
IMG=/dev/ram0
MNT=/mnt
mkfs.ext4 $IMG
mount $IMG $MNT
#Enable feature directly on disk, on mounted fs
tune2fs -O metadata_csum  $IMG
# Provoke metadata update, likey result in OOPS
touch $MNT/test
umount $MNT
#Testcase_END

# Replacement script
@@
expression E;
@@
- EXT4_HAS_RO_COMPAT_FEATURE(E, EXT4_FEATURE_RO_COMPAT_METADATA_CSUM)
+ ext4_has_metadata_csum(E)

https://bugzilla.kernel.org/show_bug.cgi?id=82201

Signed-off-by: Dmitry Monakhov <dmonakhov@openvz.org>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index a0811cc..5afe42d 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -140,8 +140,7 @@
 static int ext4_superblock_csum_verify(struct super_block *sb,
 				       struct ext4_super_block *es)
 {
-	if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
-				       EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
+	if (!ext4_has_metadata_csum(sb))
 		return 1;
 
 	return es->s_checksum == ext4_superblock_csum(sb, es);
@@ -151,8 +150,7 @@
 {
 	struct ext4_super_block *es = EXT4_SB(sb)->s_es;
 
-	if (!EXT4_HAS_RO_COMPAT_FEATURE(sb,
-		EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
+	if (!ext4_has_metadata_csum(sb))
 		return;
 
 	es->s_checksum = ext4_superblock_csum(sb, es);
@@ -1989,8 +1987,7 @@
 	__u16 crc = 0;
 	__le32 le_group = cpu_to_le32(block_group);
 
-	if ((sbi->s_es->s_feature_ro_compat &
-	     cpu_to_le32(EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))) {
+	if (ext4_has_metadata_csum(sbi->s_sb)) {
 		/* Use new metadata_csum algorithm */
 		__le16 save_csum;
 		__u32 csum32;
@@ -3199,8 +3196,7 @@
 	int compat, incompat;
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
 
-	if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
-				       EXT4_FEATURE_RO_COMPAT_METADATA_CSUM)) {
+	if (ext4_has_metadata_csum(sb)) {
 		/* journal checksum v3 */
 		compat = 0;
 		incompat = JBD2_FEATURE_INCOMPAT_CSUM_V3;
@@ -3508,8 +3504,7 @@
 	}
 
 	/* Precompute checksum seed for all metadata */
-	if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
-			EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))
+	if (ext4_has_metadata_csum(sb))
 		sbi->s_csum_seed = ext4_chksum(sbi, ~0, es->s_uuid,
 					       sizeof(es->s_uuid));