FAILED: patch "[PATCH] jbd2: fix the inconsistency between checksum and data in" failed to apply to 6.6-stable tree

The patch below does not apply to the 6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

To reproduce the conflict and resubmit, you may use the following commands:

git fetch https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ linux-6.6.y
git checkout FETCH_HEAD
git cherry-pick -x 6abfe107894af7e8ce3a2e120c619d81ee764ad5
# <resolve conflicts, build, test, etc.>
git commit -s
git send-email --to '<[email protected]>' --in-reply-to '2025122901-exciting-strained-363f@gregkh' --subject-prefix 'PATCH 6.6.y' HEAD^..

Possible dependencies:

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 6abfe107894af7e8ce3a2e120c619d81ee764ad5 Mon Sep 17 00:00:00 2001
From: Ye Bin <[email protected]>
Date: Mon, 3 Nov 2025 09:01:23 +0800
Subject: [PATCH] jbd2: fix the inconsistency between checksum and data in
memory for journal sb

Copying the file system while it is mounted as read-only results in a mount failure:
[~]# mkfs.ext4 -F /dev/sdc
[~]# mount /dev/sdc -o ro /mnt/test
[~]# dd if=/dev/sdc of=/dev/sda bs=1M
[~]# mount /dev/sda /mnt/test1

[ 1094.849826] JBD2: journal checksum error
[ 1094.850927] EXT4-fs (sda): Could not load journal inode

mount: mount /dev/sda on /mnt/test1 failed: Bad message

The process described above is just an abstracted way I came up with to reproduce the issue. In the actual scenario, the file system was mounted read-only and then copied while it was still mounted. It was found that the mount operation failed. The user intended to verify the data or use it as a backup, and this action was performed during a version upgrade. Above issue may happen as follows:
ext4_fill_super
set_journal_csum_feature_set(sb)
if (ext4_has_metadata_csum(sb))
incompat = JBD2_FEATURE_INCOMPAT_CSUM_V3;
if (test_opt(sb, JOURNAL_CHECKSUM)

   jbd2_journal_set_features(sbi->s_journal, compat, 0, incompat);
    lock_buffer(journal->j_sb_buffer);
    sb->s_feature_incompat  |= cpu_to_be32(incompat);
    //The data in the journal sb was modified, but the checksum was not
      updated, so the data remaining in memory has a mismatch between the
      data and the checksum.
    unlock_buffer(journal->j_sb_buffer);

In this case, the journal sb copied over is in a state where the checksum and data are inconsistent, so mounting fails.
To solve the above issue, update the checksum in memory after modifying the journal sb.

Message-ID: <[email protected]>

index 2fe1786a8f1b..c973162d5b31 100644
@@ -2354,6 +2354,12 @@ int jbd2_journal_set_features(journal_t *journal, unsigned long compat,
 	sb->s_feature_compat    |= cpu_to_be32(compat);
 	sb->s_feature_ro_compat |= cpu_to_be32(ro);
 	sb->s_feature_incompat  |= cpu_to_be32(incompat);
+	/*
+	 * Update the checksum now so that it is valid even for read-only
+	 * filesystems where jbd2_write_superblock() doesn't get called.
+	 */
+	if (jbd2_journal_has_csum_v2or3(journal))
+		sb->s_checksum = jbd2_superblock_csum(sb);
 	unlock_buffer(journal->j_sb_buffer);
 	jbd2_journal_init_transaction_limits(journal);
 

@@ -2383,9 +2389,17 @@ void jbd2_journal_clear_features(journal_t *journal, unsigned long compat,
 
 	sb = journal->j_superblock;
 
+	lock_buffer(journal->j_sb_buffer);
 	sb->s_feature_compat    &= ~cpu_to_be32(compat);
 	sb->s_feature_ro_compat &= ~cpu_to_be32(ro);
 	sb->s_feature_incompat  &= ~cpu_to_be32(incompat);
+	/*
+	 * Update the checksum now so that it is valid even for read-only
+	 * filesystems where jbd2_write_superblock() doesn't get called.
+	 */
+	if (jbd2_journal_has_csum_v2or3(journal))
+		sb->s_checksum = jbd2_superblock_csum(sb);
+	unlock_buffer(journal->j_sb_buffer);
 	jbd2_journal_init_transaction_limits(journal);
 }
 EXPORT_SYMBOL(jbd2_journal_clear_features);

From: Ye Bin <[email protected]>

[ Upstream commit 6abfe107894af7e8ce3a2e120c619d81ee764ad5 ]

Copying the file system while it is mounted as read-only results in a mount failure:
[~]# mkfs.ext4 -F /dev/sdc
[~]# mount /dev/sdc -o ro /mnt/test
[~]# dd if=/dev/sdc of=/dev/sda bs=1M
[~]# mount /dev/sda /mnt/test1

[ 1094.849826] JBD2: journal checksum error
[ 1094.850927] EXT4-fs (sda): Could not load journal inode

mount: mount /dev/sda on /mnt/test1 failed: Bad message

The process described above is just an abstracted way I came up with to reproduce the issue. In the actual scenario, the file system was mounted read-only and then copied while it was still mounted. It was found that the mount operation failed. The user intended to verify the data or use it as a backup, and this action was performed during a version upgrade. Above issue may happen as follows:
ext4_fill_super
set_journal_csum_feature_set(sb)
if (ext4_has_metadata_csum(sb))
incompat = JBD2_FEATURE_INCOMPAT_CSUM_V3;
if (test_opt(sb, JOURNAL_CHECKSUM)

   jbd2_journal_set_features(sbi->s_journal, compat, 0, incompat);
    lock_buffer(journal->j_sb_buffer);
    sb->s_feature_incompat  |= cpu_to_be32(incompat);
    //The data in the journal sb was modified, but the checksum was not
      updated, so the data remaining in memory has a mismatch between the
      data and the checksum.
    unlock_buffer(journal->j_sb_buffer);

In this case, the journal sb copied over is in a state where the checksum and data are inconsistent, so mounting fails.
To solve the above issue, update the checksum in memory after modifying the journal sb.

Message-ID: <[email protected]>

---
 fs/jbd2/journal.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

index ddde73299d62..9465f3f52ebb 100644
@@ -2403,6 +2403,12 @@ int jbd2_journal_set_features(journal_t *journal, unsigned long compat,
 	sb->s_feature_compat    |= cpu_to_be32(compat);
 	sb->s_feature_ro_compat |= cpu_to_be32(ro);
 	sb->s_feature_incompat  |= cpu_to_be32(incompat);
+	/*
+	 * Update the checksum now so that it is valid even for read-only
+	 * filesystems where jbd2_write_superblock() doesn't get called.
+	 */
+	if (jbd2_journal_has_csum_v2or3(journal))
+		sb->s_checksum = jbd2_superblock_csum(journal, sb);
 	unlock_buffer(journal->j_sb_buffer);
 	jbd2_journal_init_transaction_limits(journal);
 

@@ -2432,9 +2438,17 @@ void jbd2_journal_clear_features(journal_t *journal, unsigned long compat,
 
 	sb = journal->j_superblock;
 
+	lock_buffer(journal->j_sb_buffer);
 	sb->s_feature_compat    &= ~cpu_to_be32(compat);
 	sb->s_feature_ro_compat &= ~cpu_to_be32(ro);
 	sb->s_feature_incompat  &= ~cpu_to_be32(incompat);
+	/*
+	 * Update the checksum now so that it is valid even for read-only
+	 * filesystems where jbd2_write_superblock() doesn't get called.
+	 */
+	if (jbd2_journal_has_csum_v2or3(journal))
+		sb->s_checksum = jbd2_superblock_csum(journal, sb);
+	unlock_buffer(journal->j_sb_buffer);
 	jbd2_journal_init_transaction_limits(journal);
 }
 EXPORT_SYMBOL(jbd2_journal_clear_features);

2.51.0