The patch below does not apply to the 6.12-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 stable@vger.kernel.org.
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-6.12.y git checkout FETCH_HEAD git cherry-pick -x 6abfe107894af7e8ce3a2e120c619d81ee764ad5 # <resolve conflicts, build, test, etc.> git commit -s git send-email --to 'stable@vger.kernel.org' --in-reply-to '2025122927-germicide-venus-61d2@gregkh' --subject-prefix 'PATCH 6.12.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 yebin10@huawei.com 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.
Fixes: 4fd5ea43bc11 ("jbd2: checksum journal superblock") Signed-off-by: Ye Bin yebin10@huawei.com Reviewed-by: Baokun Li libaokun1@huawei.com Reviewed-by: Darrick J. Wong djwong@kernel.org Reviewed-by: Jan Kara jack@suse.cz Message-ID: 20251103010123.3753631-1-yebin@huaweicloud.com Signed-off-by: Theodore Ts'o tytso@mit.edu Cc: stable@kernel.org
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c index 2fe1786a8f1b..c973162d5b31 100644 --- a/fs/jbd2/journal.c +++ b/fs/jbd2/journal.c @@ -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);