jbd2: flush filesystem device before updating tail sequence

When committing transaction in jbd2_journal_commit_transaction(), the
disk caches for the filesystem device should be flushed before updating
the journal tail sequence. However, this step is missed if the journal
is not located on the filesystem device. As a result, the filesystem may
become inconsistent following a power failure or system crash. Fix it by
ensuring that the filesystem device is flushed appropriately.

Fixes: 3339578 ("jbd2: cleanup journal tail after transaction commit")
Signed-off-by: Zhang Yi <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Christian Brauner <[email protected]>

Author: zhangyi089

fs/jbd2/commit.c

@@ -772,9 +772,9 @@ void jbd2_journal_commit_transaction(journal_t *journal)
 	/*
 	 * If the journal is not located on the file system device,
 	 * then we must flush the file system device before we issue
-	 * the commit record
+	 * the commit record and update the journal tail sequence.
 	 */
-	if (commit_transaction->t_need_data_flush &&
+	if ((commit_transaction->t_need_data_flush || update_tail) &&
 	    (journal->j_fs_dev != journal->j_dev) &&
 	    (journal->j_flags & JBD2_BARRIER))
 		blkdev_issue_flush(journal->j_fs_dev);