This comment fixes commit eeecef0af5ea in a different way. The
original bug was that the following sequence:
# truncate --size=1g fsfile
# mkfs.ext4 -F fsfile
# mount -o loop,ro fsfile /mnt
# umount /mnt
# dmesg | tail
results in an IO error when unmounting the RO filesystem:
[ 318.020828] Buffer I/O error on device loop1, logical block 196608
[ 318.027024] lost page write due to I/O error on loop1
[ 318.032088] JBD2: Error -5 detected when updating journal superblock for l
And this was a regression introduced by commit 24bcc89c7e7c: "jbd2:
split updating of journal superblock and marking journal empty".
Here, we fix this bug by explicitly checking to see if the journal's
block device is read-only. If it is read-only, we then do a sanity
check to make sure that sb->s_start is zero. If it is non-zero, that
implies that one or more transactions has been committed to the
journal, which is a "can't happen" scenario if the block device is
read-only. So we will print a warning message and abort the journal
in that case.
Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
Cc: Nix <nix@xxxxxxxxxxxxx>
Cc: Toralf Förster <toralf.foerster@xxxxxx>
---
fs/jbd2/journal.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index bd23f2e..dcea89f 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1357,6 +1357,24 @@ static void jbd2_mark_journal_empty(journal_t *journal)
jbd_debug(1, "JBD2: Marking journal as empty (seq %d)\n",
journal->j_tail_sequence);
+ if (bdev_read_only(journal->j_dev)) {
+ __be32 s_start = sb->s_start;
+
+ read_unlock(&journal->j_state_lock);
+ if (s_start != 0) {
+ /*
+ * should never happen, but aborting the
+ * journal is nicer than a BUG_ON
+ */
+ printk(KERN_ERR
+ "JBD2: trying to empty non-empty journal for r/o device %s\n",
+ journal->j_devname);
+ WARN_ON(1);
+ jbd2_journal_abort(journal, -EROFS);
+ }
+ return;
+ }
+
sb->s_sequence = cpu_to_be32(journal->j_tail_sequence);
sb->s_start = cpu_to_be32(0);
read_unlock(&journal->j_state_lock);
--
1.7.12.rc0.22.gcdd159b
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