Commit c41303ce authored by Maciej Żenczykowski's avatar Maciej Żenczykowski Committed by Theodore Ts'o
Browse files

ext4: don't update sb journal_devnum when RO dev

An ext4 filesystem on a read-only device, with an external journal
which is at a different device number then recorded in the superblock
will fail to honor the read-only setting of the device and trigger
a superblock update (write).

For example:
  - ext4 on a software raid which is in read-only mode
  - external journal on a read-write device which has changed device num
  - attempt to mount with -o journal_dev=<new_number>
  - hits BUG_ON(mddev->ro = 1) in md.c

Cc: Theodore Ts'o <>
Signed-off-by: default avatarMaciej Żenczykowski <>
Signed-off-by: default avatar"Theodore Ts'o" <>
parent 2407518d
......@@ -3908,7 +3908,7 @@ static int ext4_load_journal(struct super_block *sb,
EXT4_SB(sb)->s_journal = journal;
ext4_clear_journal_err(sb, es);
if (journal_devnum &&
if (!really_read_only && journal_devnum &&
journal_devnum != le32_to_cpu(es->s_journal_dev)) {
es->s_journal_dev = cpu_to_le32(journal_devnum);
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