On umount path, jbd2_journal_destroy() writes latest transaction ID
(->j_tail_sequence) to be used at next mount.
The bug is that ->j_tail_sequence is not holding latest transaction ID
in some cases. So, at next mount, there is chance to conflict with
remaining (not overwritten yet) transactions.
mount (id=10)
write transaction (id=11)
write transaction (id=12)
umount (id=10) <= the bug doesn't write latest ID
mount (id=10)
write transaction (id=11)
crash
mount
[recovery process]
transaction (id=11)
transaction (id=12) <= valid transaction ID, but old commit
must not replay
Like above, this bug become the cause of recovery failure, or FS
corruption.
So why ->j_tail_sequence doesn't point latest ID?
Because if checkpoint transactions was reclaimed by memory pressure
(i.e. bdev_try_to_free_page()), then ->j_tail_sequence is not updated.
(And another case is, __jbd2_journal_clean_checkpoint_list() is called
with empty transaction.)
So in above cases, ->j_tail_sequence is not pointing latest
transaction ID at umount path. Plus, REQ_FLUSH for checkpoint is not
done too.
So, to fix this problem with minimum changes, this patch updates
->j_tail_sequence, and issue REQ_FLUSH. (With more complex changes,
some optimizations would be possible to avoid unnecessary REQ_FLUSH
for example though.)
BTW,
journal->j_tail_sequence =
++journal->j_transaction_sequence;
Increment of ->j_transaction_sequence seems to be unnecessary, but
ext3 does this.
v2: Fix "make htmldocs" warning
Signed-off-by: OGAWA Hirofumi <hirofumi@mail.parknet.co.jp>
Cc: <redacted>
---
fs/jbd2/journal.c | 17 ++++++++++++-----
1 file changed, 12 insertions(+), 5 deletions(-)
diff -puN fs/jbd2/journal.c~ext4-umount-fix fs/jbd2/journal.c--- linux/fs/jbd2/journal.c~ext4-umount-fix 2016-02-28 10:16:41.997093008 +0900
+++ linux-hirofumi/fs/jbd2/journal.c 2016-02-28 23:01:25.865647233 +0900
@@ -1408,11 +1408,12 @@ out:
/**
* jbd2_mark_journal_empty() - Mark on disk journal as empty.
* @journal: The journal to update.
+ * @write_op: With which operation should we write the journal sb
*
* Update a journal's dynamic superblock fields to show that journal is empty.
* Write updated superblock to disk waiting for IO to complete.
*/
-static void jbd2_mark_journal_empty(journal_t *journal)
+static void jbd2_mark_journal_empty(journal_t *journal, int write_op)
{
journal_superblock_t *sb = journal->j_superblock;
@@ -1430,7 +1431,7 @@ static void jbd2_mark_journal_empty(jour
sb->s_start = cpu_to_be32(0);
read_unlock(&journal->j_state_lock);
- jbd2_write_superblock(journal, WRITE_FUA);
+ jbd2_write_superblock(journal, write_op);
/* Log is no longer empty */
write_lock(&journal->j_state_lock);
@@ -1716,7 +1717,13 @@ int jbd2_journal_destroy(journal_t *jour
if (journal->j_sb_buffer) {
if (!is_journal_aborted(journal)) {
mutex_lock(&journal->j_checkpoint_mutex);
- jbd2_mark_journal_empty(journal);
+
+ write_lock(&journal->j_state_lock);
+ journal->j_tail_sequence =
+ ++journal->j_transaction_sequence;
+ write_unlock(&journal->j_state_lock);
+
+ jbd2_mark_journal_empty(journal, WRITE_FLUSH_FUA);
mutex_unlock(&journal->j_checkpoint_mutex);
} else
err = -EIO;@@ -1975,7 +1982,7 @@ int jbd2_journal_flush(journal_t *journa
* the magic code for a fully-recovered superblock. Any future
* commits of data to the journal will restore the current
* s_start value. */
- jbd2_mark_journal_empty(journal);
+ jbd2_mark_journal_empty(journal, WRITE_FUA);
mutex_unlock(&journal->j_checkpoint_mutex);
write_lock(&journal->j_state_lock);
J_ASSERT(!journal->j_running_transaction);
@@ -2021,7 +2028,7 @@ int jbd2_journal_wipe(journal_t *journal
if (write) {
/* Lock to make assertions happy... */
mutex_lock(&journal->j_checkpoint_mutex);
- jbd2_mark_journal_empty(journal);
+ jbd2_mark_journal_empty(journal, WRITE_FUA);
mutex_unlock(&journal->j_checkpoint_mutex);
}
_
--
OGAWA Hirofumi [off-list ref]