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ext4/jbd2: Fix FS corruption possibility on umount path

PATCH New OGAWA Hirofumi 1 participant 1 message Feb 28, 2016

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VFS Journalling layer for block devices (JBD2)
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OGAWA Hirofumi

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PATCH v2 1/1 ext4/jbd2: Fix FS corruption possibility on umount path

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 <[email protected]>
Cc [email protected]

---

 fs/jbd2/journal.c |   17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)
fs/jbd2/journal.c renamed from fs/jbd2/journal.c~ext4-umount-fix +12 -5
diff -puN fs/jbd2/journal.c~ext4-umount-fix fs/jbd2/journal.c
@@ -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);
 	}

_

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OGAWA Hirofumi <[email protected]>