2009-02-11 21:05:32

by Andrew Morton

[permalink] [raw]
Subject: [patch 07/24] jbd: fix return value of journal_start_commit()

From: Jan Kara <[email protected]>

journal_start_commit() returns 1 if either a transaction is committing or
the function has queued a transaction commit. But it returns 0 if we
raced with somebody queueing the transaction commit as well. This
resulted in ext3_sync_fs() not functioning correctly (description from
Arthur Jones): In the case of a data=ordered umount with pending long
symlinks which are delayed due to a long list of other I/O on the backing
block device, this causes the buffer associated with the long symlinks to
not be moved to the inode dirty list in the second phase of fsync_super.
Then, before they can be dirtied again, kjournald exits, seeing the UMOUNT
flag and the dirty pages are never written to the backing block device,
causing long symlink corruption and exposing new or previously freed block
data to userspace.

This can be reproduced with a script created by Eric Sandeen
<[email protected]>:


umount /mnt/test2
mount /dev/sdb4 /mnt/test2
rm -f /mnt/test2/*
dd if=/dev/zero of=/mnt/test2/bigfile bs=1M count=512
touch /mnt/test2/thisisveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryverylongfilename
ln -s /mnt/test2/thisisveryveryveryveryveryveryveryveryveryveryveryveryveryveryveryverylongfilename
umount /mnt/test2
mount /dev/sdb4 /mnt/test2
ls /mnt/test2/

This patch fixes journal_start_commit() to always return 1 when there's
a transaction committing or queued for commit.

Cc: Eric Sandeen <[email protected]>
Cc: Mike Snitzer <[email protected]>
Cc: <[email protected]>
Signed-off-by: Jan Kara <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

fs/jbd/journal.c | 17 +++++++++++------
1 file changed, 11 insertions(+), 6 deletions(-)

diff -puN fs/jbd/journal.c~jbd-fix-return-value-of-journal_start_commit fs/jbd/journal.c
--- a/fs/jbd/journal.c~jbd-fix-return-value-of-journal_start_commit
+++ a/fs/jbd/journal.c
@@ -427,7 +427,7 @@ int __log_space_left(journal_t *journal)

- * Called under j_state_lock. Returns true if a transaction was started.
+ * Called under j_state_lock. Returns true if a transaction commit was started.
int __log_start_commit(journal_t *journal, tid_t target)
@@ -495,7 +495,8 @@ int journal_force_commit_nested(journal_

* Start a commit of the current running transaction (if any). Returns true
- * if a transaction was started, and fills its tid in at *ptid
+ * if a transaction is going to be committed (or is currently already
+ * committing), and fills its tid in at *ptid
int journal_start_commit(journal_t *journal, tid_t *ptid)
@@ -505,15 +506,19 @@ int journal_start_commit(journal_t *jour
if (journal->j_running_transaction) {
tid_t tid = journal->j_running_transaction->t_tid;

- ret = __log_start_commit(journal, tid);
- if (ret && ptid)
+ __log_start_commit(journal, tid);
+ /* There's a running transaction and we've just made sure
+ * it's commit has been scheduled. */
+ if (ptid)
*ptid = tid;
- } else if (journal->j_committing_transaction && ptid) {
+ ret = 1;
+ } else if (journal->j_committing_transaction) {
* If ext3_write_super() recently started a commit, then we
* have to wait for completion of that transaction
- *ptid = journal->j_committing_transaction->t_tid;
+ if (ptid)
+ *ptid = journal->j_committing_transaction->t_tid;
ret = 1;