2007-11-29 22:18:55

by Andrew Morton

[permalink] [raw]
Subject: + jbd-fix-assertion-failure-in-fs-jbd-checkpointc.patch added to -mm tree

The patch titled
jbd: Fix assertion failure in fs/jbd/checkpoint.c
has been added to the -mm tree. Its filename is

*** Remember to use Documentation/SubmitChecklist when testing your code ***

See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this

Subject: jbd: Fix assertion failure in fs/jbd/checkpoint.c
From: Jan Kara <[email protected]>

Before we start committing a transaction, we call
__journal_clean_checkpoint_list() to cleanup transaction's written-back

If this call happens to remove all of them (and there were already some
buffers), __journal_remove_checkpoint() will decide to free the transaction
because it isn't (yet) a committing transaction and soon we fail some
assertion - the transaction really isn't ready to be freed :).

We change the check in __journal_remove_checkpoint() to free only a
transaction in T_FINISHED state. The locking there is subtle though (as
everywhere in JBD ;(). We use j_list_lock to protect the check and a
subsequent call to __journal_drop_transaction() and do the same in the end
of journal_commit_transaction() which is the only place where a transaction
can get to T_FINISHED state.

Probably I'm too paranoid here and such locking is not really necessary -
checkpoint lists are processed only from log_do_checkpoint() where a
transaction must be already committed to be processed or from
__journal_clean_checkpoint_list() where kjournald itself calls it and thus
transaction cannot change state either. Better be safe if something
changes in future...

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

fs/jbd/checkpoint.c | 12 ++++++------
fs/jbd/commit.c | 8 ++++----
include/linux/jbd.h | 2 ++
3 files changed, 12 insertions(+), 10 deletions(-)

diff -puN fs/jbd/checkpoint.c~jbd-fix-assertion-failure-in-fs-jbd-checkpointc fs/jbd/checkpoint.c
--- a/fs/jbd/checkpoint.c~jbd-fix-assertion-failure-in-fs-jbd-checkpointc
+++ a/fs/jbd/checkpoint.c
@@ -602,15 +602,15 @@ int __journal_remove_checkpoint(struct j

* There is one special case to worry about: if we have just pulled the
- * buffer off a committing transaction's forget list, then even if the
- * checkpoint list is empty, the transaction obviously cannot be
- * dropped!
+ * buffer off a running or committing transaction's checkpoing list,
+ * then even if the checkpoint list is empty, the transaction obviously
+ * cannot be dropped!
- * The locking here around j_committing_transaction is a bit sleazy.
+ * The locking here around t_state is a bit sleazy.
* See the comment at the end of journal_commit_transaction().
- if (transaction == journal->j_committing_transaction) {
- JBUFFER_TRACE(jh, "belongs to committing transaction");
+ if (transaction->t_state != T_FINISHED) {
+ JBUFFER_TRACE(jh, "belongs to running/committing transaction");
goto out;

diff -puN fs/jbd/commit.c~jbd-fix-assertion-failure-in-fs-jbd-checkpointc fs/jbd/commit.c
--- a/fs/jbd/commit.c~jbd-fix-assertion-failure-in-fs-jbd-checkpointc
+++ a/fs/jbd/commit.c
@@ -858,10 +858,10 @@ restart_loop:
- * This is a bit sleazy. We borrow j_list_lock to protect
- * journal->j_committing_transaction in __journal_remove_checkpoint.
- * Really, __journal_remove_checkpoint should be using j_state_lock but
- * it's a bit hassle to hold that across __journal_remove_checkpoint
+ * This is a bit sleazy. We use j_list_lock to protect transition
+ * of a transaction into T_FINISHED state and calling
+ * __journal_drop_transaction(). Otherwise we could race with
+ * other checkpointing code processing the transaction...
diff -puN include/linux/jbd.h~jbd-fix-assertion-failure-in-fs-jbd-checkpointc include/linux/jbd.h
--- a/include/linux/jbd.h~jbd-fix-assertion-failure-in-fs-jbd-checkpointc
+++ a/include/linux/jbd.h
@@ -439,6 +439,8 @@ struct transaction_s
* Transaction's current state
* [no locking - only kjournald alters this]
+ * [j_list_lock] guards transition of a transaction into T_FINISHED
+ * state and subsequent call of __journal_drop_transaction()
* FIXME: needs barriers
* KLUDGE: [use j_state_lock]

Patches currently in -mm which might be from [email protected] are