jbd: Fix assertion failure in fs/jbd/checkpoint.c

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

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 <jack@suse.cz>
Cc: <linux-ext4@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 6 insertions, 6 deletions

diff --git a/fs/jbd/checkpoint.c b/fs/jbd/checkpoint.c
index 47552d4a6324..0f69c416eebc 100644
--- a/fs/jbd/checkpoint.c
+++ b/fs/jbd/checkpoint.c
@@ -602,15 +602,15 @@ int __journal_remove_checkpoint(struct journal_head *jh)
 
         /*
          * 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;
         }