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

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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>
This commit is contained in:
Jan Kara
2007-12-04 23:45:27 -08:00
committed by Linus Torvalds
parent 369b8f5a70
commit d4beaf4ab5
3 changed files with 12 additions and 10 deletions
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12
fs/jbd/checkpoint.c
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@ -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;
}