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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
View file

@ -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;
}

8
fs/jbd/commit.c
View file

@ -858,10 +858,10 @@ restart_loop:
}
spin_unlock(&journal->j_list_lock);
/*
* 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...
*/
spin_lock(&journal->j_state_lock);
spin_lock(&journal->j_list_lock);

2
include/linux/jbd.h
View file

@ -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]
*/