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Date:	Thu, 31 Jan 2008 12:35:43 -0700
From:	Andreas Dilger <adilger@....com>
To:	Josef Bacik <jbacik@...hat.com>
Cc:	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] jbd: fix assertion failure in journal_next_log_block

On Jan 31, 2008  11:14 -0500, Josef Bacik wrote:
[snip excellent analysis]
> So you get into this situation where
> t_nr_buffers (the actual number of buffers that are on the transaction) is
> greater than the number of buffers accounted for via t_outstanding_credits.
> This presents a problem since as we loop through writting buffers to the
> journal, we decrement t_outstanding_credits, and if t_nr_buffers is more than
> t_outstanding_credits then we end up with a negative number for
> t_outstanding_credits
> 
> Signed-off-by: Josef Bacik <jbacik@...hat.com>

Do you know what kernel this problem was introduced in, or is this a
long standing problem?  Presumably the same is needed for jbd2?

Once we have some decent amount of testing going on with ext4, I think
it makes sense to merge the jbd2 changes back into jbd and return to
a single code base, since there is nothing in the jbd2 code that ext3
can't also work with (i.e. all of the changes are properly isolated
with compatibility flags and such).

> @@ -1056,7 +1056,7 @@ static inline int jbd_space_needed(journal_t *journal)
>  	int nblocks = journal->j_max_transaction_buffers;
>  	if (journal->j_committing_transaction)
>  		nblocks += journal->j_committing_transaction->
> -					t_outstanding_credits;
> +					t_nr_buffers;

(trivial) this can be moved back onto the previous line.

> @@ -1168,7 +1168,7 @@ static inline int jbd_space_needed(journal_t *journal)
>  	int nblocks = journal->j_max_transaction_buffers;
>  	if (journal->j_committing_transaction)
>  		nblocks += journal->j_committing_transaction->
> -					t_outstanding_credits;
> +					t_nr_buffers;

Same...

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.

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