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Date: Thu, 31 Jan 2008 16:50:25 -0800
From: Mingming Cao <cmm@...ibm.com>
To: Josef Bacik <jbacik@...hat.com>
Cc: Andreas Dilger <adilger@....com>, linux-ext4@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] jbd: fix assertion failure in journal_next_log_block
On Thu, 2008-01-31 at 16:52 -0500, Josef Bacik wrote:
> On Thu, Jan 31, 2008 at 12:35:43PM -0700, Andreas Dilger wrote:
> > 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...
> >
>
> The original issue was reported on RHEL4, so thats 2.6.9, and looking through
> the old-bkcvs git tree I can't see where this was introduced, so it's probably
> existed before that. The same problem looks to exist in jbd2 though I haven't
> tested it myself, I just went ahead and included the fixes. Here is the updated
> patch, thanks much for the comments.
>
Added to ext4 patch queue.
Thanks,
Mingming
> Signed-off-by: Josef Bacik <jbacik@...hat.com>
>
>
> diff --git a/fs/jbd/commit.c b/fs/jbd/commit.c
> index 31853eb..e385a5c 100644
> --- a/fs/jbd/commit.c
> +++ b/fs/jbd/commit.c
> @@ -561,13 +561,6 @@ void journal_commit_transaction(journal_t *journal)
> continue;
> }
>
> - /*
> - * start_this_handle() uses t_outstanding_credits to determine
> - * the free space in the log, but this counter is changed
> - * by journal_next_log_block() also.
> - */
> - commit_transaction->t_outstanding_credits--;
> -
> /* Bump b_count to prevent truncate from stumbling over
> the shadowed buffer! @@@ This can go if we ever get
> rid of the BJ_IO/BJ_Shadow pairing of buffers. */
> diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
> index 4f302d2..c0f93f5 100644
> --- a/fs/jbd2/commit.c
> +++ b/fs/jbd2/commit.c
> @@ -580,7 +580,7 @@ void jbd2_journal_commit_transaction(journal_t *journal)
> stats.u.run.rs_logging = jiffies;
> stats.u.run.rs_flushing = jbd2_time_diff(stats.u.run.rs_flushing,
> stats.u.run.rs_logging);
> - stats.u.run.rs_blocks = commit_transaction->t_outstanding_credits;
> + stats.u.run.rs_blocks = commit_transaction->t_nr_buffers;
> stats.u.run.rs_blocks_logged = 0;
>
> descriptor = NULL;
> @@ -655,13 +655,6 @@ void jbd2_journal_commit_transaction(journal_t *journal)
> continue;
> }
>
> - /*
> - * start_this_handle() uses t_outstanding_credits to determine
> - * the free space in the log, but this counter is changed
> - * by jbd2_journal_next_log_block() also.
> - */
> - commit_transaction->t_outstanding_credits--;
> -
> /* Bump b_count to prevent truncate from stumbling over
> the shadowed buffer! @@@ This can go if we ever get
> rid of the BJ_IO/BJ_Shadow pairing of buffers. */
> diff --git a/include/linux/jbd.h b/include/linux/jbd.h
> index d9ecd13..eaeb3db 100644
> --- a/include/linux/jbd.h
> +++ b/include/linux/jbd.h
> @@ -1055,8 +1055,7 @@ 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;
> + nblocks += journal->j_committing_transaction->t_nr_buffers;
> return nblocks;
> }
>
> diff --git a/include/linux/jbd2.h b/include/linux/jbd2.h
> index 2cbf6fd..acf9d34 100644
> --- a/include/linux/jbd2.h
> +++ b/include/linux/jbd2.h
> @@ -1167,8 +1167,7 @@ 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;
> + nblocks += journal->j_committing_transaction->t_nr_buffers;
> return nblocks;
> }
>
> -
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