Re: [PATCH] jbd: fix assertion failure in journal_next_log_block

[Mingming Cao <cmm@us.ibm.com>]

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@redhat.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@redhat.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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