Re: [PATCH, RFC] jbd2: Call the commit callback before the transaction could get dropped

[Eric Sandeen <sandeen@redhat.com>]

Theodore Tso wrote:
> This is what I plan to send to Linus to fix the problem.
> 
> commit 6fecbc3c7d27800e90a5f5fbca2fb2847e2c2854
> Author: Theodore Ts'o <tytso@mit.edu>
> Date:   Mon Oct 27 22:11:39 2008 -0400
> 
>     jbd2: Call the commit callback before the transaction could get dropped
>     
>     The transaction can potentially get dropped if there are no buffers
>     that need to be written.  Make sure we call the commit callback before
>     potentially deciding to drop the transaction.  Also avoid
>     dereferencing the commit_transaction pointer in the marker for the
>     same reason.
>     
>     This patch fixes the bug reported by Eric Paris at:
>     http://bugzilla.kernel.org/show_bug.cgi?id=11838
>     
>     Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

Acked-by: Eric Sandeen <sandeen@redhat.com>

> diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
> index 8b119e1..ebc667b 100644
> --- a/fs/jbd2/commit.c
> +++ b/fs/jbd2/commit.c
> @@ -974,6 +974,9 @@ restart_loop:
>  	journal->j_committing_transaction = NULL;
>  	spin_unlock(&journal->j_state_lock);
>  
> +	if (journal->j_commit_callback)
> +		journal->j_commit_callback(journal, commit_transaction);
> +
>  	if (commit_transaction->t_checkpoint_list == NULL &&
>  	    commit_transaction->t_checkpoint_io_list == NULL) {
>  		__jbd2_journal_drop_transaction(journal, commit_transaction);
> @@ -995,11 +998,8 @@ restart_loop:
>  	}
>  	spin_unlock(&journal->j_list_lock);
>  
> -	if (journal->j_commit_callback)
> -		journal->j_commit_callback(journal, commit_transaction);
> -
>  	trace_mark(jbd2_end_commit, "dev %s transaction %d head %d",
> -		   journal->j_devname, commit_transaction->t_tid,
> +		   journal->j_devname, journal->j_commit_sequence,
>  		   journal->j_tail_sequence);
>  	jbd_debug(1, "JBD: commit %d complete, head %d\n",
>  		  journal->j_commit_sequence, journal->j_tail_sequence);