[Ocfs2-devel] [PATCH v2] ocfs2: Rework transaction rollback in ocfs2_relink_block_group()

[Andrew Morton]

On Thu, 20 Jun 2013 13:29:33 +0800 Jeff Liu <jeff.liu at oracle.com> wrote:

> From: Jie Liu <jeff.liu at oracle.com>
> 
> In ocfs2_relink_block_group(), we roll back all those changes if
> notify intent to modify buffers for metadata update failed even
> if the relevant buffer has not yet been modified/got dirty at that
> point, that are not quite right because of:
> 
> - None buffer has been modified/dirty if failed to call
>   ocfs2_journal_access_gd() against the previous block group buffer
> - Only the previous block group buffer has got dirty if failed to
>   call ocfs2_journal_access_gd() against the block group buffer
> - There is no need to roll back the change for file entry buffer at all
> 
> Those problems will not cause anything wrong but unnecessary.
> This patch fix them and kill the useless bg_ptr variable as well.
> 
> ...
>
> --- a/fs/ocfs2/suballoc.c
> +++ b/fs/ocfs2/suballoc.c
> @@ -1422,7 +1422,7 @@ static int ocfs2_relink_block_group(handle_t *handle,
>  	int status;
>  	/* there is a really tiny chance the journal calls could fail,
>  	 * but we wouldn't want inconsistent blocks in *any* case. */
> -	u64 fe_ptr, bg_ptr, prev_bg_ptr;
> +	u64 bg_ptr, prev_bg_ptr;
>  	struct ocfs2_dinode *fe = (struct ocfs2_dinode *) fe_bh->b_data;
>  	struct ocfs2_group_desc *bg = (struct ocfs2_group_desc *) bg_bh->b_data;
>  	struct ocfs2_group_desc *prev_bg = (struct ocfs2_group_desc *) prev_bg_bh->b_data;
> @@ -1437,7 +1437,6 @@ static int ocfs2_relink_block_group(handle_t *handle,
>  		(unsigned long long)le64_to_cpu(bg->bg_blkno),
>  		(unsigned long long)le64_to_cpu(prev_bg->bg_blkno));
>  
> -	fe_ptr = le64_to_cpu(fe->id2.i_chain.cl_recs[chain].c_blkno);
>  	bg_ptr = le64_to_cpu(bg->bg_next_group);
>  	prev_bg_ptr = le64_to_cpu(prev_bg->bg_next_group);
>  
> @@ -1446,7 +1445,7 @@ static int ocfs2_relink_block_group(handle_t *handle,
>  					 OCFS2_JOURNAL_ACCESS_WRITE);
>  	if (status < 0) {
>  		mlog_errno(status);
> -		goto out_rollback;
> +		goto out;
>  	}
>  
>  	prev_bg->bg_next_group = bg->bg_next_group;
> @@ -1456,7 +1455,7 @@ static int ocfs2_relink_block_group(handle_t *handle,
>  					 bg_bh, OCFS2_JOURNAL_ACCESS_WRITE);
>  	if (status < 0) {
>  		mlog_errno(status);
> -		goto out_rollback;
> +		goto out_rollback_prev_bg;
>  	}
>  
>  	bg->bg_next_group = fe->id2.i_chain.cl_recs[chain].c_blkno;
> @@ -1466,21 +1465,21 @@ static int ocfs2_relink_block_group(handle_t *handle,
>  					 fe_bh, OCFS2_JOURNAL_ACCESS_WRITE);
>  	if (status < 0) {
>  		mlog_errno(status);
> -		goto out_rollback;
> +		goto out_rollback_bg;
>  	}
>  
>  	fe->id2.i_chain.cl_recs[chain].c_blkno = bg->bg_blkno;
>  	ocfs2_journal_dirty(handle, fe_bh);
>  
> -out_rollback:
> -	if (status < 0) {
> -		fe->id2.i_chain.cl_recs[chain].c_blkno = cpu_to_le64(fe_ptr);
> -		bg->bg_next_group = cpu_to_le64(bg_ptr);
> -		prev_bg->bg_next_group = cpu_to_le64(prev_bg_ptr);
> -	}
> +out:
> +	return status;
>  
> -	if (status)
> -		mlog_errno(status);
> +out_rollback_bg:
> +	bg->bg_next_group = cpu_to_le64(bg_ptr);
> +out_rollback_prev_bg:
> +	prev_bg->bg_next_group = cpu_to_le64(prev_bg_ptr);
> +
> +	mlog_errno(status);

We already called mlog_errno() for this status in all cases.

How does this look?

--- a/fs/ocfs2/suballoc.c~ocfs2-rework-transaction-rollback-in-ocfs2_relink_block_group-fix
+++ a/fs/ocfs2/suballoc.c
@@ -1443,44 +1443,38 @@ static int ocfs2_relink_block_group(hand
 	status = ocfs2_journal_access_gd(handle, INODE_CACHE(alloc_inode),
 					 prev_bg_bh,
 					 OCFS2_JOURNAL_ACCESS_WRITE);
-	if (status < 0) {
-		mlog_errno(status);
+	if (status < 0)
 		goto out;
-	}
 
 	prev_bg->bg_next_group = bg->bg_next_group;
 	ocfs2_journal_dirty(handle, prev_bg_bh);
 
 	status = ocfs2_journal_access_gd(handle, INODE_CACHE(alloc_inode),
 					 bg_bh, OCFS2_JOURNAL_ACCESS_WRITE);
-	if (status < 0) {
-		mlog_errno(status);
+	if (status < 0)
 		goto out_rollback_prev_bg;
-	}
 
 	bg->bg_next_group = fe->id2.i_chain.cl_recs[chain].c_blkno;
 	ocfs2_journal_dirty(handle, bg_bh);
 
 	status = ocfs2_journal_access_di(handle, INODE_CACHE(alloc_inode),
 					 fe_bh, OCFS2_JOURNAL_ACCESS_WRITE);
-	if (status < 0) {
-		mlog_errno(status);
+	if (status < 0)
 		goto out_rollback_bg;
-	}
 
 	fe->id2.i_chain.cl_recs[chain].c_blkno = bg->bg_blkno;
 	ocfs2_journal_dirty(handle, fe_bh);
 
 out:
+	if (status < 0)
+		mlog_errno(status);
 	return status;
 
 out_rollback_bg:
 	bg->bg_next_group = cpu_to_le64(bg_ptr);
 out_rollback_prev_bg:
 	prev_bg->bg_next_group = cpu_to_le64(prev_bg_ptr);
-
-	mlog_errno(status);
-	return status;
+	goto out;
 }


btw, the ocfs2 source and executable cold be made about half the size if
mlog_errno() were to immediately return if status>=0.