Re: [PATCH] xfs: fix node forward in xfs_node_toosmall

[Dave Chinner <david@fromorbit.com>]

On Fri, Sep 20, 2013 at 05:05:08PM -0500, Mark Tinguely wrote:
> Commit f5ea1100 cleans up the disk to host conversions for
> node directory entries, but because a variable is reused in
> xfs_node_toosmall() the next node is not correctly found.
> If the original node is small enough (<= 3/8 of the node size),
> this change may incorrectly cause a node collapse when it should
> not. That will cause an assert in xfstest generic/319:
> 
>    Assertion failed: first <= last && last < BBTOB(bp->b_length),
>    file: /root/newest/xfs/fs/xfs/xfs_trans_buf.c, line: 569
> 
> Keep the original node header to get the correct forward node.
> 
> Signed-off-by: Mark Tinguely <tinguely@sgi.com>
> ---
>  fs/xfs/xfs_da_btree.c |    6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> Index: b/fs/xfs/xfs_da_btree.c
> ===================================================================
> --- a/fs/xfs/xfs_da_btree.c
> +++ b/fs/xfs/xfs_da_btree.c
> @@ -1163,6 +1163,7 @@ xfs_da3_node_toosmall(
>  	xfs_dablk_t		blkno;
>  	struct xfs_buf		*bp;
>  	struct xfs_da3_icnode_hdr nodehdr;
> +	struct xfs_da3_icnode_hdr firstnhdr;
>  	int			count;
>  	int			forward;
>  	int			error;
> @@ -1221,13 +1222,14 @@ xfs_da3_node_toosmall(
>  	count -= state->node_ents >> 2;
>  	count -= nodehdr.count;
>  
> +	firstnhdr = nodehdr;
>  	/* start with smaller blk num */
>  	forward = nodehdr.forw < nodehdr.back;
>  	for (i = 0; i < 2; forward = !forward, i++) {
>  		if (forward)
> -			blkno = nodehdr.forw;
> +			blkno = firstnhdr.forw;
>  		else
> -			blkno = nodehdr.back;
> +			blkno = firstnhdr.back;
>  		if (blkno == 0)
>  			continue;
>  		error = xfs_da3_node_read(state->args->trans, state->args->dp,

Yes, that definitely a bug, but I think that the change doesn't
scope correctly. The original node header doesn't need to be saved
like this - the node header decoded in the loop needs a loop-scope
variable. i.e.:

	/* start with smaller blk num */
	forward = nodehdr.forw < nodehdr.back;
	for (i = 0; i < 2; forward = !forward, i++) {
+		struct xfs_da3_icnode_hdr thdr;
+
		if (forward)
			blkno = nodehdr.forw;
		else
			blkno = nodehdr.back;
		if (blkno == 0)
			continue;
		error = xfs_da3_node_read(state->args->trans, state->args->dp,
					blkno, -1, &bp, state->args->whichfork);
		if (error)
			return(error);

		node = bp->b_addr;
-		xfs_da3_node_hdr_from_disk(&nodehdr, node);
+		xfs_da3_node_hdr_from_disk(&thdr, node);
		xfs_trans_brelse(state->args->trans, bp);

-		if (count - nodehdr.count >= 0)
+		if (count - thdr.count >= 0)
			break;  /* fits with at least 25% to spare */
	}

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com

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