Re: [PATCH 6/9] xfs: refactor unlinked list search and mapping to a separate function

[Brian Foster <bfoster@redhat.com>]

On Wed, Feb 06, 2019 at 08:55:17AM -0800, Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> There's a loop that searches an unlinked bucket list to find the inode
> that points to a given inode.  Hoist this into a separate function;
> later we'll use our iunlink backref cache to bypass the slow list
> operation.  No functional changes.
> 
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/xfs/xfs_inode.c |  135 +++++++++++++++++++++++++++++++++++++---------------
>  1 file changed, 96 insertions(+), 39 deletions(-)
> 
> 
> diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
> index eb51fa33f91a..161d8da459aa 100644
> --- a/fs/xfs/xfs_inode.c
> +++ b/fs/xfs/xfs_inode.c
> @@ -2082,6 +2082,96 @@ xfs_iunlink(
>  	return xfs_iunlink_update_bucket(tp, agno, agibp, bucket_index, agino);
>  }
>  
...
> +STATIC int
> +xfs_iunlink_map_prev(
> +	struct xfs_trans	*tp,
> +	xfs_agnumber_t		agno,
> +	xfs_agino_t		head_agino,
> +	xfs_agino_t		target_agino,
> +	xfs_agino_t		*agino,
> +	struct xfs_imap		*imap,
> +	struct xfs_dinode	**dipp,
> +	struct xfs_buf		**bpp)
> +{
> +	struct xfs_mount	*mp = tp->t_mountp;
> +	xfs_agino_t		next_agino;
> +	int			error;
> +
> +	ASSERT(head_agino != target_agino);
> +
> +	next_agino = head_agino;
> +	while (next_agino != target_agino) {
> +		xfs_agino_t	unlinked_agino;
> +
> +		if (*bpp)
> +			xfs_trans_brelse(tp, *bpp);

Just because we have this check here, it might be appropriate to set
*bpp to NULL at the start of this function. Otherwise looks fine:

Reviewed-by: Brian Foster <bfoster@redhat.com>

> +
> +		*agino = next_agino;
> +		error = xfs_iunlink_map_ino(tp, agno, next_agino, imap, dipp,
> +				bpp);
> +		if (error)
> +			return error;
> +
> +		unlinked_agino = be32_to_cpu((*dipp)->di_next_unlinked);
> +		/*
> +		 * Make sure this pointer is valid and isn't an obvious
> +		 * infinite loop.
> +		 */
> +		if (!xfs_verify_agino(mp, agno, unlinked_agino) ||
> +		    next_agino == unlinked_agino) {
> +			XFS_CORRUPTION_ERROR(__func__,
> +					XFS_ERRLEVEL_LOW, mp,
> +					*dipp, sizeof(**dipp));
> +			error = -EFSCORRUPTED;
> +			return error;
> +		}
> +		next_agino = unlinked_agino;
> +	}
> +
> +	return 0;
> +}
> +
>  /*
>   * Pull the on-disk inode from the AGI unlinked list.
>   */
> @@ -2093,9 +2183,8 @@ xfs_iunlink_remove(
>  	struct xfs_mount	*mp = tp->t_mountp;
>  	struct xfs_agi		*agi;
>  	struct xfs_buf		*agibp;
> -	struct xfs_buf		*last_ibp;
> +	struct xfs_buf		*last_ibp = NULL;
>  	struct xfs_dinode	*last_dip = NULL;
> -	xfs_ino_t		next_ino;
>  	xfs_agnumber_t		agno = XFS_INO_TO_AGNO(mp, ip->i_ino);
>  	xfs_agino_t		agino = XFS_INO_TO_AGINO(mp, ip->i_ino);
>  	xfs_agino_t		next_agino;
> @@ -2138,43 +2227,11 @@ xfs_iunlink_remove(
>  		struct xfs_imap	imap;
>  		xfs_agino_t	prev_agino;
>  
> -		/*
> -		 * We need to search the list for the inode being freed.
> -		 */
> -		last_ibp = NULL;
> -		while (next_agino != agino) {
> -			if (last_ibp)
> -				xfs_trans_brelse(tp, last_ibp);
> -
> -			imap.im_blkno = 0;
> -			next_ino = XFS_AGINO_TO_INO(mp, agno, next_agino);
> -
> -			error = xfs_imap(mp, tp, next_ino, &imap, 0);
> -			if (error) {
> -				xfs_warn(mp,
> -	"%s: xfs_imap returned error %d.",
> -					 __func__, error);
> -				return error;
> -			}
> -
> -			error = xfs_imap_to_bp(mp, tp, &imap, &last_dip,
> -					       &last_ibp, 0, 0);
> -			if (error) {
> -				xfs_warn(mp,
> -	"%s: xfs_imap_to_bp returned error %d.",
> -					__func__, error);
> -				return error;
> -			}
> -
> -			prev_agino = next_agino;
> -			next_agino = be32_to_cpu(last_dip->di_next_unlinked);
> -			if (!xfs_verify_agino(mp, agno, next_agino)) {
> -				XFS_CORRUPTION_ERROR(__func__,
> -						XFS_ERRLEVEL_LOW, mp,
> -						last_dip, sizeof(*last_dip));
> -				return -EFSCORRUPTED;
> -			}
> -		}
> +		/* We need to search the list for the inode being freed. */
> +		error = xfs_iunlink_map_prev(tp, agno, next_agino, agino,
> +				&prev_agino, &imap, &last_dip, &last_ibp);
> +		if (error)
> +			return error;
>  
>  		/*
>  		 * Now last_ibp points to the buffer previous to us on the
>