Re: [PATCH V2] xfs: scrub: Disable check for unoptimized data fork bmbt node

["Darrick J. Wong" <djwong@kernel.org>]

On Tue, Apr 06, 2021 at 12:25:19PM +0530, Chandan Babu R wrote:
> xchk_btree_check_minrecs() checks if the contents of the immediate child of a
> bmbt root block can fit within the root block. This check could fail on inodes
> with an attr fork since xfs_bmap_add_attrfork_btree() used to demote the
> current root node of the data fork as the child of a newly allocated root node
> if it found that the size of "struct xfs_btree_block" along with the space
> required for records exceeded that of space available in the data fork.
> 
> xfs_bmap_add_attrfork_btree() should have used "struct xfs_bmdr_block" instead
> of "struct xfs_btree_block" for the above mentioned space requirement
> calculation. This commit disables the check for unoptimized (in terms of
> disk space usage) data fork bmbt trees since there could be filesystems
> in use that already have such a layout.
> 
> Suggested-by: Darrick J. Wong <djwong@kernel.org>
> Signed-off-by: Chandan Babu R <chandanrlinux@gmail.com>

Looks good!
Reviewed-by: Darrick J. Wong <djwong@kernel.org>

--D

> ---
> Changelog:
>  V1 -> V2:
>    1. Apply "minimum records check" restriction only to BMBT btrees.
>    
>  fs/xfs/scrub/btree.c | 30 ++++++++++++++++++++++++++++--
>  1 file changed, 28 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/xfs/scrub/btree.c b/fs/xfs/scrub/btree.c
> index debf392e0515..a94bd8122c60 100644
> --- a/fs/xfs/scrub/btree.c
> +++ b/fs/xfs/scrub/btree.c
> @@ -9,6 +9,7 @@
>  #include "xfs_format.h"
>  #include "xfs_trans_resv.h"
>  #include "xfs_mount.h"
> +#include "xfs_inode.h"
>  #include "xfs_btree.h"
>  #include "scrub/scrub.h"
>  #include "scrub/common.h"
> @@ -442,6 +443,30 @@ xchk_btree_check_owner(
>  	return xchk_btree_check_block_owner(bs, level, XFS_BUF_ADDR(bp));
>  }
>  
> +/* Decide if we want to check minrecs of a btree block in the inode root. */
> +static inline bool
> +xchk_btree_check_iroot_minrecs(
> +	struct xchk_btree	*bs)
> +{
> +	/*
> +	 * xfs_bmap_add_attrfork_btree had an implementation bug wherein it
> +	 * would miscalculate the space required for the data fork bmbt root
> +	 * when adding an attr fork, and promote the iroot contents to an
> +	 * external block unnecessarily.  This went unnoticed for many years
> +	 * until scrub found filesystems in this state.  Inode rooted btrees are
> +	 * not supposed to have immediate child blocks that are small enough
> +	 * that the contents could fit in the inode root, but we can't fail
> +	 * existing filesystems, so instead we disable the check for data fork
> +	 * bmap btrees when there's an attr fork.
> +	 */
> +	if (bs->cur->bc_btnum == XFS_BTNUM_BMAP &&
> +	    bs->cur->bc_ino.whichfork == XFS_DATA_FORK &&
> +	    XFS_IFORK_Q(bs->sc->ip))
> +		return false;
> +
> +	return true;
> +}
> +
>  /*
>   * Check that this btree block has at least minrecs records or is one of the
>   * special blocks that don't require that.
> @@ -475,8 +500,9 @@ xchk_btree_check_minrecs(
>  
>  		root_block = xfs_btree_get_block(cur, root_level, &root_bp);
>  		root_maxrecs = cur->bc_ops->get_dmaxrecs(cur, root_level);
> -		if (be16_to_cpu(root_block->bb_numrecs) != 1 ||
> -		    numrecs <= root_maxrecs)
> +		if (xchk_btree_check_iroot_minrecs(bs) &&
> +		    (be16_to_cpu(root_block->bb_numrecs) != 1 ||
> +		     numrecs <= root_maxrecs))
>  			xchk_btree_set_corrupt(bs->sc, cur, level);
>  		return;
>  	}
> -- 
> 2.29.2
>