Re: [PATCH 2/4] xfs: fix the minrecs logic when dealing with inode root child blocks

[Chandan Babu R <chandanrlinux@gmail.com>]

On Monday 9 November 2020 11:47:45 PM IST Darrick J. Wong wrote:
> From: Darrick J. Wong <darrick.wong@oracle.com>
> 
> The comment and logic in xchk_btree_check_minrecs for dealing with
> inode-rooted btrees isn't quite correct.  While the direct children of
> the inode root are allowed to have fewer records than what would
> normally be allowed for a regular ondisk btree block, this is only true
> if there is only one child block and the number of records don't fit in
> the inode root.
>

The code changes are consistent with rules provided in the comments.

Reviewed-by: Chandan Babu R <chandanrlinux@gmail.com>

> Fixes: 08a3a692ef58 ("xfs: btree scrub should check minrecs")
> Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> ---
>  fs/xfs/scrub/btree.c |   45 +++++++++++++++++++++++++++------------------
>  1 file changed, 27 insertions(+), 18 deletions(-)
> 
> 
> diff --git a/fs/xfs/scrub/btree.c b/fs/xfs/scrub/btree.c
> index f52a7b8256f9..debf392e0515 100644
> --- a/fs/xfs/scrub/btree.c
> +++ b/fs/xfs/scrub/btree.c
> @@ -452,32 +452,41 @@ xchk_btree_check_minrecs(
>  	int			level,
>  	struct xfs_btree_block	*block)
>  {
> -	unsigned int		numrecs;
> -	int			ok_level;
> -
> -	numrecs = be16_to_cpu(block->bb_numrecs);
> +	struct xfs_btree_cur	*cur = bs->cur;
> +	unsigned int		root_level = cur->bc_nlevels - 1;
> +	unsigned int		numrecs = be16_to_cpu(block->bb_numrecs);
>  
>  	/* More records than minrecs means the block is ok. */
> -	if (numrecs >= bs->cur->bc_ops->get_minrecs(bs->cur, level))
> +	if (numrecs >= cur->bc_ops->get_minrecs(cur, level))
>  		return;
>  
>  	/*
> -	 * Certain btree blocks /can/ have fewer than minrecs records.  Any
> -	 * level greater than or equal to the level of the highest dedicated
> -	 * btree block are allowed to violate this constraint.
> -	 *
> -	 * For a btree rooted in a block, the btree root can have fewer than
> -	 * minrecs records.  If the btree is rooted in an inode and does not
> -	 * store records in the root, the direct children of the root and the
> -	 * root itself can have fewer than minrecs records.
> +	 * For btrees rooted in the inode, it's possible that the root block
> +	 * contents spilled into a regular ondisk block because there wasn't
> +	 * enough space in the inode root.  The number of records in that
> +	 * child block might be less than the standard minrecs, but that's ok
> +	 * provided that there's only one direct child of the root.
>  	 */
> -	ok_level = bs->cur->bc_nlevels - 1;
> -	if (bs->cur->bc_flags & XFS_BTREE_ROOT_IN_INODE)
> -		ok_level--;
> -	if (level >= ok_level)
> +	if ((cur->bc_flags & XFS_BTREE_ROOT_IN_INODE) &&
> +	    level == cur->bc_nlevels - 2) {
> +		struct xfs_btree_block	*root_block;
> +		struct xfs_buf		*root_bp;
> +		int			root_maxrecs;
> +
> +		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)
> +			xchk_btree_set_corrupt(bs->sc, cur, level);
>  		return;
> +	}
>  
> -	xchk_btree_set_corrupt(bs->sc, bs->cur, level);
> +	/*
> +	 * Otherwise, only the root level is allowed to have fewer than minrecs
> +	 * records or keyptrs.
> +	 */
> +	if (level < root_level)
> +		xchk_btree_set_corrupt(bs->sc, cur, level);
>  }
>  
>  /*
> 
> 


-- 
chandan