xfs: fix the minrecs logic when dealing with inode root child blocks

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.

Fixes: 08a3a69 ("xfs: btree scrub should check minrecs")
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Chandan Babu R <chandanrlinux@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

Author: djwong

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);
 }
 
 /*