1 files 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;
 	}