XArray: Fix xas_find returning too many entries

If you call xas_find() with the initial index > max, it should have
returned NULL but was returning the entry at index.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: stable@vger.kernel.org
diff --git a/lib/test_xarray.c b/lib/test_xarray.c
index c8cc97d..55c14e8 100644
--- a/lib/test_xarray.c
+++ b/lib/test_xarray.c
@@ -2,6 +2,7 @@
 /*
  * test_xarray.c: Test the XArray API
  * Copyright (c) 2017-2018 Microsoft Corporation
+ * Copyright (c) 2019-2020 Oracle
  * Author: Matthew Wilcox <willy@infradead.org>
  */
 
@@ -911,6 +912,7 @@ static noinline void check_multi_find_1(struct xarray *xa, unsigned order)
 
 	xa_store_order(xa, multi, order, xa_mk_value(multi), GFP_KERNEL);
 	XA_BUG_ON(xa, xa_store_index(xa, next, GFP_KERNEL) != NULL);
+	XA_BUG_ON(xa, xa_store_index(xa, next + 1, GFP_KERNEL) != NULL);
 
 	index = 0;
 	XA_BUG_ON(xa, xa_find(xa, &index, ULONG_MAX, XA_PRESENT) !=
@@ -923,9 +925,12 @@ static noinline void check_multi_find_1(struct xarray *xa, unsigned order)
 	XA_BUG_ON(xa, xa_find_after(xa, &index, ULONG_MAX, XA_PRESENT) !=
 			xa_mk_value(next));
 	XA_BUG_ON(xa, index != next);
+	XA_BUG_ON(xa, xa_find_after(xa, &index, next, XA_PRESENT) != NULL);
+	XA_BUG_ON(xa, index != next);
 
 	xa_erase_index(xa, multi);
 	xa_erase_index(xa, next);
+	xa_erase_index(xa, next + 1);
 	XA_BUG_ON(xa, !xa_empty(xa));
 #endif
 }