XArray: Test two more things about xa_cmpxchg

1. If we xa_cmpxchg() an entry in, it marks the index as not free.
2. If we xa_cmpxchg() NULL in, it marks the index as free.
Signed-off-by: NMatthew Wilcox (Oracle) <willy@infradead.org>

lib/test_xarray.c

@@ -393,6 +393,9 @@ static noinline void check_cmpxchg(struct xarray *xa)
 	XA_BUG_ON(xa, xa_cmpxchg(xa, 12345678, FIVE, LOTS, GFP_KERNEL) != FIVE);
 	XA_BUG_ON(xa, xa_cmpxchg(xa, 5, FIVE, NULL, GFP_KERNEL) != NULL);
 	XA_BUG_ON(xa, xa_cmpxchg(xa, 5, NULL, FIVE, GFP_KERNEL) != NULL);
+	XA_BUG_ON(xa, xa_insert(xa, 5, FIVE, GFP_KERNEL) != -EBUSY);
+	XA_BUG_ON(xa, xa_cmpxchg(xa, 5, FIVE, NULL, GFP_KERNEL) != FIVE);
+	XA_BUG_ON(xa, xa_insert(xa, 5, FIVE, GFP_KERNEL) == -EBUSY);
 	xa_erase_index(xa, 12345678);
 	xa_erase_index(xa, 5);
 	XA_BUG_ON(xa, !xa_empty(xa));