XArray: Fix splitting to non-zero orders

Splitting an order-4 entry into order-2 entries would leave the array
containing pointers to 000040008000c000 instead of 000044448888cccc.
This is a one-character fix, but enhance the test suite to check this
case.
Reported-by: Zi Yan <ziy@nvidia.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

lib/test_xarray.c

@@ -1530,24 +1530,24 @@ static noinline void check_store_range(struct xarray *xa)
 
 #ifdef CONFIG_XARRAY_MULTI
 static void check_split_1(struct xarray *xa, unsigned long index,
-							unsigned int order)
+				unsigned int order, unsigned int new_order)
 {
-	XA_STATE(xas, xa, index);
-	void *entry;
-	unsigned int i = 0;
+	XA_STATE_ORDER(xas, xa, index, new_order);
+	unsigned int i;
 
 	xa_store_order(xa, index, order, xa, GFP_KERNEL);
 
 	xas_split_alloc(&xas, xa, order, GFP_KERNEL);
 	xas_lock(&xas);
 	xas_split(&xas, xa, order);
+	for (i = 0; i < (1 << order); i += (1 << new_order))
+		__xa_store(xa, index + i, xa_mk_index(index + i), 0);
 	xas_unlock(&xas);
 
-	xa_for_each(xa, index, entry) {
-		XA_BUG_ON(xa, entry != xa);
-		i++;
+	for (i = 0; i < (1 << order); i++) {
+		unsigned int val = index + (i & ~((1 << new_order) - 1));
+		XA_BUG_ON(xa, xa_load(xa, index + i) != xa_mk_index(val));
 	}
-	XA_BUG_ON(xa, i != 1 << order);
 
 	xa_set_mark(xa, index, XA_MARK_0);
 	XA_BUG_ON(xa, !xa_get_mark(xa, index, XA_MARK_0));
@@ -1557,14 +1557,16 @@ static void check_split_1(struct xarray *xa, unsigned long index,
 
 static noinline void check_split(struct xarray *xa)
 {
-	unsigned int order;
+	unsigned int order, new_order;
 
 	XA_BUG_ON(xa, !xa_empty(xa));
 
 	for (order = 1; order < 2 * XA_CHUNK_SHIFT; order++) {
-		check_split_1(xa, 0, order);
-		check_split_1(xa, 1UL << order, order);
-		check_split_1(xa, 3UL << order, order);
+		for (new_order = 0; new_order < order; new_order++) {
+			check_split_1(xa, 0, order, new_order);
+			check_split_1(xa, 1UL << order, order, new_order);
+			check_split_1(xa, 3UL << order, order, new_order);
+		}
 	}
 }
 #else

lib/xarray.c

@@ -1011,7 +1011,7 @@ void xas_split_alloc(struct xa_state *xas, void *entry, unsigned int order,
 
 	do {
 		unsigned int i;
-		void *sibling;
+		void *sibling = NULL;
 		struct xa_node *node;
 
 		node = kmem_cache_alloc(radix_tree_node_cachep, gfp);
@@ -1021,7 +1021,7 @@ void xas_split_alloc(struct xa_state *xas, void *entry, unsigned int order,
 		for (i = 0; i < XA_CHUNK_SIZE; i++) {
 			if ((i & mask) == 0) {
 				RCU_INIT_POINTER(node->slots[i], entry);
-				sibling = xa_mk_sibling(0);
+				sibling = xa_mk_sibling(i);
 			} else {
 				RCU_INIT_POINTER(node->slots[i], sibling);
 			}