xarray: Destroy an XArray

This function frees all the internal memory allocated to the xarray
and reinitialises it to be empty.

Signed-off-by: Matthew Wilcox <willy@infradead.org>

include/linux/xarray.h

@@ -286,6 +286,7 @@ void *xa_find_after(struct xarray *xa, unsigned long *index,
 		unsigned long max, xa_mark_t) __attribute__((nonnull(2)));
 unsigned int xa_extract(struct xarray *, void **dst, unsigned long start,
 		unsigned long max, unsigned int n, xa_mark_t);
+void xa_destroy(struct xarray *);
 
 /**
  * xa_init() - Initialise an empty XArray.

lib/test_xarray.c

@@ -465,6 +465,39 @@ static noinline void check_find(struct xarray *xa)
 	check_multi_find_2(xa);
 }
 
+static noinline void check_destroy(struct xarray *xa)
+{
+	unsigned long index;
+
+	XA_BUG_ON(xa, !xa_empty(xa));
+
+	/* Destroying an empty array is a no-op */
+	xa_destroy(xa);
+	XA_BUG_ON(xa, !xa_empty(xa));
+
+	/* Destroying an array with a single entry */
+	for (index = 0; index < 1000; index++) {
+		xa_store_index(xa, index, GFP_KERNEL);
+		XA_BUG_ON(xa, xa_empty(xa));
+		xa_destroy(xa);
+		XA_BUG_ON(xa, !xa_empty(xa));
+	}
+
+	/* Destroying an array with a single entry at ULONG_MAX */
+	xa_store(xa, ULONG_MAX, xa, GFP_KERNEL);
+	XA_BUG_ON(xa, xa_empty(xa));
+	xa_destroy(xa);
+	XA_BUG_ON(xa, !xa_empty(xa));
+
+#ifdef CONFIG_XARRAY_MULTI
+	/* Destroying an array with a multi-index entry */
+	xa_store_order(xa, 1 << 11, 11, xa, GFP_KERNEL);
+	XA_BUG_ON(xa, xa_empty(xa));
+	xa_destroy(xa);
+	XA_BUG_ON(xa, !xa_empty(xa));
+#endif
+}
+
 static DEFINE_XARRAY(array);
 
 static int xarray_checks(void)
@@ -478,6 +511,7 @@ static int xarray_checks(void)
 	check_cmpxchg(&array);
 	check_multi_store(&array);
 	check_find(&array);
+	check_destroy(&array);
 
 	printk("XArray: %u of %u tests passed\n", tests_passed, tests_run);
 	return (tests_run == tests_passed) ? 0 : -EINVAL;

lib/xarray.c

@@ -1524,6 +1524,34 @@ unsigned int xa_extract(struct xarray *xa, void **dst, unsigned long start,
 }
 EXPORT_SYMBOL(xa_extract);
 
+/**
+ * xa_destroy() - Free all internal data structures.
+ * @xa: XArray.
+ *
+ * After calling this function, the XArray is empty and has freed all memory
+ * allocated for its internal data structures.  You are responsible for
+ * freeing the objects referenced by the XArray.
+ *
+ * Context: Any context.  Takes and releases the xa_lock, interrupt-safe.
+ */
+void xa_destroy(struct xarray *xa)
+{
+	XA_STATE(xas, xa, 0);
+	unsigned long flags;
+	void *entry;
+
+	xas.xa_node = NULL;
+	xas_lock_irqsave(&xas, flags);
+	entry = xa_head_locked(xa);
+	RCU_INIT_POINTER(xa->xa_head, NULL);
+	xas_init_marks(&xas);
+	/* lockdep checks we're still holding the lock in xas_free_nodes() */
+	if (xa_is_node(entry))
+		xas_free_nodes(&xas, xa_to_node(entry));
+	xas_unlock_irqrestore(&xas, flags);
+}
+EXPORT_SYMBOL(xa_destroy);
+
 #ifdef XA_DEBUG
 void xa_dump_node(const struct xa_node *node)
 {