radix-tree: move declarations to header

The xarray.c file contains the only call to radix_tree_node_rcu_free(),
and it comes with its own extern declaration for it.  This means the
function definition causes a missing-prototype warning:

lib/radix-tree.c:288:6: error: no previous prototype for 'radix_tree_node_rcu_free' [-Werror=missing-prototypes]

Instead, move the declaration for this function to a new header that can
be included by both, and do the same for the radix_tree_node_cachep
variable that has the same underlying problem but does not cause a warning
with gcc.

[zhangpeng.00@bytedance.com: fix building radix tree test suite]
  Link: https://lkml.kernel.org/r/20230521095450.21332-1-zhangpeng.00@bytedance.com
Link: https://lkml.kernel.org/r/20230516194212.548910-1-arnd@kernel.org
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

Author: arndb

lib/radix-tree.c

@@ -27,6 +27,8 @@
 #include <linux/string.h>
 #include <linux/xarray.h>
 
+#include "radix-tree.h"
+
 /*
  * Radix tree node cache.
  */

lib/radix-tree.h

@@ -0,0 +1,8 @@
+// SPDX-License-Identifier: GPL-2.0+
+/* radix-tree helpers that are only shared with xarray */
+
+struct kmem_cache;
+struct rcu_head;
+
+extern struct kmem_cache *radix_tree_node_cachep;
+extern void radix_tree_node_rcu_free(struct rcu_head *head);

lib/xarray.c

@@ -12,6 +12,8 @@
 #include <linux/slab.h>
 #include <linux/xarray.h>
 
+#include "radix-tree.h"
+
 /*
  * Coding conventions in this file:
  *
@@ -247,10 +249,6 @@ void *xas_load(struct xa_state *xas)
 }
 EXPORT_SYMBOL_GPL(xas_load);
 
-/* Move the radix tree node cache here */
-extern struct kmem_cache *radix_tree_node_cachep;
-extern void radix_tree_node_rcu_free(struct rcu_head *head);
-
 #define XA_RCU_FREE	((struct xarray *)1)
 
 static void xa_node_free(struct xa_node *node)

tools/testing/radix-tree/Makefile

@@ -1,7 +1,7 @@
 # SPDX-License-Identifier: GPL-2.0
 
-CFLAGS += -I. -I../../include -g -Og -Wall -D_LGPL_SOURCE -fsanitize=address \
-	  -fsanitize=undefined
+CFLAGS += -I. -I../../include -I../../../lib -g -Og -Wall \
+	  -D_LGPL_SOURCE -fsanitize=address -fsanitize=undefined
 LDFLAGS += -fsanitize=address -fsanitize=undefined
 LDLIBS+= -lpthread -lurcu
 TARGETS = main idr-test multiorder xarray maple
@@ -49,6 +49,7 @@ $(OFILES): Makefile *.h */*.h generated/map-shift.h generated/bit-length.h \
 	../../../include/linux/xarray.h \
 	../../../include/linux/maple_tree.h \
 	../../../include/linux/radix-tree.h \
+	../../../lib/radix-tree.h \
 	../../../include/linux/idr.h
 
 radix-tree.c: ../../../lib/radix-tree.c