perf maps: Add maps__refcnt() accessor to allow checking maps pointer

To remove one more direct access to 'struct maps' so that we can
intercept accesses to its instantiations and refcount check it to catch
use after free, etc.
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/perf/tests/thread-maps-share.c

@@ -43,7 +43,7 @@ static int test__thread_maps_share(struct test_suite *test __maybe_unused, int s
 			leader && t1 && t2 && t3 && other);
 
 	maps = leader->maps;
-	TEST_ASSERT_EQUAL("wrong refcnt", refcount_read(&maps->refcnt), 4);
+	TEST_ASSERT_EQUAL("wrong refcnt", refcount_read(maps__refcnt(maps)), 4);
 
 	/* test the maps pointer is shared */
 	TEST_ASSERT_VAL("maps don't match", maps == t1->maps);
@@ -71,25 +71,25 @@ static int test__thread_maps_share(struct test_suite *test __maybe_unused, int s
 	machine__remove_thread(machine, other_leader);
 
 	other_maps = other->maps;
-	TEST_ASSERT_EQUAL("wrong refcnt", refcount_read(&other_maps->refcnt), 2);
+	TEST_ASSERT_EQUAL("wrong refcnt", refcount_read(maps__refcnt(other_maps)), 2);
 
 	TEST_ASSERT_VAL("maps don't match", other_maps == other_leader->maps);
 
 	/* release thread group */
 	thread__put(leader);
-	TEST_ASSERT_EQUAL("wrong refcnt", refcount_read(&maps->refcnt), 3);
+	TEST_ASSERT_EQUAL("wrong refcnt", refcount_read(maps__refcnt(maps)), 3);
 
 	thread__put(t1);
-	TEST_ASSERT_EQUAL("wrong refcnt", refcount_read(&maps->refcnt), 2);
+	TEST_ASSERT_EQUAL("wrong refcnt", refcount_read(maps__refcnt(maps)), 2);
 
 	thread__put(t2);
-	TEST_ASSERT_EQUAL("wrong refcnt", refcount_read(&maps->refcnt), 1);
+	TEST_ASSERT_EQUAL("wrong refcnt", refcount_read(maps__refcnt(maps)), 1);
 
 	thread__put(t3);
 
 	/* release other group  */
 	thread__put(other_leader);
-	TEST_ASSERT_EQUAL("wrong refcnt", refcount_read(&other_maps->refcnt), 1);
+	TEST_ASSERT_EQUAL("wrong refcnt", refcount_read(maps__refcnt(other_maps)), 1);
 
 	thread__put(other);
 

tools/perf/util/maps.c

@@ -12,13 +12,13 @@
 
 static void maps__init(struct maps *maps, struct machine *machine)
 {
+	refcount_set(maps__refcnt(maps), 1);
 	maps->entries = RB_ROOT;
 	init_rwsem(maps__lock(maps));
 	maps->machine = machine;
 	maps->last_search_by_name = NULL;
 	maps->nr_maps = 0;
 	maps->maps_by_name = NULL;
-	refcount_set(&maps->refcnt, 1);
 }
 
 static void __maps__free_maps_by_name(struct maps *maps)
@@ -180,14 +180,14 @@ void maps__delete(struct maps *maps)
 struct maps *maps__get(struct maps *maps)
 {
 	if (maps)
-		refcount_inc(&maps->refcnt);
+		refcount_inc(maps__refcnt(maps));
 
 	return maps;
 }
 
 void maps__put(struct maps *maps)
 {
-	if (maps && refcount_dec_and_test(&maps->refcnt))
+	if (maps && refcount_dec_and_test(maps__refcnt(maps)))
 		maps__delete(maps);
 }
 

tools/perf/util/maps.h

@@ -88,6 +88,11 @@ static inline unsigned int maps__nr_maps(const struct maps *maps)
 	return maps->nr_maps;
 }
 
+static inline refcount_t *maps__refcnt(struct maps *maps)
+{
+	return &maps->refcnt;
+}
+
 #ifdef HAVE_LIBUNWIND_SUPPORT
 static inline void *maps__addr_space(struct maps *maps)
 {