perf maps: Locking tidy up of nr_maps

After this change maps__nr_maps is only used by tests, existing users
are migrated to maps__empty. Compute maps__empty under the read lock.

Signed-off-by: Ian Rogers <[e-mail]>
Acked-by: Namhyung Kim <[e-mail]>
Cc: K Prateek Nayak <[e-mail]>
Cc: James Clark <[e-mail]>
Cc: Vincent Whitchurch <[e-mail]>
Cc: Alexey Dobriyan <[e-mail]>
Cc: Colin Ian King <[e-mail]>
Cc: Changbin Du <[e-mail]>
Cc: Masami Hiramatsu <[e-mail]>
Cc: Song Liu <[e-mail]>
Cc: Leo Yan <[e-mail]>
Cc: Athira Rajeev <[e-mail]>
Cc: Liam Howlett <[e-mail]>
Cc: Artem Savkov <[e-mail]>
Cc: [e-mail]
Signed-off-by: Namhyung Kim <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

tools/perf/util/machine.c

···
 		return NULL;
 
 	/* Assume maps are set up if there are any */
-	if (maps__nr_maps(thread__maps(thread)))
+	if (!maps__empty(thread__maps(thread)))
 		return thread;
 
 	host_thread = machine__find_thread(host_machine, -1, pid);

tools/perf/util/maps.c

···
 
 bool maps__empty(struct maps *maps)
 {
-	return maps__nr_maps(maps) == 0;
+	bool res;
+
+	down_read(maps__lock(maps));
+	res = maps__nr_maps(maps) == 0;
+	up_read(maps__lock(maps));
+
+	return res;
 }
 
 bool maps__equal(struct maps *a, struct maps *b)
···
 
 	parent_maps_by_address = maps__maps_by_address(parent);
 	n = maps__nr_maps(parent);
-	if (maps__empty(dest)) {
+	if (maps__nr_maps(dest) == 0) {
 		/* No existing mappings so just copy from parent to avoid reallocs in insert. */
 		unsigned int nr_maps_allocated = RC_CHK_ACCESS(parent)->nr_maps_allocated;
 		struct map **dest_maps_by_address =

tools/perf/util/maps.h

···
 void maps__remove_maps(struct maps *maps, bool (*cb)(struct map *map, void *data), void *data);
 
 struct machine *maps__machine(const struct maps *maps);
-unsigned int maps__nr_maps(const struct maps *maps);
-refcount_t *maps__refcnt(struct maps *maps);
+unsigned int maps__nr_maps(const struct maps *maps); /* Test only. */
+refcount_t *maps__refcnt(struct maps *maps); /* Test only. */
 
 #ifdef HAVE_LIBUNWIND_SUPPORT
 void *maps__addr_space(const struct maps *maps);