[PATCH v2 6/6] perf maps: Locking tidy up of nr_maps

[Ian Rogers <irogers@google.com>]

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 <irogers@google.com>
Acked-by: Namhyung Kim <namhyung@kernel.org>
---
 tools/perf/util/machine.c |  2 +-
 tools/perf/util/maps.c    | 10 ++++++++--
 tools/perf/util/maps.h    |  4 ++--
 3 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/tools/perf/util/machine.c b/tools/perf/util/machine.c
index 4911734411b5..3da92f18814a 100644
--- a/tools/perf/util/machine.c
+++ b/tools/perf/util/machine.c
@@ -440,7 +440,7 @@ static struct thread *findnew_guest_code(struct machine *machine,
 		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);
diff --git a/tools/perf/util/maps.c b/tools/perf/util/maps.c
index 0ab19e1de190..e59118648524 100644
--- a/tools/perf/util/maps.c
+++ b/tools/perf/util/maps.c
@@ -541,7 +541,13 @@ void maps__remove(struct maps *maps, struct map *map)
 
 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)
@@ -865,7 +871,7 @@ int maps__copy_from(struct maps *dest, struct maps *parent)
 
 	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 =
diff --git a/tools/perf/util/maps.h b/tools/perf/util/maps.h
index 4bcba136ffe5..d9aa62ed968a 100644
--- a/tools/perf/util/maps.h
+++ b/tools/perf/util/maps.h
@@ -43,8 +43,8 @@ int maps__for_each_map(struct maps *maps, int (*cb)(struct map *map, void *data)
 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);
-- 
2.43.0.594.gd9cf4e227d-goog