[PATCH v5 21/50] perf maps: Add maps__load_first

[Ian Rogers]

Avoid bpf_lock_contention_touching the internal maps data structure by
adding a helper function. As access is done directly on the map in
maps, hold the read lock to stop it being removed.

Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 tools/perf/util/bpf_lock_contention.c |  2 +-
 tools/perf/util/maps.c                | 13 +++++++++++++
 tools/perf/util/maps.h                |  2 ++
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/tools/perf/util/bpf_lock_contention.c b/tools/perf/util/bpf_lock_contention.c
index e105245eb905..d9720a910330 100644
--- a/tools/perf/util/bpf_lock_contention.c
+++ b/tools/perf/util/bpf_lock_contention.c
@@ -317,7 +317,7 @@ int lock_contention_read(struct lock_contention *con)
 	}
 
 	/* make sure it loads the kernel map */
-	map__load(maps__first(machine->kmaps)->map);
+	maps__load_first(machine->kmaps);
 
 	prev_key = NULL;
 	while (!bpf_map_get_next_key(fd, prev_key, &key)) {
diff --git a/tools/perf/util/maps.c b/tools/perf/util/maps.c
index 85bea2a6dca9..9a84d26328a7 100644
--- a/tools/perf/util/maps.c
+++ b/tools/perf/util/maps.c
@@ -792,3 +792,16 @@ int maps__merge_in(struct maps *kmaps, struct map *new_map)
 	}
 	return err;
 }
+
+void maps__load_first(struct maps *maps)
+{
+	struct map_rb_node *first;
+
+	down_read(maps__lock(maps));
+
+	first = maps__first(maps);
+	if (first)
+		map__load(first->map);
+
+	up_read(maps__lock(maps));
+}
diff --git a/tools/perf/util/maps.h b/tools/perf/util/maps.h
index e4a49d6ff5cf..b7ab3ec61b7c 100644
--- a/tools/perf/util/maps.h
+++ b/tools/perf/util/maps.h
@@ -142,4 +142,6 @@ void __maps__sort_by_name(struct maps *maps);
 
 void maps__fixup_end(struct maps *maps);
 
+void maps__load_first(struct maps *maps);
+
 #endif // __PERF_MAPS_H
-- 
2.43.0.rc1.413.gea7ed67945-goog