[PATCH v3 16/17] perf maps: Fix lock inversion in maps__load_first() and bounds check in __maps__remove()

[Ian Rogers]

In maps__load_first(), take a reference to the first map and drop
maps__lock(maps) before calling map__load() to avoid a read-to-write
self-deadlock when loading kernel maps inserts extra trampoline maps.

In __maps__remove(), check that the index returned by
maps__by_address_index() and maps__by_name_index() is within nr_maps
before indexing and removing the entry, in case a concurrent thread
already removed the map.

Signed-off-by: Ian Rogers <irogers@xxxxxxxxxx>
---
 tools/perf/util/maps.c | 25 ++++++++++++++++++-------
 1 file changed, 18 insertions(+), 7 deletions(-)

diff --git a/tools/perf/util/maps.c b/tools/perf/util/maps.c
index f808df2fe77b..c0fccb776bed 100644
--- a/tools/perf/util/maps.c
+++ b/tools/perf/util/maps.c
@@ -548,6 +548,8 @@ static void __maps__remove(struct maps *maps, struct map *map)
 
 	/* Slide later mappings over the one to remove */
 	address_idx = maps__by_address_index(maps, map);
+	if (address_idx >= nr_maps)
+		return;
 	map__put(maps_by_address[address_idx]);
 	memmove(&maps_by_address[address_idx],
 		&maps_by_address[address_idx + 1],
@@ -556,10 +558,14 @@ static void __maps__remove(struct maps *maps, struct map *map)
 	if (maps_by_name) {
 		unsigned int name_idx = maps__by_name_index(maps, map);
 
-		map__put(maps_by_name[name_idx]);
-		memmove(&maps_by_name[name_idx],
-			&maps_by_name[name_idx + 1],
-			(nr_maps - name_idx - 1) *  sizeof(*maps_by_name));
+		if (name_idx < nr_maps) {
+			map__put(maps_by_name[name_idx]);
+			memmove(&maps_by_name[name_idx],
+				&maps_by_name[name_idx + 1],
+				(nr_maps - name_idx - 1) * sizeof(*maps_by_name));
+		} else {
+			__maps__free_maps_by_name(maps);
+		}
 	}
 
 	--RC_CHK_ACCESS(maps)->nr_maps;
@@ -1459,10 +1465,15 @@ int maps__merge_in(struct maps *kmaps, struct map *new_map)
 
 void maps__load_first(struct maps *maps)
 {
-	down_read(maps__lock(maps));
+	struct map *first = NULL;
 
+	down_read(maps__lock(maps));
 	if (maps__nr_maps(maps) > 0)
-		map__load(maps__maps_by_address(maps)[0]);
-
+		first = map__get(maps__maps_by_address(maps)[0]);
 	up_read(maps__lock(maps));
+
+	if (first) {
+		map__load(first);
+		map__put(first);
+	}
 }
-- 
2.56.0.212.g129ede20d9-goog