Merge branch 'Fix pining maps after reuse map fd'

Hangbin Liu says:

====================
When a user reuse map fd after creating a map manually and set the
pin_path, then load the object via libbpf. bpf_object__create_maps()
will skip pinning map if map fd exist. Fix it by add moving bpf creation
to else condition and go on checking map pin_path after that.

v3:
for selftest: use CHECK() for bpf_object__open_file() and close map fd on error

v2:
a) close map fd if init map slots failed
b) add bpf selftest for this scenario
====================

Signed-off-by: Alexei Starovoitov <ast@kernel.org>

tools/lib/bpf/libbpf.c

@@ -4203,6 +4203,36 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map)
 	return 0;
 }
 
+static int init_map_slots(struct bpf_map *map)
+{
+	const struct bpf_map *targ_map;
+	unsigned int i;
+	int fd, err;
+
+	for (i = 0; i < map->init_slots_sz; i++) {
+		if (!map->init_slots[i])
+			continue;
+
+		targ_map = map->init_slots[i];
+		fd = bpf_map__fd(targ_map);
+		err = bpf_map_update_elem(map->fd, &i, &fd, 0);
+		if (err) {
+			err = -errno;
+			pr_warn("map '%s': failed to initialize slot [%d] to map '%s' fd=%d: %d\n",
+				map->name, i, targ_map->name,
+				fd, err);
+			return err;
+		}
+		pr_debug("map '%s': slot [%d] set to map '%s' fd=%d\n",
+			 map->name, i, targ_map->name, fd);
+	}
+
+	zfree(&map->init_slots);
+	map->init_slots_sz = 0;
+
+	return 0;
+}
+
 static int
 bpf_object__create_maps(struct bpf_object *obj)
 {
@@ -4226,47 +4256,29 @@ bpf_object__create_maps(struct bpf_object *obj)
 		if (map->fd >= 0) {
 			pr_debug("map '%s': skipping creation (preset fd=%d)\n",
 				 map->name, map->fd);
-			continue;
-		}
-
-		err = bpf_object__create_map(obj, map);
-		if (err)
-			goto err_out;
-
-		pr_debug("map '%s': created successfully, fd=%d\n", map->name,
-			 map->fd);
-
-		if (bpf_map__is_internal(map)) {
-			err = bpf_object__populate_internal_map(obj, map);
-			if (err < 0) {
-				zclose(map->fd);
+		} else {
+			err = bpf_object__create_map(obj, map);
+			if (err)
 				goto err_out;
-			}
-		}
 
-		if (map->init_slots_sz) {
-			for (j = 0; j < map->init_slots_sz; j++) {
-				const struct bpf_map *targ_map;
-				int fd;
+			pr_debug("map '%s': created successfully, fd=%d\n",
+				 map->name, map->fd);
 
-				if (!map->init_slots[j])
-					continue;
+			if (bpf_map__is_internal(map)) {
+				err = bpf_object__populate_internal_map(obj, map);
+				if (err < 0) {
+					zclose(map->fd);
+					goto err_out;
+				}
+			}
 
-				targ_map = map->init_slots[j];
-				fd = bpf_map__fd(targ_map);
-				err = bpf_map_update_elem(map->fd, &j, &fd, 0);
-				if (err) {
-					err = -errno;
-					pr_warn("map '%s': failed to initialize slot [%d] to map '%s' fd=%d: %d\n",
-						map->name, j, targ_map->name,
-						fd, err);
+			if (map->init_slots_sz) {
+				err = init_map_slots(map);
+				if (err < 0) {
+					zclose(map->fd);
 					goto err_out;
 				}
-				pr_debug("map '%s': slot [%d] set to map '%s' fd=%d\n",
-					 map->name, j, targ_map->name, fd);
 			}
-			zfree(&map->init_slots);
-			map->init_slots_sz = 0;
 		}
 
 		if (map->pin_path && !map->pinned) {

tools/testing/selftests/bpf/prog_tests/pinning.c

@@ -37,7 +37,7 @@ void test_pinning(void)
 	struct stat statbuf = {};
 	struct bpf_object *obj;
 	struct bpf_map *map;
-	int err;
+	int err, map_fd;
 	DECLARE_LIBBPF_OPTS(bpf_object_open_opts, opts,
 		.pin_root_path = custpath,
 	);
@@ -213,6 +213,53 @@ void test_pinning(void)
 	if (CHECK(err, "stat custpinpath", "err %d errno %d\n", err, errno))
 		goto out;
 
+	/* remove the custom pin path to re-test it with reuse fd below */
+	err = unlink(custpinpath);
+	if (CHECK(err, "unlink custpinpath", "err %d errno %d\n", err, errno))
+		goto out;
+
+	err = rmdir(custpath);
+	if (CHECK(err, "rmdir custpindir", "err %d errno %d\n", err, errno))
+		goto out;
+
+	bpf_object__close(obj);
+
+	/* test pinning at custom path with reuse fd */
+	obj = bpf_object__open_file(file, NULL);
+	err = libbpf_get_error(obj);
+	if (CHECK(err, "default open", "err %d errno %d\n", err, errno)) {
+		obj = NULL;
+		goto out;
+	}
+
+	map_fd = bpf_create_map(BPF_MAP_TYPE_ARRAY, sizeof(__u32),
+				sizeof(__u64), 1, 0);
+	if (CHECK(map_fd < 0, "create pinmap manually", "fd %d\n", map_fd))
+		goto out;
+
+	map = bpf_object__find_map_by_name(obj, "pinmap");
+	if (CHECK(!map, "find map", "NULL map"))
+		goto close_map_fd;
+
+	err = bpf_map__reuse_fd(map, map_fd);
+	if (CHECK(err, "reuse pinmap fd", "err %d errno %d\n", err, errno))
+		goto close_map_fd;
+
+	err = bpf_map__set_pin_path(map, custpinpath);
+	if (CHECK(err, "set pin path", "err %d errno %d\n", err, errno))
+		goto close_map_fd;
+
+	err = bpf_object__load(obj);
+	if (CHECK(err, "custom load", "err %d errno %d\n", err, errno))
+		goto close_map_fd;
+
+	/* check that pinmap was pinned at the custom path */
+	err = stat(custpinpath, &statbuf);
+	if (CHECK(err, "stat custpinpath", "err %d errno %d\n", err, errno))
+		goto close_map_fd;
+
+close_map_fd:
+	close(map_fd);
 out:
 	unlink(pinpath);
 	unlink(nopinpath);