libbpf: Unpin auto-pinned maps if loading fails

Since the automatic map-pinning happens during load, it will leave pinned
maps around if the load fails at a later stage. Fix this by unpinning any
pinned maps on cleanup. To avoid unpinning pinned maps that were reused
rather than newly pinned, add a new boolean property on struct bpf_map to
keep track of whether that map was reused or not; and only unpin those maps
that were not reused.

Fixes: 57a00f41 ("libbpf: Add auto-pinning of maps when loading BPF objects")
Signed-off-by: Toke Høiland-Jørgensen <toke@redhat.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/157333184731.88376.9992935027056165873.stgit@toke.dk

tools/lib/bpf/libbpf.c

@@ -229,6 +229,7 @@ struct bpf_map {
 	enum libbpf_map_type libbpf_type;
 	char *pin_path;
 	bool pinned;
+	bool reused;
 };
 
 struct bpf_secdata {
@@ -1995,6 +1996,7 @@ int bpf_map__reuse_fd(struct bpf_map *map, int fd)
 	map->def.map_flags = info.map_flags;
 	map->btf_key_type_id = info.btf_key_type_id;
 	map->btf_value_type_id = info.btf_value_type_id;
+	map->reused = true;
 
 	return 0;
 
@@ -4026,7 +4028,7 @@ int bpf_object__unload(struct bpf_object *obj)
 int bpf_object__load_xattr(struct bpf_object_load_attr *attr)
 {
 	struct bpf_object *obj;
-	int err;
+	int err, i;
 
 	if (!attr)
 		return -EINVAL;
@@ -4047,6 +4049,11 @@ int bpf_object__load_xattr(struct bpf_object_load_attr *attr)
 
 	return 0;
 out:
+	/* unpin any maps that were auto-pinned during load */
+	for (i = 0; i < obj->nr_maps; i++)
+		if (obj->maps[i].pinned && !obj->maps[i].reused)
+			bpf_map__unpin(&obj->maps[i], NULL);
+
 	bpf_object__unload(obj);
 	pr_warn("failed to load object '%s'\n", obj->path);
 	return err;