Commit a4fbfdd7 authored by Stijn Tintel's avatar Stijn Tintel Committed by Daniel Borkmann
Browse files

libbpf: Fix BPF_MAP_TYPE_PERF_EVENT_ARRAY auto-pinning 



When a BPF map of type BPF_MAP_TYPE_PERF_EVENT_ARRAY doesn't have the
max_entries parameter set, the map will be created with max_entries set
to the number of available CPUs. When we try to reuse such a pinned map,
map_is_reuse_compat will return false, as max_entries in the map
definition differs from max_entries of the existing map, causing the
following error:

  libbpf: couldn't reuse pinned map at '/sys/fs/bpf/m_logging': parameter mismatch

Fix this by overwriting max_entries in the map definition. For this to
work, we need to do this in bpf_object__create_maps, before calling
bpf_object__reuse_map.

Fixes: 57a00f41 ("libbpf: Add auto-pinning of maps when loading BPF objects")
Signed-off-by: default avatarStijn Tintel <stijn@linux-ipv6.be>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
Acked-by: default avatarSong Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20220225152355.315204-1-stijn@linux-ipv6.be
parent 07609c19

tools/lib/bpf/libbpf.c

+25 −19
Original line number Diff line number Diff line
@@ -4859,7 +4859,6 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map, b 
	LIBBPF_OPTS(bpf_map_create_opts, create_attr);

	struct bpf_map_def *def = &map->def;

	const char *map_name = NULL;

	__u32 max_entries;

	int err = 0;



	if (kernel_supports(obj, FEAT_PROG_NAME))
@@ -4869,21 +4868,6 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map, b 
	create_attr.numa_node = map->numa_node;

	create_attr.map_extra = map->map_extra;



	if (def->type == BPF_MAP_TYPE_PERF_EVENT_ARRAY && !def->max_entries) {

		int nr_cpus;



		nr_cpus = libbpf_num_possible_cpus();

		if (nr_cpus < 0) {

			pr_warn("map '%s': failed to determine number of system CPUs: %d\n",

				map->name, nr_cpus);

			return nr_cpus;

		}

		pr_debug("map '%s': setting size to %d\n", map->name, nr_cpus);

		max_entries = nr_cpus;

	} else {

		max_entries = def->max_entries;

	}



	if (bpf_map__is_struct_ops(map))

		create_attr.btf_vmlinux_value_type_id = map->btf_vmlinux_value_type_id;
@@ -4933,7 +4917,7 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map, b 


	if (obj->gen_loader) {

		bpf_gen__map_create(obj->gen_loader, def->type, map_name,

				    def->key_size, def->value_size, max_entries,

				    def->key_size, def->value_size, def->max_entries,

				    &create_attr, is_inner ? -1 : map - obj->maps);

		/* Pretend to have valid FD to pass various fd >= 0 checks.

		 * This fd == 0 will not be used with any syscall and will be reset to -1 eventually.
@@ -4942,7 +4926,7 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map, b 
	} else {

		map->fd = bpf_map_create(def->type, map_name,

					 def->key_size, def->value_size,

					 max_entries, &create_attr);

					 def->max_entries, &create_attr);

	}

	if (map->fd < 0 && (create_attr.btf_key_type_id ||

			    create_attr.btf_value_type_id)) {
@@ -4959,7 +4943,7 @@ static int bpf_object__create_map(struct bpf_object *obj, struct bpf_map *map, b 
		map->btf_value_type_id = 0;

		map->fd = bpf_map_create(def->type, map_name,

					 def->key_size, def->value_size,

					 max_entries, &create_attr);

					 def->max_entries, &create_attr);

	}



	err = map->fd < 0 ? -errno : 0;
@@ -5063,6 +5047,24 @@ static int bpf_object_init_prog_arrays(struct bpf_object *obj) 
	return 0;

}



static int map_set_def_max_entries(struct bpf_map *map)

{

	if (map->def.type == BPF_MAP_TYPE_PERF_EVENT_ARRAY && !map->def.max_entries) {

		int nr_cpus;



		nr_cpus = libbpf_num_possible_cpus();

		if (nr_cpus < 0) {

			pr_warn("map '%s': failed to determine number of system CPUs: %d\n",

				map->name, nr_cpus);

			return nr_cpus;

		}

		pr_debug("map '%s': setting size to %d\n", map->name, nr_cpus);

		map->def.max_entries = nr_cpus;

	}



	return 0;

}



static int

bpf_object__create_maps(struct bpf_object *obj)

{
@@ -5095,6 +5097,10 @@ bpf_object__create_maps(struct bpf_object *obj) 
			continue;

		}



		err = map_set_def_max_entries(map);

		if (err)

			goto err_out;



		retried = false;

retry:

		if (map->pin_path) {