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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: 57a00f4164 ("libbpf: Add auto-pinning of maps when loading BPF objects")
Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Song Liu <songliubraving@fb.com>
Link: https://lore.kernel.org/bpf/20220225152355.315204-1-stijn@linux-ipv6.be
This commit is contained in:
Stijn Tintel 2022-02-25 17:23:55 +02:00 committed by Daniel Borkmann
parent 07609c193a
commit a4fbfdd7a1
1 changed files with 25 additions and 19 deletions
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44
tools/lib/bpf/libbpf.c
View File

@ -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) {