[PATCH 5.17 0616/1126] libbpf: Fix BPF_MAP_TYPE_PERF_EVENT_ARRAY auto-pinning

Greg Kroah-Hartman
2022-04-05T08:22:46Z

From: Stijn Tintel <stijn@linux-ipv6.be>

[ Upstream commit a4fbfdd7a160eccaafc093eb5b34f838b1ca0bf0 ]

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: 57a00f41644f ("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
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
tools/lib/bpf/libbpf.c | 44 ++++++++++++++++++++++++------------------
1 file changed, 25 insertions(+), 19 deletions(-)

diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index fdb3536afa7d..94a6a8543cbc 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -4854,7 +4854,6 @@ 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))
@@ -4864,21 +4863,6 @@ 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;

@@ -4928,7 +4912,7 @@ 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.
@@ -4937,7 +4921,7 @@ 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)) {
@@ -4954,7 +4938,7 @@ 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;
@@ -5058,6 +5042,24 @@ 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)
{
@@ -5090,6 +5092,10 @@ 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) {
--
2.34.1