From: Martynas Pumputis m@lambda.lt
[ Upstream commit 043c5bb3c4f43670ab4fea0b847373ab42d25f3e ]
When loading in parallel multiple programs which use the same to-be pinned map, it is possible that two instances of the loader will call bpf_object__create_maps() at the same time. If the map doesn't exist when both instances call bpf_object__reuse_map(), then one of the instances will fail with EEXIST when calling bpf_map__pin().
Fix the race by retrying reusing a map if bpf_map__pin() returns EEXIST. The fix is similar to the one in iproute2: e4c4685fd6e4 ("bpf: Fix race condition with map pinning").
Before retrying the pinning, we don't do any special cleaning of an internal map state. The closer code inspection revealed that it's not required:
- bpf_object__create_map(): map->inner_map is destroyed after a successful call, map->fd is closed if pinning fails. - bpf_object__populate_internal_map(): created map elements is destroyed upon close(map->fd). - init_map_slots(): slots are freed after their initialization.
Signed-off-by: Martynas Pumputis m@lambda.lt Signed-off-by: Andrii Nakryiko andrii@kernel.org Link: https://lore.kernel.org/bpf/20210726152001.34845-1-m@lambda.lt Signed-off-by: Sasha Levin sashal@kernel.org --- tools/lib/bpf/libbpf.c | 15 ++++++++++++++- 1 file changed, 14 insertions(+), 1 deletion(-)
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index a4e61dd5d8b3..d24531bb69d4 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -4286,10 +4286,13 @@ bpf_object__create_maps(struct bpf_object *obj) char *cp, errmsg[STRERR_BUFSIZE]; unsigned int i, j; int err; + bool retried;
for (i = 0; i < obj->nr_maps; i++) { map = &obj->maps[i];
+ retried = false; +retry: if (map->pin_path) { err = bpf_object__reuse_map(map); if (err) { @@ -4297,6 +4300,12 @@ bpf_object__create_maps(struct bpf_object *obj) map->name); goto err_out; } + if (retried && map->fd < 0) { + pr_warn("map '%s': cannot find pinned map\n", + map->name); + err = -ENOENT; + goto err_out; + } }
if (map->fd >= 0) { @@ -4330,9 +4339,13 @@ bpf_object__create_maps(struct bpf_object *obj) if (map->pin_path && !map->pinned) { err = bpf_map__pin(map, NULL); if (err) { + zclose(map->fd); + if (!retried && err == -EEXIST) { + retried = true; + goto retry; + } pr_warn("map '%s': failed to auto-pin at '%s': %d\n", map->name, map->pin_path, err); - zclose(map->fd); goto err_out; } }