Subject: Re: [PATCH bpf-next v2 1/6] libbpf: Unpin auto-pinned maps if loading fails

From: Toke Høiland-Jørgensen <[email-masked]>
Date: Sat, 09 Nov 2019 00:33:25 +0100

Andrii Nakryiko <[email-masked]> writes:

> On Fri, Nov 8, 2019 at 1:33 PM Toke Høiland-Jørgensen <[email-masked]> wrote:
>>
>> From: Toke Høiland-Jørgensen <[email-masked]>
>>
>> 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: 57a00f41644f ("libbpf: Add auto-pinning of maps when loading BPF objects")
>> Acked-by: Song Liu <[email-masked]>
>> Signed-off-by: Toke Høiland-Jørgensen <[email-masked]>
>> ---
>>  tools/lib/bpf/libbpf.c |   16 +++++++++++++---
>>  1 file changed, 13 insertions(+), 3 deletions(-)
>>
>> diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
>> index be4af95d5a2c..cea61b2ec9d3 100644
>> --- a/tools/lib/bpf/libbpf.c
>> +++ b/tools/lib/bpf/libbpf.c
>> @@ -229,6 +229,7 @@ struct bpf_map {
>>         enum libbpf_map_type libbpf_type;
>>         char *pin_path;
>>         bool pinned;
>> +       bool was_reused;
>
> nit: just reused, similar to pinned?
>
>>  };
>>
>>  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->was_reused = true;
>>
>>         return 0;
>>
>> @@ -4007,15 +4009,18 @@ bpf_object__open_buffer(const void *obj_buf, size_t obj_buf_sz,
>>         return bpf_object__open_mem(obj_buf, obj_buf_sz, &opts);
>>  }
>>
>> -int bpf_object__unload(struct bpf_object *obj)
>> +static int __bpf_object__unload(struct bpf_object *obj, bool unpin)
>>  {
>>         size_t i;
>>
>>         if (!obj)
>>                 return -EINVAL;
>>
>> -       for (i = 0; i < obj->nr_maps; i++)
>> +       for (i = 0; i < obj->nr_maps; i++) {
>>                 zclose(obj->maps[i].fd);
>> +               if (unpin && obj->maps[i].pinned && !obj->maps[i].was_reused)
>> +                       bpf_map__unpin(&obj->maps[i], NULL);
>> +       }
>>
>>         for (i = 0; i < obj->nr_programs; i++)
>>                 bpf_program__unload(&obj->programs[i]);
>> @@ -4023,6 +4028,11 @@ int bpf_object__unload(struct bpf_object *obj)
>>         return 0;
>>  }
>>
>> +int bpf_object__unload(struct bpf_object *obj)
>> +{
>> +       return __bpf_object__unload(obj, false);
>> +}
>> +
>>  int bpf_object__load_xattr(struct bpf_object_load_attr *attr)
>>  {
>>         struct bpf_object *obj;
>> @@ -4047,7 +4057,7 @@ int bpf_object__load_xattr(struct bpf_object_load_attr *attr)
>>
>>         return 0;
>>  out:
>> -       bpf_object__unload(obj);
>> +       __bpf_object__unload(obj, true);
>
> giving this is the only (special) case of auto-unpinning auto-pinned
> maps, why not do a trivial loop here, instead of having this extra
> unpin flag and extra __bpf_object__unload function?

Oh, you mean just do a loop in addition to the call to __unload? Sure, I
guess we can do that instead...

-Toke