Re: [PATCH bpf] xdp: use flags field to disambiguate broadcast redirect

[Martin KaFai Lau <martin.lau@linux.dev>]

On 4/20/24 3:24 AM, Toke Høiland-Jørgensen wrote:
>>   From reading the "waits for...NAPI being the relevant context here..." comment
>> in dev_map_free(), I wonder if moving synchronize_rcu() before
>> bpf_clear_redirect_map() would also work? Actually, does it need to call
>> bpf_clear_redirect_map(). The on-going xdp_do_redirect() should be the last one
>> using the map in ri->map anyway and no xdp prog can set it again to
>>   ri->map.
> I think we do need to retain the current behaviour, because of the
> decoupling between the helper and the return code. Otherwise, you could

Forgot there could be a disconnect here.

Applied. Thanks.

> have a program that calls the bpf_redirect_map() helper, but returns a
> different value (say, XDP_DROP). In this case, the map pointer will
> stick around in struct bpf_redirect_info, and if a subsequent XDP
> program then returns XDP_REDIRECT (*without*  calling
> bpf_redirect_map()), it will use the stale pointer value and cause a