Re: [PATCH bpf-next v3 4/5] bpf: Add support for writing to nf_conn:mark

[Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx>]

On Sat, 20 Aug 2022 at 01:46, Kumar Kartikeya Dwivedi <memxor@xxxxxxxxx> wrote:
>
> CPU 0                                              CPU 1
> sa = READ_ONCE(nf_ct_bsa);
>
> delete_module("nf_conntrack", ..);
>
> WRITE_ONCE(nf_ct_bsa, NULL);
>                                                          // finishes
> successfully
> if (sa)
>     return sa(...); // oops
>

Ew, I completely screwed it up. Not trying again.

CPU 0 does:
sa = READ_ONCE(nf_ct_bsa);
then CPU 1 does:
delete_module("nf_conntrack", ...);
   WRITE_ONCE(nf_ct_bsa, NULL);
then CPU 0 does:
if (sa) sa(...); // bad