Messages in this thread | | | Date | Wed, 17 Aug 2022 12:28:55 -0600 | From | "Daniel Xu" <> | Subject | Re: [PATCH bpf-next 2/3] bpf: Add support for writing to nf_conn:mark |
| |
Hi Florian,
On Mon, Aug 15, 2022, at 4:40 PM, Florian Westphal wrote: > Toke Høiland-Jørgensen <toke@kernel.org> wrote: >> > Support direct writes to nf_conn:mark from TC and XDP prog types. This >> > is useful when applications want to store per-connection metadata. This >> > is also particularly useful for applications that run both bpf and >> > iptables/nftables because the latter can trivially access this metadata. >> > >> > One example use case would be if a bpf prog is responsible for advanced >> > packet classification and iptables/nftables is later used for routing >> > due to pre-existing/legacy code. >> > >> > Signed-off-by: Daniel Xu <dxu@dxuuu.xyz> >> >> Didn't we agree the last time around that all field access should be >> using helper kfuncs instead of allowing direct writes to struct nf_conn? > > I don't see why ct->mark needs special handling. > > It might be possible we need to change accesses on nf/tc side to use > READ/WRITE_ONCE though.
I reviewed some of the LKMM literature and I would concur that READ/WRITE_ONCE() is necessary. Especially after this patchset.
However, it's unclear to me if this is a latent issue. IOW: is reading ct->mark protected by a lock? I only briefly looked but it doesn't seem like it.
I'll do some more digging.
In the meantime, I'll send out a v2 on this patchset and I'll plan on sending out a followup patchset for adding READ/WRITE_ONCE() to ct->mark accesses.
Thanks, Daniel
| |