Hi Florian, On Mon, Aug 15, 2022, at 4:40 PM, Florian Westphal wrote: > Toke Høiland-Jørgensen <toke@xxxxxxxxxx> 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@xxxxxxxxx> >> >> 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
