2024-11-12, 14:20:45 +0100, Antonio Quartulli wrote:
> On 05/11/2024 19:10, Sabrina Dubroca wrote:
> > 2024-10-29, 11:47:28 +0100, Antonio Quartulli wrote:
> > > @@ -105,6 +132,9 @@ void ovpn_decrypt_post(void *data, int ret)
> > > goto drop;
> > > }
> > > + /* keep track of last received authenticated packet for keepalive */
> > > + peer->last_recv = ktime_get_real_seconds();
> >
> > It doesn't look like we're locking the peer here so that should be a
> > WRITE_ONCE() (and READ_ONCE(peer->last_recv) for all reads).
>
> Is that because last_recv is 64 bit long (and might be more than one word on
> certain architectures)?
>
> I don't remember having to do so for reading/writing 32 bit long integers.
AFAIK it's not just that. The compiler is free to do the read/write in
any way it wants when you don't specify _ONCE. On the read side, it
could read from memory a single time or multiple times (getting
possibly different values each time), or maybe split the load
(possibly reading chunks from different values being written in
parallel).
> I presume we need a WRITE_ONCE also upon initialization in
> ovpn_peer_keepalive_set() right?
> We still want to coordinate that with other reads/writes.
I think it makes sense, yes.
> > > +
> > > /* point to encapsulated IP packet */
> > > __skb_pull(skb, payload_offset);
> > > @@ -121,6 +151,12 @@ void ovpn_decrypt_post(void *data, int ret)
> > > goto drop;
> > > }
> > > + if (ovpn_is_keepalive(skb)) {
> > > + net_dbg_ratelimited("%s: ping received from peer %u\n",
> > > + peer->ovpn->dev->name, peer->id);
> > > + goto drop;
> >
> > To help with debugging connectivity issues, maybe keepalives shouldn't
> > be counted as drops? (consume_skb instead of kfree_skb, and not
> > incrementing rx_dropped)
> > The packet was successfully received and did all it had to do.
>
> you're absolutely right. Will change that.
Thanks.
> > > + /* check for peer timeout */
> > > + expired = false;
> > > + timeout = peer->keepalive_timeout;
> > > + delta = now - peer->last_recv;
> >
> > I'm not sure that's always > 0 if we finish decrypting a packet just
> > as the workqueue starts:
> >
> > ovpn_peer_keepalive_work
> > now = ...
> >
> > ovpn_decrypt_post
> > peer->last_recv = ...
> >
> > ovpn_peer_keepalive_work_single
> > delta: now < peer->last_recv
> >
>
> Yeah, there is nothing preventing this from happening...but is this truly a
> problem? The math should still work, no?
We'll fail "delta < timeout" (which we shouldn't), so we'll end up
either in the "expired = true" case, or not updating
keepalive_recv_exp. Both of these seem not ideal.
>
> However:
>
> >
> >
> > > + if (delta < timeout) {
> > > + peer->keepalive_recv_exp = now + timeout - delta;
> >
> > I'd shorten that to
> >
> > peer->keepalive_recv_exp = peer->last_recv + timeout;
> >
> > it's a bit more readable to my eyes and avoids risks of wrapping
> > values.
> >
> > So I'd probably get rid of delta and go with:
> >
> > last_recv = READ_ONCE(peer->last_recv)
> > if (now < last_recv + timeout) {
> > peer->keepalive_recv_exp = last_recv + timeout;
> > next_run1 = peer->keepalive_recv_exp;
> > } else if ...
> >
> > > + next_run1 = peer->keepalive_recv_exp;
> > > + } else if (peer->keepalive_recv_exp > now) {
> > > + next_run1 = peer->keepalive_recv_exp;
> > > + } else {
> > > + expired = true;
> > > + }
>
> I agree this is simpler to read and gets rid of some extra operations.
>
> [note: I took inspiration from nat_keepalive_work_single() - it could be
> simplified as well I guess]
Ah, ok. I wanted to review this code when it was posted but didn't
have time :(
> >
> > [...]
> > > + /* check for peer keepalive */
> > > + expired = false;
> > > + interval = peer->keepalive_interval;
> > > + delta = now - peer->last_sent;
> > > + if (delta < interval) {
> > > + peer->keepalive_xmit_exp = now + interval - delta;
> > > + next_run2 = peer->keepalive_xmit_exp;
> >
> > and same here
>
> Yeah, will change both. Thanks!
Thanks.
--
Sabrina
