Re: [PATCH 09/14] ipv6: hand dst refs to cork setup

[Pavel Begunkov]

On 1/12/22 11:15, Paolo Abeni wrote:
> On Tue, 2022-01-11 at 20:39 +0000, Pavel Begunkov wrote:
> > On 1/11/22 17:11, Paolo Abeni wrote:
> > > On Tue, 2022-01-11 at 01:21 +0000, Pavel Begunkov wrote:
> > > > During cork->dst setup, ip6_make_skb() gets an additional reference to
> > > > a passed in dst. However, udpv6_sendmsg() doesn't need dst after calling
> > > > ip6_make_skb(), and so we can save two additional atomics by passing
> > > > dst references to ip6_make_skb(). udpv6_sendmsg() is the only caller, so
> > > > it's enough to make sure it doesn't use dst afterwards.
> > >
> > > What about the corked path in udp6_sendmsg()? I mean:
> >
> > It doesn't change it for callers, so the ref stays with udp6_sendmsg() when
> > corking. To compensate for ip6_setup_cork() there is an explicit dst_hold()
> > in ip6_append_data, should be fine.
>
> Whoops, I underlooked that chunk, thanks for pointing it out!
>
> Yes, it looks fine.

perfect, thanks


> > @@ -1784,6 +1784,7 @@ int ip6_append_data(struct sock *sk,
> >    		/*
> >    		 * setup for corking
> >    		 */
> > +		dst_hold(&rt->dst);
> >    		err = ip6_setup_cork(sk, &inet->cork, &np->cork,
> >    				     ipc6, rt);
> >
> >
> > I don't care much about corking perf, but might be better to implement
> > this "handing away" for ip6_append_data() as well to be more consistent
> > with ip6_make_skb().
>
> I'm personally fine with the the added dst_hold() in ip6_append_data()
--
Pavel Begunkov