On Tue, Nov 20, 2018 at 10:01 AM David Miller <da...@davemloft.net> wrote: > > From: Eric Dumazet <eduma...@google.com> > Date: Mon, 19 Nov 2018 17:45:55 -0800 > > > Under stress, softirq rx handler often hits a socket owned by the user, > > and has to queue the packet into socket backlog. > > > > When this happens, skb dst refcount is taken before we escape rcu > > protected region. This is done from __sk_add_backlog() calling > > skb_dst_force(). > > > > Consumer will have to perform the opposite costly operation. > > > > AFAIK nothing in tcp stack requests the dst after skb was stored > > in the backlog. If this was the case, we would have had failures > > already since skb_dst_force() can end up clearing skb dst anyway. > > > > Signed-off-by: Eric Dumazet <eduma...@google.com> > > Hmmm, it seems to be used by connection completion code to setup the > socket cached rx dst, right? > > For example tcp_finish_connect() --> icsk->icsk_af_ops->sk_rx_dst_set(sk, skb)
We already cope with skb->dst being NULL there I believe. For reference look at commit 5037e9ef9454917b047f9f3a19b4dd179fbf7cd4 net: fix IP early demux races
