From: Lorenz Bauer lmb@isovalent.com Date: Mon, 3 Jul 2023 10:57:23 +0100
On Wed, Jun 28, 2023 at 7:54 PM Kuniyuki Iwashima kuniyu@amazon.com wrote:
reuse_sk = inet6_lookup_reuseport(net, sk, skb, doff,saddr, sport, daddr, ntohs(dport),ehashfn);if (!reuse_sk || reuse_sk == sk)return sk;/* We've chosen a new reuseport sock which is never refcounted. This* implies that sk also isn't refcounted.*/WARN_ON_ONCE(*refcounted);One more nit.
WARN_ON_ONCE() should be tested before inet6?_lookup_reuseport() not to miss the !reuse_sk case.
I was just pondering that as well, but I came to the opposite conclusion. In the !reuse_sk case we don't really know anything about sk, except that it isn't part of a reuseport group. How can we be sure that it's not refcounted?
Sorry for late reply.
What we know about sk before inet6?_lookup_reuseport() are
(1) sk was full socket in bpf_sk_assign() (2) sk had SOCK_RCU_FREE in bpf_sk_assign() (3) sk was TCP_LISTEN here if TCP
After bpf_sk_assign(), reqsk is never converted to fullsock, and UDP never clears SOCK_RCU_FREE. If sk is TCP, now we are in the RCU grace period and confirmed sk->sk_state was TCP_LISTEN. Then, TCP_LISTEN sk cannot be reused and SOCK_RCU_FREE is never cleared.
So, before/after inet6?_lookup_reuseport(), the fact that sk is not refcounted here should not change in spite of that reuse_sk is NULL.
What do you think ?