On Thu, Jan 23, 2020 at 08:15 PM CET, John Fastabend wrote: > Jakub Sitnicki wrote: >> On Thu, Jan 23, 2020 at 06:18 PM CET, Eric Dumazet wrote: >> > On 1/23/20 7:55 AM, Jakub Sitnicki wrote: >> >> sk_msg and ULP frameworks override protocol callbacks pointer in >> >> sk->sk_prot, while tcp accesses it locklessly when cloning the listening >> >> socket, that is with neither sk_lock nor sk_callback_lock held. >> >> >> >> Once we enable use of listening sockets with sockmap (and hence sk_msg), >> >> there will be shared access to sk->sk_prot if socket is getting cloned >> >> while being inserted/deleted to/from the sockmap from another CPU: > > [...] > >> >> include/linux/skmsg.h | 3 ++- >> >> net/core/sock.c | 5 +++-- >> >> net/ipv4/tcp_bpf.c | 4 +++- >> >> net/ipv4/tcp_ulp.c | 3 ++- >> >> net/tls/tls_main.c | 3 ++- >> >> 5 files changed, 12 insertions(+), 6 deletions(-) >> >> >> >> diff --git a/include/linux/skmsg.h b/include/linux/skmsg.h >> >> index 41ea1258d15e..55c834a5c25e 100644 >> >> --- a/include/linux/skmsg.h >> >> +++ b/include/linux/skmsg.h >> >> @@ -352,7 +352,8 @@ static inline void sk_psock_update_proto(struct sock *sk, >> >> psock->saved_write_space = sk->sk_write_space; >> >> >> >> psock->sk_proto = sk->sk_prot; >> >> - sk->sk_prot = ops; >> >> + /* Pairs with lockless read in sk_clone_lock() */ >> >> + WRITE_ONCE(sk->sk_prot, ops); >> > >> > >> > Note there are dozens of calls like >> > >> > if (sk->sk_prot->handler) >> > sk->sk_prot->handler(...); >> > >> > Some of them being done lockless. >> > >> > I know it is painful, but presumably we need > > Correct. > >> > >> > const struct proto *ops = READ_ONCE(sk->sk_prot); >> > >> > if (ops->handler) >> > ops->handler(....); [...] >> >> Considering these are lacking today, can I do it as a follow up? > > In my opinion yes. I think pulling your patches in is OK and I started > doing this conversion already so we can have a fix shortly. I didn't > want to push it into rc7 though so I'll push it next week or into > net-next tree. Thanks, John. I'll take a look if there is any access to sk_prot, apart from the clone path, applicable only to TCP listening sockets that needs annotating.
