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Message-ID: <YzCdHXtgKPciEusR@pop-os.localdomain> Date: Sun, 25 Sep 2022 11:25:33 -0700 From: Cong Wang <xiyou.wangcong@...il.com> To: "liujian (CE)" <liujian56@...wei.com> Cc: John Fastabend <john.fastabend@...il.com>, Jakub Sitnicki <jakub@...udflare.com>, Eric Dumazet <edumazet@...gle.com>, davem <davem@...emloft.net>, "yoshfuji@...ux-ipv6.org" <yoshfuji@...ux-ipv6.org>, "dsahern@...nel.org" <dsahern@...nel.org>, Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, netdev <netdev@...r.kernel.org>, "bpf@...r.kernel.org" <bpf@...r.kernel.org> Subject: Re: [bug report] one possible out-of-order issue in sockmap On Sat, Sep 24, 2022 at 07:59:15AM +0000, liujian (CE) wrote: > Hello, > > I had a scp failure problem here. I analyze the code, and the reasons may be as follows: > > From commit e7a5f1f1cd00 ("bpf/sockmap: Read psock ingress_msg before > sk_receive_queue", if we use sockops (BPF_SOCK_OPS_ACTIVE_ESTABLISHED_CB > and BPF_SOCK_OPS_PASSIVE_ESTABLISHED_CB) to enable socket's sockmap > function, and don't enable strparse and verdict function, the out-of-order > problem may occur in the following process. > > client SK server SK > -------------------------------------------------------------------------- > tcp_rcv_synsent_state_process > tcp_finish_connect > tcp_init_transfer > tcp_set_state(sk, TCP_ESTABLISHED); > // insert SK to sockmap > wake up waitter > tcp_send_ack > > tcp_bpf_sendmsg(msgA) > // msgA will go tcp stack > tcp_rcv_state_process > tcp_init_transfer > //insert SK to sockmap > tcp_set_state(sk, > TCP_ESTABLISHED) > wake up waitter Here after the socket is inserted to a sockmap, its ->sk_data_ready() is already replaced with sk_psock_verdict_data_ready(), so msgA should go to sockmap, not TCP stack? > tcp_bpf_sendmsg(msgB) > // msgB go sockmap > tcp_bpf_recvmsg > //msgB, out-of-order > tcp_bpf_recvmsg > //msgA, out-of-order > > > Even if msgA arrives earlier than msgB (in most cases), tcp_bpf_recvmsg receives msg from the psock queue first. > The worst case is that msgA waits for serverSK to change to TCP_ESTABLISHED in the protocol stack. msgA may arrive at the serverSK receive queue later than msgB. > If msgA befor than msgB, > > If the ACK packets of the three-way TCP handshake are dropped for a period of time, the OOO problem is easily reproduced. > > iptables -A INPUT -p tcp -m tcp --dport 5006 --tcp-flags SYN,RST,ACK,FIN ACK -j DROP > ... > iptables -D INPUT -p tcp -m tcp --dport 5006 --tcp-flags SYN,RST,ACK,FIN ACK -j DROP > > Best Wishes > Liu Jian
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