From: Arjun Roy <arjunroy@google.com> stable inclusion from linux-4.19.155 commit f5a4ea7839b15d702fb9c731eddcca3e3fecf8d8 -------------------------------- [ Upstream commit 435ccfa894e35e3d4a1799e6ac030e48a7b69ef5 ] With SO_RCVLOWAT, under memory pressure, it is possible to enter a state where: 1. We have not received enough bytes to satisfy SO_RCVLOWAT. 2. We have not entered buffer pressure (see tcp_rmem_pressure()). 3. But, we do not have enough buffer space to accept more packets. In this case, we advertise 0 rwnd (due to #3) but the application does not drain the receive queue (no wakeup because of #1 and #2) so the flow stalls. Modify the heuristic for SO_RCVLOWAT so that, if we are advertising rwnd<=rcv_mss, force a wakeup to prevent a stall. Without this patch, setting tcp_rmem to 6143 and disabling TCP autotune causes a stalled flow. With this patch, no stall occurs. This is with RPC-style traffic with large messages. Fixes: 03f45c883c6f ("tcp: avoid extra wakeups for SO_RCVLOWAT users") Signed-off-by: Arjun Roy <arjunroy@google.com> Acked-by: Soheil Hassas Yeganeh <soheil@google.com> Acked-by: Neal Cardwell <ncardwell@google.com> Signed-off-by: Eric Dumazet <edumazet@google.com> Link: https://lore.kernel.org/r/20201023184709.217614-1-arjunroy.kdev@gmail.com Signed-off-by: Jakub Kicinski <kuba@kernel.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> Signed-off-by: Yang Yingliang <yangyingliang@huawei.com> --- net/ipv4/tcp.c | 2 ++ net/ipv4/tcp_input.c | 3 ++- 2 files changed, 4 insertions(+), 1 deletion(-) diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 4ce3397e6fcf..98e8ee8bb759 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -495,6 +495,8 @@ static inline bool tcp_stream_is_readable(const struct tcp_sock *tp, return true; if (tcp_rmem_pressure(sk)) return true; + if (tcp_receive_window(tp) <= inet_csk(sk)->icsk_ack.rcv_mss) + return true; } if (sk->sk_prot->stream_memory_read) return sk->sk_prot->stream_memory_read(sk); diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index 8f04d2eb2799..0b3f8637d4fa 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -4712,7 +4712,8 @@ void tcp_data_ready(struct sock *sk) int avail = tp->rcv_nxt - tp->copied_seq; if (avail < sk->sk_rcvlowat && !tcp_rmem_pressure(sk) && - !sock_flag(sk, SOCK_DONE)) + !sock_flag(sk, SOCK_DONE) && + tcp_receive_window(tp) > inet_csk(sk)->icsk_ack.rcv_mss) return; sk->sk_data_ready(sk); -- 2.25.1