From f969dc5a885736842c3511ecdea240fbb02d25d9 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 12 Feb 2021 15:22:13 -0800 Subject: [PATCH 1/2] tcp: fix SO_RCVLOWAT related hangs under mem pressure While commit 24adbc1676af ("tcp: fix SO_RCVLOWAT hangs with fat skbs") fixed an issue vs too small sk_rcvbuf for given sk_rcvlowat constraint, it missed to address issue caused by memory pressure. 1) If we are under memory pressure and socket receive queue is empty. First incoming packet is allowed to be queued, after commit 76dfa6082032 ("tcp: allow one skb to be received per socket under memory pressure") But we do not send EPOLLIN yet, in case tcp_data_ready() sees sk_rcvlowat is bigger than skb length. 2) Then, when next packet comes, it is dropped, and we directly call sk->sk_data_ready(). 3) If application is using poll(), tcp_poll() will then use tcp_stream_is_readable() and decide the socket receive queue is not yet filled, so nothing will happen. Even when sender retransmits packets, phases 2) & 3) repeat and flow is effectively frozen, until memory pressure is off. Fix is to consider tcp_under_memory_pressure() to take care of global memory pressure or memcg pressure. Fixes: 24adbc1676af ("tcp: fix SO_RCVLOWAT hangs with fat skbs") Signed-off-by: Eric Dumazet Reported-by: Arjun Roy Suggested-by: Wei Wang Reviewed-by: Wei Wang Signed-off-by: David S. Miller --- include/net/tcp.h | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/include/net/tcp.h b/include/net/tcp.h index 25bbada379c46..244208f6f6c2a 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1431,8 +1431,13 @@ void tcp_cleanup_rbuf(struct sock *sk, int copied); */ static inline bool tcp_rmem_pressure(const struct sock *sk) { - int rcvbuf = READ_ONCE(sk->sk_rcvbuf); - int threshold = rcvbuf - (rcvbuf >> 3); + int rcvbuf, threshold; + + if (tcp_under_memory_pressure(sk)) + return true; + + rcvbuf = READ_ONCE(sk->sk_rcvbuf); + threshold = rcvbuf - (rcvbuf >> 3); return atomic_read(&sk->sk_rmem_alloc) > threshold; } From 05dc72aba364d374a27de567fac58c199ff5ee97 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Fri, 12 Feb 2021 15:22:14 -0800 Subject: [PATCH 2/2] tcp: factorize logic into tcp_epollin_ready() Both tcp_data_ready() and tcp_stream_is_readable() share the same logic. Add tcp_epollin_ready() helper to avoid duplication. Signed-off-by: Eric Dumazet Cc: Arjun Roy Cc: Wei Wang Signed-off-by: David S. Miller --- include/net/tcp.h | 12 ++++++++++++ net/ipv4/tcp.c | 18 +++++------------- net/ipv4/tcp_input.c | 11 ++--------- 3 files changed, 19 insertions(+), 22 deletions(-) diff --git a/include/net/tcp.h b/include/net/tcp.h index 244208f6f6c2a..484eb2362645f 100644 --- a/include/net/tcp.h +++ b/include/net/tcp.h @@ -1442,6 +1442,18 @@ static inline bool tcp_rmem_pressure(const struct sock *sk) return atomic_read(&sk->sk_rmem_alloc) > threshold; } +static inline bool tcp_epollin_ready(const struct sock *sk, int target) +{ + const struct tcp_sock *tp = tcp_sk(sk); + int avail = READ_ONCE(tp->rcv_nxt) - READ_ONCE(tp->copied_seq); + + if (avail <= 0) + return false; + + return (avail >= target) || tcp_rmem_pressure(sk) || + (tcp_receive_window(tp) <= inet_csk(sk)->icsk_ack.rcv_mss); +} + extern void tcp_openreq_init_rwin(struct request_sock *req, const struct sock *sk_listener, const struct dst_entry *dst); diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c index 9896ca10bb340..7a6b58ae408d1 100644 --- a/net/ipv4/tcp.c +++ b/net/ipv4/tcp.c @@ -481,19 +481,11 @@ static void tcp_tx_timestamp(struct sock *sk, u16 tsflags) } } -static inline bool tcp_stream_is_readable(const struct tcp_sock *tp, - int target, struct sock *sk) +static bool tcp_stream_is_readable(struct sock *sk, int target) { - int avail = READ_ONCE(tp->rcv_nxt) - READ_ONCE(tp->copied_seq); - - if (avail > 0) { - if (avail >= target) - return true; - if (tcp_rmem_pressure(sk)) - return true; - if (tcp_receive_window(tp) <= inet_csk(sk)->icsk_ack.rcv_mss) - return true; - } + if (tcp_epollin_ready(sk, target)) + return true; + if (sk->sk_prot->stream_memory_read) return sk->sk_prot->stream_memory_read(sk); return false; @@ -568,7 +560,7 @@ __poll_t tcp_poll(struct file *file, struct socket *sock, poll_table *wait) tp->urg_data) target++; - if (tcp_stream_is_readable(tp, target, sk)) + if (tcp_stream_is_readable(sk, target)) mask |= EPOLLIN | EPOLLRDNORM; if (!(sk->sk_shutdown & SEND_SHUTDOWN)) { diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c index a8f8f98159531..e32a7056cb764 100644 --- a/net/ipv4/tcp_input.c +++ b/net/ipv4/tcp_input.c @@ -4924,15 +4924,8 @@ int tcp_send_rcvq(struct sock *sk, struct msghdr *msg, size_t size) void tcp_data_ready(struct sock *sk) { - const struct tcp_sock *tp = tcp_sk(sk); - int avail = tp->rcv_nxt - tp->copied_seq; - - if (avail < sk->sk_rcvlowat && !tcp_rmem_pressure(sk) && - !sock_flag(sk, SOCK_DONE) && - tcp_receive_window(tp) > inet_csk(sk)->icsk_ack.rcv_mss) - return; - - sk->sk_data_ready(sk); + if (tcp_epollin_ready(sk, sk->sk_rcvlowat)) + sk->sk_data_ready(sk); } static void tcp_data_queue(struct sock *sk, struct sk_buff *skb)