path: root/net
diff options
authorArjun Roy <arjunroy@google.com>2020-10-23 11:47:09 -0700
committerJakub Kicinski <kuba@kernel.org>2020-10-23 19:11:20 -0700
commit435ccfa894e35e3d4a1799e6ac030e48a7b69ef5 (patch)
treef0674f64461ee9997fcad0c1616433ddcb8835a8 /net
parentdab234227cbdc6a088c6f9bce38b5dcfefe90832 (diff)
tcp: Prevent low rmem stalls with SO_RCVLOWAT.
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>
Diffstat (limited to 'net')
2 files changed, 4 insertions, 1 deletions
diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
index bae4284bf542..b2bc3d7fe9e8 100644
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -485,6 +485,8 @@ 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 fc445833b5e5..389d1b340248 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4908,7 +4908,8 @@ 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)