From: Arjun Roy <arjunroy@xxxxxxxxxx>
[ 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@xxxxxxxxxx>
Acked-by: Soheil Hassas Yeganeh <soheil@xxxxxxxxxx>
Acked-by: Neal Cardwell <ncardwell@xxxxxxxxxx>
Signed-off-by: Eric Dumazet <edumazet@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20201023184709.217614-1-arjunroy.kdev@xxxxxxxxx
Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
net/ipv4/tcp.c | 2 ++
net/ipv4/tcp_input.c | 3 ++-
2 files changed, 4 insertions(+), 1 deletion(-)
--- a/net/ipv4/tcp.c
+++ b/net/ipv4/tcp.c
@@ -495,6 +495,8 @@ static inline bool tcp_stream_is_readabl
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);
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -4704,7 +4704,8 @@ 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);
