| Message ID | 20230808115835.2862058-4-imagedong@tencent.com (mailing list archive) |
|---|---|
| State | Superseded |
| Delegated to: | Netdev Maintainers |
| Headers | show |
| Series | net: tcp: support probing OOM | expand |
On Tue, Aug 8, 2023 at 1:59 PM <menglong8.dong@gmail.com> wrote: > > From: Menglong Dong <imagedong@tencent.com> > > In tcp_retransmit_timer(), a window shrunk connection will be regarded > as timeout if 'tcp_jiffies32 - tp->rcv_tstamp > TCP_RTO_MAX'. This is not > right all the time. > > The retransmits will become zero-window probes in tcp_retransmit_timer() > if the 'snd_wnd==0'. Therefore, the icsk->icsk_rto will come up to > TCP_RTO_MAX sooner or later. > > However, the timer can be delayed and be triggered after 122877ms, not > TCP_RTO_MAX, as I tested. > > Therefore, 'tcp_jiffies32 - tp->rcv_tstamp > TCP_RTO_MAX' is always true > once the RTO come up to TCP_RTO_MAX, and the socket will die. > > Fix this by replacing the 'tcp_jiffies32' with '(u32)icsk->icsk_timeout', > which is exact the timestamp of the timeout. Meanwhile, using the later > one of tp->retrans_stamp and tp->rcv_tstamp as the last updated timestamp > in the receiving path, as "tp->rcv_tstamp" can restart from idle, then > tp->rcv_tstamp could already be a long time (minutes or hours) in the > past even on the first RTO. > > Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2") > Link: https://lore.kernel.org/netdev/CADxym3YyMiO+zMD4zj03YPM3FBi-1LHi6gSD2XT8pyAMM096pg@mail.gmail.com/ > Signed-off-by: Menglong Dong <imagedong@tencent.com> > --- > v3: > - use after() instead of max() in tcp_rtx_probe0_timed_out() > v2: > - consider the case of the connection restart from idle, as Neal comment > --- > net/ipv4/tcp_timer.c | 14 +++++++++++++- > 1 file changed, 13 insertions(+), 1 deletion(-) > > diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c > index d45c96c7f5a4..f30d1467771c 100644 > --- a/net/ipv4/tcp_timer.c > +++ b/net/ipv4/tcp_timer.c > @@ -454,6 +454,18 @@ static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req) > req->timeout << req->num_timeout, TCP_RTO_MAX); > } > > +static bool tcp_rtx_probe0_timed_out(struct sock *sk) const struct sock *sk > +{ > + struct tcp_sock *tp = tcp_sk(sk); const struct tcp_sock *tp = tcp_sk(sk); > + u32 timeout_ts, rtx_ts, rcv_ts; > + > + rtx_ts = tp->retrans_stamp; > + rcv_ts = tp->rcv_tstamp; > + timeout_ts = after(rtx_ts, rcv_ts) ? rtx_ts : rcv_ts; > + timeout_ts += TCP_RTO_MAX; If we are concerned with a socket dying too soon, I would suggest adding 2*TCP_RTO_MAX instead of TCP_RTO_MAX When a receiver is OOMing, it is possible the ACK RWIN 0 can not be sent all, so tp->rcv_tstamp will not be refreshed. Or ACK could be lost in the network path. This also suggests the net_dbg_ratelimited("Peer %pI4:%u/%u unexpectedly shrunk window %u:%u (repaired)\n"...) messages are slightly wrong, because they could be printed even if we did not receive a new ACK packet from the remote peer. Perhaps we should change them to include delays (how long @skb stayed in rtx queue, how old is the last ACK we received) > + > + return after(inet_csk(sk)->icsk_timeout, timeout_ts); > +} > > /** > * tcp_retransmit_timer() - The TCP retransmit timeout handler > @@ -519,7 +531,7 @@ void tcp_retransmit_timer(struct sock *sk) > tp->snd_una, tp->snd_nxt); > } > #endif > - if (tcp_jiffies32 - tp->rcv_tstamp > TCP_RTO_MAX) { > + if (tcp_rtx_probe0_timed_out(sk)) { > tcp_write_err(sk); > goto out; > } > -- > 2.40.1 >
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c index d45c96c7f5a4..f30d1467771c 100644 --- a/net/ipv4/tcp_timer.c +++ b/net/ipv4/tcp_timer.c @@ -454,6 +454,18 @@ static void tcp_fastopen_synack_timer(struct sock *sk, struct request_sock *req) req->timeout << req->num_timeout, TCP_RTO_MAX); } +static bool tcp_rtx_probe0_timed_out(struct sock *sk) +{ + struct tcp_sock *tp = tcp_sk(sk); + u32 timeout_ts, rtx_ts, rcv_ts; + + rtx_ts = tp->retrans_stamp; + rcv_ts = tp->rcv_tstamp; + timeout_ts = after(rtx_ts, rcv_ts) ? rtx_ts : rcv_ts; + timeout_ts += TCP_RTO_MAX; + + return after(inet_csk(sk)->icsk_timeout, timeout_ts); +} /** * tcp_retransmit_timer() - The TCP retransmit timeout handler @@ -519,7 +531,7 @@ void tcp_retransmit_timer(struct sock *sk) tp->snd_una, tp->snd_nxt); } #endif - if (tcp_jiffies32 - tp->rcv_tstamp > TCP_RTO_MAX) { + if (tcp_rtx_probe0_timed_out(sk)) { tcp_write_err(sk); goto out; }