Messages in this thread Patch in this message | | | From | menglong8.dong@gmail ... | Subject | [PATCH net-next v2 3/3] net: tcp: fix unexcepted socket die when snd_wnd is 0 | Date | Mon, 7 Aug 2023 21:45:47 +0800 |
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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 is not precise enough, as it base on timer wheel. Sorry that I am not good at timer, but I know the concept of time-wheel. The longer of the timer, the rougher it will be. So the timeout is not triggered after TCP_RTO_MAX, but 122877ms 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 "max(tp->retrans_stamp, 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> --- v2: - consider the case of the connection restart from idle, as Neal comment --- net/ipv4/tcp_timer.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c index d45c96c7f5a4..e4b2d8706cae 100644 --- a/net/ipv4/tcp_timer.c +++ b/net/ipv4/tcp_timer.c @@ -454,6 +454,14 @@ 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 last_ts; + + last_ts = max(tp->retrans_stamp, tp->rcv_tstamp); + return inet_csk(sk)->icsk_timeout - last_ts > TCP_RTO_MAX; +} /** * tcp_retransmit_timer() - The TCP retransmit timeout handler @@ -519,7 +527,7 @@ 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
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