Re: [PATCH] tcp: keepalive fixes

Hi, Yuchung:

I have attached the python script that reproduces the keepalive issues.
The script is a slight modification of the one written by Marek Majkowski:

https://github.com/cloudflare/cloudflare-blog/blob/master/2019-09-tcp-keepalives/test-zero.py

Please note that only the TCP keepalive is configured, and not the user timeout.

Thanks.  -- Enke

On Tue, Jan 12, 2021 at 02:48:01PM -0800, Yuchung Cheng wrote:

On Tue, Jan 12, 2021 at 2:31 PM Enke Chen [off-list ref] wrote:

quoted

From: Enke Chen <redacted>

In this patch two issues with TCP keepalives are fixed:

1) TCP keepalive does not timeout when there are data waiting to be
   delivered and then the connection got broken. The TCP keepalive
   timeout is not evaluated in that condition.

hi enke
Do you have an example to demonstrate this issue -- in theory when
there is data inflight, an RTO timer should be pending (which
considers user-timeout setting). based on the user-timeout description
(man tcp), the user timeout should abort the socket per the specified
time after data commences. some data would help to understand the
issue.

------
#! /usr/bin/python

import io
import os
import select
import socket
import time
import utils
import ctypes

utils.new_ns()

port = 1

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0)
s.bind(('127.0.0.1', port))
s.setsockopt(socket.SOL_SOCKET, socket.SO_RCVBUF, 1024)

s.listen(16)

tcpdump = utils.tcpdump_start(port)
c = socket.socket(socket.AF_INET, socket.SOCK_STREAM, 0)
c.setsockopt(socket.SOL_SOCKET, socket.SO_RCVBUF, 1024)
c.connect(('127.0.0.1', port))

x, _ = s.accept()

if False:
    c.setsockopt(socket.IPPROTO_TCP, socket.TCP_USER_TIMEOUT, 90*1000)

if True:
    c.setsockopt(socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1)
    c.setsockopt(socket.IPPROTO_TCP, socket.TCP_KEEPCNT, 5)
    c.setsockopt(socket.IPPROTO_TCP, socket.TCP_KEEPIDLE, 10)
    c.setsockopt(socket.IPPROTO_TCP, socket.TCP_KEEPINTVL, 10)

time.sleep(0.2)
print("[ ] c.send()")
import fcntl
TIOCOUTQ=0x5411
c.setblocking(False)
while True:
    bytes_avail = ctypes.c_int()
    fcntl.ioctl(c.fileno(), TIOCOUTQ, bytes_avail)
    if bytes_avail.value > 64*1024:
        break
    try:
        c.send(b"A" * 16384 * 4)
    except io.BlockingIOError:
        break
c.setblocking(True)
time.sleep(0.2)
utils.ss(port)
utils.check_buffer(c)

t0 = time.time()

if True:
    utils.drop_start(dport=port)
    utils.drop_start(sport=port)

poll = select.poll()
poll.register(c, select.POLLIN)
poll.poll()

utils.ss(port)


e = c.getsockopt(socket.SOL_SOCKET, socket.SO_ERROR)
print("[ ] SO_ERROR = %s" % (e,))

t1 = time.time()
print("[ ] took: %f seconds" % (t1-t0,))