On Mon, Aug 15, 2022 at 6:30 AM Neal Cardwell ncardwell@google.com wrote:
On Mon, Aug 15, 2022 at 3:48 AM Jiri Slaby jirislaby@kernel.org wrote:
On 06. 08. 22, 16:41, Jiri Slaby wrote:
On 06. 08. 22, 13:24, Neal Cardwell wrote:
On Sat, Aug 6, 2022 at 6:02 AM Jiri Slaby jirislaby@kernel.org wrote:
On 21. 07. 22, 22:44, Wei Wang wrote:
This reverts commit 4a41f453bedfd5e9cd040bad509d9da49feb3e2c.
This to-be-reverted commit was meant to apply a stricter rule for the stack to enter pingpong mode. However, the condition used to check for interactive session "before(tp->lsndtime, icsk->icsk_ack.lrcvtime)" is jiffy based and might be too coarse, which delays the stack entering pingpong mode. We revert this patch so that we no longer use the above condition to determine interactive session, and also reduce pingpong threshold to 1.
Fixes: 4a41f453bedf ("tcp: change pingpong threshold to 3") Reported-by: LemmyHuang hlm3280@163.com Suggested-by: Neal Cardwell ncardwell@google.com Signed-off-by: Wei Wang weiwan@google.com
This breaks python-eventlet [1] (and was backported to stable trees): ________________ TestHttpd.test_018b_http_10_keepalive_framing _________________
self = <tests.wsgi_test.TestHttpd testMethod=test_018b_http_10_keepalive_framing>
def test_018b_http_10_keepalive_framing(self): # verify that if an http/1.0 client sends connection:keep-alive # that we don't mangle the request framing if the app doesn't read the request def app(environ, start_response): resp_body = { '/1': b'first response', '/2': b'second response', '/3': b'third response', }.get(environ['PATH_INFO']) if resp_body is None: resp_body = 'Unexpected path: ' + environ['PATH_INFO'] if six.PY3: resp_body = resp_body.encode('latin1') # Never look at wsgi.input! start_response('200 OK', [('Content-type', 'text/plain')]) return [resp_body]
self.site.application = app sock = eventlet.connect(self.server_addr) req_body = b'GET /tricksy HTTP/1.1\r\n' body_len = str(len(req_body)).encode('ascii') sock.sendall(b'PUT /1 HTTP/1.0\r\nHost:localhost\r\nConnection: keep-alive\r\n' b'Content-Length: ' + body_len + b'\r\n\r\n' + req_body) result1 = read_http(sock) self.assertEqual(b'first response', result1.body) self.assertEqual(result1.headers_original.get('Connection'), 'keep-alive')
sock.sendall(b'PUT /2 HTTP/1.0\r\nHost:localhost\r\nConnection: keep-alive\r\n' b'Content-Length: ' + body_len + b'\r\nExpect: 100-continue\r\n\r\n') # Client may have a short timeout waiting on that 100 Continue # and basically immediately send its body sock.sendall(req_body) result2 = read_http(sock) self.assertEqual(b'second response', result2.body) self.assertEqual(result2.headers_original.get('Connection'), 'close')
sock.sendall(b'PUT /3 HTTP/1.0\r\nHost:localhost\r\nConnection: close\r\n\r\n')
tests/wsgi_test.py:648: _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ eventlet/greenio/base.py:407: in sendall tail = self.send(data, flags) eventlet/greenio/base.py:401: in send return self._send_loop(self.fd.send, data, flags) _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _
self = <eventlet.greenio.base.GreenSocket object at 0x7f5f2f73c9a0> send_method = <built-in method send of socket object at 0x7f5f2f73d520> data = b'PUT /3 HTTP/1.0\r\nHost: localhost\r\nConnection: close\r\n\r\n' args = (0,), _timeout_exc = timeout('timed out'), eno = 32
def _send_loop(self, send_method, data, *args): if self.act_non_blocking: return send_method(data, *args) _timeout_exc = socket_timeout('timed out') while True: try:return send_method(data, *args)E BrokenPipeError: [Errno 32] Broken pipe
eventlet/greenio/base.py:388: BrokenPipeError
Reverting this revert on the top of 5.19 solves the issue.
Any ideas?
Interesting. This revert should return the kernel back to the delayed ACK behavior it had for many years before May 2019 and Linux 5.1, which contains the commit it is reverting:
4a41f453bedfd tcp: change pingpong threshold to 3
It sounds like perhaps this test you mention has an implicit dependence on the timing of delayed ACKs.
A few questions:
Dunno. I am only an openSUSE kernel maintainer and this popped out at me. Feel free to dig to eventlet's sources on your own :P.
Any updates on this or should I send a revert directly?
The "before() &&" part of the patch makes the difference. That is this diff: --- a/net/ipv4/tcp_output.c +++ b/net/ipv4/tcp_output.c @@ -172,9 +172,17 @@ static void tcp_event_data_sent(struct tcp_sock *tp, * and it is a reply for ato after last received packet, * increase pingpong count. */
if (before(tp->lsndtime, icsk->icsk_ack.lrcvtime) &&(u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato)
pr_info("%s: sk=%p (%llx:%x) now=%u lsndtime=%u lrcvtime=%uping=%u\n",
__func__, sk, sk->sk_addrpair, sk->sk_portpair, now,tp->lsndtime, icsk->icsk_ack.lrcvtime,inet_csk(sk)->icsk_ack.pingpong);if (//before(tp->lsndtime, icsk->icsk_ack.lrcvtime) &&(u32)(now - icsk->icsk_ack.lrcvtime) < icsk->icsk_ack.ato) { inet_csk_inc_pingpong_cnt(sk);pr_info("\tINC ping=%u before=%u\n",inet_csk(sk)->icsk_ack.pingpong,before(tp->lsndtime,icsk->icsk_ack.lrcvtime));
} tp->lsndtime = now;}
makes it work again, and outputs this:
Is the above patch made on top of my reverted patch? It seems not according to this part of diff. Then what is the definition of TCP_PINGPONG_THRESH in the working case? I think that is the key, regardless of the result of: before(tp->lsndtime, icsk->icsk_ack.lrcvtime)
I tried to look into what exactly the test is doing, and can't tell why it is failing. I don't see any check that is based on the timing of the reply. :( I hope someone could explain more about what this test is doing.
TCP: tcp_event_data_sent: sk=00000000fd67cf8d
(100007f0100007f:e858b18b) now=4294902140 lsndtime=4294902140 lrcvtime=4294902140 ping=0
TCP: tcp_event_data_sent: sk=00000000a4becf82
(100007f0100007f:8bb158e8) now=4294902143 lsndtime=4294902140 lrcvtime=4294902142 ping=0
TCP: INC ping=1 before=1 TCP: tcp_event_data_sent: sk=00000000fd67cf8d
(100007f0100007f:e858b18b) now=4294902145 lsndtime=4294902140 lrcvtime=4294902144 ping=0
TCP: INC ping=1 before=1 TCP: tcp_event_data_sent: sk=00000000fd67cf8d
(100007f0100007f:e858b18b) now=4294902147 lsndtime=4294902145 lrcvtime=4294902144 ping=1
TCP: INC ping=2 before=0
IMO, this "before=0" is the "source" of the problem. But I have no idea what this means at all...
TCP: tcp_event_data_sent: sk=00000000a4becf82
(100007f0100007f:8bb158e8) now=4294902149 lsndtime=4294902143 lrcvtime=4294902148 ping=1
TCP: INC ping=2 before=1 TCP: tcp_event_data_sent: sk=00000000fd67cf8d
(100007f0100007f:e858b18b) now=4294902151 lsndtime=4294902147 lrcvtime=4294902150 ping=3
TCP: INC ping=4 before=1 TCP: tcp_event_data_sent: sk=00000000c7a417e9
(100007f0100007f:e85ab18b) now=4294902153 lsndtime=4294902153 lrcvtime=4294902153 ping=0
TCP: tcp_event_data_sent: sk=000000008681183e
(100007f0100007f:8bb15ae8) now=4294902155 lsndtime=4294902153 lrcvtime=4294902154 ping=0
TCP: INC ping=1 before=1
It sounds like this test has a very specific dependence on the buggy delayed ACK timing behavior from the buggy commit 4a41f453bedfd5e9cd040bad509d9da49feb3e2c.
IMHO I don't think we can revert a kernel bug fix based on a test that decided to depend on the exact timing of delayed ACKs during a time when that delayed ACK behavior was buggy. :-)
best regards, neal