Hi Eric, On Wed, 24 Apr 2019 08:47:27 -0700 Eric Dumazet wrote: > On Wed, Apr 24, 2019 at 7:51 AM Bruno Prémont wrote: > > > > Hi Eric, > > > > I'm seeing issues with this patch as well, not as regular as for > > Richard but still (about up to one in 30-50 TCP sessions). > > > > In my case I have a virtual machine (on VMWare) with this patch where > > NGINX as reverse proxy misses part (end) of payload from its upstream > > and times out on the upstream connection (while according to tcpdump all > > packets including upstream's FIN were sent and the upstream did get > > ACKs from the VM). > > > > From when browsers get from NGINX it feels as if at some point reading > > from the socket or waiting for data using select() never returned data > > that arrived as more than just EOF is missing. > > > > The upstream is a hardware machine in the same subnet. > > > > My VM is using VMware VMXNET3 Ethernet Controller [15ad:07b0] (rev 01) > > as network adapter which lists the following features: > > > > Hi Bruno. > > I suspect a EPOLLIN notification being lost by the application. > > Fact that TCP backlog contains 1 instead of 2+ packets should not > change stack behavior, > this packet should land into socket receive queue eventually. > > Are you using epoll() in Edge Trigger mode. You mention select() but > select() is a rather old and inefficient API.
nginx is using epoll (c.f. http://nginx.org/en/docs/events.html) For source, see here https://trac.nginx.org/nginx/browser/nginx/src/event/modules/ngx_epoll_module.c?rev=ebf8c9686b8ce7428f975d8a567935ea3722da70 > Could you watch/report the output of " ss -temoi " for the frozen TCP flow ? Here it is, three distinct reproducing attempts: State Recv-Q Send-Q Local Address:Port Peer Address:Port ESTAB 0 0 158.64.2.228:44248 158.64.2.217:webcache uid:83 ino:13245 sk:87 <-> skmem:(r0,rb131072,t0,tb46080,f0,w0,o0,bl0,d0) ts sack cubic wscale:7,7 rto:210 rtt:0.24/0.118 ato:40 mss:1448 rcvmss:1448 advmss:1448 cwnd:10 bytes_acked:949 bytes_received:28381 segs_out:12 segs_in:12 data_segs_out:1 data_segs_in:10 send 482.7Mbps lastsnd:46810 lastrcv:46790 lastack:46790 pacing_rate 965.3Mbps delivery_rate 74.3Mbps app_limited rcv_rtt:1 rcv_space:14480 minrtt:0.156 ESTAB 0 0 2001:a18:1:6::228:33572 2001:a18:1:6::217:webcache uid:83 ino:16699 sk:e1 <-> skmem:(r0,rb131072,t0,tb46080,f0,w0,o0,bl0,d0) ts sack cubic wscale:7,7 rto:210 rtt:0.231/0.11 ato:40 mss:1428 rcvmss:1428 advmss:1428 cwnd:10 bytes_acked:948 bytes_received:28474 segs_out:12 segs_in:12 data_segs_out:1 data_segs_in:10 send 494.5Mbps lastsnd:8380 lastrcv:8360 lastack:8360 pacing_rate 989.1Mbps delivery_rate 71.0Mbps app_limited rcv_rtt:1.109 rcv_space:14280 minrtt:0.161 ESTAB 0 0 158.64.2.228:44578 158.64.2.217:webcache uid:83 ino:17628 sk:12c <-> skmem:(r0,rb131072,t0,tb46080,f0,w0,o0,bl0,d0) ts sack cubic wscale:7,7 rto:210 rtt:0.279/0.136 ato:40 mss:1448 rcvmss:1448 advmss:1448 cwnd:10 bytes_acked:949 bytes_received:28481 segs_out:12 segs_in:12 data_segs_out:1 data_segs_in:10 send 415.2Mbps lastsnd:11360 lastrcv:11330 lastack:11340 pacing_rate 828.2Mbps delivery_rate 61.9Mbps app_limited rcv_rtt:1 rcv_space:14480 minrtt:0.187 From nginx debug logging I don't get a real clue though it seems for working connections the last event obtained is 2005 (EPOLLMSG | EPOLLWRBAND | EPOLLWRNORM | EPOLLRDBAND | EPOLLRDNORM | EPOLLHUP | EPOLLIN | EPOLLOUT) - previous ones are 5 while for failing connections it looks like last event seen is 5 (EPOLLIN | EPOLLOUT). > This migtht give us a clue about packets being dropped, say the the > accumulated packet became too big. The following minor patch (might be white-space mangled) does prevent the issue happening for me: diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c index 4904250a9aac..c102cd367c79 100644 --- a/net/ipv4/tcp_ipv4.c +++ b/net/ipv4/tcp_ipv4.c @@ -1667,7 +1667,7 @@ bool tcp_add_backlog(struct sock *sk, struct sk_buff *skb) if (TCP_SKB_CB(tail)->end_seq != TCP_SKB_CB(skb)->seq || TCP_SKB_CB(tail)->ip_dsfield != TCP_SKB_CB(skb)->ip_dsfield || ((TCP_SKB_CB(tail)->tcp_flags | - TCP_SKB_CB(skb)->tcp_flags) & TCPHDR_URG) || + TCP_SKB_CB(skb)->tcp_flags) & (TCPHDR_URG | TCPHDR_FIN)) || ((TCP_SKB_CB(tail)->tcp_flags ^ TCP_SKB_CB(skb)->tcp_flags) & (TCPHDR_ECE | TCPHDR_CWR)) || #ifdef CONFIG_TLS_DEVICE Cheers, Bruno > > rx-checksumming: on > > tx-checksumming: on > > tx-checksum-ipv4: off [fixed] > > tx-checksum-ip-generic: on > > tx-checksum-ipv6: off [fixed] > > tx-checksum-fcoe-crc: off [fixed] > > tx-checksum-sctp: off [fixed] > > scatter-gather: on > > tx-scatter-gather: on > > tx-scatter-gather-fraglist: off [fixed] > > tcp-segmentation-offload: on > > tx-tcp-segmentation: on > > tx-tcp-ecn-segmentation: off [fixed] > > tx-tcp-mangleid-segmentation: off > > tx-tcp6-segmentation: on > > udp-fragmentation-offload: off > > generic-segmentation-offload: on > > generic-receive-offload: on > > large-receive-offload: on > > rx-vlan-offload: on > > tx-vlan-offload: on > > ntuple-filters: off [fixed] > > receive-hashing: off [fixed] > > highdma: on > > rx-vlan-filter: on [fixed] > > vlan-challenged: off [fixed] > > tx-lockless: off [fixed] > > netns-local: off [fixed] > > tx-gso-robust: off [fixed] > > tx-fcoe-segmentation: off [fixed] > > tx-gre-segmentation: off [fixed] > > tx-gre-csum-segmentation: off [fixed] > > tx-ipxip4-segmentation: off [fixed] > > tx-ipxip6-segmentation: off [fixed] > > tx-udp_tnl-segmentation: off [fixed] > > tx-udp_tnl-csum-segmentation: off [fixed] > > tx-gso-partial: off [fixed] > > tx-sctp-segmentation: off [fixed] > > tx-esp-segmentation: off [fixed] > > tx-udp-segmentation: off [fixed] > > fcoe-mtu: off [fixed] > > tx-nocache-copy: off > > loopback: off [fixed] > > rx-fcs: off [fixed] > > rx-all: off [fixed] > > tx-vlan-stag-hw-insert: off [fixed] > > rx-vlan-stag-hw-parse: off [fixed] > > rx-vlan-stag-filter: off [fixed] > > l2-fwd-offload: off [fixed] > > hw-tc-offload: off [fixed] > > esp-hw-offload: off [fixed] > > esp-tx-csum-hw-offload: off [fixed] > > rx-udp_tunnel-port-offload: off [fixed] > > tls-hw-tx-offload: off [fixed] > > tls-hw-rx-offload: off [fixed] > > rx-gro-hw: off [fixed] > > tls-hw-record: off [fixed] > > > > > > I can reproduce the issue with kernels 5.0.x and as recent as 5.1-rc6. > > > > Cheers, > > Bruno > > > > On Sunday, April 7, 2019 11:28:30 PM CEST, > > richard.pur...@linuxfoundation.org wrote: > > > Hi, > > > > > > I've been chasing down why a python test from the python3 testsuite > > > started failing and it seems to point to this kernel change in the > > > networking stack. > > > > > > In kernels beyond commit 4f693b55c3d2d2239b8a0094b518a1e533cf75d5 the > > > test hangs about 90% of the time (I've reproduced with 5.1-rc3, 5.0.7, > > > 5.0-rc1 but not 4.18, 4.19 or 4.20). The reproducer is: > > > > > > $ python3 -m test test_httplib -v > > > == CPython 3.7.2 (default, Apr 5 2019, 15:17:15) [GCC 8.3.0] > > > == Linux-5.0.0-yocto-standard-x86_64-with-glibc2.2.5 little-endian > > > == cwd: /var/volatile/tmp/test_python_288 > > > == CPU count: 1 > > > == encodings: locale=UTF-8, FS=utf-8 > > > [...] > > > test_response_fileno (test.test_httplib.BasicTest) ... > > > > > > and it hangs in test_response_fileno. > > > > > > The test in question comes from Lib/test/test_httplib.py in the python > > > source tree and the code is: > > > > > > def test_response_fileno(self): > > > # Make sure fd returned by fileno is valid. > > > serv = socket.socket( > > > socket.AF_INET, socket.SOCK_STREAM, socket.IPPROTO_TCP) > > > self.addCleanup(serv.close) > > > serv.bind((HOST, 0)) > > > serv.listen() > > > > > > result = None > > > def run_server(): > > > [conn, address] = serv.accept() > > > with conn, conn.makefile("rb") as reader: > > > # Read the request header until a blank line > > > while True: > > > line = reader.readline() > > > if not line.rstrip(b"\r\n"): > > > break > > > conn.sendall(b"HTTP/1.1 200 Connection > > > established\r\n\r\n") > > > nonlocal result > > > result = reader.read() > > > > > > thread = threading.Thread(target=run_server) > > > thread.start() > > > self.addCleanup(thread.join, float(1)) > > > conn = client.HTTPConnection(*serv.getsockname()) > > > conn.request("CONNECT", "dummy:1234") > > > response = conn.getresponse() > > > try: > > > self.assertEqual(response.status, client.OK) > > > s = socket.socket(fileno=response.fileno()) > > > try: > > > s.sendall(b"proxied data\n") > > > finally: > > > s.detach() > > > finally: > > > response.close() > > > conn.close() > > > thread.join() > > > self.assertEqual(result, b"proxied data\n") > > > > > > I was hoping someone with more understanding of the networking stack > > > could look at this and tell whether its a bug in the python test, the > > > kernel change or otherwise give a pointer to where the problem might > > > be? I'll freely admit this is not an area I know much about. > > > > > > Cheers, > > > > > > Richard > > > > > > > > >
