tue...@freebsd.org wrote: [stuff snipped] >OK. What is the FreeBSD version you are using? main Dec. 23, 2020.
> >It seems that the TCP connection on the FreeBSD is still alive, >Linux has decided to start a new TCP connection using the old >port numbers. So it sends a SYN. The response is a challenge ACK >and Linux responds with a RST. This looks good so far. However, >FreeBSD should accept the RST and kill the TCP connection. The >next SYN from the Linux side would establish a new TCP connection. > >So I'm wondering why the RST is not accepted. I made the timestamp >checking stricter but introduced a bug where RST segments without >timestamps were ignored. This was fixed. > >Introduced in main on 2020/11/09: > https://svnweb.freebsd.org/changeset/base/367530 >Introduced in stable/12 on 2020/11/30: > https://svnweb.freebsd.org/changeset/base/36818 >Fix in main on 2021/01/13: > > https://cgit.FreeBSD.org/src/commit/?id=cc3c34859eab1b317d0f38731355b53f7d978c97 >Fix in stable/12 on 2021/01/24: > > https://cgit.FreeBSD.org/src/commit/?id=d05d908d6d3c85479c84c707f931148439ae826b > >Are you using a version which is affected by this bug? I was. Now I've applied the patch. Bad News. It did not fix the problem. It still gets into an endless "ignore RST" and stay established when the Send-Q is empty. If the Send-Q is non-empty when I partition, it recovers fine, sometimes not even needing to see an RST. rick ps: If you think there might be other recent changes that matter, just say the word and I'll upgrade to bits de jur. rick Best regards Michael > > If I wait long enough before healing the partition, it will > go to FIN_WAIT_1, and then if I plug it back in, it does not > do battle (at least not for long). > > Btw, I have one running now that seems stuck really good. > It has been 20minutes since I plugged the net cable back in. > (Unfortunately, I didn't have tcpdump running until after > I saw it was not progressing after healing. > --> There is one difference. There was a 6minute timeout > enabled on the server krpc for "no activity", which is > now disabled like it is for NFSv4.1 in freebsd-current. > I had forgotten to re-disable it. > So, when it does battle, it might have been the 6minute > timeout, which would then do the soshutdown(..SHUT_WR) > which kept it from getting "stuck" forever. > -->This time I had to reboot the FreeBSD NFS server to > get the Linux client unstuck, so this one looked a lot > like what has been reported. > The pcap for this one, started after the network was plugged > back in and I noticed it was stuck for quite a while is here: > fetch https://people.freebsd.org/~rmacklem/stuck.pcap > > In it, there is just a bunch of RST followed by SYN sent > from client->FreeBSD and FreeBSD just keeps sending > acks for the old segment back. > --> It looks like FreeBSD did the "RST, ACK" after the > krpc did a soshutdown(..SHUT_WR) on the socket, > for the one you've been looking at. > I'll test some more... > >> I would like to understand why the reestablishment of the connection >> did not work... > It is looking like it takes either a non-empty send-q or a > soshutdown(..SHUT_WR) to get the FreeBSD socket > out of established, where it just ignores the RSTs and > SYN packets. > > Thanks for looking at it, rick > > Best regards > Michael >> >> Have fun with it, rick >> >> >> ________________________________________ >> From: tue...@freebsd.org <tue...@freebsd.org> >> Sent: Sunday, April 4, 2021 12:41 PM >> To: Rick Macklem >> Cc: Scheffenegger, Richard; Youssef GHORBAL; freebsd-net@freebsd.org >> Subject: Re: NFS Mount Hangs >> >> CAUTION: This email originated from outside of the University of Guelph. Do >> not click links or open attachments unless you recognize the sender and know >> the content is safe. If in doubt, forward suspicious emails to >> ith...@uoguelph.ca >> >> >>> On 4. Apr 2021, at 17:27, Rick Macklem <rmack...@uoguelph.ca> wrote: >>> >>> Well, I'm going to cheat and top post, since this is elated info. and >>> not really part of the discussion... >>> >>> I've been testing network partitioning between a Linux client (5.2 kernel) >>> and a FreeBSD-current NFS server. I have not gotten a solid hang, but >>> I have had the Linux client doing "battle" with the FreeBSD server for >>> several minutes after un-partitioning the connection. >>> >>> The battle basically consists of the Linux client sending an RST, followed >>> by a SYN. >>> The FreeBSD server ignores the RST and just replies with the same old ack. >>> --> This varies from "just a SYN" that succeeds to 100+ cycles of the above >>> over several minutes. >>> >>> I had thought that an RST was a "pretty heavy hammer", but FreeBSD seems >>> pretty good at ignoring it. >>> >>> A full packet capture of one of these is in >>> /home/rmacklem/linuxtofreenfs.pcap >>> in case anyone wants to look at it. >> On freefall? I would like to take a look at it... >> >> Best regards >> Michael >>> >>> Here's a tcpdump snippet of the interesting part (see the *** comments): >>> 19:10:09.305775 IP nfsv4-new3.home.rick.nfsd > >>> nfsv4-linux.home.rick.apex-mesh: Flags [P.], seq 202585:202749, ack 212293, >>> win 29128, options [nop,nop,TS val 2073636037 ecr 2671204825], length 164: >>> NFS reply xid 613153685 reply ok 160 getattr NON 4 ids 0/33554432 sz 0 >>> 19:10:09.305850 IP nfsv4-linux.home.rick.apex-mesh > >>> nfsv4-new3.home.rick.nfsd: Flags [.], ack 202749, win 501, options >>> [nop,nop,TS val 2671204825 ecr 2073636037], length 0 >>> *** Network is now partitioned... >>> >>> 19:10:09.407840 IP nfsv4-linux.home.rick.apex-mesh > >>> nfsv4-new3.home.rick.nfsd: Flags [P.], seq 212293:212525, ack 202749, win >>> 501, options [nop,nop,TS val 2671204927 ecr 2073636037], length 232: NFS >>> request xid 629930901 228 getattr fh 0,1/53 >>> 19:10:09.615779 IP nfsv4-linux.home.rick.apex-mesh > >>> nfsv4-new3.home.rick.nfsd: Flags [P.], seq 212293:212525, ack 202749, win >>> 501, options [nop,nop,TS val 2671205135 ecr 2073636037], length 232: NFS >>> request xid 629930901 228 getattr fh 0,1/53 >>> 19:10:09.823780 IP nfsv4-linux.home.rick.apex-mesh > >>> nfsv4-new3.home.rick.nfsd: Flags [P.], seq 212293:212525, ack 202749, win >>> 501, options [nop,nop,TS val 2671205343 ecr 2073636037], length 232: NFS >>> request xid 629930901 228 getattr fh 0,1/53 >>> *** Lots of lines snipped. >>> >>> >>> 19:13:41.295783 ARP, Request who-has nfsv4-new3.home.rick tell >>> nfsv4-linux.home.rick, length 28 >>> 19:13:42.319767 ARP, Request who-has nfsv4-new3.home.rick tell >>> nfsv4-linux.home.rick, length 28 >>> 19:13:46.351966 ARP, Request who-has nfsv4-new3.home.rick tell >>> nfsv4-linux.home.rick, length 28 >>> 19:13:47.375790 ARP, Request who-has nfsv4-new3.home.rick tell >>> nfsv4-linux.home.rick, length 28 >>> 19:13:48.399786 ARP, Request who-has nfsv4-new3.home.rick tell >>> nfsv4-linux.home.rick, length 28 >>> *** Network is now unpartitioned... >>> >>> 19:13:48.399990 ARP, Reply nfsv4-new3.home.rick is-at d4:be:d9:07:81:72 >>> (oui Unknown), length 46 >>> 19:13:48.400002 IP nfsv4-linux.home.rick.apex-mesh > >>> nfsv4-new3.home.rick.nfsd: Flags [S], seq 416692300, win 64240, options >>> [mss 1460,sackOK,TS val 2671421871 ecr 0,nop,wscale 7], length 0 >>> 19:13:48.400185 IP nfsv4-new3.home.rick.nfsd > >>> nfsv4-linux.home.rick.apex-mesh: Flags [.], ack 212293, win 29127, options >>> [nop,nop,TS val 2073855137 ecr 2671204825], length 0 >>> 19:13:48.400273 IP nfsv4-linux.home.rick.apex-mesh > >>> nfsv4-new3.home.rick.nfsd: Flags [R], seq 964161458, win 0, length 0 >>> 19:13:49.423833 IP nfsv4-linux.home.rick.apex-mesh > >>> nfsv4-new3.home.rick.nfsd: Flags [S], seq 416692300, win 64240, options >>> [mss 1460,sackOK,TS val 2671424943 ecr 0,nop,wscale 7], length 0 >>> 19:13:49.424056 IP nfsv4-new3.home.rick.nfsd > >>> nfsv4-linux.home.rick.apex-mesh: Flags [.], ack 212293, win 29127, options >>> [nop,nop,TS val 2073856161 ecr 2671204825], length 0 >>> *** This "battle" goes on for 223sec... >>> I snipped out 13 cycles of this "Linux sends an RST, followed by SYN" >>> "FreeBSD replies with same old ACK". In another test run I saw this >>> cycle continue non-stop for several minutes. This time, the Linux >>> client paused for a while (see ARPs below). >>> >>> 19:13:49.424101 IP nfsv4-linux.home.rick.apex-mesh > >>> nfsv4-new3.home.rick.nfsd: Flags [R], seq 964161458, win 0, length 0 >>> 19:13:53.455867 IP nfsv4-linux.home.rick.apex-mesh > >>> nfsv4-new3.home.rick.nfsd: Flags [S], seq 416692300, win 64240, options >>> [mss 1460,sackOK,TS val 2671428975 ecr 0,nop,wscale 7], length 0 >>> 19:13:53.455991 IP nfsv4-new3.home.rick.nfsd > >>> nfsv4-linux.home.rick.apex-mesh: Flags [.], ack 212293, win 29127, options >>> [nop,nop,TS val 2073860193 ecr 2671204825], length 0 >>> *** Snipped a bunch of stuff out, mostly ARPs, plus one more RST. >>> >>> 19:16:57.775780 ARP, Request who-has nfsv4-new3.home.rick tell >>> nfsv4-linux.home.rick, length 28 >>> 19:16:57.775937 ARP, Reply nfsv4-new3.home.rick is-at d4:be:d9:07:81:72 >>> (oui Unknown), length 46 >>> 19:16:57.980240 ARP, Request who-has nfsv4-new3.home.rick tell >>> 192.168.1.254, length 46 >>> 19:16:58.555663 ARP, Request who-has nfsv4-new3.home.rick tell >>> 192.168.1.254, length 46 >>> 19:17:00.104701 IP nfsv4-new3.home.rick.nfsd > >>> nfsv4-linux.home.rick.apex-mesh: Flags [F.], seq 202749, ack 212293, win >>> 29128, options [nop,nop,TS val 2074046846 ecr 2671204825], length 0 >>> 19:17:15.664354 IP nfsv4-new3.home.rick.nfsd > >>> nfsv4-linux.home.rick.apex-mesh: Flags [F.], seq 202749, ack 212293, win >>> 29128, options [nop,nop,TS val 2074062406 ecr 2671204825], length 0 >>> 19:17:31.239246 IP nfsv4-new3.home.rick.nfsd > >>> nfsv4-linux.home.rick.apex-mesh: Flags [R.], seq 202750, ack 212293, win 0, >>> options [nop,nop,TS val 2074077981 ecr 2671204825], length 0 >>> *** FreeBSD finally acknowledges the RST 38sec after Linux sent the last >>> of 13 (100+ for another test run). >>> >>> 19:17:51.535979 IP nfsv4-linux.home.rick.apex-mesh > >>> nfsv4-new3.home.rick.nfsd: Flags [S], seq 4247692373, win 64240, options >>> [mss 1460,sackOK,TS val 2671667055 ecr 0,nop,wscale 7], length 0 >>> 19:17:51.536130 IP nfsv4-new3.home.rick.nfsd > >>> nfsv4-linux.home.rick.apex-mesh: Flags [S.], seq 661237469, ack 4247692374, >>> win 65535, options [mss 1460,nop,wscale 6,sackOK,TS val 2074098278 ecr >>> 2671667055], length 0 >>> *** Now back in business... >>> >>> 19:17:51.536218 IP nfsv4-linux.home.rick.apex-mesh > >>> nfsv4-new3.home.rick.nfsd: Flags [.], ack 1, win 502, options [nop,nop,TS >>> val 2671667055 ecr 2074098278], length 0 >>> 19:17:51.536295 IP nfsv4-linux.home.rick.apex-mesh > >>> nfsv4-new3.home.rick.nfsd: Flags [P.], seq 1:233, ack 1, win 502, options >>> [nop,nop,TS val 2671667056 ecr 2074098278], length 232: NFS request xid >>> 629930901 228 getattr fh 0,1/53 >>> 19:17:51.536346 IP nfsv4-linux.home.rick.apex-mesh > >>> nfsv4-new3.home.rick.nfsd: Flags [P.], seq 233:505, ack 1, win 502, options >>> [nop,nop,TS val 2671667056 ecr 2074098278], length 272: NFS request xid >>> 697039765 132 getattr fh 0,1/53 >>> 19:17:51.536515 IP nfsv4-new3.home.rick.nfsd > >>> nfsv4-linux.home.rick.apex-mesh: Flags [.], ack 505, win 29128, options >>> [nop,nop,TS val 2074098279 ecr 2671667056], length 0 >>> 19:17:51.536553 IP nfsv4-linux.home.rick.apex-mesh > >>> nfsv4-new3.home.rick.nfsd: Flags [P.], seq 505:641, ack 1, win 502, options >>> [nop,nop,TS val 2671667056 ecr 2074098279], length 136: NFS request xid >>> 730594197 132 getattr fh 0,1/53 >>> 19:17:51.536562 IP nfsv4-new3.home.rick.nfsd > >>> nfsv4-linux.home.rick.apex-mesh: Flags [P.], seq 1:49, ack 505, win 29128, >>> options [nop,nop,TS val 2074098279 ecr 2671667056], length 48: NFS reply >>> xid 697039765 reply ok 44 getattr ERROR: unk 10063 >>> >>> This error 10063 after the partition heals is also "bad news". It indicates >>> the Session >>> (which is supposed to maintain "exactly once" RPC semantics is broken). >>> I'll admit I >>> suspect a Linux client bug, but will be investigating further. >>> >>> So, hopefully TCP conversant folk can confirm if the above is correct >>> behaviour >>> or if the RST should be ack'd sooner? >>> >>> I could also see this becoming a "forever" TCP battle for other versions of >>> Linux client. >>> >>> rick >>> >>> >>> ________________________________________ >>> From: Scheffenegger, Richard <richard.scheffeneg...@netapp.com> >>> Sent: Sunday, April 4, 2021 7:50 AM >>> To: Rick Macklem; tue...@freebsd.org >>> Cc: Youssef GHORBAL; freebsd-net@freebsd.org >>> Subject: Re: NFS Mount Hangs >>> >>> CAUTION: This email originated from outside of the University of Guelph. Do >>> not click links or open attachments unless you recognize the sender and >>> know the content is safe. If in doubt, forward suspicious emails to >>> ith...@uoguelph.ca >>> >>> >>> For what it‘s worth, suse found two bugs in the linux nfconntrack (stateful >>> firewall), and pfifo-fast scheduler, which could conspire to make tcp >>> sessions hang forever. >>> >>> One is a missed updaten when the cöient is not using the noresvport moint >>> option, which makes tje firewall think rsts are illegal (and drop them); >>> >>> The fast scheduler can run into an issue if only a single packet should be >>> forwarded (note that this is not the default scheduler, but often >>> recommended for perf, as it runs lockless and lower cpu cost that pfq >>> (default). If no other/additional packet pushes out that last packet of a >>> flow, it can become stuck forever... >>> >>> I can try getting the relevant bug info next week... >>> >>> ________________________________ >>> Von: owner-freebsd-...@freebsd.org <owner-freebsd-...@freebsd.org> im >>> Auftrag von Rick Macklem <rmack...@uoguelph.ca> >>> Gesendet: Friday, April 2, 2021 11:31:01 PM >>> An: tue...@freebsd.org <tue...@freebsd.org> >>> Cc: Youssef GHORBAL <youssef.ghor...@pasteur.fr>; freebsd-net@freebsd.org >>> <freebsd-net@freebsd.org> >>> Betreff: Re: NFS Mount Hangs >>> >>> NetApp Security WARNING: This is an external email. Do not click links or >>> open attachments unless you recognize the sender and know the content is >>> safe. >>> >>> >>> >>> >>> tue...@freebsd.org wrote: >>>>> On 2. Apr 2021, at 02:07, Rick Macklem <rmack...@uoguelph.ca> wrote: >>>>> >>>>> I hope you don't mind a top post... >>>>> I've been testing network partitioning between the only Linux client >>>>> I have (5.2 kernel) and a FreeBSD server with the xprtdied.patch >>>>> (does soshutdown(..SHUT_WR) when it knows the socket is broken) >>>>> applied to it. >>>>> >>>>> I'm not enough of a TCP guy to know if this is useful, but here's what >>>>> I see... >>>>> >>>>> While partitioned: >>>>> On the FreeBSD server end, the socket either goes to CLOSED during >>>>> the network partition or stays ESTABLISHED. >>>> If it goes to CLOSED you called shutdown(, SHUT_WR) and the peer also >>>> sent a FIN, but you never called close() on the socket. >>>> If the socket stays in ESTABLISHED, there is no communication ongoing, >>>> I guess, and therefore the server does not even detect that the peer >>>> is not reachable. >>>>> On the Linux end, the socket seems to remain ESTABLISHED for a >>>>> little while, and then disappears. >>>> So how does Linux detect the peer is not reachable? >>> Well, here's what I see in a packet capture in the Linux client once >>> I partition it (just unplug the net cable): >>> - lots of retransmits of the same segment (with ACK) for 54sec >>> - then only ARP queries >>> >>> Once I plug the net cable back in: >>> - ARP works >>> - one more retransmit of the same segement >>> - receives RST from FreeBSD >>> ** So, is this now a "new" TCP connection, despite >>> using the same port#. >>> --> It matters for NFS, since "new connection" >>> implies "must retry all outstanding RPCs". >>> - sends SYN >>> - receives SYN, ACK from FreeBSD >>> --> connection starts working again >>> Always uses same port#. >>> >>> On the FreeBSD server end: >>> - receives the last retransmit of the segment (with ACK) >>> - sends RST >>> - receives SYN >>> - sends SYN, ACK >>> >>> I thought that there was no RST in the capture I looked at >>> yesterday, so I'm not sure if FreeBSD always sends an RST, >>> but the Linux client behaviour was the same. (Sent a SYN, etc). >>> The socket disappears from the Linux "netstat -a" and I >>> suspect that happens after about 54sec, but I am not sure >>> about the timing. >>> >>>>> >>>>> After unpartitioning: >>>>> On the FreeBSD server end, you get another socket showing up at >>>>> the same port# >>>>> Active Internet connections (including servers) >>>>> Proto Recv-Q Send-Q Local Address Foreign Address (state) >>>>> tcp4 0 0 nfsv4-new3.nfsd nfsv4-linux.678 >>>>> ESTABLISHED >>>>> tcp4 0 0 nfsv4-new3.nfsd nfsv4-linux.678 CLOSED >>>>> >>>>> The Linux client shows the same connection ESTABLISHED. >>> But disappears from "netstat -a" for a while during the partitioning. >>> >>>>> (The mount sometimes reports an error. I haven't looked at packet >>>>> traces to see if it retries RPCs or why the errors occur.) >>> I have now done so, as above. >>> >>>>> --> However I never get hangs. >>>>> Sometimes it goes to SYN_SENT for a while and the FreeBSD server >>>>> shows FIN_WAIT_1, but then both ends go to ESTABLISHED and the >>>>> mount starts working again. >>>>> >>>>> The most obvious thing is that the Linux client always keeps using >>>>> the same port#. (The FreeBSD client will use a different port# when >>>>> it does a TCP reconnect after no response from the NFS server for >>>>> a little while.) >>>>> >>>>> What do those TCP conversant think? >>>> I guess you are you are never calling close() on the socket, for with >>>> the connection state is CLOSED. >>> Ok, that makes sense. For this case the Linux client has not done a >>> BindConnectionToSession to re-assign the back channel. >>> I'll have to bug them about this. However, I'll bet they'll answer >>> that I have to tell them the back channel needs re-assignment >>> or something like that. >>> >>> I am pretty certain they are broken, in that the client needs to >>> retry all outstanding RPCs. >>> >>> For others, here's the long winded version of this that I just >>> put on the phabricator review: >>> In the server side kernel RPC, the socket (struct socket *) is in a >>> structure called SVCXPRT (normally pointed to by "xprt"). >>> These structures a ref counted and the soclose() is done >>> when the ref. cnt goes to zero. My understanding is that >>> "struct socket *" is free'd by soclose() so this cannot be done >>> before the xprt ref. cnt goes to zero. >>> >>> For NFSv4.1/4.2 there is something called a back channel >>> which means that a "xprt" is used for server->client RPCs, >>> although the TCP connection is established by the client >>> to the server. >>> --> This back channel holds a ref cnt on "xprt" until the >>> >>> client re-assigns it to a different TCP connection >>> via an operation called BindConnectionToSession >>> and the Linux client is not doing this soon enough, >>> it appears. >>> >>> So, the soclose() is delayed, which is why I think the >>> TCP connection gets stuck in CLOSE_WAIT and that is >>> why I've added the soshutdown(..SHUT_WR) calls, >>> which can happen before the client gets around to >>> re-assigning the back channel. >>> >>> Thanks for your help with this Michael, rick >>> >>> Best regards >>> Michael >>>> >>>> rick >>>> ps: I can capture packets while doing this, if anyone has a use >>>> for them. >>>> >>>> >>>> >>>> >>>> >>>> >>>> ________________________________________ >>>> From: owner-freebsd-...@freebsd.org <owner-freebsd-...@freebsd.org> on >>>> behalf of Youssef GHORBAL <youssef.ghor...@pasteur.fr> >>>> Sent: Saturday, March 27, 2021 6:57 PM >>>> To: Jason Breitman >>>> Cc: Rick Macklem; freebsd-net@freebsd.org >>>> Subject: Re: NFS Mount Hangs >>>> >>>> CAUTION: This email originated from outside of the University of Guelph. >>>> Do not click links or open attachments unless you recognize the sender and >>>> know the content is safe. If in doubt, forward suspicious emails to >>>> ith...@uoguelph.ca >>>> >>>> >>>> >>>> >>>> On 27 Mar 2021, at 13:20, Jason Breitman >>>> <jbreit...@tildenparkcapital.com<mailto:jbreit...@tildenparkcapital.com>> >>>> wrote: >>>> >>>> The issue happened again so we can say that disabling TSO and LRO on the >>>> NIC did not resolve this issue. >>>> # ifconfig lagg0 -rxcsum -rxcsum6 -txcsum -txcsum6 -lro -tso -vlanhwtso >>>> # ifconfig lagg0 >>>> lagg0: flags=8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> metric 0 >>>> mtu 1500 >>>> >>>> options=8100b8<VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,VLAN_HWCSUM,VLAN_HWFILTER> >>>> >>>> We can also say that the sysctl settings did not resolve this issue. >>>> >>>> # sysctl net.inet.tcp.fast_finwait2_recycle=1 >>>> net.inet.tcp.fast_finwait2_recycle: 0 -> 1 >>>> >>>> # sysctl net.inet.tcp.finwait2_timeout=1000 >>>> net.inet.tcp.finwait2_timeout: 60000 -> 1000 >>>> >>>> I don’t think those will do anything in your case since the FIN_WAIT2 are >>>> on the client side and those sysctls are for BSD. >>>> By the way it seems that Linux recycles automatically TCP sessions in >>>> FIN_WAIT2 after 60 seconds (sysctl net.ipv4.tcp_fin_timeout) >>>> >>>> tcp_fin_timeout (integer; default: 60; since Linux 2.2) >>>> This specifies how many seconds to wait for a final FIN >>>> packet before the socket is forcibly closed. This is >>>> strictly a violation of the TCP specification, but >>>> required to prevent denial-of-service attacks. In Linux >>>> 2.2, the default value was 180. >>>> >>>> So I don’t get why it stucks in the FIN_WAIT2 state anyway. >>>> >>>> You really need to have a packet capture during the outage (client and >>>> server side) so you’ll get over the wire chat and start speculating from >>>> there. >>>> No need to capture the beginning of the outage for now. All you have to >>>> do, is run a tcpdump for 10 minutes or so when you notice a client stuck. >>>> >>>> * I have not rebooted the NFS Server nor have I restarted nfsd, but do not >>>> believe that is required as these settings are at the TCP level and I >>>> would expect new sessions to use the updated settings. >>>> >>>> The issue occurred after 5 days following a reboot of the client machines. >>>> I ran the capture information again to make use of the situation. >>>> >>>> #!/bin/sh >>>> >>>> while true >>>> do >>>> /bin/date >> /tmp/nfs-hang.log >>>> /bin/ps axHl | grep nfsd | grep -v grep >> /tmp/nfs-hang.log >>>> /usr/bin/procstat -kk 2947 >> /tmp/nfs-hang.log >>>> /usr/bin/procstat -kk 2944 >> /tmp/nfs-hang.log >>>> /bin/sleep 60 >>>> done >>>> >>>> >>>> On the NFS Server >>>> Active Internet connections (including servers) >>>> Proto Recv-Q Send-Q Local Address Foreign Address (state) >>>> tcp4 0 0 NFS.Server.IP.X.2049 NFS.Client.IP.X.48286 >>>> CLOSE_WAIT >>>> >>>> On the NFS Client >>>> tcp 0 0 NFS.Client.IP.X:48286 NFS.Server.IP.X:2049 >>>> FIN_WAIT2 >>>> >>>> >>>> >>>> You had also asked for the output below. >>>> >>>> # nfsstat -E -s >>>> BackChannelCtBindConnToSes >>>> 0 0 >>>> >>>> # sysctl vfs.nfsd.request_space_throttle_count >>>> vfs.nfsd.request_space_throttle_count: 0 >>>> >>>> I see that you are testing a patch and I look forward to seeing the >>>> results. >>>> >>>> >>>> Jason Breitman >>>> >>>> >>>> On Mar 21, 2021, at 6:21 PM, Rick Macklem >>>> <rmack...@uoguelph.ca<mailto:rmack...@uoguelph.ca>> wrote: >>>> >>>> Youssef GHORBAL >>>> <youssef.ghor...@pasteur.fr<mailto:youssef.ghor...@pasteur.fr>> wrote: >>>>> Hi Jason, >>>>> >>>>>> On 17 Mar 2021, at 18:17, Jason Breitman >>>>>> <jbreit...@tildenparkcapital.com<mailto:jbreit...@tildenparkcapital.com>> >>>>>> wrote: >>>>>> >>>>>> Please review the details below and let me know if there is a setting >>>>>> that I should apply to my FreeBSD NFS Server or if there is a bug fix >>>>>> that I can apply to resolve my issue. >>>>>> I shared this information with the linux-nfs mailing list and they >>>>>> believe the issue is on the server side. >>>>>> >>>>>> Issue >>>>>> NFSv4 mounts periodically hang on the NFS Client. >>>>>> >>>>>> During this time, it is possible to manually mount from another NFS >>>>>> Server on the NFS Client having issues. >>>>>> Also, other NFS Clients are successfully mounting from the NFS Server in >>>>>> question. >>>>>> Rebooting the NFS Client appears to be the only solution. >>>>> >>>>> I had experienced a similar weird situation with periodically stuck Linux >>>>> NFS clients >mounting Isilon NFS servers (Isilon is FreeBSD based but >>>>> they seem to have there >own nfsd) >>>> Yes, my understanding is that Isilon uses a proprietary user space nfsd and >>>> not the kernel based RPC and nfsd in FreeBSD. >>>> >>>>> We’ve had better luck and we did manage to have packet captures on both >>>>> sides >during the issue. The gist of it goes like follows: >>>>> >>>>> - Data flows correctly between SERVER and the CLIENT >>>>> - At some point SERVER starts decreasing it's TCP Receive Window until it >>>>> reachs 0 >>>>> - The client (eager to send data) can only ack data sent by SERVER. >>>>> - When SERVER was done sending data, the client starts sending TCP Window >>>>> >Probes hoping that the TCP Window opens again so he can flush its >>>>> buffers. >>>>> - SERVER responds with a TCP Zero Window to those probes. >>>> Having the window size drop to zero is not necessarily incorrect. >>>> If the server is overloaded (has a backlog of NFS requests), it can stop >>>> doing >>>> soreceive() on the socket (so the socket rcv buffer can fill up and the >>>> TCP window >>>> closes). This results in "backpressure" to stop the NFS client from >>>> flooding the >>>> NFS server with requests. >>>> --> However, once the backlog is handled, the nfsd should start to >>>> soreceive() >>>> again and this shouls cause the window to open back up. >>>> --> Maybe this is broken in the socket/TCP code. I quickly got lost in >>>> tcp_output() when it decides what to do about the rcvwin. >>>> >>>>> - After 6 minutes (the NFS server default Idle timeout) SERVER racefully >>>>> closes the >TCP connection sending a FIN Packet (and still a TCP Window 0) >>>> This probably does not happen for Jason's case, since the 6minute timeout >>>> is disabled when the TCP connection is assigned as a backchannel (most >>>> likely >>>> the case for NFSv4.1). >>>> >>>>> - CLIENT ACK that FIN. >>>>> - SERVER goes in FIN_WAIT_2 state >>>>> - CLIENT closes its half part part of the socket and goes in LAST_ACK >>>>> state. >>>>> - FIN is never sent by the client since there still data in its SendQ and >>>>> receiver TCP >Window is still 0. At this stage the client starts sending >>>>> TCP Window Probes again >and again hoping that the server opens its TCP >>>>> Window so it can flush it's buffers >and terminate its side of the socket. >>>>> - SERVER keeps responding with a TCP Zero Window to those probes. >>>>> => The last two steps goes on and on for hours/days freezing the NFS >>>>> mount bound >to that TCP session. >>>>> >>>>> If we had a situation where CLIENT was responsible for closing the TCP >>>>> Window (and >initiating the TCP FIN first) and server wanting to send >>>>> data we’ll end up in the same >state as you I think. >>>>> >>>>> We’ve never had the root cause of why the SERVER decided to close the TCP >>>>> >Window and no more acccept data, the fix on the Isilon part was to >>>>> recycle more >aggressively the FIN_WAIT_2 sockets >>>>> (net.inet.tcp.fast_finwait2_recycle=1 & >>>>> >net.inet.tcp.finwait2_timeout=5000). Once the socket recycled and at the >>>>> next >occurence of CLIENT TCP Window probe, SERVER sends a RST, >>>>> triggering the >teardown of the session on the client side, a new TCP >>>>> handchake, etc and traffic >flows again (NFS starts responding) >>>>> >>>>> To avoid rebooting the client (and before the aggressive FIN_WAIT_2 was >>>>> >implemented on the Isilon side) we’ve added a check script on the client >>>>> that detects >LAST_ACK sockets on the client and through iptables rule >>>>> enforces a TCP RST, >Something like: -A OUTPUT -p tcp -d $nfs_server_addr >>>>> --sport $local_port -j REJECT >--reject-with tcp-reset (the script >>>>> removes this iptables rule as soon as the LAST_ACK >disappears) >>>>> >>>>> The bottom line would be to have a packet capture during the outage >>>>> (client and/or >server side), it will show you at least the shape of the >>>>> TCP exchange when NFS is >stuck. >>>> Interesting story and good work w.r.t. sluething, Youssef, thanks. >>>> >>>> I looked at Jason's log and it shows everything is ok w.r.t the nfsd >>>> threads. >>>> (They're just waiting for RPC requests.) >>>> However, I do now think I know why the soclose() does not happen. >>>> When the TCP connection is assigned as a backchannel, that takes a >>>> reference >>>> cnt on the structure. This refcnt won't be released until the connection is >>>> replaced by a BindConnectiotoSession operation from the client. But that >>>> won't >>>> happen until the client creates a new TCP connection. >>>> --> No refcnt release-->no refcnt of 0-->no soclose(). >>>> >>>> I've created the attached patch (completely different from the previous >>>> one) >>>> that adds soshutdown(SHUT_WR) calls in the three places where the TCP >>>> connection is going away. This seems to get it past CLOSE_WAIT without a >>>> soclose(). >>>> --> I know you are not comfortable with patching your server, but I do >>>> think >>>> this change will get the socket shutdown to complete. >>>> >>>> There are a couple more things you can check on the server... >>>> # nfsstat -E -s >>>> --> Look for the count under "BindConnToSes". >>>> --> If non-zero, backchannels have been assigned >>>> # sysctl -a | fgrep request_space_throttle_count >>>> --> If non-zero, the server has been overloaded at some point. >>>> >>>> I think the attached patch might work around the problem. >>>> The code that should open up the receive window needs to be checked. >>>> I am also looking at enabling the 6minute timeout when a backchannel is >>>> assigned. >>>> >>>> rick >>>> >>>> Youssef >>>> >>>> _______________________________________________ >>>> freebsd-net@freebsd.org<mailto:freebsd-net@freebsd.org> mailing list >>>> https://urldefense.com/v3/__https://lists.freebsd.org/mailman/listinfo/freebsd-net__;!!JFdNOqOXpB6UZW0!_c2MFNbir59GXudWPVdE5bNBm-qqjXeBuJ2UEmFv5OZciLj4ObR_drJNv5yryaERfIbhKR2d$ >>>> To unsubscribe, send any mail to >>>> "freebsd-net-unsubscr...@freebsd.org<mailto:freebsd-net-unsubscr...@freebsd.org>" >>>> <xprtdied.patch> >>>> >>>> <nfs-hang.log.gz> >>>> >>>> _______________________________________________ >>>> freebsd-net@freebsd.org mailing list >>>> https://lists.freebsd.org/mailman/listinfo/freebsd-net >>>> To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org" >>>> _______________________________________________ >>>> freebsd-net@freebsd.org mailing list >>>> https://lists.freebsd.org/mailman/listinfo/freebsd-net >>>> To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org" >>> >>> _______________________________________________ >>> freebsd-net@freebsd.org mailing list >>> https://lists.freebsd.org/mailman/listinfo/freebsd-net >>> To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org" >>> _______________________________________________ >>> freebsd-net@freebsd.org mailing list >>> https://lists.freebsd.org/mailman/listinfo/freebsd-net >>> To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org" >> > _______________________________________________ freebsd-net@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-net To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org" _______________________________________________ freebsd-net@freebsd.org mailing list https://lists.freebsd.org/mailman/listinfo/freebsd-net To unsubscribe, send any mail to "freebsd-net-unsubscr...@freebsd.org"
