Date: Mon, 5 Apr 2021 00:08:40 +0200 From: tuexen@freebsd.org To: Rick Macklem <rmacklem@uoguelph.ca> Cc: "Scheffenegger, Richard" <Richard.Scheffenegger@netapp.com>, Youssef GHORBAL <youssef.ghorbal@pasteur.fr>, "freebsd-net@freebsd.org" <freebsd-net@freebsd.org> Subject: Re: NFS Mount Hangs Message-ID: <2B189169-C0C9-4DE6-A01A-BE916F10BABA@freebsd.org> In-Reply-To: <YQXPR0101MB096876B44F33BAD8991B62C8DD789@YQXPR0101MB0968.CANPRD01.PROD.OUTLOOK.COM> References: <C643BB9C-6B61-4DAC-8CF9-CE04EA7292D0@tildenparkcapital.com> <3750001D-3F1C-4D9A-A9D9-98BCA6CA65A4@tildenparkcapital.com> <33693DE3-7FF8-4FAB-9A75-75576B88A566@tildenparkcapital.com> <D67AF317-D238-4EC0-8C7F-22D54AD5144C@pasteur.fr> <YQXPR0101MB09684AB7BEFA911213604467DD669@YQXPR0101MB0968.CANPRD01.PROD.OUTLOOK.COM> <C87066D3-BBF1-44E1-8398-E4EB6903B0F2@tildenparkcapital.com> <8E745920-1092-4312-B251-B49D11FE8028@pasteur.fr> <YQXPR0101MB0968C44C7C82A3EB64F384D0DD7B9@YQXPR0101MB0968.CANPRD01.PROD.OUTLOOK.COM> <DEF8564D-0FE9-4C2C-9F3B-9BCDD423377C@freebsd.org> <YQXPR0101MB0968E0A17D8BCACFAF132225DD7A9@YQXPR0101MB0968.CANPRD01.PROD.OUTLOOK.COM> <SN4PR0601MB3728E392BCA494EAD49605FE86789@SN4PR0601MB3728.namprd06.prod.outlook.com> <YQXPR0101MB09686B4F921B96DCAFEBF874DD789@YQXPR0101MB0968.CANPRD01.PROD.OUTLOOK.COM> <765CE1CD-6AAB-4BEF-97C6-C2A1F0FF4AC5@freebsd.org> <YQXPR0101MB096876B44F33BAD8991B62C8DD789@YQXPR0101MB0968.CANPRD01.PROD.OUTLOOK.COM>
next in thread | previous in thread | raw e-mail | index | archive | help
> On 4. Apr 2021, at 22:28, Rick Macklem <rmacklem@uoguelph.ca> wrote: >=20 > Oops, yes the packet capture is on freefall (forgot to mention = that;-). > You should be able to: > % fetch https://people.freebsd.org/~rmacklem/linuxtofreenfs.pcap >=20 > Some useful packet #s are: > 1949 - partitioning starts > 2005 - partition healed > 2060 - last RST > 2067 - SYN -> gets going again >=20 > This was taken at the Linux end. I have FreeBSD end too, although I > don't think it tells you anything more. Hi Rick, I would like to look at the FreeBSD side, too. Do you also know, what the state of the TCP connection was when the SYN / ACK / RST game was going on? I would like to understand why the reestablishment of the connection did not work... Best regards Michael >=20 > Have fun with it, rick >=20 >=20 > ________________________________________ > From: tuexen@freebsd.org <tuexen@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 >=20 > 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 IThelp@uoguelph.ca >=20 >=20 >> On 4. Apr 2021, at 17:27, Rick Macklem <rmacklem@uoguelph.ca> wrote: >>=20 >> Well, I'm going to cheat and top post, since this is elated info. and >> not really part of the discussion... >>=20 >> 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. >>=20 >> 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. >>=20 >> I had thought that an RST was a "pretty heavy hammer", but FreeBSD = seems >> pretty good at ignoring it. >>=20 >> 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... >=20 > Best regards > Michael >>=20 >> 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... >>=20 >> 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. >>=20 >>=20 >> 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... >>=20 >> 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). >>=20 >> 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. >>=20 >> 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). >>=20 >> 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... >>=20 >> 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 >>=20 >> 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. >>=20 >> So, hopefully TCP conversant folk can confirm if the above is correct = behaviour >> or if the RST should be ack'd sooner? >>=20 >> I could also see this becoming a "forever" TCP battle for other = versions of Linux client. >>=20 >> rick >>=20 >>=20 >> ________________________________________ >> From: Scheffenegger, Richard <Richard.Scheffenegger@netapp.com> >> Sent: Sunday, April 4, 2021 7:50 AM >> To: Rick Macklem; tuexen@freebsd.org >> Cc: Youssef GHORBAL; freebsd-net@freebsd.org >> Subject: Re: NFS Mount Hangs >>=20 >> 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 IThelp@uoguelph.ca >>=20 >>=20 >> For what it=E2=80=98s worth, suse found two bugs in the linux = nfconntrack (stateful firewall), and pfifo-fast scheduler, which could = conspire to make tcp sessions hang forever. >>=20 >> One is a missed updaten when the c=C3=B6ient is not using the = noresvport moint option, which makes tje firewall think rsts are illegal = (and drop them); >>=20 >> 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... >>=20 >> I can try getting the relevant bug info next week... >>=20 >> ________________________________ >> Von: owner-freebsd-net@freebsd.org <owner-freebsd-net@freebsd.org> im = Auftrag von Rick Macklem <rmacklem@uoguelph.ca> >> Gesendet: Friday, April 2, 2021 11:31:01 PM >> An: tuexen@freebsd.org <tuexen@freebsd.org> >> Cc: Youssef GHORBAL <youssef.ghorbal@pasteur.fr>; = freebsd-net@freebsd.org <freebsd-net@freebsd.org> >> Betreff: Re: NFS Mount Hangs >>=20 >> 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. >>=20 >>=20 >>=20 >>=20 >> tuexen@freebsd.org wrote: >>>> On 2. Apr 2021, at 02:07, Rick Macklem <rmacklem@uoguelph.ca> = wrote: >>>>=20 >>>> 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. >>>>=20 >>>> I'm not enough of a TCP guy to know if this is useful, but here's = what >>>> I see... >>>>=20 >>>> 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 >>=20 >> 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#. >>=20 >> On the FreeBSD server end: >> - receives the last retransmit of the segment (with ACK) >> - sends RST >> - receives SYN >> - sends SYN, ACK >>=20 >> 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. >>=20 >>>>=20 >>>> 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 >>>>=20 >>>> The Linux client shows the same connection ESTABLISHED. >> But disappears from "netstat -a" for a while during the partitioning. >>=20 >>>> (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. >>=20 >>>> --> 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. >>>>=20 >>>> 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.) >>>>=20 >>>> 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. >>=20 >> I am pretty certain they are broken, in that the client needs to >> retry all outstanding RPCs. >>=20 >> 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. >>=20 >> 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 >>=20 >> 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. >>=20 >> 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. >>=20 >> Thanks for your help with this Michael, rick >>=20 >> Best regards >> Michael >>>=20 >>> rick >>> ps: I can capture packets while doing this, if anyone has a use >>> for them. >>>=20 >>>=20 >>>=20 >>>=20 >>>=20 >>>=20 >>> ________________________________________ >>> From: owner-freebsd-net@freebsd.org <owner-freebsd-net@freebsd.org> = on behalf of Youssef GHORBAL <youssef.ghorbal@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 >>>=20 >>> 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 IThelp@uoguelph.ca >>>=20 >>>=20 >>>=20 >>>=20 >>> On 27 Mar 2021, at 13:20, Jason Breitman = <jbreitman@tildenparkcapital.com<mailto:jbreitman@tildenparkcapital.com>> = wrote: >>>=20 >>> 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=3D8943<UP,BROADCAST,RUNNING,PROMISC,SIMPLEX,MULTICAST> = metric 0 mtu 1500 >>> = options=3D8100b8<VLAN_MTU,VLAN_HWTAGGING,JUMBO_MTU,VLAN_HWCSUM,VLAN_HWFILT= ER> >>>=20 >>> We can also say that the sysctl settings did not resolve this issue. >>>=20 >>> # sysctl net.inet.tcp.fast_finwait2_recycle=3D1 >>> net.inet.tcp.fast_finwait2_recycle: 0 -> 1 >>>=20 >>> # sysctl net.inet.tcp.finwait2_timeout=3D1000 >>> net.inet.tcp.finwait2_timeout: 60000 -> 1000 >>>=20 >>> I don=E2=80=99t 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) >>>=20 >>> 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. >>>=20 >>> So I don=E2=80=99t get why it stucks in the FIN_WAIT2 state anyway. >>>=20 >>> You really need to have a packet capture during the outage (client = and server side) so you=E2=80=99ll 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. >>>=20 >>> * 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. >>>=20 >>> 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. >>>=20 >>> #!/bin/sh >>>=20 >>> 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 >>>=20 >>>=20 >>> 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 >>>=20 >>> On the NFS Client >>> tcp 0 0 NFS.Client.IP.X:48286 NFS.Server.IP.X:2049 = FIN_WAIT2 >>>=20 >>>=20 >>>=20 >>> You had also asked for the output below. >>>=20 >>> # nfsstat -E -s >>> BackChannelCtBindConnToSes >>> 0 0 >>>=20 >>> # sysctl vfs.nfsd.request_space_throttle_count >>> vfs.nfsd.request_space_throttle_count: 0 >>>=20 >>> I see that you are testing a patch and I look forward to seeing the = results. >>>=20 >>>=20 >>> Jason Breitman >>>=20 >>>=20 >>> On Mar 21, 2021, at 6:21 PM, Rick Macklem = <rmacklem@uoguelph.ca<mailto:rmacklem@uoguelph.ca>> wrote: >>>=20 >>> Youssef GHORBAL = <youssef.ghorbal@pasteur.fr<mailto:youssef.ghorbal@pasteur.fr>> wrote: >>>> Hi Jason, >>>>=20 >>>>> On 17 Mar 2021, at 18:17, Jason Breitman = <jbreitman@tildenparkcapital.com<mailto:jbreitman@tildenparkcapital.com>> = wrote: >>>>>=20 >>>>> 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. >>>>>=20 >>>>> Issue >>>>> NFSv4 mounts periodically hang on the NFS Client. >>>>>=20 >>>>> 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. >>>>=20 >>>> 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. >>>=20 >>>> We=E2=80=99ve had better luck and we did manage to have packet = captures on both sides >during the issue. The gist of it goes like = follows: >>>>=20 >>>> - 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. >>>=20 >>>> - 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). >>>=20 >>>> - 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. >>>> =3D> The last two steps goes on and on for hours/days freezing the = NFS mount bound >to that TCP session. >>>>=20 >>>> 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=E2=80=99ll end up in the same >state as you I think. >>>>=20 >>>> We=E2=80=99ve 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=3D1 & = >net.inet.tcp.finwait2_timeout=3D5000). 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) >>>>=20 >>>> To avoid rebooting the client (and before the aggressive FIN_WAIT_2 = was >implemented on the Isilon side) we=E2=80=99ve 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) >>>>=20 >>>> 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. >>>=20 >>> 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(). >>>=20 >>> 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. >>>=20 >>> 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. >>>=20 >>> 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. >>>=20 >>> rick >>>=20 >>> Youssef >>>=20 >>> _______________________________________________ >>> freebsd-net@freebsd.org<mailto:freebsd-net@freebsd.org> mailing list >>> = https://urldefense.com/v3/__https://lists.freebsd.org/mailman/listinfo/fre= ebsd-net__;!!JFdNOqOXpB6UZW0!_c2MFNbir59GXudWPVdE5bNBm-qqjXeBuJ2UEmFv5OZci= Lj4ObR_drJNv5yryaERfIbhKR2d$ >>> To unsubscribe, send any mail to = "freebsd-net-unsubscribe@freebsd.org<mailto:freebsd-net-unsubscribe@freebs= d.org>" >>> <xprtdied.patch> >>>=20 >>> <nfs-hang.log.gz> >>>=20 >>> _______________________________________________ >>> freebsd-net@freebsd.org mailing list >>> https://lists.freebsd.org/mailman/listinfo/freebsd-net >>> To unsubscribe, send any mail to = "freebsd-net-unsubscribe@freebsd.org" >>> _______________________________________________ >>> freebsd-net@freebsd.org mailing list >>> https://lists.freebsd.org/mailman/listinfo/freebsd-net >>> To unsubscribe, send any mail to = "freebsd-net-unsubscribe@freebsd.org" >>=20 >> _______________________________________________ >> freebsd-net@freebsd.org mailing list >> https://lists.freebsd.org/mailman/listinfo/freebsd-net >> To unsubscribe, send any mail to = "freebsd-net-unsubscribe@freebsd.org" >> _______________________________________________ >> freebsd-net@freebsd.org mailing list >> https://lists.freebsd.org/mailman/listinfo/freebsd-net >> To unsubscribe, send any mail to = "freebsd-net-unsubscribe@freebsd.org" >=20
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?2B189169-C0C9-4DE6-A01A-BE916F10BABA>