> 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"
