Date: Sun, 5 Jul 2015 18:28:53 -0400 (EDT) From: Rick Macklem <rmacklem@uoguelph.ca> To: Ahmed Kamal <email.ahmedkamal@googlemail.com> Cc: Julian Elischer <julian@freebsd.org>, freebsd-fs@freebsd.org, Xin LI <d@delphij.net> Subject: Re: Linux NFSv4 clients are getting (bad sequence-id error!) Message-ID: <1463698530.4486572.1436135333962.JavaMail.zimbra@uoguelph.ca> In-Reply-To: <CANzjMX6EoPOcY9V5EQeu5KO1WhwFxxo7-mYRhccVvKiaDW8nGQ@mail.gmail.com> References: <CANzjMX45QaC8yZx2nHPAohJRvQjmUOHuhMQWP9nX%2BsrJs707Hg@mail.gmail.com> <1022558302.2863702.1435838360534.JavaMail.zimbra@uoguelph.ca> <CANzjMX5eN1FsnHMf6KGZe_b3vwxxF=dy3fJUHxeGO4BXuNzfPA@mail.gmail.com> <791936587.3443190.1435873993955.JavaMail.zimbra@uoguelph.ca> <CANzjMX427XNQJ1o6Wh2CVy1LF1ivspGcfNeRCmv%2BOyApK2UhJg@mail.gmail.com> <CANzjMX5xyUz6OkMKS4O-MrV2w58YT9ricOPLJWVtAR5Ci-LMew@mail.gmail.com> <2010996878.3611963.1435884702063.JavaMail.zimbra@uoguelph.ca> <CANzjMX6EoPOcY9V5EQeu5KO1WhwFxxo7-mYRhccVvKiaDW8nGQ@mail.gmail.com>
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Ahmed Kamal wrote: > Hi folks, > > Just a quick update. I did not test Xin's patches yet .. What I did so far > is to increase the tcp highwater tunable and increase nfsd threads to 60. > Today (a working day) I noticed I only got one bad sequence error message! > Check this: > > # grep 'bad sequence' messages* | awk '{print $1 $2}' | uniq -c > 1 messages:Jul5 > 39 messages.1:Jun28 > 15 messages.1:Jun29 > 4 messages.1:Jun30 > 9 messages.1:Jul1 > 23 messages.1:Jul2 > 1 messages.1:Jul4 > 1 messages.2:Jun28 > > So there seems to be an improvement! Not sure if the Linux nfs4 client is > able to somehow recover from those bad-sequence situations or not .. I did > get some user complaints that running "ls -l" is sometimes slow and takes a > couple of seconds to finish. > > One final question .. Do you folks think nfs4.1 is more reliable in general > than nfs4 .. I've always only used nfs3 (I guess it can't work here with > /home/* being separate zfs filesystems) .. So should I go through the pain > of upgrading a few servers to RHEL-6 to try out nfs4.1 ? Basically do you > expect the protocol to be more solid ? I know it's a fluffy question, just > give me your thoughts. Thanks a lot! > All I can say is that the "bad seqid" errors should not occur, since NFSv4.1 doesn't use the seqid#s to order RPCs. Also I would say that a correctly implemented NFSv4.1 protocol should function "more correctly" since all RPCs and performed "exactly once". (How much effect this will have in practice, I can't say.) On the other hand, NFSv4.1 is a newer protocol (with an RFC of over 500pages), so it is hard to say how mature the implementations are. I think only testing will give you the answer. I would suggest that you test Xi Lin's patch that allows the "seqid + 2" case and see if that makes the "bad seqid" errors go away. (Even though I think this would indicate a client bug, adding this in way that it can be enabled via a sysctl seems reasonable.) Btw, I haven't seen any additional posts from nfsv4@ietf.org on this, rick > > > On Fri, Jul 3, 2015 at 2:51 AM, Rick Macklem <rmacklem@uoguelph.ca> wrote: > > > Ahmed Kamal wrote: > > > PS: Today (after adjusting tcp.highwater) I didn't get any screaming > > > reports from users about hung vnc sessions. So maybe just maybe, linux > > > clients are able to somehow recover from this bad sequence messages. I > > > could still see the bad sequence error message in logs though > > > > > > Why isn't the highwater tunable set to something better by default ? I > > mean > > > this server is certainly not under a high or unusual load (it's only 40 > > PCs > > > mounting from it) > > > > > > On Fri, Jul 3, 2015 at 1:15 AM, Ahmed Kamal < > > email.ahmedkamal@googlemail.com > > > > wrote: > > > > > > > Thanks all .. I understand now we're doing the "right thing" .. > > Although > > > > if mounting keeps wedging, I will have to solve it somehow! Either > > using > > > > Xin's patch .. or Upgrading RHEL to 6.x and using NFS4.1. > > > > > > > > Regarding Xin's patch, is it possible to build the patched nfsd code, > > as a > > > > kernel module ? I'm looking to minimize my delta to upstream. > > > > > > Yes, you can build the nfsd as a module. If your kernel config does not > > include > > "options NFSD" the module will get loaded/used. It is also possible to > > replace > > the module without rebooting, but you need to kill of the nfsd daemon then > > kldunload nfsd.ko and replace nfsd.ko with the new one. (In > > /boot/<kernel-name>.) > > > > > > Also would adopting Xin's patch and hiding it behind a > > > > kern.nfs.allow_linux_broken_client be an option (I'm probably not the > > last > > > > person on earth to hit this) ? > > > > > > If it fixes your problem, I think this is reasonable. > > I'm also hoping that someone that works on the Linux client reports > > if/when this > > was changed. > > > > rick > > > > > > Thanks a lot for all the help! > > > > > > > > On Thu, Jul 2, 2015 at 11:53 PM, Rick Macklem <rmacklem@uoguelph.ca> > > > > wrote: > > > > > > > >> Ahmed Kamal wrote: > > > >> > Appreciating the fruitful discussion! Can someone please explain to > > me, > > > >> > what would happen in the current situation (linux client doing this > > > >> > skip-by-1 thing, and freebsd not doing it) ? What is the effect of > > that? > > > >> Well, as you've seen, the Linux client doesn't function correctly > > against > > > >> the FreeBSD server (and probably others that don't support this > > > >> "skip-by-1" > > > >> case). > > > >> > > > >> > What do users see? Any chances of data loss? > > > >> Hmm. Mostly it will cause Opens to fail, but I can't guess what the > > Linux > > > >> client behaviour is after receiving NFS4ERR_BAD_SEQID. You're the guy > > > >> observing > > > >> it. > > > >> > > > >> > > > > >> > Also, I find it strange that netapp have acknowledged this is a bug > > on > > > >> > their side, which has been fixed since then! > > > >> Yea, I think Netapp screwed up. For some reason their server allowed > > this, > > > >> then was fixed to not allow it and then someone decided that was > > broken > > > >> and > > > >> reversed it. > > > >> > > > >> > I also find it strange that I'm the first to hit this :) Is no one > > > >> running > > > >> > nfs4 yet! > > > >> > > > > >> Well, it seems to be slowly catching on. I suspect that the Linux > > client > > > >> mounting a Netapp is the most common use of it. Since it appears that > > they > > > >> flip flopped w.r.t. who's bug this is, it has probably persisted. > > > >> > > > >> It may turn out that the Linux client has been fixed or it may turn > > out > > > >> that most servers allowed this "skip-by-1" even though David Noveck > > (one > > > >> of the main authors of the protocol) seems to agree with me that it > > should > > > >> not be allowed. > > > >> > > > >> It is possible that others have bumped into this, but it wasn't > > isolated > > > >> (I wouldn't have guessed it, so it was good you pointed to the RedHat > > > >> discussion) > > > >> and they worked around it by reverting to NFSv3 or similar. > > > >> The protocol is rather complex in this area and changed completely for > > > >> NFSv4.1, > > > >> so many have also probably moved onto NFSv4.1 where this won't be an > > > >> issue. > > > >> (NFSv4.1 uses sessions to provide exactly once RPC semantics and > > doesn't > > > >> use > > > >> these seqid fields.) > > > >> > > > >> This is all just mho, rick > > > >> > > > >> > On Thu, Jul 2, 2015 at 1:59 PM, Rick Macklem <rmacklem@uoguelph.ca> > > > >> wrote: > > > >> > > > > >> > > Julian Elischer wrote: > > > >> > > > On 7/2/15 9:09 AM, Rick Macklem wrote: > > > >> > > > > I am going to post to nfsv4@ietf.org to see what they say. > > Please > > > >> > > > > let me know if Xin Li's patch resolves your problem, even > > though I > > > >> > > > > don't believe it is correct except for the UINT32_MAX case. > > Good > > > >> > > > > luck with it, rick > > > >> > > > and please keep us all in the loop as to what they say! > > > >> > > > > > > >> > > > the general N+2 bit sounds like bullshit to me.. its always N+1 > > in a > > > >> > > > number field that has a > > > >> > > > bit of slack at wrap time (probably due to some ambiguity in the > > > >> > > > original spec). > > > >> > > > > > > >> > > Actually, since N is the lock op already done, N + 1 is the next > > lock > > > >> > > operation in order. Since lock ops need to be strictly ordered, > > > >> allowing > > > >> > > N + 2 (which means N + 2 would be done before N + 1) makes no > > sense. > > > >> > > > > > >> > > I think the author of the RFC meant that N + 2 or greater fails, > > but > > > >> it > > > >> > > was poorly worded. > > > >> > > > > > >> > > I will pass along whatever I get from nfsv4@ietf.org. (There is > > an > > > >> archive > > > >> > > of it somewhere, but I can't remember where.;-) > > > >> > > > > > >> > > rick > > > >> > > _______________________________________________ > > > >> > > freebsd-fs@freebsd.org mailing list > > > >> > > http://lists.freebsd.org/mailman/listinfo/freebsd-fs > > > >> > > To unsubscribe, send any mail to " > > freebsd-fs-unsubscribe@freebsd.org" > > > >> > > > > > >> > > > > >> > > > > > > > > > > > > > >
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