On Sep 6, 2016, at 12:38 PM, Chuck Lever wrote: > >> On Sep 6, 2016, at 11:47 AM, Oleg Drokin <green@xxxxxxxxxxxxxx> wrote: >> >> >> On Sep 6, 2016, at 11:18 AM, Jeff Layton wrote: >> >>> On Tue, 2016-09-06 at 10:58 -0400, Oleg Drokin wrote: >>>> On Sep 6, 2016, at 10:30 AM, Jeff Layton wrote: >>>> >>>>> >>>>> On Mon, 2016-09-05 at 00:55 -0400, Oleg Drokin wrote: >>>>>> >>>>>> Hello! >>>>>> >>>>>> I have a somewhat mysterious problem with my nfs test rig that I suspect is something >>>>>> stupid I am missing, but I cannot figure it out and would appreciate any help. >>>>>> >>>>>> NFS server is Fedora23 with 4.6.7-200.fc23.x86_64 as the kernel. >>>>>> Clients are a bunch of 4.8-rc5 nodes, nfsroot. >>>>>> If I only start one of them, all is fine, if I start all 9 or 10, then suddenly all >>>>>> operations ground to a half (nfs-wise). NFS server side there's very little load. >>>>>> >>>>>> I hit this (or something similar) back in June, when testing 4.6-rcs (and the server >>>>>> was running 4.4.something I believe), and back then after some mucking around >>>>>> I set: >>>>>> net.core.rmem_default=268435456 >>>>>> net.core.wmem_default=268435456 >>>>>> net.core.rmem_max=268435456 >>>>>> net.core.wmem_max=268435456 >>>>>> >>>>>> and while no idea why, that helped, so I stopped looking into it completely. >>>>>> >>>>>> Now fast forward to now, I am back at the same problem and the workaround above >>>>>> does not help anymore. >>>>>> >>>>>> I also have a bunch of "NFSD: client 192.168.10.191 testing state ID with incorrect client ID" >>>>>> in my logs (also had in June. Tried to disable nfs 4.2 and 4.1 and that did not >>>>>> help). >>>>>> >>>>>> So anyway I discovered the nfsdcltrack and such and I noticed that whenever >>>>>> the kernel calls it, it's always with the same hexid of >>>>>> 4c696e7578204e465376342e32206c6f63616c686f7374 >>>>>> >>>>>> NAturally if I try to list the content of the sqlite file, I get: >>>>>> sqlite> select * from clients; >>>>>> Linux NFSv4.2 localhost|1473049735|1 >>>>>> sqlite> select * from clients; >>>>>> Linux NFSv4.2 localhost|1473049736|1 >>>>>> sqlite> select * from clients; >>>>>> Linux NFSv4.2 localhost|1473049737|1 >>>>>> sqlite> select * from clients; >>>>>> Linux NFSv4.2 localhost|1473049751|1 >>>>>> sqlite> select * from clients; >>>>>> Linux NFSv4.2 localhost|1473049752|1 >>>>>> sqlite> >>>>>> >>>>> >>>>> Well, not exactly. It sounds like the clients are all using the same >>>>> long-form clientid string. The server sees that and tosses out any >>>>> state that was previously established by the earlier client, because it >>>>> assumes that the client rebooted. >>>>> >>>>> The easiest way to work around this is to use the nfs4_unique_id nfs.ko >>>>> module parm on the clients to give them each a unique string id. That >>>>> should prevent the collisions. >>>> >>>> Hm, but it did work ok in the past. >>>> What determines the unique id now by default? >>>> The clients do start with a different ip address for one, so that >>>> seems to make that a much more good proxy for unique id >>>> (or local ip/server ip as is in case of centos7) than whatever local >>>> hostname is at any random point in time during boot >>>> (where it might not be set yet apparently). >>>> >>> >>> The v4.1+ clientid is (by default) determined entirely from the >>> hostname. >>> >>> IP addresses are a poor choice given that they can easily change for >>> clients that have them dynamically assigned. That's the main reason >>> that v4.0 behaves differently here. The big problems there really come >>> into play with NFSv4 migration. See this RFC draft for the gory >>> details: >>> >>> https://tools.ietf.org/html/draft-ietf-nfsv4-migration-issues-10 >> >> Duh, so "ip addresses are unreliable, let's use something even less >> reliable". hostname is also dynamic in a bunch of cases, btw. >> Worst of all, there are very many valid cases where nfs might be mounted >> before hostname is set (or do you regard that as a bug in the environment >> and I should just file a ticket in Fedora bugzilla?) > > That's a bug IMO. How can network activity be done before the host is > properly configured? If the host has an IP address, it can perform > a reverse-lookup and find out the matching hostname and use that. > > At any rate, if NFS needs the hostname set before performing a mount, > that dependency should be added to the O/S's start-up logic. I guess so. Since the later startup sets the hostname somehow, there's no reason this logic cannot be brought into initramfs either. Though it's also a bit strange that dhcpd does not seem to supply hostname from the host declaration like one would imagine it would Anyway, for the record, doing this in dhcpd.conf seems to avert the immediate problem for me (so whoever finds this thread might use the same trick, does require reverse dns lookups to return a sensible value): get-lease-hostnames true; >> Looking over the draft, the two cases are: >> what if client reboots, how do we reclaim state ASAP and >> what if there is server migration, but same client. >> >> The second case is trivial as long as the client id stays constant no matter >> what server you connect to and might be any number of constant identifiers, >> be it random, or not. >> >> On the other hand the rebooted client is more interesting. Of course there's >> also a lease expiration (that's what we do in Lustre too, if the client dies, >> it'll be expired eventually, but also if we talk to it and it does not reply, >> we kick it out as well, and this has a much shorter timeout, so not as disruptive). >> >> Cannot some more unique identifier be used by default? > > There is no good way to do this. We picked a way that works in many > convenient cases, and provided a mechanism for setting a unique ID > in the cases where the default behavior does not work. That's the > best that can be done. > > Ideally, we would want O/S installation to generate a random value > (say, a UUID) and store that persistently on the client to use as > its client ID. A diskless client does not have persistent storage, > however. True, while there's machine-id(5), diskless-clients cannot really access it before getting onto the network first, and in case of nfsroot, that means mounting before it's available. I just suspect you traded one problem for a very similar another one, though. Imagine that you have a truly dynamic ip addresses (and hostnames depend on them). Then if the ip address changes, so does the hostname. This is all fine while the client is alive, since clientid stays constant across such a mount, but on reboot, once the ip address (and corresponding hostname) are lost, you are back to square one - rebooted client could not be mapped back into the existing lease. The extra complication (same as with old ip one too) is once you lost your ip and somebody gets it and happens to mount the same server - you will get two clients with the same id. Now if both of the clients are fairly active, tracking down why all of a sudden performance have dropped might be less than trivial. Hopefully the migration is not compromised by this either (when wrong client with the same client id comes to the other server on migration first). All of this makes me wonder, is lease expiration such an expensive and long thing? Cannot you just make that more lighter-weight? Potentially this will be easier than having robust persistent node ids for all cases. >> Say "mac address of the primary interface, whatever that happens to be", >> in that case as long as your client remains on the same physical box >> (and the network card has not changed), you should be fine. > > That has all the same caveats as using hostname or IP address. Given that > Linux is notoriously bad about the "ordering" of hardware devices after > a reboot, it's difficult to claim that this would be more reliable than > using a hostname. Yes, I guess this can be a real problem. On the other hand diskless clients typically have only one "primary" interface anyway, the one that gets the ip address first. >> I guess there are other ways. >> Ideally, kernel would offer an API (might be there is already, but I cannot find it) >> that could be queried for a unique id like that (with inputs from mac addresses, >> various serial numbers identifiable and such). > > The IESG had some trouble with that; namely that (if I recall correctly) > it makes it possible for an attacker to see that serial number on the > wire, tracking that host and its MACs and PRNG. Yes, tracking is a problem. On the other hand MAC addresses are visible on the local subnet anyway, and your current scheme is the same - you still give away a "unique" id, it's just only exposed if the host happens to be an nfs client, so some degree of tracking is still possible - i.e. if I have a constant hostname (not a diskless host) and I mount nfs - now attacker (that can see that nfs traffic) knows my IP address, possibly my MAC address, can get info about other network interfaces potentially, and info about PRNGs too. > We carefully considered all of this when authoring that document. And, > implementations of NFSv4 are free to use whatever they like in that > client ID. The text in that document is a suggestion, not a normative > requirement. Yes, I understand that. I guess I was just too disappointed by a working configuration suddenly breaking, to see how the new scheme is an improvement over the old one ;) Thanks. Bye, Oleg-- To unsubscribe from this list: send the line "unsubscribe linux-nfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
