Major issues with nfsv4

[Warner Losh]

On Fri, Jan 15, 2021, 10:24 PM J David <j.david.lists at gmail.com> wrote:

> On Thu, Jan 14, 2021 at 5:30 PM Rick Macklem <rmacklem at uoguelph.ca> wrote:
> > One thing to try (other than a FreeBSD13/head system, if possible)
> > is the "oneopenown" mount option.
>
> The odds of being able to run an unreleased version of FreeBSD on
> production servers are slim to none.
>

We run FreeBSD current on all our production systems at Netflix. We update
monthly and run most of the updates...  to be fair, though, we don't use
NFS..

Warner

While trying to develop a reproduction, I think I have narrowed down
> what the problem is.  There are no jails or nullfs involved here, just
> NFSv4.1.
>
> Window 1: (to track OpenOwner/Opens)
>
> while true; do date; nfsstat -E -c | fgrep -A1 OpenOwner; sleep 1; done
>
> Window 2:
>
> mount -o ro,nfsv4,minorversion=1,nosuid fileserver:/path/to/freesbd/root
> /mnt
> chroot /mnt
>
> (OpenOwner is now 1 and Opens is now 9.)
>
> Window 3:
>
> chroot /mnt
> (OpenOwner is now 2 and Opens is now 18.)
> ls
> (OpenOwner is now 3 and Opens is now 21.)
> ls
> (OpenOwner is now 4 and Opens is now 24.)
> ls
> (OpenOwner is now 5 and Opens is now 27.)
> ls
> (OpenOwner is now 6 and Opens is now 30.)
> ls
> (OpenOwner is now 7 and Opens is now 33.)
> bash
> while true; do ls | true; done
> (Allow about a minute to pass, hit CTRL-C.  OpenOwner is now 4647 and
> Opens is now 13957)
> exit
> exit
> (OpenOwner is now 4647 and Opens is now 13952.)
>
> Back in Window 2:
>
> exit
> (wait about 30 seconds, OpenOwner is now 0 and Opens is now 0.)
>
> So it looks like the NFSv4 code can't let go of *any* Opens on a
> file/directory until *all* references to that file/directory are
> closed.
>
> If chroot is too much, "vi /mnt/etc/motd" in Window 2 and "cat
> /mnt/etc/motd" in Window 3 have the same effect, leaking one Open per
> cat instead of 3.  You probably don't even need a FreeBSD install on
> the NFS mount; just hold a single file open in one window and
> open/close it repeatedly in another.
>
> Then I re-tested this with "-o
> ro,nfsv4,minorversion=1,nosuid,oneopenown."  At least for this simple
> case, the problem did not occur with oneopenown set.
>
> Are there downsides to the oneopenown flag other than breaking delegations?
>
> Thanks!
> _______________________________________________
> freebsd-fs at freebsd.org mailing list
> https://lists.freebsd.org/mailman/listinfo/freebsd-fs
> To unsubscribe, send any mail to "freebsd-fs-unsubscribe at freebsd.org"
>