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DescriptionBenjamin Coddington
2022-07-25 16:23:52 UTC
While testing a RHEL-9 server, I observed increased RPC counts and decreased performance of the NFS client as compared to RHEL-8. On closer inspection, I saw the NFS client unable to maintain a working access cache. The client would send repeated duplicate ACCESS RPC calls for the same inodes.
The NFS client was depending on the server returning valid results from OPEN's post-op changeid, and it appears that RHEL-9 servers are missing upstream fix:
58f258f65267 Revert "nfsd: skip some unnecessary stats in the v4 case"
.. which will cause OPEN(CREATE) post-op to be zero on filesystems that do not yet support iversion (ext4, tmpfs..).
I'd like to take both patches from the upstream posting:
https://lore.kernel.org/linux-nfs/164078891040.2414.11995954842150988952.stgit@bazille.1015granger.net/
A simple reproducer is export an ext4 filesystem, and observe if a file created on an nfsv4 mount of that export has nfs.changeid4.after set to zero:
A broken server replies for an OPEN and REMOVE
[root@bcodding-rhel9 ~]# tshark -r rhel9.pcap -T fields -e frame.number -e nfs.opcode -e nfs.changeid4.after nfs.changeid4.after==0
5 53,22,18,10,3,9 0
17 53,22,28 0
A working server replies for the same (no results for the tshark filter):
[root@bcodding-rhel9 ~]# tshark -r /tmp/pcap -T fields -e frame.number -e nfs.opcode -e nfs.changeid4.after nfs.changeid4.after==0
Since the problem described in this bug report should be
resolved in a recent advisory, it has been closed with a
resolution of ERRATA.
For information on the advisory (Moderate: kernel security, bug fix, and enhancement update), and where to find the updated
files, follow the link below.
If the solution does not work for you, open a new bug report.
https://access.redhat.com/errata/RHSA-2022:8267