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Bug 2110576 - RHEL-9 nfsd server post_wcc fixes - clients see increased revalidations
Summary: RHEL-9 nfsd server post_wcc fixes - clients see increased revalidations
Keywords:
Status: CLOSED ERRATA
Alias: None
Deadline: 2022-08-29
Product: Red Hat Enterprise Linux 9
Classification: Red Hat
Component: kernel
Version: 9.0
Hardware: Unspecified
OS: Unspecified
unspecified
unspecified
Target Milestone: rc
: 9.1
Assignee: Benjamin Coddington
QA Contact: Yongcheng Yang
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+ depends on / blocked
 
Reported: 2022-07-25 16:23 UTC by Benjamin Coddington
Modified: 2022-11-15 12:48 UTC (History)
3 users (show)

Fixed In Version: kernel-5.14.0-138.el9
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
Environment:
Last Closed: 2022-11-15 11:10:03 UTC
Type: Bug
Target Upstream Version:
Embargoed:

Attachments (Terms of Use)


Links
System ID Private Priority Status Summary Last Updated
Gitlab redhat/centos-stream/src/kernel centos-stream-9 merge_requests 1175 0 None opened RHEL-9 nfsd server post_wcc fixes - clients see increased revalidations 2022-07-25 21:22:16 UTC
Red Hat Issue Tracker RHELPLAN-128918 0 None None None 2022-07-25 16:27:00 UTC
Red Hat Product Errata RHSA-2022:8267 0 None None None 2022-11-15 11:10:28 UTC

Description Benjamin 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
Comment 11 errata-xmlrpc 2022-11-15 11:10:03 UTC 
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
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