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Bug 2051329

Summary: systemd-sysctl couldn't write settings to 'vm/unprivileged_userfaultfd'
Product: Red Hat Enterprise Linux 8 Reporter: Frank Liang <xiliang>
Component: libvirtAssignee: Jiri Denemark <jdenemar>
Status: CLOSED NOTABUG QA Contact: yalzhang <yalzhang>
Severity: medium Docs Contact:
Priority: medium    
Version: 8.6CC: fsumsal, jdenemar, linl, lmen, ribarry, systemd-maint-list, virt-maint, vkuznets, xuazhao, xuzhang, ymao
Target Milestone: rcKeywords: Reopened, Triaged
Target Release: ---Flags: pm-rhel: mirror+
Hardware: All   
OS: All   
Whiteboard:
Fixed In Version: Doc Type: If docs needed, set a value
Doc Text:
Story Points: ---
Clone Of: Environment:
Last Closed: 2022-02-09 10:54:59 UTC Type: Bug
Regression: --- Mount Type: ---
Documentation: --- CRM:
Verified Versions: Category: ---
oVirt Team: --- RHEL 7.3 requirements from Atomic Host:
Cloudforms Team: --- Target Upstream Version:
Embargoed:
Bug Depends On: 2037807    
Bug Blocks:    
Attachments:
Description Flags
os_tests.tests.test_general_check.TestGeneralCheck.test_check_journalctl_not_found.debug none

Description Frank Liang 2022-02-07 03:17:43 UTC 
Created attachment 1859496 [details]
os_tests.tests.test_general_check.TestGeneralCheck.test_check_journalctl_not_found.debug

Description of problem:
Found below error in RHEL-8.6.0-20220205.2 testing.

# journalctl -u systemd-sysctl
-- Logs begin at Mon 2022-02-07 02:16:38 UTC, end at Mon 2022-02-07 02:51:07 UTC. --
Feb 07 02:16:39 localhost systemd[1]: Starting Apply Kernel Variables...
Feb 07 02:16:39 localhost systemd-sysctl[335]: Couldn't write '0 2147483647' to '-net/ipv4/ping_group_range', ignoring: No such file or directory
Feb 07 02:16:39 localhost systemd-sysctl[335]: Couldn't write '1' to 'vm/unprivileged_userfaultfd', ignoring: No such file or directory
Feb 07 02:16:39 localhost systemd[1]: Started Apply Kernel Variables.
Feb 07 02:16:43 localhost systemd[1]: systemd-sysctl.service: Succeeded.
Feb 07 02:16:43 localhost systemd[1]: Stopped Apply Kernel Variables.

# grep -R ping_group_range
50-default.conf:-net.ipv4.ping_group_range = 0 2147483647
# grep -R unprivileged_userfaultfd
60-qemu-postcopy-migration.conf:vm.unprivileged_userfaultfd = 1
# rpm -qf /usr/lib/sysctl.d/50-default.conf
systemd-239-56.el8.x86_64
# sysctl net.ipv4.ping_group_range
net.ipv4.ping_group_range = 1 0
# sysctl vm.unprivileged_userfaultfd
sysctl: cannot stat /proc/sys/vm/unprivileged_userfaultfd: No such file or directory

RHEL Version:
RHEL-8.6(4.18.0-364.el8.x86_64)

How reproducible:
100%

Steps to Reproduce:
1.  Start a RHEL-8.6 instance
2. Run 'journalctl -u systemd-sysctl'

Actual results:
Some options are not set
Expected results:
All options should be applied successfully

Additional info:
- No such issue in RHEL-9.
# sysctl vm.unprivileged_userfaultfd
vm.unprivileged_userfaultfd = 1
#  sysctl net.ipv4.ping_group_range
net.ipv4.ping_group_range = 0 2147483647
# rpm -q systemd
systemd-249-9.el9.x86_64
Comment 1 Frantisek Sumsal 2022-02-07 08:00:09 UTC 

*** This bug has been marked as a duplicate of bug 2037807 ***
Comment 2 Frank Liang 2022-02-07 08:09:42 UTC 
I see bug 2037807 talking about "systemd-sysctl[335]: Couldn't write '0 2147483647' to '-net/ipv4/ping_group_range', ignoring: No such file or directory".

Is below error fixed together?
Feb 07 02:16:39 localhost systemd-sysctl[335]: Couldn't write '1' to 'vm/unprivileged_userfaultfd', ignoring: No such file or directory
Comment 3 Frantisek Sumsal 2022-02-07 08:16:25 UTC 
/proc/sys/vm/unprivileged_userfaultfd was introduced in kernel 5.2, thus it's not present in RHEL 8 as far as I know, so the error is expected. I'm not sure where 60-qemu-postcopy-migration.conf comes from, but it's definitely not systemd.
Comment 4 Frank Liang 2022-02-07 08:26:33 UTC 
Thanks, Frantisek

60-qemu-postcopy-migration.conf belongs to libvirt-daemon-driver-qemu.

Hi Vitaly,

I think we can reopen this bug to fix below error (not supported in RHEL-8 as above comment#3) and reassign it to libvirt team, do you have other comments? Thanks
 
Feb 07 02:16:39 localhost systemd-sysctl[335]: Couldn't write '1' to 'vm/unprivileged_userfaultfd', ignoring: No such file or directory
Comment 6 Jiri Denemark 2022-02-09 10:54:59 UTC 
Well, I wouldn't consider this a bug. We added the conf file upstream because
the sysctl needs to be set to 1 on new(ish) kernels to support post-copy
migration. This is needed for RHEL-9, for example. In RHEL-8 such sysctl does
not exist and does not need to be set, but I think it's better to keep the
config file around anyway in case vm.unprivileged_userfaultfd is backported
(it was added upstream as some kind of a security enhancement).

And since systemd-sysctl already ignores any failures caused by attempts to
set missing sysctl knobs, I don't think there's anything to fix here. Well, we
should add "-" prefix upstream so that non-systemd sysctl tool ignores the
errors too, but doing so would have no effect in RHEL-8 (actually adding the
dash would need an updated systemd to work properly, see bug 2037807).

The error message seen in the log is harmless and it's even marked as such by
systemd:

# journalctl --output=verbose --grep userfaultfd --boot
-- Logs begin at Wed 2022-02-09 09:20:40 UTC, end at Wed 2022-02-09 10:26:33 UTC. --
Wed 2022-02-09 09:56:21.694825 UTC [s=fb5ea867bc2d48b5967a76bd59d21500;i=daa;b=da50b75465b4437fa63d703ca9d87a1c;m=2f12aa;t=5d792d88a6a77;x=492e7e8a7dcc1b7e]
    _BOOT_ID=da50b75465b4437fa63d703ca9d87a1c
    _MACHINE_ID=9db0456ca73e65891e0ab7956d91da96
    _HOSTNAME=rhel86-dev.virt
    PRIORITY=5
    SYSLOG_FACILITY=3
    _UID=0
    _GID=0
    CODE_FILE=../src/sysctl/sysctl.c
    CODE_LINE=91
    CODE_FUNC=apply_all
    ERRNO=2
    SYSLOG_IDENTIFIER=systemd-sysctl
    MESSAGE=Couldn't write '1' to 'vm/unprivileged_userfaultfd', ignoring: No such file or directory
    _TRANSPORT=journal
    _PID=626
    _COMM=systemd-sysctl
    _CAP_EFFECTIVE=1ffffffffff
    _SELINUX_CONTEXT=system_u:system_r:systemd_sysctl_t:s0
    _SOURCE_REALTIME_TIMESTAMP=1644400581694825

You can see the message is logged with PRIORITY=5, that is NOTICE, which is a
fairly low priority and it should not bother anyone as it's the same priority
that is used for a lot of other common messages, e.g., "anacron[1656]: Anacron
started on 2022-02-09".