1450960 – Libvirt's nodedev udev backend reports 'udev_monitor_receive_device returned NULL' when a great amount of device 'add' events are emitted by udev

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Bug 1450960 - Libvirt's nodedev udev backend reports 'udev_monitor_receive_device returned NULL' when a great amount of device 'add' events are emitted by udev

Summary: Libvirt's nodedev udev backend reports 'udev_monitor_receive_device returned ...

Keywords:
Status:	CLOSED ERRATA
Alias:	None
Product:	Red Hat Enterprise Linux 7
Classification:	Red Hat
Component:	libvirt
Sub Component:
Version:	7.3
Hardware:	x86_64
OS:	Linux
Priority:	unspecified
Severity:	unspecified
Target Milestone:	rc
Target Release:	---
Assignee:	Erik Skultety
QA Contact:	yafu
Docs Contact:
URL:
Whiteboard:
Depends On:
Blocks:
TreeView+	depends on / blocked

Reported:	2017-05-15 13:05 UTC by Ning Bo
Modified:	2017-08-02 01:32 UTC (History)
CC List:	9 users (show)
Fixed In Version:	libvirt-3.2.0-7.el7
Doc Type:	If docs needed, set a value
Doc Text:
Clone Of:
Environment:
Last Closed:	2017-08-02 00:08:25 UTC
Target Upstream Version:
Embargoed:

Attachments	(Terms of Use)
a simple fix to change the buffer size of udev monitor (519 bytes, patch) 2017-05-15 13:32 UTC, Ning Bo	no flags	Details \| Diff
View All

Links
System	ID	Private	Priority	Status	Summary	Last Updated
Red Hat Bugzilla	1442307	1	None	None	None	2021-06-10 12:11:32 UTC
Red Hat Product Errata	RHEA-2017:1846	0	normal	SHIPPED_LIVE	libvirt bug fix and enhancement update	2017-08-01 18:02:50 UTC

Internal Links: 1442307

Description Ning Bo 2017-05-15 13:05:10 UTC

Description of problem:
When create Virtual Function for Inter XL710 use below commands:
for i in `seq 0 1`; do
        echo 63 > /sys/devices/pci0000:00/0000:00:03.2/0000:07:00.$i/sriov_numvfs
done
for i in `seq 0 3`; do
        echo 31 > /sys/devices/pci0000:80/0000:80:02.2/0000:82:00.$i/sriov_numvfs
done

The libvirtd will missing some udev events, the result of libvirt-python API
listDevices('pci') will not list all pci devices.


How reproducible:
100%

Steps to Reproduce:
1.Execute above commands or other operation that can cause kernel report lots udev event.
2.compare the result of libvirt-python API listDevices('pci') and command 'lspci'
3.

Actual results:
listDevices('pci') list all pci devices.

Expected results:
listDevices('pci') NOT list all pci devices.

Additional info:

Comment 1 Ning Bo 2017-05-15 13:32:17 UTC

Created attachment 1278999 [details]
a simple fix to change the buffer size of udev monitor

The reason is that the buffer of udev monitor default size cann't save all udev
events reported by kernel.
So we need change buffer size so that we can receive as much events as possible
whitin a short time.

Comment 3 Erik Skultety 2017-05-17 06:58:51 UTC

(In reply to Ning Bo from comment #1)
> Created attachment 1278999 [details]
> a simple fix to change the buffer size of udev monitor
> 
> The reason is that the buffer of udev monitor default size cann't save all
> udev
> events reported by kernel.
> So we need change buffer size so that we can receive as much events as
> possible
> whitin a short time.

There was an upstream discussion to your patch [1]. Would you send a v2 containing a check for privileges, or shall I do that? I'm trying to reproduce it in the meantime and get more information out of libudev. Although I'm able to reproduce it only in about 75-80% cases, I haven't had much luck with regards to libudev for the time being.

[1] https://www.redhat.com/archives/libvir-list/2017-May/msg00264.html

Comment 4 Ning Bo 2017-05-17 10:12:49 UTC

I'm not familiar with privilege, i'm sorry for that, would you help me to improve the patch?(In reply to Erik Skultety from comment #3)
> (In reply to Ning Bo from comment #1)
> > Created attachment 1278999 [details]
> > a simple fix to change the buffer size of udev monitor
> > 
> > The reason is that the buffer of udev monitor default size cann't save all
> > udev
> > events reported by kernel.
> > So we need change buffer size so that we can receive as much events as
> > possible
> > whitin a short time.
> 
> There was an upstream discussion to your patch [1]. Would you send a v2
> containing a check for privileges, or shall I do that? I'm trying to
> reproduce it in the meantime and get more information out of libudev.
> Although I'm able to reproduce it only in about 75-80% cases, I haven't had
> much luck with regards to libudev for the time being.
> 
> [1] https://www.redhat.com/archives/libvir-list/2017-May/msg00264.html

I'm not familiar with privilege, i'm sorry for that, would you help me to improve the patch?

Comment 5 Erik Skultety 2017-05-19 13:17:18 UTC

I confirmed with GDB, that we indeed get ENOBUFFS from libudev and sent a v2 of your patch to the list [1].

[1] https://www.redhat.com/archives/libvir-list/2017-May/msg00732.html

Comment 6 Erik Skultety 2017-05-29 14:19:18 UTC

Fixed upstream by:
commit d1eea6c12aad5cb503562a52915138bf0d0a70a2
Refs: v3.4.0-rc1-2-gd1eea6c12
Author:     ning.bo <ning.bo9.cn>
AuthorDate: Tue May 9 10:09:07 2017 +0800
Commit:     Erik Skultety <eskultet>
CommitDate: Mon May 29 15:57:04 2017 +0200

    nodedev: Increase the netlink socket buffer size to the one used by udev

    When a number of SRIOV VFs (up to 128 on Intel XL710) is created:
    for i in `seq 0 1`; do
      echo 63 > /sys/class/net/<interface>/device/sriov_numvfs
    done

    libvirtd will then report "udev_monitor_receive_device returned NULL"
    error because the netlink socket buffer is not big enough (using GDB on
    libudev confirmed this with ENOBUFFS) and thus some udev events were
    dropped. This results in some devices being missing in the nodedev-list
    output. This patch overrides the system's rmem_max limit but for that,
    we need to make sure we've got root privileges.

    https://bugzilla.redhat.com/show_bug.cgi?id=1450960

    Signed-off-by: ning.bo <ning.bo9.cn>
    Signed-off-by: Erik Skultety <eskultet>

Comment 9 yafu 2017-06-21 12:35:26 UTC

Reproduced with libvirt-3.2.0-5.el7.

Verify with:
libvirt-3.2.0-13.el7.x86_64
systemd-219-41.el7.x86_64
kernel-3.10.0-682.el7.x86_64

Test steps(Test on ixgbe and i40e driver):
1.Create 126 vfs in the short time:
# for i in `seq 1 2`; do echo 63 > /sys/class/net/p7p$i/device/sriov_numvfs ;done

2.Check the log in the syslog(The warning and error log of libvirtd will output in the syslog by default):
#cat /var/log/messages | grep "udev_monitor"
no error outputs

3.Since only increase the netlink socket buffer size to the one used by udev with privileged user, so there still errors in the libvirtd log started by non-privileged user, which is the expected result.

Comment 10 errata-xmlrpc 2017-08-02 00:08:25 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, 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/RHEA-2017:1846

Comment 11 errata-xmlrpc 2017-08-02 01:32:35 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, 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/RHEA-2017:1846

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