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Bug 1463285 - mediated devices are not shown in nodedev-list --cap mdev output
Summary: mediated devices are not shown in nodedev-list --cap mdev output
Keywords:
Status: CLOSED ERRATA
Alias: None
Product: Red Hat Enterprise Linux 7
Classification: Red Hat
Component: libvirt
Version: 7.4
Hardware: Unspecified
OS: Unspecified
high
high
Target Milestone: rc
: ---
Assignee: Erik Skultety
QA Contact: zhe peng
URL:
Whiteboard:
Depends On: 1376907 1528122
Blocks: 1452072 1469590
TreeView+ depends on / blocked
 
Reported: 2017-06-20 13:38 UTC by Erik Skultety
Modified: 2018-04-10 10:52 UTC (History)
5 users (show)

Fixed In Version: libvirt-3.9.0-1.el7
Doc Type: If docs needed, set a value
Doc Text:
Clone Of:
Environment:
Last Closed: 2018-04-10 10:50:46 UTC
Target Upstream Version:
Embargoed:

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System ID Private Priority Status Summary Last Updated
Red Hat Product Errata RHEA-2018:0704 0 None None None 2018-04-10 10:52:02 UTC

Description Erik Skultety 2017-06-20 13:38:56 UTC 
Description of problem:
If a mediated device is created during libvirtd run, there's a chance the device won't be listed by the following command:

#virsh nodedev-list --cap mdev

Version-Release number of selected component (if applicable):
libvirt-3.2.0-9.virtcov.el7.x86_64

How reproducible:
depending on the environment (on some env 100%, 0% on others)

Steps to Reproduce:
1. start libvirtd
2. create a mediated device
# echo `uuidgen` > \ /sys/class/mdev_bus/<pci_address>/mdev_supported_types/nvidia-X/create
3. virsh nodedev-list --cap mdev returns an empty list

Actual results:
The device won't show up in the output list until the daemon is restarted.

Expected results:
The device shows up in the output list

Additional info:
This is apparently due to a kernel uevent race, where the 'add' uevent is sent prior to creating the whole sysfs device tree, thus at the time of processing the device, some of the requested sysfs attributes might not be exposed yet.

Until this is fixed in the upstream kernel, libvirt needs a workaround fix.
Comment 5 Erik Skultety 2017-08-28 11:25:59 UTC 
v3 of the workaround posted upstream:
https://www.redhat.com/archives/libvir-list/2017-August/msg00703.html
Comment 6 Erik Skultety 2017-10-19 07:18:57 UTC 
Workaround pushed upstream:

commit 1af45804088c5b1f19fca8631821ba5ae94cf3dd
Author:     Erik Skultety <eskultet>
AuthorDate: Tue Jun 20 16:15:22 2017 +0200
Commit:     Erik Skultety <eskultet>
CommitDate: Thu Oct 19 08:54:53 2017 +0200

    nodedev: udev: Hook up virFileWaitForAccess to work around uevent race

    If we find ourselves in the situation that the 'add' uevent has been
    fired earlier than the sysfs tree for a device was created, we should
    use the best-effort approach and give kernel some predetermined amount
    of time, thus waiting for the attributes to be ready rather than
    discarding the device from our device list forever. If those don't appear
    in the given time frame, we need to move on, since libvirt can't wait
    indefinitely.

    Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1463285

    Signed-off-by: Erik Skultety <eskultet>
Comment 8 zhe peng 2018-01-25 03:37:24 UTC 
verify with build:
libvirt-3.9.0-7.el7.x86_64
kernel-3.10.0-837.el7.x86_64
NVIDIA-Linux-x86_64-390.21-vgpu-kvm.run

step:
1. start libvirtd
2. create a mediated device
# echo `uuidgen` > /sys/class/mdev_bus/<pci_address>/mdev_supported_types/nvidia-X/create
3. virsh nodedev-list --cap mdev
mdev_1a8a1bbc_a095_4c59_8a17_341a3eff9c63

the device can show up, move to verified.
Comment 12 errata-xmlrpc 2018-04-10 10:50:46 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-2018:0704
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