And after executing steps in comment 0, can not list any mdev device if libvirtd quit after timeout:
# sleep 120
# virsh nodedev-list --cap mdev --inactive
no output

Ah, the support for non-unique UUIDs in mdevctl rears its head. Thanks, I'll investigate.

Potential patch sent upstream.

https://listman.redhat.com/archives/libvir-list/2021-July/msg00111.html

(In reply to Jonathon Jongsma from comment #2)
> Ah, the support for non-unique UUIDs in mdevctl rears its head. Thanks, I'll
> investigate.

Hi Jonathon,

The uuids used in comment 0 are unique.  

# mdevctl list -d
***8e21b099-b7a0-4c79-ad9e-6744362e2b77*** 0000:5b:00.0 nvidia-260 auto
***8e21b099-b7a0-4c79-ad9e-6744362e2b66*** 0000:9b:00.0 nvidia-260 auto

Also can not list mdev device successfully with the following uuids:
# mdevctl list -d
c11fa1ca-18f6-4793-aa58-dcbfbb2e52db 0000:5b:00.0 nvidia-260 auto
83a54ae7-09b1-4046-b0e2-b31de31505a0 0000:9b:00.0 nvidia-264 auto

# virsh nodedev-list --cap mdev --inactive
mdev_83a54ae7_09b1_4046_b0e2_b31de31505a0

Oh, sorry. I read the initial report too quickly so I did not notice the difference in UUIDs. (The patch I sent upstream is still fixing a real issue, but I guess it won't solve this particular issue.)

Can you attach the output from the following command?
$ mdevctl list --defined --dumpjson

(In reply to Jonathon Jongsma from comment #5)
> Oh, sorry. I read the initial report too quickly so I did not notice the
> difference in UUIDs. (The patch I sent upstream is still fixing a real
> issue, but I guess it won't solve this particular issue.)
> 
> Can you attach the output from the following command?
> $ mdevctl list --defined --dumpjson

# mdevctl list --defined --dumpjson
[
  {
    "0000:5b:00.0": [
      {
        "8e21b099-b7a0-4c79-ad9e-6744362e2b33": {
          "mdev_type": "nvidia-260",
          "start": "auto"
        }
      }
    ],
    "0000:9b:00.0": [
      {
        "8af4c8c3-959b-4596-bf0e-5eedc709b0b6": {
          "mdev_type": "nvidia-262",
          "start": "auto"
        }
      }
    ]
  }
]

Ah, this bug is solved by a patch that was just recently merged upstream. I can't reproduce it on git master anymore.

commit e9b534905f4fb03d8f31d007a0d1aa1c911e2a2c
Author: Jonathon Jongsma <jjongsma>
Date:   Thu Jun 10 13:15:37 2021 -0500

    nodedev: handle mdevs from multiple parents
    
    Due to a rather unfortunate misunderstanding, we were parsing the list
    of defined devices from mdevctl incorrectly. Since my primary
    development machine only has a single device capable of mdevs, I
    apparently neglected to test multiple parent devices and made some
    assumptions based on reading the mdevctl code. These assumptions turned
    out to be incorrect, so the parsing failed when devices from more than
    one parent device were returned.
    
    The details: mdevctl returns an array of objects representing the
    defined devices. But instead of an array of multiple objects (with each
    object representing a parent device), the array always contains only a
    single object. That object has a separate property for each parent
    device.
    
    Signed-off-by: Jonathon Jongsma <jjongsma>
    Reviewed-by: Michal Privoznik <mprivozn>

*** Bug 1979998 has been marked as a duplicate of this bug. ***

*** Bug 1979951 has been marked as a duplicate of this bug. ***

Verified with libvirt-7.6.0-1.module+el8.5.0+12097+2c77910b.x86_64.

Test steps:
1.Define 2 mdev device with different parent address:
#mdevctl define --uuid=8e21b099-b7a0-4c79-ad9e-6744362e2b66 --parent=0000:21:00.0 --type=nvidia-231 -a
# mdevctl define --uuid=83a54ae7-09b1-4046-b0e2-b31de31505a0 --parent=0000:41:00.0 --type=nvidia-231 -a

2.List the mdev device with 'virsh nodedev-list':
# virsh nodedev-list --cap mdev --all
mdev_83a54ae7_09b1_4046_b0e2_b31de31505a0
mdev_8e21b099_b7a0_4c79_ad9e_6744362e2b66

3.Start one mdev device:
# mdevctl start --uuid=8e21b099-b7a0-4c79-ad9e-6744362e2b66

4.List the active mdev device with 'virsh nodedev-list', the result can be refreshed:
# virsh nodedev-list --cap mdev
mdev_8e21b099_b7a0_4c79_ad9e_6744362e2b66

5.Destroy the mdev device and list again:
# virsh nodedev-list --cap mdev

# virsh nodedev-list --cap mdev --all
mdev_83a54ae7_09b1_4046_b0e2_b31de31505a0
mdev_8e21b099_b7a0_4c79_ad9e_6744362e2b66


6.Undefine both of the mdev devices and list again:
# virsh nodedev-undefine mdev_83a54ae7_09b1_4046_b0e2_b31de31505a0
Undefined node device 'mdev_83a54ae7_09b1_4046_b0e2_b31de31505a0'
# virsh nodedev-undefine mdev_8e21b099_b7a0_4c79_ad9e_6744362e2b66
Undefined node device 'mdev_8e21b099_b7a0_4c79_ad9e_6744362e2b66'

# virsh nodedev-list --cap mdev --all
no output

7.Also test define 2 different parent address mdev devices with 'virsh nodedev-define', it works well.

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 (virt:av 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/RHBA-2021:4684