nvme disk cannot be hotplugged after removal

[Oguz Bektas]

Hello,

When I try to re-add an nvme disk shortly after removing it, I get an error about duplicate ID.

See the following commands to reproduce. This happens consistently on all VMs that I tested:

attach
==========

$VAR1 = {
          'arguments' => {
                           'command-line' => 'drive_add auto "file=/dev/zvol/rpool/data/vm-20000-disk-1,if=none,id=drive-nvme1,format=raw,cache=none,aio=native,detect-zeroes=on"'
                         },
          'execute' => 'human-monitor-command'
        };
$VAR1 = {
          'execute' => 'device_add',
          'arguments' => {
                           'serial' => 'nvme1',
                           'drive' => 'drive-nvme1',
                           'driver' => 'nvme',
                           'id' => 'nvme1'
                         }
        };

detach
===========
$VAR1 = {
          'arguments' => {
                           'id' => 'nvme1'
                         },
          'execute' => 'device_del'
        };
$VAR1 = {
          'execute' => 'human-monitor-command',
          'arguments' => {
                           'command-line' => 'drive_del drive-nvme1'
                         }
        };

reattach
===========
$VAR1 = {
          'arguments' => {
                           'command-line' => 'drive_add auto "file=/dev/zvol/rpool/data/vm-20000-disk-1,if=none,id=drive-nvme1,format=raw,cache=none,aio=native,detect-zeroes=on"'
                         },
          'execute' => 'human-monitor-command'
        };

and I get:
"Duplicate ID 'drive-nvme1' for drive"

although it does not show up in query-block or query-pci anymore after the first detach.

Is this a bug or am I missing something? Please advise.

Best regards,
Oguz

[Klaus Jensen (birkelund)]

Hi,

What QEMU version is this happening on? Is this the -rc4, is it a regression?

[Oguz Bektas (obektas)]

Hi,

this is happening on qemu 5.2.0

[Oguz Bektas (obektas)]

BTW Re: Regression, I think it's not, because this didn't work a year ago either, but I wasn't sure if it's a bug.

[Klaus Jensen (birkelund)]

So, I had to investigate this a bit, since it is a part of QEMU that I'm not too familiar with.

My understanding is that this is the expected behavior. The reason is that the drive cannot be deleted immediately when the device is hot-unplugged, since it might not be safe (other parts of QEMU could be using it, like background block jobs).

What we *can* do, is make sure we mark the drive for auto deletion when it is safe to do so. I'll add a patch for that.

On the other hand, the fact that if the drive is removed explicitly through QMP (or in the monitor with drive_del), the drive id is remains "in use". This might be a completely different bug that is unrelated to the nvme device.

[Oguz Bektas (obektas)]

> My understanding is that this is the expected behavior. The reason is that the drive cannot be deleted immediately when the device is hot-unplugged, since it might not be safe (other parts of QEMU could be using it, like background block jobs).

> On the other hand, the fact that if the drive is removed explicitly through QMP (or in the monitor with drive_del), the drive id is remains "in use". This might be a completely different bug that is unrelated to the nvme device.

using the same commands I can hot-plug and hot-unplug a scsi disk like this without issue - this behavior only appeared on nvme devices.

[Thomas Huth (th-huth)]

The QEMU project is currently moving its bug tracking to another system.
For this we need to know how to transfer the bug to the new system if
(if still necessary). Thus we're setting the status to "Incomplete" now.

In the unlikely case that the bug has already been fixed in the latest
upstream version of QEMU, then please close this ticket as "Fix released".

If it is not fixed yet and you think that this bug report here should be
moved to the new system, then you have two options:

1) If you already have an account on gitlab.com, please open a new ticket
for this problem in our new tracker here:

    https://gitlab.com/qemu-project/qemu/-/issues

and then close this ticket here on Launchpad (or let it expire auto-
matically after 60 days). Please mention the URL of this bug ticket on
Launchpad in the new ticket on GitLab.

2) If you don't have an account on gitlab.com and don't intend to get
one, but still would like to keep this ticket opened, then please switch
the state back to "New" or "Confirmed" within the next 60 days (other-
wise it will get closed as "Expired"). We will then eventually migrate
the ticket automatically to the new system (but you won't be the reporter
of the bug in the new system and thus you won't get notified on changes
anymore).

Thank you and sorry for the inconvenience.

[Thomas Huth (th-huth)]

This issue has been moved to the new bug tracker here:

 https://gitlab.com/qemu-project/qemu/-/issues/423

Thus let's close this version in the Launchpad tracker now.