Re: [PATCH v2 0/4] virtio_balloon: quiesce balloon work on device shutdown

On 7/3/26 00:33, Michael S. Tsirkin wrote:
> On Thu, Jul 02, 2026 at 09:30:26PM +0200, David Hildenbrand (Arm) wrote:
>> On 7/2/26 19:50, Denis V. Lunev wrote:
>>> On 6/24/26 16:08, Denis V. Lunev wrote:
>>>> This email originated from an IP that might not be authorized by the domain it was sent from.
>>>> Do not click links or open attachments unless it is an email you expected to receive.
>>>> Since commit 8bd2fa086a04 ("virtio: break and reset virtio devices on
>>>> device_shutdown()") the virtio bus breaks and resets every virtio device
>>>> during device_shutdown(), i.e. on reboot and kexec. virtio_balloon has no
>>>> .shutdown of its own, so that generic path runs while the balloon's
>>>> asynchronous work is still armed: the free page reporting worker, the
>>>> inflate/deflate and stats workers, the OOM notifier and the free page
>>>> shrinker.
>>>>
>>>> Once the device has been broken, virtqueue_add_inbuf() in
>>>> virtballoon_free_page_report() returns -EIO and trips its WARN_ON_ONCE().
>>>> On a kernel booted with panic_on_warn that turns an ordinary reboot into a
>>>> fatal panic in the middle of device_shutdown(), so the machine never
>>>> reaches the new kernel. The inflate/deflate and OOM paths do not warn but
>>>> are no better off: they call wait_event(vb->acked, ...) and would block
>>>> forever on a queue that can no longer complete.
>>>>
>>>> This was hit in the field as an intermittent failure of a virtualization
>>>> cluster upgrade: guest storage nodes were rebooted via kexec into the new
>>>> kernel, and the ones whose free page reporting happened to run during
>>>> device_shutdown() panicked (the guests run with panic_on_warn) and never
>>>> came back, stalling the rolling upgrade. The crash dump showed the WARN at
>>>> virtio_balloon.c:216 in a page_reporting kworker, with all the balloon
>>>> virtqueues already broken.
>>>>
>>>> Validated by churning balloon inflate/deflate from the host while
>>>> kexec-rebooting the guest in a loop under panic_on_warn: the unpatched
>>>> kernel reproduces the WARN within a couple of cycles, while the patched
>>>> kernel survives many consecutive kexec cycles cleanly (12/12 in the final
>>>> run, 0 WARNs). checkpatch is clean across the series.
>>>>
>>>> Changes in v2:
>>>> - Add a virtio_device_shutdown() core helper and call it from the balloon
>>>>   .shutdown handler instead of open-coding break + synchronize_cbs + reset
>>>>   (David Hildenbrand).
>>>> - New patch: make tell_host() warn and bail instead of hanging if a buffer
>>>>   add ever fails (David Hildenbrand); kept as a separate patch
>>>>   (Michael S. Tsirkin).
>>>>
>>>> v1: https://lore.kernel.org/all/[email protected]
>>>>
>>>> Denis V. Lunev (4):
>>>>   virtio: add virtio_device_shutdown() helper
>>>>   virtio_balloon: factor out virtballoon_quiesce()
>>>>   virtio_balloon: quiesce balloon work before device shutdown
>>>>   virtio_balloon: warn on failed buffer add in tell_host()
>>>>
>>>>  drivers/virtio/virtio.c         | 41 ++++++++++++++++++++++-----------
>>>>  drivers/virtio/virtio_balloon.c | 40 ++++++++++++++++++++++++--------
>>>>  include/linux/virtio.h          |  1 +
>>>>  3 files changed, 59 insertions(+), 23 deletions(-)
>>>>
>>> Hi, David!
>> Hi! :)
>>
>>> Is this good to go in? I have not seen the confirmation that the
>>> series is taken into your tree.
>> I don't have a tree (yet), and once I have one it will likely be more mm focused :)
>>
>> @MST, I think this is good to go!
>>
>> -- 
>> Cheers,
>>
>> David
> Indeed, it's just a bugfix and I'm trying to get features into qemu
> now before their freeze. I'll work on linux end of next week.
>
Hi, Michael!

Have you had a chance to take series into your tree, i.e.
should I continue to track this submission?

Thank you in advance,
    Den