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

["Denis V. Lunev" <den@virtuozzo.com>]

On 6/24/26 16:08, Denis V. Lunev wrote:
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> 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/20260622133715.3707707-1-den@openvz.org
>
> 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!

Is this good to go in? I have not seen the confirmation that the
series is taken into your tree.

Thank you in advance,
    Den