On 6/22/26 15:37, Denis V. Lunev wrote:
> 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.
>
> Patch 1 factors the teardown out of virtballoon_remove() into a
> virtballoon_quiesce() helper (no functional change). Patch 2 adds a
> virtio_balloon .shutdown handler that quiesces via that helper while the
> device is still alive, then breaks and resets it the way the generic
> virtio_dev_shutdown() would.
>
> Relaxing the single WARN_ON_ONCE() instead was considered and rejected: it
> would silence the panic but leave the inflate/deflate and OOM paths
> hanging on the broken device. The device has to be quiesced, not just kept
> quiet.
Do you have a link to that discussion you could add?
--
Cheers,
David
