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

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Jul 13, 2026 at 10:32:29PM +0200, Denis V. Lunev wrote:
> 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/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!
> >> 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

Hi!
It's on my queue and will be in the next Linux release, don't worry.

-- 
MST