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Lunev" , mst@redhat.com Cc: virtualization@lists.linux.dev, linux-kernel@vger.kernel.org References: <20260622133715.3707707-1-den@openvz.org> <20260622133715.3707707-3-den@openvz.org> <8b83f251-3a3e-4fc9-8ea9-8d101fb92919@kernel.org> Content-Language: en-US From: "Denis V. 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Lunev wrote: >> Commit 8bd2fa086a04 ("virtio: break and reset virtio devices on >> device_shutdown()") added a generic virtio bus .shutdown handler that >> breaks and resets every virtio device during device_shutdown(), i.e. on >> reboot and kexec. >> >> virtio_balloon provides no .shutdown of its own, so that generic path >> runs while the balloon's asynchronous work is still armed. 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, for example a kexec based upgrade, into a fatal panic >> in the middle of device_shutdown(), so the machine never reaches the >> new kernel. >> >> Relaxing that single WARN_ON_ONCE() would only hide the symptom: the >> inflate/deflate and OOM paths do not warn, they call >> wait_event(vb->acked, ...) and would instead block forever on a broken >> queue that can no longer complete. The device has to be quiesced, not >> just kept quiet. > Ah, so > > /* We should always be able to add one buffer to an empty queue. */ > virtqueue_add_outbuf(vq, &sg, 1, vb, GFP_KERNEL); > > is not actually correct. > > Yeah, quiescing sounds cleaner, although I am thinking whether we should also > warn if virtqueue_add_outbuf() fails, similar to what we do in > virtballoon_free_page_report(). Good catch, will do., >> Add a .shutdown handler that quiesces the balloon via the shared >> virtballoon_quiesce() helper while the device is still alive, and only >> then breaks and resets it. The break and reset are repeated here rather >> than reused from virtio_dev_shutdown(): drv->shutdown replaces the >> generic handler rather than augmenting it, so that drivers such as >> virtio-gpu can opt out of the reset. Unlike virtballoon_remove() the >> balloon workqueue is not destroyed, as shutdown does not free the >> device and cancel_work_sync() together with stop_update already prevent >> any further work from being queued. >> >> Fixes: 8bd2fa086a04 ("virtio: break and reset virtio devices on device_shutdown()") >> Signed-off-by: Denis V. Lunev >> --- >> drivers/virtio/virtio_balloon.c | 10 ++++++++++ >> 1 file changed, 10 insertions(+) >> >> diff --git a/drivers/virtio/virtio_balloon.c b/drivers/virtio/virtio_balloon.c >> index 5b02d9191ac6..e35ada767b4b 100644 >> --- a/drivers/virtio/virtio_balloon.c >> +++ b/drivers/virtio/virtio_balloon.c >> @@ -1137,6 +1137,15 @@ static void virtballoon_remove(struct virtio_device *vdev) >> kfree(vb); >> } >> >> +static void virtballoon_shutdown(struct virtio_device *vdev) >> +{ >> + virtballoon_quiesce(vdev->priv); >> + >> + virtio_break_device(vdev); >> + virtio_synchronize_cbs(vdev); >> + vdev->config->reset(vdev); > I guess it would be good if we wouldn't have to copy what the default handler > does, but could instead just have it in a reusable core function? Ok. Sounds great. Will do. Thanks for review,     Den