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Re: [PATCH] virtio: Add corresponding memory_listener_unregister to unre

From: Peter Xu
Subject: Re: [PATCH] virtio: Add corresponding memory_listener_unregister to unrealize
Date: Mon, 25 Jan 2021 12:18:04 -0500

On Mon, Jan 25, 2021 at 05:55:35PM +0100, Eugenio Perez Martin wrote:
> On Mon, Jan 25, 2021 at 4:15 AM Jason Wang <jasowang@redhat.com> wrote:
> >
> >
> > On 2021/1/23 上午4:08, Eugenio Pérez wrote:
> > > Cannot destroy address spaces of IOMMU-aware virtio devices without it,
> > > since they can contain memory listeners.
> >
> >
> > It's better to explain why the one in finalize doesn't work here.
> >
> Hi Jason! Good point. The other call is at virtio_device_instance_finalize.
> Function virtio_device_instance_finalize is called after
> address_space_destroy if we follow steps of buglink.
> Address_space_destroy is called by
> pci_qdev_unrealize/do_pci_unregister_device, after call to
> virtio_device_unrealize. After that call,
> virtio_device_instance_finalize is called through object_deinit,
> freeing the bus.
> Also, memory_listener_unregister can be called again because it checks
> for listener->address_space != NULL at start, and sets it to NULL at
> end.
> In regular shutdown, nothing of this is called, so maybe we could
> safely delete the call to memory_listener_unregister at
> virtio_device_instance_finalize?

I didn't notice this; if so we'd better remove that call if it's destined to be
a noop after all.

> If not, should I send again the patch with a new commit message?

Maybe attach the full backtrace too along with above?  The assertion itself
could be a very good explanation of what's happened.


Peter Xu

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