Re: [Qemu-devel] [PATCH 10/10] qdev: fix create in place obj's life cycle problem

[Avi Kivity]

On 08/27/2012 12:38 PM, Jan Kiszka wrote:
> >> Even worse, apply
> >> restrictions on how the dispatched objects, the regions, have to be
> >> treated because of this.
> > 
> > Please elaborate.
>
> The fact that you can't manipulate a memory region object arbitrarily
> after removing it from the mapping because you track the references to
> the object that the region points to, not the region itself. The region
> remains in use by the dispatching layer and potentially the called
> device, even after deregistration.

That object will be a container_of() the region, usually literally but
sometimes only in spirit.  Reference counting the regions means they
cannot be embedded into other objects any more.

We can probably figure out a way to flush out accesses.  After switching
to rcu, for example, all we need is synchronize_rcu() in a
non-deadlocking place.  But my bet is that it will not be needed.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.