Re: [PATCH 3/4] device-core: use atomic_set on .realized property

[Maxim Levitsky]

On Mon, 2020-05-04 at 13:22 +0200, Paolo Bonzini wrote:
> On 04/05/20 12:45, Stefan Hajnoczi wrote:
> > > @@ -983,7 +983,7 @@ static void device_set_realized(Object *obj, bool 
> > > value, Error **errp)
> > >      }
> > >  
> > >      assert(local_err == NULL);
> > > -    dev->realized = value;
> > > +    atomic_set(&dev->realized, value);
> > 
> > A memory barrier is probably needed so that the atomic_read() thread
> > sees up-to-date dev fields.
> 
> Yes, it should be a store-release for the false->true case.  The
> true->false case probably doesn't matter as much.

On second thought, I think both cases matter, after I examined the device 
removal case.
In device removal case, the device is first un-realized and then removed from 
the bus,
so just like in device hotplug case, the scsi_device_find can give you an 
unrealized device.

I will change this patch to set .realized to false at the start (if needed) of 
the function and to true at the end (also if needed)
Will atomic_rcu_set work? or atomic_store_release?
(Both are the same thing, but former documents the purpose of using with RCU.

Best regards,
        Maxim Levitsky



> 
> Paolo
>