Re: [Qemu-devel] [PATCH v3 1/6] vfio-ccw: make it safe to access channel programs

[Halil Pasic <pasic@linux.ibm.com>]

On Thu, 31 Jan 2019 12:52:20 +0100
Cornelia Huck <cohuck@redhat.com> wrote:

> On Wed, 30 Jan 2019 19:51:27 +0100
> Halil Pasic <pasic@linux.ibm.com> wrote:
> 
> > On Wed, 30 Jan 2019 14:22:07 +0100
> > Cornelia Huck <cohuck@redhat.com> wrote:
> > 
> > > When we get a solicited interrupt, the start function may have
> > > been cleared by a csch, but we still have a channel program
> > > structure allocated. Make it safe to call the cp accessors in
> > > any case, so we can call them unconditionally.  
> > 
> > I read this like it is supposed to be safe regardless of
> > parallelism and threads. However I don't see any explicit
> > synchronization done for cp->initialized.
> > 
> > I've managed to figure out how is that supposed to be safe
> > for the cp_free() (which is probably our main concern) in
> > vfio_ccw_sch_io_todo(), but if fail when it comes to the one
> > in vfio_ccw_mdev_notifier().
> > 
> > Can you explain us how does the synchronization work?
> 
> You read that wrong, I don't add synchronization, I just add a check.
> 

Now I'm confused. Does that mean we don't need synchronization for this?

Regards,
Halil