Re: [Qemu-devel] [PATCH v2 2/5] vfio-ccw: concurrent I/O handling

[Cornelia Huck <cohuck@redhat.com>]

On Wed, 23 Jan 2019 14:30:51 +0100
Halil Pasic <pasic@linux.ibm.com> wrote:

> On Wed, 23 Jan 2019 11:21:12 +0100
> Cornelia Huck <cohuck@redhat.com> wrote:
> 
> > On Tue, 22 Jan 2019 19:33:46 +0100
> > Halil Pasic <pasic@linux.ibm.com> wrote:
> >   
> > > On Mon, 21 Jan 2019 12:03:51 +0100
> > > Cornelia Huck <cohuck@redhat.com> wrote:
> > >   
> > > > --- a/drivers/s390/cio/vfio_ccw_private.h
> > > > +++ b/drivers/s390/cio/vfio_ccw_private.h
> > > > @@ -28,6 +28,7 @@
> > > >   * @mdev: pointer to the mediated device
> > > >   * @nb: notifier for vfio events
> > > >   * @io_region: MMIO region to input/output I/O arguments/results
> > > > + * @io_mutex: protect against concurrent update of I/O structures    
> > > 
> > > We could be a bit more specific about what does this mutex guard.
> > > Is it only io_region, or cp, irb and the new regions a well? ->state does
> > > not seem to be covered, but should need some sort of synchronisation
> > > too, or?  
> > 
> > I'm not sure. IIRC Pierre had some ideas about locking in the fsm?
> >   
> 
> Yes there was something. I usually do review by sanity checking the
> resulting code. IMHO the fsm stuff is broken now and differently broken
> after this series. If we don't want to fix what we are touching, maybe a
> pointing out ignored problems in patch descriptions and a
> minimal-invasive approach could help ease review.

So, would changing the description above to reference "the I/O
regions" (as it will also be taken when writing to the async region)
and stating that this handles concurrent reading/writing of the regions
help? I really don't want to enumerate everything I don't fix...

> 
> Regards,
> Halil
> 
> > >   
> > > >   * @cp: channel program for the current I/O operation
> > > >   * @irb: irb info received from interrupt
> > > >   * @scsw: scsw info
> > > > @@ -42,6 +43,7 @@ struct vfio_ccw_private {
> > > >  	struct mdev_device	*mdev;
> > > >  	struct notifier_block	nb;
> > > >  	struct ccw_io_region	*io_region;
> > > > +	struct mutex		io_mutex;
> > > >  
> > > >  	struct channel_program	cp;
> > > >  	struct irb		irb;
> > > > --     
> > >   
> > 
> >   
>