Re: [PATCH v2 06/10] vfio: ccw: Make FSM functions atomic

[Pierre Morel]

On 05/06/2018 13:38, Cornelia Huck wrote:
> On Fri, 25 May 2018 12:21:14 +0200
> Pierre Morel <pmorel@xxxxxxxxxxxxxxxxxx> wrote:
>
> > We use mutex around the FSM function call to make the FSM
> > event handling and state change atomic.
> I'm still not really clear as to what this mutex is supposed to
> serialize:
>
> - Modification of the state?
> - Any calls in the state machine?
> - A combination? (That would imply that we only deal with the state in
>    the state machine.)

yes to all

> > Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxxxxxxx>
> > ---
> >   drivers/s390/cio/vfio_ccw_drv.c     | 3 +--
> >   drivers/s390/cio/vfio_ccw_private.h | 3 +++
> >   2 files changed, 4 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/s390/cio/vfio_ccw_drv.c b/drivers/s390/cio/vfio_ccw_drv.c
> > index 6b7112e..98951d5 100644
> > --- a/drivers/s390/cio/vfio_ccw_drv.c
> > +++ b/drivers/s390/cio/vfio_ccw_drv.c
> > @@ -73,8 +73,6 @@ static void vfio_ccw_sch_io_todo(struct work_struct *work)
> >   
> >   	private = container_of(work, struct vfio_ccw_private, io_work);
> >   	vfio_ccw_fsm_event(private, VFIO_CCW_EVENT_INTERRUPT);
> > -	if (private->mdev)
> > -		private->state = VFIO_CCW_STATE_IDLE;
> Looks like an unrelated change? If you want to do all state changes
> under the mutex, that should rather be moved than deleted, shouldn't it?

It is moved to fsm_irq() which is called under mutex.
fsm_irq() returns VFIO_CCW_STATE_IDLE.

> >   }
> >   
> >   static void vfio_ccw_sch_event_todo(struct work_struct *work)


--
Pierre Morel
Linux/KVM/QEMU in BÃblingen - Germany