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

Cornelia Huck
2018-06-05T13:35:39Z

On Tue, 5 Jun 2018 15:10:11 +0200
Pierre Morel <pmorel@linux.ibm.com> wrote:

> On 05/06/2018 13:38, Cornelia Huck wrote:
> > On Fri, 25 May 2018 12:21:14 +0200
> > Pierre Morel <pmorel@linux.vnet.ibm.com> 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

But wouldn't that imply that you need to either take the mutex if you
do something dependent on the state, or fire an event in that case?

>
> >
> >> Signed-off-by: Pierre Morel <pmorel@linux.vnet.ibm.com>
> >> ---
> >> 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.

So, should that go into another patch?

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