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

Pierre Morel
2018-06-05T14:21:03Z

On 05/06/2018 15:35, Cornelia Huck wrote:
> 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?

Yes, if it is not I forgot something important (like I did in patch 10)
vfio_ccw_fsm_event(private, event) takes the mutex on firering an event.

I have some cases where I do not respect this.
This is false and I must handle this with a new private variable,
this is where I test the state after having fired an event.
I will need to change this, in quiesce, reset, probe and open (others?).

>
>>>
>>>> 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?

I will see if I can put it inside the patch 01/10 moving state change
out of IRQ context.

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