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

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Date:   Tue, 5 Jun 2018 15:10:11 +0200
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Cornelia Huck <cohuck@...hat.com>,
        Pierre Morel <pmorel@...ux.vnet.ibm.com>
Cc:     pasic@...ux.vnet.ibm.com, bjsdjshi@...ux.vnet.ibm.com,
        linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH v2 06/10] vfio: ccw: Make FSM functions atomic

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

>
>> Signed-off-by: Pierre Morel <pmorel@...ux.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.

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


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