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

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Message-ID: <20180605133850.3509a3d3.cohuck@redhat.com>
Date:   Tue, 5 Jun 2018 13:38:50 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     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 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.)

> 
> 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?

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