linux-kernel - Re: [PATCH v2 01/10] vfio: ccw: Moving state change out of IRQ context

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Message-ID: <20180604155231.42c139ac.cohuck@redhat.com>
Date:   Mon, 4 Jun 2018 15:52:31 +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 01/10] vfio: ccw: Moving state change out of IRQ
 context

On Fri, 25 May 2018 12:21:09 +0200
Pierre Morel <pmorel@...ux.vnet.ibm.com> wrote:

> Let's move the state change from the IRQ routine to the
> workqueue callback.
> 
> Signed-off-by: Pierre Morel <pmorel@...ux.vnet.ibm.com>
> ---
>  drivers/s390/cio/vfio_ccw_drv.c | 20 +++++++-------------
>  drivers/s390/cio/vfio_ccw_fsm.c | 14 ++++++++------
>  2 files changed, 15 insertions(+), 19 deletions(-)

This causes a change in behaviour for devices in the notoper state.

Now:
- vfio_ccw_sch_irq is called
- via the state machine, disabling the subchannel is (re-)triggered

With your patch:
- the work function is queued in any case; eventually, it will change
  the device's state to idle (unless we don't have an mdev at that
  point in time)
- completion is signaled

I'm not sure that's what we want.