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

[Pierre Morel]

On 05/06/2018 15:52, Cornelia Huck wrote:
> On Tue, 5 Jun 2018 15:34:52 +0200
> Pierre Morel <pmorel@xxxxxxxxxxxxx> wrote:
>
> > On 04/06/2018 15:52, Cornelia Huck wrote:
> > > On Fri, 25 May 2018 12:21:09 +0200
> > > Pierre Morel <pmorel@xxxxxxxxxxxxxxxxxx> wrote:
> > >   
> > > > Let's move the state change from the IRQ routine to the
> > > > workqueue callback.
> > > >
> > > > Signed-off-by: Pierre Morel <pmorel@xxxxxxxxxxxxxxxxxx>
> > > > ---
> > > >    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
> > This should not be done if the subchannel is not operational.
> >
> > > - via the state machine, disabling the subchannel is (re-)triggered
> > I removed the fsm_disabled_irq() callback from VFIO_CCW_STATE_NOT_OPER
> > because the subchannel is not even initialized at that moment.
> > We have no reference to the subchannel.
> >
> > In the previous driver NOT_OPER and STANDBY were quite the same.
> > Now NOT_OPER means "we can not operate on this sub channel"
> > because we do not have it in a correct state (no ISC, no mediated device,
> > the probe is not finiched)
> >
> > Now STANDBY means we have the device ready but is disabled.
> > In this case the software infrastructure is ready and if an interrupt comes
> > (what should not happen) we will disable the subchannel again.
> >
> > > 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.
> > >   
> > Yes it is queued in any case but the IRQ is really treated only if the
> > subchannel is in the right state (STANDBY, BUSY, IDLE and QUIESCING).
> >
> > In the NOT_OPER state we do not have the mdev not the driver initialized.
> But all of this is only true after the whole series has been applied,
> isn't it? Is there any way to do the changes without breaking things
> inbetween?

I will think about this.
May be just disable the all thing untill all patches applied?

> What would also be very helpful is a sketch of the state machine after
> your rework is done. Otherwise, this leaves me a bit unsure about the
> intended semantics if I just look at the individual patches.

Right, I must enhance the cover letter.


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