Re: [PATCH] vfio-ccw: process ssch with interrupts disabled

Cornelia Huck
2018-04-19T15:22:48Z

On Thu, 19 Apr 2018 16:14:25 +0200
Pierre Morel <pmorel@linux.vnet.ibm.com> wrote:

> On 13/04/2018 16:05, Cornelia Huck wrote:
> > When we call ssch, an interrupt might already be pending once we
> > return from the START SUBCHANNEL instruction. Therefore we need to
> > make sure interrupts are disabled until after we're done with our
> > processing.
> >
> > Note that the subchannel lock is the same as the ccwdevice lock that
> > is mentioned in the documentation for ccw_device_start() and friends.
> >
> > Signed-off-by: Cornelia Huck <cohuck@redhat.com>
> > ---
> > drivers/s390/cio/vfio_ccw_fsm.c | 19 ++++++++++++-------
> > 1 file changed, 12 insertions(+), 7 deletions(-)
> >
> > diff --git a/drivers/s390/cio/vfio_ccw_fsm.c b/drivers/s390/cio/vfio_ccw_fsm.c
> > index ff6963ad6e39..3c800642134e 100644
> > --- a/drivers/s390/cio/vfio_ccw_fsm.c
> > +++ b/drivers/s390/cio/vfio_ccw_fsm.c
> > @@ -20,12 +20,12 @@ static int fsm_io_helper(struct vfio_ccw_private *private)
> > int ccode;
> > __u8 lpm;
> > unsigned long flags;
> > + int ret;
> >
> > sch = private->sch;
> >
> > spin_lock_irqsave(sch->lock, flags);
> > private->state = VFIO_CCW_STATE_BUSY;
> > - spin_unlock_irqrestore(sch->lock, flags);
> >
> > orb = cp_get_orb(&private->cp, (u32)(addr_t)sch, sch->lpm);
> >
> > @@ -38,10 +38,12 @@ static int fsm_io_helper(struct vfio_ccw_private *private)
> > * Initialize device status information
> > */
> > sch->schib.scsw.cmd.actl |= SCSW_ACTL_START_PEND;
> > - return 0;
> > + ret = 0;
> > + break;
> > case 1: /* Status pending */
> > case 2: /* Busy */
> > - return -EBUSY;
> > + ret = -EBUSY;
> > + break;
> > case 3: /* Device/path not operational */
> > {
> > lpm = orb->cmd.lpm;
> > @@ -51,13 +53,16 @@ static int fsm_io_helper(struct vfio_ccw_private *private)
> > sch->lpm = 0;
> >
> > if (cio_update_schib(sch))
> > - return -ENODEV;
> > -
> > - return sch->lpm ? -EACCES : -ENODEV;
> > + ret = -ENODEV;
> > + else
> > + ret = sch->lpm ? -EACCES : -ENODEV;
> > + break;
> > }
> > default:
> > - return ccode;
> > + ret = ccode;
> > }
> > + spin_unlock_irqrestore(sch->lock, flags);
> > + return ret;
> > }
> >
> > static void fsm_notoper(struct vfio_ccw_private *private,
>
>
> I have been working on a patch to solve this problem between others, I
> provide it soon.
> It is much more intrusive, reworking interrupts and state machine.
> So may be you do not like it.

I'll take a look at your state machine series later, but it is
certainly material for the next release.

[I also have my halt/clear implementation which I wanted to send this
week, but other things have been eating up my bandwidth. Well, the week
is not over yet...]

> If we stay on this patch, even this is quite a long spinlock around ssch
> and stsch,
> and we need it in the current implementation.

I'd like to queue a small patch like this for the current release which
is also suitable for stable. We can still rework things on top.

> Acked-by: Pierre Morel<pmorel@linux.vnet.ibm.com>

Thanks!