linux-kernel - Re: [PATCH V5 6/9] virtio-ccw: implement synchronize

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Date:   Thu, 19 May 2022 16:02:30 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     Cornelia Huck <cohuck@...hat.com>
Cc:     mst <mst@...hat.com>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Marc Zyngier <maz@...nel.org>,
        Halil Pasic <pasic@...ux.ibm.com>,
        eperezma <eperezma@...hat.com>, Cindy Lu <lulu@...hat.com>,
        Stefano Garzarella <sgarzare@...hat.com>,
        Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
        Vineeth Vijayan <vneethv@...ux.ibm.com>,
        Peter Oberparleiter <oberpar@...ux.ibm.com>,
        linux-s390@...r.kernel.org
Subject: Re: [PATCH V5 6/9] virtio-ccw: implement synchronize_cbs()

On Wed, May 18, 2022 at 5:32 PM Cornelia Huck <cohuck@...hat.com> wrote:
>
> On Wed, May 18 2022, Jason Wang <jasowang@...hat.com> wrote:
>
> > This patch tries to implement the synchronize_cbs() for ccw. For the
> > vring_interrupt() that is called via virtio_airq_handler(), the
> > synchronization is simply done via the airq_info's lock. For the
> > vring_interrupt() that is called via virtio_ccw_int_handler(), a per
> > device rwlock is introduced ans used in the synchronization method.
>
> s/ans/and/
>

Will fix.

> >
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: "Paul E. McKenney" <paulmck@...nel.org>
> > Cc: Marc Zyngier <maz@...nel.org>
> > Cc: Halil Pasic <pasic@...ux.ibm.com>
> > Cc: Cornelia Huck <cohuck@...hat.com>
> > Cc: Vineeth Vijayan <vneethv@...ux.ibm.com>
> > Cc: Peter Oberparleiter <oberpar@...ux.ibm.com>
> > Cc: linux-s390@...r.kernel.org
> > Signed-off-by: Jason Wang <jasowang@...hat.com>
> > ---
> >  drivers/s390/virtio/virtio_ccw.c | 27 +++++++++++++++++++++++++++
> >  1 file changed, 27 insertions(+)
> >
> > diff --git a/drivers/s390/virtio/virtio_ccw.c b/drivers/s390/virtio/virtio_ccw.c
> > index d35e7a3f7067..22d36594bcdd 100644
> > --- a/drivers/s390/virtio/virtio_ccw.c
> > +++ b/drivers/s390/virtio/virtio_ccw.c
> > @@ -62,6 +62,7 @@ struct virtio_ccw_device {
> >       unsigned int revision; /* Transport revision */
> >       wait_queue_head_t wait_q;
> >       spinlock_t lock;
> > +     rwlock_t irq_lock;
> >       struct mutex io_lock; /* Serializes I/O requests */
> >       struct list_head virtqueues;
> >       bool is_thinint;
> > @@ -984,6 +985,27 @@ static const char *virtio_ccw_bus_name(struct virtio_device *vdev)
> >       return dev_name(&vcdev->cdev->dev);
> >  }
> >
> > +static void virtio_ccw_synchronize_cbs(struct virtio_device *vdev)
> > +{
> > +     struct virtio_ccw_device *vcdev = to_vc_device(vdev);
> > +     struct airq_info *info = vcdev->airq_info;
> > +
> > +     if (info) {
> > +             /*
> > +              * Synchronize with the vring_interrupt() with airq indicator
>
> Maybe
>
> /*
>  * This device uses adapter interrupts: synchronize with
>  * vring_interrupt() called by virtio_airq_handler() via the indicator
>  * area lock.
>  */
>

Fine.

> > +              */
> > +             write_lock_irq(&info->lock);
> > +             write_unlock_irq(&info->lock);
> > +     } else {
> > +             /*
> > +              * Synchronize with the vring_interrupt() called by
> > +              * virtio_ccw_int_handler().
>
> /*
>  * This device uses classic interrupts: synchronize with
>  * vring_interrupt() called by virtio_ccw_int_handler() via the
>  * per-device irq_lock.
>  */
>

Looks fine.

> > +              */
> > +             write_lock_irq(&vcdev->irq_lock);
> > +             write_unlock_irq(&vcdev->irq_lock);
> > +     }
> > +}
> > +
> >  static const struct virtio_config_ops virtio_ccw_config_ops = {
> >       .get_features = virtio_ccw_get_features,
> >       .finalize_features = virtio_ccw_finalize_features,
> > @@ -995,6 +1017,7 @@ static const struct virtio_config_ops virtio_ccw_config_ops = {
> >       .find_vqs = virtio_ccw_find_vqs,
> >       .del_vqs = virtio_ccw_del_vqs,
> >       .bus_name = virtio_ccw_bus_name,
> > +     .synchronize_cbs = virtio_ccw_synchronize_cbs,
> >  };
> >
> >
> > @@ -1106,6 +1129,8 @@ static void virtio_ccw_int_handler(struct ccw_device *cdev,
> >                       vcdev->err = -EIO;
> >       }
> >       virtio_ccw_check_activity(vcdev, activity);
> > +     /* Local interrupt should be disabled at this time */
>
> /* Interrupts are disabled here. */
>
> ?
>
> Interrupts enabled here would surely be a bug.

Right.

Thanks

>
> > +     read_lock(&vcdev->irq_lock);
> >       for_each_set_bit(i, indicators(vcdev),
> >                        sizeof(*indicators(vcdev)) * BITS_PER_BYTE) {
> >               /* The bit clear must happen before the vring kick. */
>