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

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Message-ID: <87tu9nfaoe.fsf@redhat.com>
Date:   Wed, 18 May 2022 11:32:33 +0200
From:   Cornelia Huck <cohuck@...hat.com>
To:     Jason Wang <jasowang@...hat.com>, mst@...hat.com,
        jasowang@...hat.com, virtualization@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Cc:     tglx@...utronix.de, peterz@...radead.org, paulmck@...nel.org,
        maz@...nel.org, pasic@...ux.ibm.com, eperezma@...hat.com,
        lulu@...hat.com, sgarzare@...hat.com, 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, 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/

>
> 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.
 */

> +		 */
> +		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.
 */

> +		 */
> +		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.

> +	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. */