On Sat, May 07, 2022 at 03:19:51PM +0800, Jason Wang 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 spinlock for irq is introduced ans used in the synchronization
> method.
>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
> Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
> Cc: Marc Zyngier <maz@xxxxxxxxxx>
> Cc: Halil Pasic <pasic@xxxxxxxxxxxxx>
> Cc: Cornelia Huck <cohuck@xxxxxxxxxx>
> Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
> ---
> 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..001e1f0e6037 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
> + */
> + write_lock(&info->lock);
> + write_unlock(&info->lock);
> + } else {
> + /*
> + * Synchronize with the vring_interrupt() called by
> + * virtio_ccw_int_handler().
> + */
> + write_lock(&vcdev->irq_lock);
> + write_unlock(&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,
> };
>
>
> @@ -1079,6 +1102,7 @@ static void virtio_ccw_int_handler(struct ccw_device *cdev,
> {
> __u32 activity = intparm & VIRTIO_CCW_INTPARM_MASK;
> struct virtio_ccw_device *vcdev = dev_get_drvdata(&cdev->dev);
> + unsigned long flags;
> int i;
> struct virtqueue *vq;
>
> @@ -1106,6 +1130,7 @@ static void virtio_ccw_int_handler(struct ccw_device *cdev,
> vcdev->err = -EIO;
> }
> virtio_ccw_check_activity(vcdev, activity);
> + read_lock_irqsave(&vcdev->irq_lock, flags);
> for_each_set_bit(i, indicators(vcdev),
> sizeof(*indicators(vcdev)) * BITS_PER_BYTE) {
> /* The bit clear must happen before the vring kick. */
Cornelia sent a lockdep trace on this.
Basically I think this gets the irqsave/restore logic wrong.
It attempts to disable irqs in the handler (which is an interrupt
anyway).
And it does not disable irqs in the synchronize_cbs.
As a result in interrupt might try to take a read lock while
.synchronize_cbs has the writer lock, resulting in a deadlock.
I think you want regular read_lock + write_lock_irq.
> @@ -1114,6 +1139,7 @@ static void virtio_ccw_int_handler(struct ccw_device *cdev,
> vq = virtio_ccw_vq_by_ind(vcdev, i);
> vring_interrupt(0, vq);
> }
> + read_unlock_irqrestore(&vcdev->irq_lock, flags);
> if (test_bit(0, indicators2(vcdev))) {
> virtio_config_changed(&vcdev->vdev);
> clear_bit(0, indicators2(vcdev));
> @@ -1284,6 +1310,7 @@ static int virtio_ccw_online(struct ccw_device *cdev)
> init_waitqueue_head(&vcdev->wait_q);
> INIT_LIST_HEAD(&vcdev->virtqueues);
> spin_lock_init(&vcdev->lock);
> + rwlock_init(&vcdev->irq_lock);
> mutex_init(&vcdev->io_lock);
>
> spin_lock_irqsave(get_ccwdev_lock(cdev), flags);
> --
> 2.25.1
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