KVM: s390: Gracefully handle busy conditions on ccw_device_start

In rare cases a virtio command might try to issue a ccw before a former
ccw was answered with a tsch. This will cause CC=2 (busy). Lets just
retry in that case.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Cornelia Huck <cornelia.huck@de.ibm.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 8 insertions, 5 deletions

diff --git a/drivers/s390/kvm/virtio_ccw.c b/drivers/s390/kvm/virtio_ccw.c
index 70419a75d0e0..2edd94af131c 100644
--- a/drivers/s390/kvm/virtio_ccw.c
+++ b/drivers/s390/kvm/virtio_ccw.c
@@ -132,11 +132,14 @@ static int ccw_io_helper(struct virtio_ccw_device *vcdev,
         unsigned long flags;
         int flag = intparm & VIRTIO_CCW_INTPARM_MASK;
 
-        spin_lock_irqsave(get_ccwdev_lock(vcdev->cdev), flags);
-        ret = ccw_device_start(vcdev->cdev, ccw, intparm, 0, 0);
-        if (!ret)
-                vcdev->curr_io |= flag;
-        spin_unlock_irqrestore(get_ccwdev_lock(vcdev->cdev), flags);
+        do {
+                spin_lock_irqsave(get_ccwdev_lock(vcdev->cdev), flags);
+                ret = ccw_device_start(vcdev->cdev, ccw, intparm, 0, 0);
+                if (!ret)
+                        vcdev->curr_io |= flag;
+                spin_unlock_irqrestore(get_ccwdev_lock(vcdev->cdev), flags);
+                cpu_relax();
+        } while (ret == -EBUSY);
         wait_event(vcdev->wait_q, doing_io(vcdev, flag) == 0);
         return ret ? ret : vcdev->err;
 }