Linux Virtualization - Apr 2014 - [PATCH 0/1] virtio_ccw: exploit virtio_break_device()

Rusty,

this patch exploits the new function virtio_break_device() as of your patch
set dated January 15th on linux-kernel at vger.kernel.org.

The patch avoids hang situations during device unregister, when a (block)
device with active IO is hot-unplugged.

Heinz Graalfs (1):
  virtio_ccw: introduce device_lost in virtio_ccw_device

 drivers/s390/kvm/virtio_ccw.c | 49 ++++++++++++++++++++++++++++++++-----------
 1 file changed, 37 insertions(+), 12 deletions(-)

-- 
1.8.3.1

When a device is lost, the common I/O layer calls the notification
handler with CIO_GONE: In that event, flag device_lost as true.

In case the device had been flagged as lost when the remove/offline callbacks
are called, call the new virtio_break_device() function prior to invoking
device_unregister(). This avoids hangs of I/O triggered via the device
unregistration callbacks.

Signed-off-by: Heinz Graalfs <graalfs at linux.vnet.ibm.com>
Reviewed-by: Cornelia Huck <cornelia.huck at de.ibm.com>
---
 drivers/s390/kvm/virtio_ccw.c | 49 ++++++++++++++++++++++++++++++++-----------
 1 file changed, 37 insertions(+), 12 deletions(-)

diff --git a/drivers/s390/kvm/virtio_ccw.c b/drivers/s390/kvm/virtio_ccw.c
index 1e1fc67..d2c0b44 100644
--- a/drivers/s390/kvm/virtio_ccw.c
+++ b/drivers/s390/kvm/virtio_ccw.c
@@ -27,6 +27,7 @@
 #include <linux/module.h>
 #include <linux/io.h>
 #include <linux/kvm_para.h>
+#include <linux/notifier.h>
 #include <asm/setup.h>
 #include <asm/irq.h>
 #include <asm/cio.h>
@@ -62,6 +63,7 @@ struct virtio_ccw_device {
 	struct vq_config_block *config_block;
 	bool is_thinint;
 	bool going_away;
+	bool device_lost;
 	void *airq_info;
 };
 
@@ -1010,11 +1012,14 @@ static void virtio_ccw_remove(struct ccw_device *cdev)
 	unsigned long flags;
 	struct virtio_ccw_device *vcdev = virtio_grab_drvdata(cdev);
 
-	if (vcdev && cdev->online)
+	if (vcdev && cdev->online) {
+		if (vcdev->device_lost)
+			virtio_break_device(&vcdev->vdev);
 		unregister_virtio_device(&vcdev->vdev);
-	spin_lock_irqsave(get_ccwdev_lock(cdev), flags);
-	dev_set_drvdata(&cdev->dev, NULL);
-	spin_unlock_irqrestore(get_ccwdev_lock(cdev), flags);
+		spin_lock_irqsave(get_ccwdev_lock(cdev), flags);
+		dev_set_drvdata(&cdev->dev, NULL);
+		spin_unlock_irqrestore(get_ccwdev_lock(cdev), flags);
+	}
 	cdev->handler = NULL;
 }
 
@@ -1023,12 +1028,14 @@ static int virtio_ccw_offline(struct ccw_device *cdev)
 	unsigned long flags;
 	struct virtio_ccw_device *vcdev = virtio_grab_drvdata(cdev);
 
-	if (vcdev) {
-		unregister_virtio_device(&vcdev->vdev);
-		spin_lock_irqsave(get_ccwdev_lock(cdev), flags);
-		dev_set_drvdata(&cdev->dev, NULL);
-		spin_unlock_irqrestore(get_ccwdev_lock(cdev), flags);
-	}
+	if (!vcdev)
+		return 0;
+	if (vcdev->device_lost)
+		virtio_break_device(&vcdev->vdev);
+	unregister_virtio_device(&vcdev->vdev);
+	spin_lock_irqsave(get_ccwdev_lock(cdev), flags);
+	dev_set_drvdata(&cdev->dev, NULL);
+	spin_unlock_irqrestore(get_ccwdev_lock(cdev), flags);
 	return 0;
 }
 
@@ -1096,8 +1103,26 @@ out_free:
 
 static int virtio_ccw_cio_notify(struct ccw_device *cdev, int event)
 {
-	/* TODO: Check whether we need special handling here. */
-	return 0;
+	int rc;
+	struct virtio_ccw_device *vcdev = dev_get_drvdata(&cdev->dev);
+
+	/*
+	 * Make sure vcdev is set
+	 * i.e. set_offline/remove callback not already running
+	 */
+	if (!vcdev)
+		return NOTIFY_DONE;
+
+	switch (event) {
+	case CIO_GONE:
+		vcdev->device_lost = true;
+		rc = NOTIFY_DONE;
+		break;
+	default:
+		rc = NOTIFY_DONE;
+		break;
+	}
+	return rc;
 }
 
 static struct ccw_device_id virtio_ids[] = {
-- 
1.8.3.1

Heinz Graalfs <graalfs at linux.vnet.ibm.com>
writes:
> When a device is lost, the common I/O layer calls the notification
> handler with CIO_GONE: In that event, flag device_lost as true.
>
> In case the device had been flagged as lost when the remove/offline
callbacks
> are called, call the new virtio_break_device() function prior to invoking
> device_unregister(). This avoids hangs of I/O triggered via the device
> unregistration callbacks.
>
> Signed-off-by: Heinz Graalfs <graalfs at linux.vnet.ibm.com>
> Reviewed-by: Cornelia Huck <cornelia.huck at de.ibm.com>
Thanks!

Applied,
Rusty.