[PATCH] virtio-blk: handle block_device_operations callbacks after hot unplug

[Stefan Hajnoczi <stefanha@redhat.com>]

A virtio_blk block device can still be referenced after hot unplug by
userspace processes that hold the file descriptor.  In this case
virtblk_getgeo() can be invoked after virtblk_remove() was called.  For
example, a program that has /dev/vdb open can call ioctl(HDIO_GETGEO)
after hot unplug.

Fix this by clearing vblk->disk->private_data and checking that the
virtio_blk driver instance is still around in virtblk_getgeo().

Note that the virtblk_getgeo() function itself is guaranteed to remain
in memory after hot unplug because the virtio_blk module refcount is
still held while a block device reference exists.

Originally-by: Lance Digby <ldigby@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 drivers/block/virtio_blk.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 93468b7c6701..b50cdf37a6f7 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -300,6 +300,10 @@ static int virtblk_getgeo(struct block_device *bd, struct hd_geometry *geo)
 {
 	struct virtio_blk *vblk = bd->bd_disk->private_data;
 
+	/* Driver instance has been removed */
+	if (!vblk)
+		return -ENOTTY;
+
 	/* see if the host passed in geometry config */
 	if (virtio_has_feature(vblk->vdev, VIRTIO_BLK_F_GEOMETRY)) {
 		virtio_cread(vblk->vdev, struct virtio_blk_config,
@@ -835,6 +839,7 @@ static void virtblk_remove(struct virtio_device *vdev)
 	vdev->config->reset(vdev);
 
 	refc = kref_read(&disk_to_dev(vblk->disk)->kobj.kref);
+	vblk->disk->private_data = NULL;
 	put_disk(vblk->disk);
 	vdev->config->del_vqs(vdev);
 	kfree(vblk->vqs);
-- 
2.25.1