[PATCH v3 RFC 2/4] virtio_blk: avoid further request queueing on device loss

[Heinz Graalfs <graalfs@linux.vnet.ibm.com>]

Code is added to the remove callback to verify if a device was lost.

In case of a device loss further request queueing should be prevented
by setting appropriate queue flags prior to invoking del_gendisk().
Blocking of request queueing leads to appropriate I/O errors when data
are tried to be synched. Trying to synch data to a lost block device
doesn't make too much sense.

If the current remove callback was triggered due to an unregister driver,
and the surprize_removal is not already set (although the actual device
is already gone, e.g. virsh detach), del_gendisk() would be triggered
resulting in a hang. This is a weird situation, and most likely not
'serializable'.

Signed-off-by: Heinz Graalfs <graalfs@linux.vnet.ibm.com>
---
 drivers/block/virtio_blk.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 2d43be4..0f64282 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -875,6 +875,7 @@ static void virtblk_remove(struct virtio_device *vdev)
 {
 	struct virtio_blk *vblk = vdev->priv;
 	int index = vblk->index;
+	unsigned long flags;
 	int refc;
 
 	/* Prevent config work handler from accessing the device. */
@@ -882,6 +883,14 @@ static void virtblk_remove(struct virtio_device *vdev)
 	vblk->config_enable = false;
 	mutex_unlock(&vblk->config_lock);
 
+	if (vdev->surprize_removal) {
+		spin_lock_irqsave(vblk->disk->queue->queue_lock, flags);
+		queue_flag_set(QUEUE_FLAG_DYING, vblk->disk->queue);
+		queue_flag_set(QUEUE_FLAG_NOMERGES, vblk->disk->queue);
+		queue_flag_set(QUEUE_FLAG_NOXMERGES, vblk->disk->queue);
+		spin_unlock_irqrestore(vblk->disk->queue->queue_lock, flags);
+	}
+
 	del_gendisk(vblk->disk);
 	blk_cleanup_queue(vblk->disk->queue);
 
-- 
1.8.3.1