Linux Virtualization - Dec 2012 - [PATCH] virtio-blk: Don't free ida when disk is in use

When a file system is mounted on a virtio-blk disk, we then remove it
and then reattach it, the reattached disk gets the same disk name and
ids as the hot removed one.

This leads to very nasty effects - mostly rendering the newly attached
device completely unusable.

Trying what happens when I do the same thing with a USB device, I saw
that the sd node simply doesn't get free'd when a device gets forcefully
removed.

Imitate the same behavior for vd devices. This way broken vd devices
simply are never free'd and newly attached ones keep working just fine.

Signed-off-by: Alexander Graf <agraf at suse.de>
---
 drivers/block/virtio_blk.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
index 0bdde8f..07a18e2 100644
--- a/drivers/block/virtio_blk.c
+++ b/drivers/block/virtio_blk.c
@@ -889,6 +889,7 @@ static void __devexit virtblk_remove(struct virtio_device
*vdev)
 {
 	struct virtio_blk *vblk = vdev->priv;
 	int index = vblk->index;
+	int refc;
 
 	/* Prevent config work handler from accessing the device. */
 	mutex_lock(&vblk->config_lock);
@@ -903,11 +904,15 @@ static void __devexit virtblk_remove(struct virtio_device
*vdev)
 
 	flush_work(&vblk->config_work);
 
+	refc = atomic_read(&disk_to_dev(vblk->disk)->kobj.kref.refcount);
 	put_disk(vblk->disk);
 	mempool_destroy(vblk->pool);
 	vdev->config->del_vqs(vdev);
 	kfree(vblk);
-	ida_simple_remove(&vd_index_ida, index);
+
+	/* Only free device id if we don't have any users */
+	if (refc == 1)
+		ida_simple_remove(&vd_index_ida, index);
 }
 
 #ifdef CONFIG_PM
-- 
1.7.12.4

Alexander Graf <agraf at suse.de> writes:
> When a file system is mounted on a virtio-blk disk, we then remove it
> and then reattach it, the reattached disk gets the same disk name and
> ids as the hot removed one.
>
> This leads to very nasty effects - mostly rendering the newly attached
> device completely unusable.
>
> Trying what happens when I do the same thing with a USB device, I saw
> that the sd node simply doesn't get free'd when a device gets
forcefully
> removed.
>
> Imitate the same behavior for vd devices. This way broken vd devices
> simply are never free'd and newly attached ones keep working just fine.
>
> Signed-off-by: Alexander Graf <agraf at suse.de>
I think deserves a CC:stable, no?

I've put it in my pending queue for *next* merge window for now...

Thanks,
Rusty.

On Wed, Dec 19, 2012 at 08:40:15PM +0100, Alexander Graf
wrote:
> When a file system is mounted on a virtio-blk disk, we then remove it
> and then reattach it, the reattached disk gets the same disk name and
> ids as the hot removed one.
> 
> This leads to very nasty effects - mostly rendering the newly attached
> device completely unusable.
> 
> Trying what happens when I do the same thing with a USB device, I saw
> that the sd node simply doesn't get free'd when a device gets
forcefully
> removed.
> 
> Imitate the same behavior for vd devices. This way broken vd devices
> simply are never free'd and newly attached ones keep working just fine.
> 
> Signed-off-by: Alexander Graf <agraf at suse.de>
> ---
>  drivers/block/virtio_blk.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> index 0bdde8f..07a18e2 100644
> --- a/drivers/block/virtio_blk.c
> +++ b/drivers/block/virtio_blk.c
> @@ -889,6 +889,7 @@ static void __devexit virtblk_remove(struct
virtio_device *vdev)
>  {
>  	struct virtio_blk *vblk = vdev->priv;
>  	int index = vblk->index;
> +	int refc;
>  
>  	/* Prevent config work handler from accessing the device. */
>  	mutex_lock(&vblk->config_lock);
> @@ -903,11 +904,15 @@ static void __devexit virtblk_remove(struct
virtio_device *vdev)
>  
>  	flush_work(&vblk->config_work);
>  
> +	refc =
atomic_read(&disk_to_dev(vblk->disk)->kobj.kref.refcount);
>  	put_disk(vblk->disk);
>  	mempool_destroy(vblk->pool);
>  	vdev->config->del_vqs(vdev);
>  	kfree(vblk);
> -	ida_simple_remove(&vd_index_ida, index);
> +
> +	/* Only free device id if we don't have any users */
> +	if (refc == 1)
> +		ida_simple_remove(&vd_index_ida, index);
>  }
>  
>  #ifdef CONFIG_PM
Network devices take the approach of retrying every second.
Donnu if it makes sense here.

> -- 
> 1.7.12.4