Linux Virtualization - Sep 2012 - [PATCH] virtio: Don't access device data after unregistration.

From: Sjur Br?ndeland <sjur.brandeland at stericsson.com>

Fix panic in virtio.c when CONFIG_DEBUG_SLAB is set.
Use device_del() and put_device() instead of
device_unregister(), and access device data before
calling put_device().


Signed-off-by: Sjur Br?ndeland <sjur.brandeland at stericsson.com>
cc: Guzman Lugo, Fernadndo <fernando.lugo at ti.com>
cc: Michael S. Tsirkin <mst at redhat.com>
cc: virtualization at lists.linux-foundation.org
cc: Ohad Ben-Cohen <ohad at wizery.com>
---
 drivers/virtio/virtio.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
index c3b3f7f..71eacd1 100644
--- a/drivers/virtio/virtio.c
+++ b/drivers/virtio/virtio.c
@@ -225,8 +225,9 @@ EXPORT_SYMBOL_GPL(register_virtio_device);
 
 void unregister_virtio_device(struct virtio_device *dev)
 {
-	device_unregister(&dev->dev);
+	device_del(&dev->dev);
 	ida_simple_remove(&virtio_index_ida, dev->index);
+	put_device(&dev->dev);
 }
 EXPORT_SYMBOL_GPL(unregister_virtio_device);
 
-- 
1.7.5.4

On Mon, Sep 03, 2012 at 03:50:42PM +0200, sjur.brandeland at stericsson.com
wrote:
> From: Sjur Br?ndeland <sjur.brandeland at stericsson.com>
> 
> Fix panic in virtio.c when CONFIG_DEBUG_SLAB is set.
What's the root cause of the panic?

> Use device_del() and put_device() instead of
> device_unregister(), and access device data before
> calling put_device().
Why does this help? Does device_unregister free the
device so dev->index access crashes?
If yes virtio_pci_remove will crash too
as it accesses the device after the
call to unregister_virtio_device so the
fix won't be effective.
> Signed-off-by: Sjur Br?ndeland <sjur.brandeland at stericsson.com>
> cc: Guzman Lugo, Fernadndo <fernando.lugo at ti.com>
> cc: Michael S. Tsirkin <mst at redhat.com>
> cc: virtualization at lists.linux-foundation.org
> cc: Ohad Ben-Cohen <ohad at wizery.com>
> ---
>  drivers/virtio/virtio.c |    3 ++-
>  1 files changed, 2 insertions(+), 1 deletions(-)
> 
> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
> index c3b3f7f..71eacd1 100644
> --- a/drivers/virtio/virtio.c
> +++ b/drivers/virtio/virtio.c
> @@ -225,8 +225,9 @@ EXPORT_SYMBOL_GPL(register_virtio_device);
>  
>  void unregister_virtio_device(struct virtio_device *dev)
>  {
> -	device_unregister(&dev->dev);
> +	device_del(&dev->dev);
>  	ida_simple_remove(&virtio_index_ida, dev->index);
> +	put_device(&dev->dev);
>  }
>  EXPORT_SYMBOL_GPL(unregister_virtio_device);
>  
> -- 
> 1.7.5.4