linux-kernel - Re: [PATCH] virtio: Don't access device data after unregistration.

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Date:	Mon, 3 Sep 2012 17:14:45 +0300
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	sjur.brandeland@...ricsson.com
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Sjur Brændeland <sjurbren@...il.com>,
	linux-kernel@...r.kernel.org,
	"Guzman Lugo, Fernadndo" <fernando.lugo@...com>,
	virtualization@...ts.linux-foundation.org,
	Ohad Ben-Cohen <ohad@...ery.com>
Subject: Re: [PATCH] virtio: Don't access device data after unregistration.

On Mon, Sep 03, 2012 at 03:50:42PM +0200, sjur.brandeland@...ricsson.com wrote:
> From: Sjur Brændeland <sjur.brandeland@...ricsson.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 Brændeland <sjur.brandeland@...ricsson.com>
> cc: Guzman Lugo, Fernadndo <fernando.lugo@...com>
> cc: Michael S. Tsirkin <mst@...hat.com>
> cc: virtualization@...ts.linux-foundation.org
> cc: Ohad Ben-Cohen <ohad@...ery.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
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