linux-kernel - Re: [PATCH 2/2] virtio: don't free memory until the underlying struct device has been released

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Date:	Sun, 4 Jan 2015 13:26:41 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	linux-kernel@...r.kernel.org,
	Rusty Russell <rusty@...tcorp.com.au>,
	"open list:VIRTIO CORE, NET..." 
	<virtualization@...ts.linux-foundation.org>
Subject: Re: [PATCH 2/2] virtio: don't free memory until the underlying
 struct device has been released

On Fri, Jan 02, 2015 at 02:47:40PM -0500, Sasha Levin wrote:
> When releasing a virtio device, We can't free a struct virtio_device until the
> underlying struct device has been released, which might not happen immediately
> on device_unregister() even if that was the device's last reference.
> 
> Instead, free the memory only once we know the device is gone in the release
> callback.
> 
> Signed-off-by: Sasha Levin <sasha.levin@...cle.com>


Isn't this an old bug: do we need to copy stable on a fix?

What is the behaviour without this patch?
Is there a way to make this cause a crash?

> ---
>  drivers/virtio/virtio_pci_common.c |    9 ++++-----
>  drivers/virtio/virtio_pci_legacy.c |    1 -
>  2 files changed, 4 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_pci_common.c b/drivers/virtio/virtio_pci_common.c
> index 59d3685..caa483d 100644
> --- a/drivers/virtio/virtio_pci_common.c
> +++ b/drivers/virtio/virtio_pci_common.c
> @@ -423,11 +423,10 @@ int vp_set_vq_affinity(struct virtqueue *vq, int cpu)
>  
>  void virtio_pci_release_dev(struct device *_d)
>  {
> -	/*
> -	 * No need for a release method as we allocate/free
> -	 * all devices together with the pci devices.
> -	 * Provide an empty one to avoid getting a warning from core.
> -	 */
> +	struct virtio_device *vdev = dev_to_virtio(_d);
> +	struct virtio_pci_device *vp_dev = to_vp_device(vdev);
> +
> +	kfree(vp_dev);
>  }
>  
>  #ifdef CONFIG_PM_SLEEP
> diff --git a/drivers/virtio/virtio_pci_legacy.c b/drivers/virtio/virtio_pci_legacy.c
> index 913ca23..15e6e6d 100644
> --- a/drivers/virtio/virtio_pci_legacy.c
> +++ b/drivers/virtio/virtio_pci_legacy.c
> @@ -301,5 +301,4 @@ void virtio_pci_legacy_remove(struct pci_dev *pci_dev)
>  	pci_iounmap(pci_dev, vp_dev->ioaddr);
>  	pci_release_regions(pci_dev);
>  	pci_disable_device(pci_dev);
> -	kfree(vp_dev);
>  }


It seems inelegant to free a structure allocated in another file:
I think we should move this function to virtio_pci_legacy.
Will send a patch in a minute.





> -- 
> 1.7.10.4
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