Patchwork Fix panic in virtnet_remove

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Submitter Krishna Kumar
Date July 15, 2011, 9:16 a.m.
Message ID <20110715091650.23026.78221.sendpatchset@krkumar2.in.ibm.com>
Download mbox | patch
Permalink /patch/104774/
State Awaiting Upstream
Delegated to: David Miller
Headers show

Comments

Krishna Kumar - July 15, 2011, 9:16 a.m.
modprobe -r virtio_net panics in free_netdev() as the
dev is already freed in the newly introduced virtnet_free
(commit 3fa2a1df9094). Since virtnet_remove doesn't require
dev after unregister, I am removing the free_netdev call
in virtnet_remove instead of in virtnet_free (which seems
to be the right place to free the dev). Confirmed that
the panic is fixed with this patch.

Signed-off-by: Krishna Kumar <krkumar2@in.ibm.com>
---
 drivers/net/virtio_net.c |    2 --
 1 file changed, 2 deletions(-)

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David Miller - July 15, 2011, 3:19 p.m.
From: Krishna Kumar <krkumar2@in.ibm.com>
Date: Fri, 15 Jul 2011 14:46:50 +0530

> modprobe -r virtio_net panics in free_netdev() as the
> dev is already freed in the newly introduced virtnet_free
> (commit 3fa2a1df9094). Since virtnet_remove doesn't require
> dev after unregister, I am removing the free_netdev call
> in virtnet_remove instead of in virtnet_free (which seems
> to be the right place to free the dev). Confirmed that
> the panic is fixed with this patch.
> 
> Signed-off-by: Krishna Kumar <krkumar2@in.ibm.com>

I guess the virtio NET maintainers don't deserve to get CC:'d on a fix
like this? :-(

Michael Tsirkin is who maintains this driver actively and is the one
who will merge this kind of fix to me, therefore if you don't CC:
him it might not get integrated at all.
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Krishna Kumar - July 16, 2011, 5:32 a.m.
David Miller <davem@davemloft.net> wrote on 07/15/2011 08:49:09 PM:

> > modprobe -r virtio_net panics in free_netdev() as the
> > dev is already freed in the newly introduced virtnet_free
> > (commit 3fa2a1df9094). Since virtnet_remove doesn't require
> > dev after unregister, I am removing the free_netdev call
> > in virtnet_remove instead of in virtnet_free (which seems
> > to be the right place to free the dev). Confirmed that
> > the panic is fixed with this patch.
> >
> > Signed-off-by: Krishna Kumar <krkumar2@in.ibm.com>
>
> I guess the virtio NET maintainers don't deserve to get CC:'d on a fix
> like this? :-(
>
> Michael Tsirkin is who maintains this driver actively and is the one
> who will merge this kind of fix to me, therefore if you don't CC:
> him it might not get integrated at all.

Sorry, but it was not intentional. I saw that Stephen had
made that change so cc'd him instead.

Michael, I am attaching the patch below, please let me know if
you need it inlined:


(See attached file: patch)

Thanks,

- KK
Michael S. Tsirkin - July 17, 2011, 10:12 a.m.
On Fri, Jul 15, 2011 at 02:46:50PM +0530, Krishna Kumar wrote:
> modprobe -r virtio_net panics in free_netdev() as the
> dev is already freed in the newly introduced virtnet_free
> (commit 3fa2a1df9094).

Good catch, thanks!

> Since virtnet_remove doesn't require
> dev after unregister,

I'm not sure that true: vi used just above the line you remove
is I think the struct virtnet_info that is allocated
as part of that structure.


> I am removing the free_netdev call
> in virtnet_remove instead of in virtnet_free (which seems
> to be the right place to free the dev). Confirmed that
> the panic is fixed with this patch.

This might be just because the memory isn't reused.
Try enabling slab poisoning, I think you'll observe some problems.

Do we absolutely have to have a destructor?
Can't we move the per cpu counter free from
virtnet_free to virtnet_remove, and get rid of
virtnet_free completely?


> Signed-off-by: Krishna Kumar <krkumar2@in.ibm.com>
> ---
>  drivers/net/virtio_net.c |    2 --
>  1 file changed, 2 deletions(-)
> 
> diff -ruNp org/drivers/net/virtio_net.c new/drivers/net/virtio_net.c
> --- org/drivers/net/virtio_net.c	2011-07-04 10:38:33.000000000 +0530
> +++ new/drivers/net/virtio_net.c	2011-07-15 14:27:48.000000000 +0530
> @@ -1121,8 +1121,6 @@ static void __devexit virtnet_remove(str
>  
>  	while (vi->pages)
>  		__free_pages(get_a_page(vi, GFP_KERNEL), 0);
> -
> -	free_netdev(vi->dev);
>  }
>  
>  static struct virtio_device_id id_table[] = {
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Patch

diff -ruNp org/drivers/net/virtio_net.c new/drivers/net/virtio_net.c
--- org/drivers/net/virtio_net.c	2011-07-04 10:38:33.000000000 +0530
+++ new/drivers/net/virtio_net.c	2011-07-15 14:27:48.000000000 +0530
@@ -1121,8 +1121,6 @@  static void __devexit virtnet_remove(str
 
 	while (vi->pages)
 		__free_pages(get_a_page(vi, GFP_KERNEL), 0);
-
-	free_netdev(vi->dev);
 }
 
 static struct virtio_device_id id_table[] = {