netdev - Re: [PATCH] X.25: decrement netdev reference counts on unload

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Date:	Wed, 8 Dec 2010 09:48:30 +1100
From:	Andrew Hendry <andrew.hendry@...il.com>
To:	Apollon Oikonomopoulos <apollon@....grnet.gr>
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH] X.25: decrement netdev reference counts on unload

Thanks for the patch.
Can reproduce it on a vm here, I'll verify it when have access to some
X.25 networks tomorrow.

2010/12/8 Apollon Oikonomopoulos <apollon@....grnet.gr>:
> Hello,
>
> We came across this bug when we accidentally loaded and unloaded the x25
> kernel module on a host with KVM virtual machines. All subsequent
> attempts to stop a KVM instance resulted in the KVM process entering D
> state. Reproducing this behaviour can be done in the following way:
>
> 1. modprobe x25
> 2. tunctl && ifconfig tap0 up
> 3. rmmod x25
> 4. tunctl -d tap0 (hangs)
>
> A patch follows - we don't use X.25 ourselves so I'm not sure it won't
> panic someone's system.
>
> Regards,
> Apollon
>
> PS: I am not subscribed to the list, so please copy any replies to my
> address. Thanks!
> ----
> x25 does not decrement the network device reference counts on module unload.
> Thus unregistering any pre-existing interface after unloading the x25 module
> hangs and results in
>
>  unregister_netdevice: waiting for tap0 to become free. Usage count = 1
>
> This patch decrements the reference counts of all interfaces in x25_link_free,
> the way it is already done in x25_link_device_down for NETDEV_DOWN events.
>
> Signed-off-by: Apollon Oikonomopoulos <apollon@....grnet.gr>
> ---
>  net/x25/x25_link.c |    1 +
>  1 files changed, 1 insertions(+), 0 deletions(-)
>
> diff --git a/net/x25/x25_link.c b/net/x25/x25_link.c
> index 73e7b95..b25c646 100644
> --- a/net/x25/x25_link.c
> +++ b/net/x25/x25_link.c
> @@ -394,6 +394,7 @@ void __exit x25_link_free(void)
>        list_for_each_safe(entry, tmp, &x25_neigh_list) {
>                nb = list_entry(entry, struct x25_neigh, node);
>                __x25_remove_neigh(nb);
> +               dev_put(nb->dev);
>        }
>        write_unlock_bh(&x25_neigh_list_lock);
>  }
> --
> 1.7.1
> --
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