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

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

[Apollon Oikonomopoulos]

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@noc.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

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

[Andrew Hendry]

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@noc.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@noc.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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>

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

[David Miller]

From: Apollon Oikonomopoulos <apollon@noc.grnet.gr>
Date: Tue, 7 Dec 2010 21:43:30 +0200

> 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@noc.grnet.gr>

Applied and queued up for -stable, thanks.