Commit fcc5a03ac42564e9e255c1134dda47442289e466 makes the
register_netdevice_notifier() handle the error from the
NETDEV_REGISTER event, sent to the registering block. 

The bad news is that in this case the notifier block is 
not removed from the list, but the error is returned to the 
caller. In case the caller is in module init function and 
handles this error this can abort the module loading. The
notifier block will be then removed from the kernel, but 
will be left in the list. Oops :(

I think that the notifier block should be removed from the
chain in case of error, regardless whether this error is 
handled by the caller or not. In the worst case (the error 
is _not_ handled) module will not receive the events any 
longer.

Signed-off-by: Pavel Emelyanov <xemul@openvz.org>

---

diff --git a/net/core/dev.c b/net/core/dev.c
index dd40b35..86d6261 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1171,6 +1171,8 @@ rollback:
 			nb->notifier_call(nb, NETDEV_UNREGISTER, dev);
 		}
 	}
+
+	raw_notifier_chain_unregister(&netdev_chain, nb);
 	goto unlock;
 }

On Wed, Nov 14, 2007 at 03:08:03PM +0300, Pavel Emelyanov wrote:
> Commit fcc5a03ac42564e9e255c1134dda47442289e466 makes the
> register_netdevice_notifier() handle the error from the
> NETDEV_REGISTER event, sent to the registering block. 
> 
> The bad news is that in this case the notifier block is 
> not removed from the list, but the error is returned to the 
> caller. In case the caller is in module init function and 
> handles this error this can abort the module loading. The
> notifier block will be then removed from the kernel, but 
> will be left in the list. Oops :(
> 
> I think that the notifier block should be removed from the
> chain in case of error, regardless whether this error is 
> handled by the caller or not. In the worst case (the error 
> is _not_ handled) module will not receive the events any 
> longer.
> 
> Signed-off-by: Pavel Emelyanov <xemul@openvz.org>

Good catch.  Thanks Pavel!

Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

Herbert Xu wrote:
> On Wed, Nov 14, 2007 at 03:08:03PM +0300, Pavel Emelyanov wrote:
>> Commit fcc5a03ac42564e9e255c1134dda47442289e466 makes the
>> register_netdevice_notifier() handle the error from the
>> NETDEV_REGISTER event, sent to the registering block. 
>>
>> The bad news is that in this case the notifier block is 
>> not removed from the list, but the error is returned to the 
>> caller. In case the caller is in module init function and 
>> handles this error this can abort the module loading. The
>> notifier block will be then removed from the kernel, but 
>> will be left in the list. Oops :(
>>
>> I think that the notifier block should be removed from the
>> chain in case of error, regardless whether this error is 
>> handled by the caller or not. In the worst case (the error 
>> is _not_ handled) module will not receive the events any 
>> longer.
>>
>> Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
> 
> Good catch.  Thanks Pavel!
> 
> Acked-by: Herbert Xu <herbert@gondor.apana.org.au>

Thanks :)

BTW, I have one more question I can't find the answer to by 
myself. Why the unregister_netdevice_notifier doesn't produce 
the GOING_DOWN-DOWN-UNREGISTER event sequence for the notifier
block which is being unregistered? Was this made deliberately?

Pavel

On Wed, Nov 14, 2007 at 04:47:24PM +0300, Pavel Emelyanov wrote:
>
> BTW, I have one more question I can't find the answer to by 
> myself. Why the unregister_netdevice_notifier doesn't produce 
> the GOING_DOWN-DOWN-UNREGISTER event sequence for the notifier
> block which is being unregistered? Was this made deliberately?

I think it's more of an oversight :)

Although it has no real impact because the only user that matters
here is IPv6 and it can't be unloaded.

Cheers,
-- 
Visit Openswan at http://www.openswan.org/
Email: Herbert Xu ~{PmV>HI~} <herbert@gondor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt

From: Herbert Xu <herbert@gondor.apana.org.au>
Date: Wed, 14 Nov 2007 21:37:17 +0800

> Acked-by: Herbert Xu <herbert@gondor.apana.org.au>

Indeed, good catch, patch applied.

Thanks!