netdev - Re: [PATCH net-2.6] netns: assign NULL after pernet memory is freed

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Message-ID: <20100426133020.GE2941@psychotron.lab.eng.brq.redhat.com>
Date:	Mon, 26 Apr 2010 15:30:20 +0200
From:	Jiri Pirko <jpirko@...hat.com>
To:	netdev@...r.kernel.org
Cc:	davem@...emloft.net, ebiederm@...ssion.com
Subject: Re: [PATCH net-2.6] netns: assign NULL after pernet memory is freed

Mon, Apr 26, 2010 at 02:07:17PM CEST, jpirko@...hat.com wrote:
>Mon, Apr 26, 2010 at 01:18:07PM CEST, jpirko@...hat.com wrote:
>>This is needed to let know appropriate code (driver) know that pernet memory
>>chunk  was freed already. For example when driver has also registered netdev
>>notifier, it can be called after memory is freed which could eventually lead
>>to panic. Also a null check should be present in these notifiers.
>>
>>For example, previously, when drivers were responsible for pernet memory
>>allocation/freeing, in pppoe this assign was done in pppoe_exit_net() right
>>after pernet memory was freed. The check in notifier stayed (in pppoe_flush_dev
>>called from pppoe_device_event) but makes no sense now without this patch.
>
>Hmm, thinking about this, since the life of pernet memories is directly connected
>with the life of net, as described by Eric, this should not be needed. So please
>scrach this one too. Sorry.
>
>Anyway, I'm still wondering how to prevent netdev_notifiers from using this when
>net is gone. Going to do more research, I'm probably missing something.

Right, it becomes part of init_ns then. So this looks good then. One thing I can
still imagine what may cause problem, since netdev_notifier is registered before
register_pernet_device, the notifier can be called in between. So I think this
should be reordered, am I right?

Thanks

Jirka

>
>
>>
>>I already know about several notifiers where the check should be present,
>>patches will follow up.
>>
>>Signed-off-by: Jiri Pirko <jpirko@...hat.com>
>>
>>diff --git a/net/core/net_namespace.c b/net/core/net_namespace.c
>>index bd8c471..29f622c 100644
>>--- a/net/core/net_namespace.c
>>+++ b/net/core/net_namespace.c
>>@@ -51,6 +51,7 @@ static void ops_free(const struct pernet_operations *ops, struct net *net)
>> 	if (ops->id && ops->size) {
>> 		int id = *ops->id;
>> 		kfree(net_generic(net, id));
>>+		net_assign_generic(net, id, NULL);
>> 	}
>> }
>> 
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