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

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Date:	Mon, 26 Apr 2010 11:01:23 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Jiri Pirko <jpirko@...hat.com>
Cc:	netdev@...r.kernel.org, davem@...emloft.net
Subject: Re: [PATCH net-2.6] netns: assign NULL after pernet memory is freed

Jiri Pirko <jpirko@...hat.com> writes:

> 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.

Also semenatically net_assign_generic is only guaranteed to work once, so assigning
NULL is at least semantically wrong.

Eric


>>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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