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

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Message-ID: <20100426120716.GD2941@psychotron.lab.eng.brq.redhat.com>
Date:	Mon, 26 Apr 2010 14:07:17 +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 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.


>
>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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