netdev - Re: [non-quoted-printable PATCH] Fix caif BUG() with network namespaces

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Date:	Mon, 24 Oct 2011 17:51:54 +0200
From:	Sjur Brændeland <sjurbren@...il.com>
To:	"Woodhouse, David" <david.woodhouse@...el.com>
Cc:	"davem@...hat.com" <davem@...hat.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [non-quoted-printable PATCH] Fix caif BUG() with network namespaces

Hi David,

> The caif code will register its own pernet_operations, and then register
> a netdevice_notifier. Each time the netdevice_notifier is triggered,
> it'll do some stuff... including a lookup of its own pernet stuff with
> net_generic().
>
> If the net_generic() call ever returns NULL, the caif code will BUG().
> That doesn't seem *so* unreasonable, I suppose — it does seem like it
> should never happen.
>
> However, it *does* happen. When we clone a network namespace,
> setup_net() runs through all the pernet_operations one at a time. It
> gets to loopback before it gets to caif. And loopback_net_init()
> registers a netdevice... while caif hasn't been initialised. So the caif
> netdevice notifier triggers, and immediately goes BUG().
>
> I'm not entirely sure how best to fix this in the general case. Perhaps
> the netdevice_notifier registration should be pernet too, rather than
> global? Or perhaps we should suppress the notifier calls during
> setup_net() and flush them at the end after everything has been
> initialised?
>
> But really, I'm inclined to just take the simple approach. Make
> caif_device_notify() *not* go looking for its pernet data structures if
> the device it's being notified about isn't a caif device in the first
> place. This simple patch is sufficient to avoid the problem, and is
> probably good enough.
> Signed-off-by: David Woodhouse <David.Woodhouse@...el.com>

Thank you for analyzing and fixing this David, this looks good to me.
Acked-by: Sjur Brændeland <sjur.brandeland@...ricsson.com>
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