netdev - Re: kernel panic in latest vanilla stable, while using nameif with "alive" pppoe interfaces

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Date:	Mon, 19 Oct 2009 23:29:10 +0400
From:	Cyrill Gorcunov <gorcunov@...il.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Michal Ostrowski <mostrows@...il.com>,
	Denys Fedoryschenko <denys@...p.net.lb>,
	netdev <netdev@...r.kernel.org>, linux-ppp@...r.kernel.org,
	paulus@...ba.org, mostrows@...thlink.net
Subject: Re: kernel panic in latest vanilla stable, while using nameif with
	"alive" pppoe interfaces

[Eric Dumazet - Mon, Oct 19, 2009 at 08:44:52PM +0200]
...
| 
| Not really :)
| 
| I dont believe you should care of namespace, and/or mess with its refcount at all.
| 
| Please dont use maybe_get_net() : This function should not ever be used in drivers/net
| 
| You can add a BUG_ON(dev_net(xxxx)->count <= 0) if you really want, but if this
| assertion is false, this is not because of pppoe.
| 
...
| So pppoe_flush_dev() can run concurently and dev_put(po->ppoe_dev) at same time.
| 
| In fact pppoe_flush_dev() can change po->ppoe_dev anytime, so you should check
| all occurences of po->ppoe_dev use in the code and check if appropriate locking is done.
| 
| pppoe_rcv_core() is not safe
| pppoe_ioctl() is not safe
| pppoe_sendmsg() is not safe
| __pppoe_xmit() is not safe
| 

Sigh... seem so (which is mostly my fault not Michal). Every time we touch pppoe_dev we
should dev_hold on it and dev_put as only done all we need. Async nature
of notifier seem to be a key here.

	-- Cyrill
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