netdev - Re: [PATCH net,stable] net: cdc_mbim: __vlan_find_dev_deep need rcu_read

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Message-ID: <87ppjv8bnh.fsf@nemi.mork.no>
Date:	Sat, 03 May 2014 11:16:50 +0200
From:	Bjørn Mork <bjorn@...k.no>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	netdev@...r.kernel.org, linux-usb@...r.kernel.org,
	Greg Suarez <gsuarez@...thmicro.com>,
	Oliver Neukum <oliver@...kum.org>
Subject: Re: [PATCH net,stable] net: cdc_mbim: __vlan_find_dev_deep need rcu_read_lock

Eric Dumazet <eric.dumazet@...il.com> writes:

> While this 'removes' the warning, this doesn't solve the fundamental
> problem.
>
> If you write :
>
> rcu_read_lock();
> netdev = __vlan_find_dev_deep(...)
> rcu_read_unlock();
>
> Then you cannot dereference netdev safely after the unlock.
>
> In order to do so, you need to take a reference on netdev (aka
> dev_hold()) before doing rcu_read_unlock();
>
> And of course, release it later (aka dev_put()) when you are done with
> netdev.

Doh! Now that you tell me, this is pretty obvious.  Thanks.  Will fix
and resubmit.


Bjørn
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