netdev - Re: [PATCH] net: fix rtnl even race in register

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Date:	Tue, 03 May 2011 05:38:43 +0300
From:	Kalle Valo <kvalo@...rom.com>
To:	David Miller <davem@...emloft.net>
Cc:	netdev@...r.kernel.org, linux-wireless@...r.kernel.org
Subject: Re: [PATCH] net: fix rtnl even race in register_netdevice()

David Miller <davem@...emloft.net> writes:

> From: Kalle Valo <kvalo@...rom.com>
> Date: Fri, 29 Apr 2011 20:26:34 +0300
>
>> From: Kalle Valo <kalle.valo@...eros.com>
>> 
>> There's a race in register_netdevice so that the rtnl event is sent before
>> the device is actually ready. This was visible with flimflam, chrome os
>> connection manager:

[...]

>> The fix is to call netdev_register_kobject() after the device is added
>> to the list.
>> 
>> Signed-off-by: Kalle Valo <kalle.valo@...eros.com>
>
> This is not correct.
>
> If you move the kobject registry around, you have to change the
> error handling cleanup to match.
>
> This change will leave the netdevice on all sorts of lists, it will
> also leak a reference to the device.
>
> I also think this points a fundamental problem with this change, in
> that you can't register the kobject after the device is added to
> the various lists in list_netdevice().
>
> Once it's in those lists, any thread of control can find the device
> and those threads of control may try to get at the data backed by
> the kobject and therefore they really expect it to be there by
> then.
>
> What you can do instead is try to delay the NETREG_REGISTERED
> setting, and block the problematic notifications by testing
> reg_state or similar.

Thanks for the review. I'll investigate more about this and send v2
once I found a better solution.

-- 
Kalle Valo
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