netdev - Re: [PATCH 1/2] Remove unnecessary locks from rtnetlink

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Message-ID: <47AAF2E8.30802@balabit.hu>
Date:	Thu, 07 Feb 2008 13:00:40 +0100
From:	Laszlo Attila Toth <panther@...abit.hu>
To:	David Miller <davem@...emloft.net>
CC:	netdev@...r.kernel.org
Subject: Re: [PATCH 1/2] Remove unnecessary locks from rtnetlink

David Miller írta:
> From: Laszlo Attila Toth <panther@...abit.hu>
> Date: Fri,  1 Feb 2008 17:07:33 +0100
> 
>> The do_setlink() function is protected by rtnl, additional locks are unnecessary.
>> and the set_operstate() function is called from protected parts. Locks removed
>> from both functions.
>>
>> The set_operstate() is also called from rtnl_create_link() and from no other places.
>> In rtnl_create_link() none of the changes is protected by set_lock_bh() except
>> inside set_operstate(), different locking scheme is not necessary
>> for the operstate.
>>
>> Signed-off-by: Laszlo Attila Toth <panther@...abit.hu>
> 
> The protection using dev_base_lock() is needed.
> 
> When analyzing cases like this you need to also look at other code
> paths outside of rtnetlink that access ->operstate and ->link_mode,
> you obviously didn't do this.
> 
> For example, net/core/net-sysfs.c takes a read lock on dev_base_lock
> in order to fetch a stable copy of both netif_running() and
> dev->operstate at the same time.
> 
> Similar write locking to protect dev->operstate is made by
> net/core/link_watch.c:rfc2863_policy(), for the same reason rtnetlink
> has to make this locking.
> 
> You therefore cannot remove it.

Thanks for your answer, yes, unfortunatelly I checked only inside 
rtnetlink.c

--
Attila
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