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

From: Laszlo Attila Toth <[email-masked]>
Date: Thu, 07 Feb 2008 13:00:40 +0100

David Miller írta:
> From: Laszlo Attila Toth <[email-masked]>
> 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 <[email-masked]>
> 
> 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