Subject: Re: [Patch net-next] fib: move fib_rules_cleanup_ops() under rtnl lock

From: Alexander Duyck <[email-masked]>
Date: Thu, 26 Mar 2015 16:47:37 -0700

On 03/26/2015 04:05 PM, Cong Wang wrote:
> On Thu, Mar 26, 2015 at 3:32 PM, Cong Wang <[email-masked]> wrote:
>> On the other hand, the name rules_mod_lock already tells it is
>> just a protection for ops (module) register.
> I even doubt we really need rules_mod_lock, it is per netns,
> which is newly allocated when registering pernet and upper
> layer should guarantee no concurrent unregistering, so we
> probably only need to take rtnl lock.

I'm adding Thomas as he was the original author for the code and might 
have a better idea of what needs to be rtnl locked and what doesn't.  
You should probably CC him as well on the v2 patch.

As far as why I am so focused on moving fib4_rules_exit it is because we 
don't want to call that delete function until after the table has been 
cleared.  Otherwise you end up triggering the external_flush and unmerge 
code on a full table instead of an empty one.  The result is you end up 
allocating a bunch of memory before you then turn around and free it.  
So even if you retain the rtnl_lock changes it would still be best to 
move fib4_rules_exit call to the region after you have freed the FIB 
tables, but before you free fib_table_hash.

- Alex