Re: [PATCH net-next v4 3/8] net_sched: mirred: remove action when the target device is gone

[David Miller <davem@davemloft.net>]

From: Cong Wang <xiyou.wangcong@gmail.com>
Date: Wed, 18 Dec 2013 10:36:06 -0800

> On Wed, Dec 18, 2013 at 6:31 AM, Jamal Hadi Salim <jhs@mojatatu.com> wrote:
>> On 12/15/13 23:15, Cong Wang wrote:
>>>
>>> When the target device is removed, the mirred action is
>>> still there but with the dev pointer setting to NULL.
>>> This makes the output from 'tc filter' ugly. There is no
>>> reason to keep it.
>>>
>>
>> Sorry - this one i have problems with.
>> actions may be referenced from multiple filters,
>> you cant just delete it (that would leave other users
>> pointing to it dangling). Destroying would eventually
>> delete it when the refcount goes to 0.
> 
> How? tcf_action_init() always allocates a new action,
> it doesn't even look for an existing one.
> 
>> [And when we delete actions we send netlink events to announce
>> that]. The proper solution would require i.e tag it as to be
>> deleted and implement some form of garbage collection.
> 
> It doesn't worth to have a GC for this...
> 
> Even if what you said is true, we should just make a copy
> for each of the filters. I just tried to create two different filters
> with same and different mirred actions, my patch works
> perfectly.

Indeed, I think Jamal is confusing how he intended the code to work
vs. how it actually does :-)