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

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Message-ID: <CAM_iQpUDZa-=H53Csg8476xOL0xP+rn85O8eB1O39-eF_Jo+uw@mail.gmail.com>
Date:	Wed, 18 Dec 2013 10:36:06 -0800
From:	Cong Wang <xiyou.wangcong@...il.com>
To:	Jamal Hadi Salim <jhs@...atatu.com>
Cc:	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next v4 3/8] net_sched: mirred: remove action when the
 target device is gone

On Wed, Dec 18, 2013 at 6:31 AM, Jamal Hadi Salim <jhs@...atatu.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.
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