netdev - Re: [Patch net-next v2 3/4] net_sched: remove tc class reference counting

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Message-ID: <4892b5e7-2734-c717-ea04-1109d43b9011@mojatatu.com>
Date:   Fri, 25 Aug 2017 08:28:55 -0400
From:   Jamal Hadi Salim <jhs@...atatu.com>
To:     Cong Wang <xiyou.wangcong@...il.com>, netdev@...r.kernel.org
Subject: Re: [Patch net-next v2 3/4] net_sched: remove tc class reference
 counting

On 17-08-24 07:51 PM, Cong Wang wrote:
> For TC classes, their ->get() and ->put() are always paired, and the
> reference counting is completely useless, because:
> 
> 1) For class modification and dumping paths, we already hold RTNL lock,
>     so all of these ->get(),->change(),->put() are atomic.
> 
> 2) For filter bindiing/unbinding, we use other reference counter than
>     this one, and they should have RTNL lock too.
> 
> 3) For ->qlen_notify(), it is special because it is called on ->enqueue()
>     path, but we already hold qdisc tree lock there, and we hold this
>     tree lock when graft or delete the class too, so it should not be gone
>     or changed until we release the tree lock.
> 
> Therefore, this patch removes ->get() and ->put(), but:
> 
> 1) Adds a new ->find() to find the pointer to a class by classid, no
>     refcnt.
> 
> 2) Move the original class destroy upon the last refcnt into ->delete(),
>     right after releasing tree lock. This is fine because the class is
>     already removed from hash when holding the lock.
> 
> For those who also use ->put() as ->unbind(), just rename them to reflect
> this change.
> 
> Cc: Jamal Hadi Salim <jhs@...atatu.com>
> Signed-off-by: Cong Wang <xiyou.wangcong@...il.com>

I am a tiny bit worried about this - but i went over it and it looks
good. I cant think of any use cases where something may fall out, so:

Acked-by: Jamal Hadi Salim <jhs@...atatu.com>

cheers,
jamal