netdev - Re: [Patch net-next] net_sched: remove tc class reference counting

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Message-Id: <20170824.123220.2250866539237700218.davem@davemloft.net>
Date:   Thu, 24 Aug 2017 12:32:20 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     xiyou.wangcong@...il.com
Cc:     netdev@...r.kernel.org, jhs@...atatu.com
Subject: Re: [Patch net-next] net_sched: remove tc class reference counting

From: Cong Wang <xiyou.wangcong@...il.com>
Date: Tue, 22 Aug 2017 21:38:10 -0700

> 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>

This one looks good to me.

Jamal, please give it a quick look over and review.

Thanks!