netdev - Re: [patch net] net: sched: fix memleak for chain zero

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Message-ID: <CAM_iQpWZJ9VVD66h6RMNofobKyoFyztx2jYqBEHuE6_iAu7PNQ@mail.gmail.com>
Date:   Wed, 6 Sep 2017 10:40:02 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Jiri Pirko <jiri@...nulli.us>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Jakub Kicinski <kubakici@...pl>, mlxsw@...lanox.com
Subject: Re: [patch net] net: sched: fix memleak for chain zero

On Wed, Sep 6, 2017 at 4:14 AM, Jiri Pirko <jiri@...nulli.us> wrote:
> From: Jiri Pirko <jiri@...lanox.com>
>
> There's a memleak happening for chain 0. The thing is, chain 0 needs to
> be always present, not created on demand. Therefore tcf_block_get upon
> creation of block calls the tcf_chain_create function directly. The
> chain is created with refcnt == 1, which is not correct in this case and
> causes the memleak. So move the refcnt increment into tcf_chain_get
> function even for the case when chain needs to be created.
>

Your approach could work but you just make the code even
uglier than it is now:

1. The current code is already ugly for special-casing chain 0:

        if (--chain->refcnt == 0 && !chain->filter_chain && chain->index != 0)
                tcf_chain_destroy(chain);

2. With your patch, chain 0 has a different _initial_ refcnt with others.

3. Allowing an object (chain 0) exists with refcnt==0

Compare it with my patch:

1. No special-case for chain 0, the above ugly part is removed

2. Every chain is equal and created with refcnt==1

3. Any chain with refcnt==0 is destroyed