netdev - Re: [patch net v3 2/4] net/sched: Use action array instead of action list as parameter

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Message-ID: <CAM_iQpUz4bKhb2uUiBBeXL6f6BfdAND7sW+az5MjbjbifRnmhw@mail.gmail.com>
Date:   Tue, 17 Oct 2017 09:55:38 -0700
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Chris Mi <chrism@...lanox.com>
Cc:     Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jamal Hadi Salim <jhs@...atatu.com>,
        Lucas Bates <lucasb@...atatu.com>,
        Jiri Pirko <jiri@...nulli.us>,
        David Miller <davem@...emloft.net>
Subject: Re: [patch net v3 2/4] net/sched: Use action array instead of action
 list as parameter

On Mon, Oct 16, 2017 at 6:20 PM, Chris Mi <chrism@...lanox.com> wrote:
> When destroying filters, actions should be destroyed first.
> The pointers of each action are saved in an array. TC doesn't
> use the array directly, but put all actions in a doubly linked
> list and use that list as parameter.
>
> There is no problem if each filter has its own actions. But if
> some filters share the same action, when these filters are
> destroyed, RCU callback fl_destroy_filter() may be called at the
> same time. That means the same action's 'struct list_head list'
> could be manipulated at the same time. It may point to an invalid
> address so that system will panic.

So if we remove these RCU callbacks (by adding a sychronize_rcu)
this is not a problem, right? Or is there any other races than RCU
callbacks??


>
> This patch uses the action array directly to fix this issue.
>
> Fixes commit in pre-git era.
>
> Fixes: 1da177e4c3f4 ("Linux-2.6.12-rc2")

This is wrong too. RCU callbacks were introduced very late.