netdev - Re: [Patch net-next] net_sched: move the empty tp check from ->destroy() to ->delete()

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Message-ID: <CAM_iQpVxevmk3rgsnALC0JCqx7pOF2OBc=kpg9QDK8Cwb6P9Zw@mail.gmail.com>
Date:   Fri, 25 Nov 2016 22:46:41 -0800
From:   Cong Wang <xiyou.wangcong@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Roi Dayan <roid@...lanox.com>,
        Linux Kernel Network Developers <netdev@...r.kernel.org>,
        Jiri Pirko <jiri@...lanox.com>,
        John Fastabend <john.fastabend@...il.com>
Subject: Re: [Patch net-next] net_sched: move the empty tp check from
 ->destroy() to ->delete()

On Thu, Nov 24, 2016 at 7:20 AM, Daniel Borkmann <daniel@...earbox.net> wrote:
>
> Ok, strange, qdisc_destroy() calls into ops->destroy(), where ingress
> drops its entire chain via tcf_destroy_chain(), so that will be NULL
> eventually. The tps are freed by call_rcu() as well as qdisc itself
> later on via qdisc_rcu_free(), where it frees per-cpu bstats as well.
> Outstanding readers should either bail out due to if (!cl) or can still
> process the chain until read section ends, but during that time, cl->q
> resp. bstats should be good. Do you happen to know what's at address
> ffff880a68b04028? I was wondering wrt call_rcu() vs call_rcu_bh(), but
> at least on ingress (netif_receive_skb_internal()) we hold rcu_read_lock()
> here. The KASAN report is reliably happening at this location, right?

I am confused as well, I don't see how it could be related to my patch yet.
I will take a deep look in the weekend.

Thanks!