netdev - Re: [PATCH RFC] net: Fix race condition when removing qdisc

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Message-ID: <CALx6S34KqhnaXeMiii2kxWdV0h3FVK4dst=Lhg7OxAvLRZLshQ@mail.gmail.com>
Date:	Thu, 3 Mar 2016 16:24:53 -0800
From:	Tom Herbert <tom@...bertland.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Cong Wang <xiyou.wangcong@...il.com>,
	Linux Kernel Network Developers <netdev@...r.kernel.org>,
	Lawrence Brakmo <brakmo@...com>,
	Kernel Team <kernel-team@...com>
Subject: Re: [PATCH RFC] net: Fix race condition when removing qdisc

On Thu, Mar 3, 2016 at 3:58 PM, Tom Herbert <tom@...bertland.com> wrote:
> On Thu, Mar 3, 2016 at 3:52 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>> On jeu., 2016-03-03 at 14:24 -0800, Tom Herbert wrote:
>>> This a kernel based on 3.10. We believe the lockups coincide with
>>> removing/readding qdiscs.
>>
>> You could backport 64153ce0a7b61b2a
>> ("net_sched: htb: do not setup default rate estimators"),
>> unless you desperately want these rate estimators...
>>

Thanks for the pointer!

>> How many HTB classes do you deal with ?
>>
> ~1500.
>
> One think that looks odd to me is that htb_destroy_class is not doing
> an rcu_free (just kfree(cl)). I'm thinking that est_timer can run
> after that kfree and be accessing some of the fields in the freed
> structure (at least rate_est).

I suppose that case is protected by est_lock and e->bstats == NULL.

>
> Tom