linux-kernel - Re: [PATCH net,v2] net: sched: tbf: don't call qdisc

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Date:   Wed, 7 Sep 2022 09:24:58 +0800
From:   shaozhengchao <shaozhengchao@...wei.com>
To:     Cong Wang <xiyou.wangcong@...il.com>
CC:     <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <davem@...emloft.net>, <edumazet@...gle.com>, <kuba@...nel.org>,
        <pabeni@...hat.com>, <jhs@...atatu.com>, <jiri@...nulli.us>,
        <vladbu@...lanox.com>, <weiyongjun1@...wei.com>,
        <yuehaibing@...wei.com>
Subject: Re: [PATCH net,v2] net: sched: tbf: don't call qdisc_put() while
 holding tree lock



On 2022/9/6 2:13, Cong Wang wrote:
> On Fri, Aug 26, 2022 at 09:39:30AM +0800, Zhengchao Shao wrote:
>> The issue is the same to commit c2999f7fb05b ("net: sched: multiq: don't
>> call qdisc_put() while holding tree lock"). Qdiscs call qdisc_put() while
>> holding sch tree spinlock, which results sleeping-while-atomic BUG.
>>
> 
> Hm, did you see an actual warning here??
> 
> The commit you mentioned above is a classful Qdisc which accepts
> user-specified child Qdisc, but TBF technically does not, I don't think
> you can change its default fifo.
> 
> Thanks.

Hi Wang:
	Thank you for your reply. My apologise. I don't see the
warning here. Yes, TBF is classless qdisc, its default fifo is
bfifo and reset or destroy process will not sleep. So, it's not
a issue. Should I revert it, or keep it in this format(qdisc_put
out of holding sch tree spinlock).


Zhengchao Shao