netdev - Re: 回复: INFO: rcu detected stall in tc_modify

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Message-ID: <87tuxqxhgq.fsf@intel.com>
Date:   Wed, 29 Jul 2020 12:13:25 -0700
From:   Vinicius Costa Gomes <vinicius.gomes@...el.com>
To:     "Zhang\, Qiang" <Qiang.Zhang@...driver.com>,
        syzbot <syzbot+9f78d5c664a8c33f4cce@...kaller.appspotmail.com>,
        "davem\@davemloft.net" <davem@...emloft.net>,
        "fweisbec\@gmail.com" <fweisbec@...il.com>,
        "jhs\@mojatatu.com" <jhs@...atatu.com>,
        "jiri\@resnulli.us" <jiri@...nulli.us>,
        "linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
        "mingo\@kernel.org" <mingo@...nel.org>,
        "netdev\@vger.kernel.org" <netdev@...r.kernel.org>,
        "syzkaller-bugs\@googlegroups.com" <syzkaller-bugs@...glegroups.com>,
        "tglx\@linutronix.de" <tglx@...utronix.de>,
        "xiyou.wangcong\@gmail.com" <xiyou.wangcong@...il.com>
Subject: Re: 回复: INFO: rcu detected stall in
 tc_modify_qdisc

Hi,

"Zhang, Qiang" <Qiang.Zhang@...driver.com> writes:

> ________________________________________
> 发件人: linux-kernel-owner@...r.kernel.org <linux-kernel-owner@...r.kernel.org> 代表 syzbot <syzbot+9f78d5c664a8c33f4cce@...kaller.appspotmail.com>
> 发送时间: 2020年7月29日 13:53
> 收件人: davem@...emloft.net; fweisbec@...il.com; jhs@...atatu.com; jiri@...nulli.us; linux-kernel@...r.kernel.org; mingo@...nel.org; netdev@...r.kernel.org; syzkaller-bugs@...glegroups.com; tglx@...utronix.de; vinicius.gomes@...el.com; xiyou.wangcong@...il.com
> 主题: INFO: rcu detected stall in tc_modify_qdisc
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    181964e6 fix a braino in cmsghdr_from_user_compat_to_kern()
> git tree:       net
> console output: https://syzkaller.appspot.com/x/log.txt?x=12925e38900000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=f87a5e4232fdb267
> dashboard link: https://syzkaller.appspot.com/bug?extid=9f78d5c664a8c33f4cce
> compiler:       gcc (GCC) 10.1.0-syz 20200507
> syz repro:
> https://syzkaller.appspot.com/x/repro.syz?x=16587f8c900000

It seems that syzkaller is generating an schedule with too small
intervals (3ns in this case) which causes a hrtimer busy-loop which
starves other kernel threads.

We could put some limits on the interval when running in software mode,
but I don't like this too much, because we are talking about users with
CAP_NET_ADMIN and they have easier ways to do bad things to the system.


Cheers,
-- 
Vinicius