linux-kernel - Re: INFO: rcu detected stall in sys

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Date:   Wed, 8 Jan 2020 09:19:34 -0800
From:   Casey Schaufler <casey@...aufler-ca.com>
To:     Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
        Dmitry Vyukov <dvyukov@...gle.com>
Cc:     syzbot <syzbot+de8d933e7d153aa0c1bb@...kaller.appspotmail.com>,
        kasan-dev <kasan-dev@...glegroups.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        LKML <linux-kernel@...r.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        Casey Schaufler <casey@...aufler-ca.com>
Subject: Re: INFO: rcu detected stall in sys_kill

On 1/8/2020 2:25 AM, Tetsuo Handa wrote:
> On 2020/01/08 15:20, Dmitry Vyukov wrote:
>> I temporarily re-enabled smack instance and it produced another 50
>> stalls all over the kernel, and now keeps spewing a dozen every hour.

Do I have to be using clang to test this? I'm setting up to work on this,
and don't want to waste time using my current tool chain if the problem
is clang specific.

> Since we can get stall reports rather easily, can we try modifying
> kernel command line (e.g. lsm=smack) and/or kernel config (e.g. no kasan) ?
>
>> I've mailed 3 new samples, you can see them here:
>> https://syzkaller.appspot.com/bug?extid=de8d933e7d153aa0c1bb
>>
>> The config is provided, command line args are here:
>> https://github.com/google/syzkaller/blob/master/dashboard/config/upstream-smack.cmdline
>> Some non-default sysctls that syzbot sets are here:
>> https://github.com/google/syzkaller/blob/master/dashboard/config/upstream.sysctl
>> Image can be downloaded from here:
>> https://github.com/google/syzkaller/blob/master/docs/syzbot.md#crash-does-not-reproduce
>> syzbot uses GCE VMs with 2 CPUs and 7.5GB memory, but this does not
>> look to be virtualization-related (?) so probably should reproduce in
>> qemu too.
> Is it possible to add instance for linux-next.git that uses these configs?
> If yes, we could try adding some debug printk() under CONFIG_DEBUG_AID_FOR_SYZBOT=y .