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From:   Dmitry Vyukov <dvyukov@google.com>
Date:   Thu, 9 Jan 2020 09:19:57 +0100
Message-ID: <CACT4Y+bURugCpLm5TG37-7voFEeEoXo_Gb=3sy75_RELZotXHw@mail.gmail.com>
Subject: Re: INFO: rcu detected stall in sys_kill
To:     Casey Schaufler <casey@schaufler-ca.com>
Cc:     Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>,
        syzbot <syzbot+de8d933e7d153aa0c1bb@syzkaller.appspotmail.com>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        LKML <linux-kernel@vger.kernel.org>,
        syzkaller-bugs <syzkaller-bugs@googlegroups.com>
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On Wed, Jan 8, 2020 at 6:19 PM Casey Schaufler <casey@schaufler-ca.com> wrote:
>
> 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.

Humm, interesting. Initially I was going to say that most likely it's
not clang-related. Bug smack instance is actually the only one that
uses clang as well (except for KMSAN of course). So maybe it's indeed
clang-related rather than smack-related. Let me try to build a kernel
with clang.

> > 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 .