Message-ID: <CACT4Y+avizeUd=nY2w1B_LbEC1cP5prBfpnANYaxhgS_fcL6ag@mail.gmail.com>
Date:   Thu, 9 Jan 2020 09:50:12 +0100
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     Casey Schaufler <casey@...aufler-ca.com>,
        Daniel Axtens <dja@...ens.net>,
        Alexander Potapenko <glider@...gle.com>,
        clang-built-linux <clang-built-linux@...glegroups.com>
Cc:     Tetsuo Handa <penguin-kernel@...ove.sakura.ne.jp>,
        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>
Subject: Re: INFO: rcu detected stall in sys_kill

On Thu, Jan 9, 2020 at 9:19 AM Dmitry Vyukov <dvyukov@...gle.com> wrote:
>
> On Wed, Jan 8, 2020 at 6:19 PM Casey Schaufler <casey@...aufler-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.

+clang-built-linux, glider

[clang-built linux is severe broken since early Dec]

Building kernel with clang I can immediately reproduce this locally:

$ syz-manager
2020/01/09 09:27:15 loading corpus...
2020/01/09 09:27:17 serving http on http://0.0.0.0:50001
2020/01/09 09:27:17 serving rpc on tcp://[::]:45851
2020/01/09 09:27:17 booting test machines...
2020/01/09 09:27:17 wait for the connection from test machine...
2020/01/09 09:29:23 machine check:
2020/01/09 09:29:23 syscalls                : 2961/3195
2020/01/09 09:29:23 code coverage           : enabled
2020/01/09 09:29:23 comparison tracing      : enabled
2020/01/09 09:29:23 extra coverage          : enabled
2020/01/09 09:29:23 setuid sandbox          : enabled
2020/01/09 09:29:23 namespace sandbox       : enabled
2020/01/09 09:29:23 Android sandbox         : /sys/fs/selinux/policy
does not exist
2020/01/09 09:29:23 fault injection         : enabled
2020/01/09 09:29:23 leak checking           : CONFIG_DEBUG_KMEMLEAK is
not enabled
2020/01/09 09:29:23 net packet injection    : enabled
2020/01/09 09:29:23 net device setup        : enabled
2020/01/09 09:29:23 concurrency sanitizer   : /sys/kernel/debug/kcsan
does not exist
2020/01/09 09:29:23 devlink PCI setup       : PCI device 0000:00:10.0
is not available
2020/01/09 09:29:27 corpus                  : 50226 (0 deleted)
2020/01/09 09:29:27 VMs 20, executed 0, cover 0, crashes 0, repro 0
2020/01/09 09:29:37 VMs 20, executed 45, cover 0, crashes 0, repro 0
2020/01/09 09:29:47 VMs 20, executed 74, cover 0, crashes 0, repro 0
2020/01/09 09:29:57 VMs 20, executed 80, cover 0, crashes 0, repro 0
2020/01/09 09:30:07 VMs 20, executed 80, cover 0, crashes 0, repro 0
2020/01/09 09:30:17 VMs 20, executed 80, cover 0, crashes 0, repro 0
2020/01/09 09:30:27 VMs 20, executed 80, cover 0, crashes 0, repro 0
2020/01/09 09:30:37 VMs 20, executed 80, cover 0, crashes 0, repro 0
2020/01/09 09:30:47 VMs 20, executed 80, cover 0, crashes 0, repro 0
2020/01/09 09:30:57 VMs 20, executed 80, cover 0, crashes 0, repro 0
2020/01/09 09:31:07 VMs 20, executed 80, cover 0, crashes 0, repro 0
2020/01/09 09:31:17 VMs 20, executed 80, cover 0, crashes 0, repro 0
2020/01/09 09:31:26 vm-10: crash: INFO: rcu detected stall in do_idle
2020/01/09 09:31:27 VMs 13, executed 80, cover 0, crashes 0, repro 0
2020/01/09 09:31:28 vm-1: crash: INFO: rcu detected stall in sys_futex
2020/01/09 09:31:29 vm-4: crash: INFO: rcu detected stall in sys_futex
2020/01/09 09:31:31 vm-0: crash: INFO: rcu detected stall in sys_getsockopt
2020/01/09 09:31:33 vm-18: crash: INFO: rcu detected stall in sys_clone3
2020/01/09 09:31:35 vm-3: crash: INFO: rcu detected stall in sys_futex
2020/01/09 09:31:36 vm-8: crash: INFO: rcu detected stall in do_idle
2020/01/09 09:31:37 VMs 7, executed 80, cover 0, crashes 6, repro 0
2020/01/09 09:31:38 vm-19: crash: INFO: rcu detected stall in schedule_tail
2020/01/09 09:31:40 vm-6: crash: INFO: rcu detected stall in schedule_tail
2020/01/09 09:31:42 vm-2: crash: INFO: rcu detected stall in schedule_tail
2020/01/09 09:31:44 vm-12: crash: INFO: rcu detected stall in sys_futex
2020/01/09 09:31:46 vm-15: crash: INFO: rcu detected stall in sys_nanosleep
2020/01/09 09:31:47 VMs 1, executed 80, cover 0, crashes 11, repro 0
2020/01/09 09:31:48 vm-16: crash: INFO: rcu detected stall in sys_futex
2020/01/09 09:31:50 vm-9: crash: INFO: rcu detected stall in schedule
2020/01/09 09:31:52 vm-13: crash: INFO: rcu detected stall in schedule_tail
2020/01/09 09:31:54 vm-11: crash: INFO: rcu detected stall in schedule_tail
2020/01/09 09:31:56 vm-17: crash: INFO: rcu detected stall in sys_futex
2020/01/09 09:31:57 VMs 0, executed 80, cover 0, crashes 16, repro 0
2020/01/09 09:31:58 vm-7: crash: INFO: rcu detected stall in sys_futex
2020/01/09 09:32:00 vm-5: crash: INFO: rcu detected stall in dput
2020/01/09 09:32:02 vm-14: crash: INFO: rcu detected stall in sys_nanosleep


Then I switched LSM to selinux and I _still_ can reproduce this. So,
Casey, you may relax, this is not smack-specific :)

Then I disabled CONFIG_KASAN_VMALLOC and CONFIG_VMAP_STACK and it
started working normally.

So this is somehow related to both clang and KASAN/VMAP_STACK.

The clang I used is:
https://storage.googleapis.com/syzkaller/clang-kmsan-362913.tar.gz
(the one we use on syzbot).

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