Re: unexpected kernel reboot (3)

Jose R Rodriguez
2021-03-04T14:58:28Z

On Mon, 2018-07-16 at 12:09 +0200, Dmitry Vyukov wrote:
> On Fri, Jul 13, 2018 at 11:58 PM, Andrew Morton
> <akpm@linux-foundation.org> wrote:
> > On Fri, 13 Jul 2018 14:39:02 -0700 syzbot <
> > syzbot+cce9ef2dd25246f815ee@syzkaller.appspotmail.com> wrote:
> >
> > > Hello,
> > >
> > > syzbot found the following crash on:
> >
> > hm, I don't think I've seen an "unexpected reboot" report before.
> >
> > Can you expand on specifically what happened here?  Did the machine
> > simply magically reboot itself?  Or did an external monitor whack it,
> > or...
>
> We put some user-space workload (not involving reboot syscall), and
> the machine suddenly rebooted. We don't know what triggered the
> reboot, we only see the consequences. We've seen few such bugs before,
> e.g.:
> https://syzkaller.appspot.com/bug?id=4f1db8b5e7dfcca55e20931aec0ee707c5cafc99
> Usually it involves KVM. Potentially it's a bug in the outer
> kernel/VMM, it may or may not be present in tip kernel.

I have been using GCE with my custom VirtualBox -created reiser4 root fs VMs
since at least 2018, long term mainly as web servers with LAMP / LEMP --
including some Ruby apps with Postgresql -- and short term to build our Debian
Linux kernels. I have not experienced 'suddenly rebooted' scenarios.

Note that I have been usin Intel CPUs at the Los Angeles zone us-west2-a, as
well as us-east1-b zone, and AMD Epyc CPUs at us-central1-a zone, without
abnormalities (other than it's becoming more expensive ;-)

As a matter of fact, I am currently testing a Debian'ized reiser4 (AMD Epyc -
flavored reizer4 label) -enabled Linux kernel 5.10.15-2 which has logged 17 days
+hours already and sustaining most of the apps already mentioned.
< https://metztli.it/buster/r4-5.10.15-gce.png >

>
>
> > Does this test distinguish from a kernel which simply locks up?
>
> Yes. If you look at the log:
>
> https://syzkaller.appspot.com/x/log.txt?x=17c6a6d0400000
>
> We've booted the machine, started running a program, and them boom! it
> reboots without any other diagnostics. It's not a hang.
>
>
>
> > > HEAD commit:    1e4b044d2251 Linux 4.18-rc4
> > > git tree:       upstream
> > > console output: https://syzkaller.appspot.com/x/log.txt?x=17c6a6d0400000
> > > kernel config:  https://syzkaller.appspot.com/x/.config?x=25856fac4e580aa7
> > > dashboard link:
> > > https://syzkaller.appspot.com/bug?extid=cce9ef2dd25246f815ee
> > > compiler:       gcc (GCC) 8.0.1 20180413 (experimental)
> > > syzkaller repro:https://syzkaller.appspot.com/x/repro.syz?x=165012c2400000
> > > C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=1571462c400000
> >
> > I assume the "C reproducer" is irrelevant here.
> >
> > Is it reproducible?
>
> Yes, it is reproducible and the C reproducer is relevant.
> If syzbot provides a reproducer, it means that it booted a clean
> machine, run the provided program (nothing else besides typical init
> code and ssh/scp invocation) and that's the kernel output it observed
> running this exact program.
> However in this case, the exact setup can be relevant. syzbot uses GCE
> VMs, it may or may not reproduce with other VMMs/physical hardware,
> sometimes such bugs depend on exact CPU type.
>
>
> > > IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > > Reported-by: syzbot+cce9ef2dd25246f815ee@syzkaller.appspotmail.com
> > >
> > > output_len: 0x00000000092459b0
> > > kernel_total_size: 0x000000000a505000
> > > trampoline_32bit: 0x000000000009d000
> > >
> > > Decompressing Linux... Parsing ELF... done.
> > > Booting the kernel.
> > > [    0.000000] Linux version 4.18.0-rc4+ (syzkaller@ci) (gcc version 8.0.1
> > > 20180413 (experimental) (GCC)) #138 SMP Mon Jul 9 10:45:11 UTC 2018
> > > [    0.000000] Command line: BOOT_IMAGE=/vmlinuz root=/dev/sda1
> > > console=ttyS0 earlyprintk=serial vsyscall=native rodata=n
> > > ftrace_dump_on_oops=orig_cpu oops=panic panic_on_warn=1 nmi_watchdog=panic
> > > panic=86400 workqueue.watchdog_thresh=140 kvm-intel.nested=1
> > >
> > > ...
> > >
> > > regulatory database
> > > [    4.519364] cfg80211: Loaded X.509 cert 'sforshee: 00b28ddf47aef9cea7'
> > > [    4.520839] platform regulatory.0: Direct firmware load for
> > > regulatory.db failed with error -2
> > > [    4.522155] cfg80211: failed to load regulatory.db
> > > [    4.522185] ALSA device list:
> > > [    4.523499]   #0: Dummy 1
> > > [    4.523951]   #1: Loopback 1
> > > [    4.524389]   #2: Virtual MIDI Card 1
> > > [    4.825991] input: ImExPS/2 Generic Explorer Mouse as
> > > /devices/platform/i8042/serio1/input/input4
> > > [    4.829533] md: Waiting for all devices to be available before
> > > autodetect
> > > [    4.830562] md: If you don't use raid, use raid=noautodetect
> > > [    4.835237] md: Autodetecting RAID arrays.
> > > [    4.835882] md: autorun ...
> > > [    4.836364] md: ... autorun DONE.
> >
> > Can we assume that the failure occurred in or immediately after the MD code,
> > or might some output have been truncated?
> >
> > It would be useful to know what the kernel was initializing immediately
> > after MD.  Do you have a kernel log for the same config when the kerenl
> > didn't fail?  Or maybe enable initcall_debug?
> >
> > --
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> > To view this discussion on the web visit
> > https://groups.google.com/d/msgid/syzkaller-bugs/20180713145811.683ffd0043cac26a5a5af725%40linux-foundation.org
> > .
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(saw your last message of just a couple of hours and...)

Hope provided info helps.

Best Professional Regards.

--
--
Jose R R
http://metztli.it
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