Re: INFO: task hung in reboot

Dmitry Vyukov
2020-11-14T14:48:03Z

On Sat, Nov 14, 2020 at 2:42 PM syzbot
<syzbot+9dec836197fea6892a28@syzkaller.appspotmail.com> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit: e7018751 usb: host: ehci-mxc: Remove the driver
> git tree: https://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git usb-testing
> console output: https://syzkaller.appspot.com/x/log.txt?x=15d0c6a1500000
> kernel config: https://syzkaller.appspot.com/x/.config?x=a84e3059298aeb27
> dashboard link: https://syzkaller.appspot.com/bug?extid=9dec836197fea6892a28
> compiler: gcc (GCC) 10.1.0-syz 20200507
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+9dec836197fea6892a28@syzkaller.appspotmail.com

It seems syzkaller has found another way to reboot the machine.
systemd initialiated shutdown:
[ [0;32m OK [0m] Stopped Raise network interfaces.

but it's unclear why.

Kernel also hanged:

[ 2599.057387][ T1] systemd-shutdown[1]: Sending SIGTERM to
remaining processes...
[ 2599.704086][ T1] systemd-shutdown[1]: Sending SIGKILL to
remaining processes...
[ 2600.107613][ T1] systemd-shutdown[1]: All loop devices detached.
[ 2746.006716][ T1253] INFO: task systemd-shutdow:1 blocked for more
than 143 seconds.
[ 2746.014884][ T1253] Not tainted 5.10.0-rc3-syzkaller #0

It seems due to some misbehaving device:

[ 2746.057796][ T1253] schedule+0xcb/0x270
[ 2746.061900][ T1253] wait_for_device_probe+0x1be/0x220
[ 2746.089974][ T1253] device_shutdown+0x18/0x5c0
[ 2746.094669][ T1253] __do_sys_reboot.cold+0x5d/0x97

Most likely some USB device because there is lots of USB-related
output before that.

> INFO: task systemd-shutdow:1 blocked for more than 143 seconds.
> Not tainted 5.10.0-rc3-syzkaller #0
> "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> task:systemd-shutdow state:D stack:23432 pid: 1 ppid: 0 flags:0x00000000
> Call Trace:
> context_switch kernel/sched/core.c:3774 [inline]
> __schedule+0x8a2/0x1f30 kernel/sched/core.c:4523
> schedule+0xcb/0x270 kernel/sched/core.c:4601
> wait_for_device_probe+0x1be/0x220 drivers/base/dd.c:702
> device_shutdown+0x18/0x5c0 drivers/base/core.c:4007
> kernel_restart_prepare kernel/reboot.c:76 [inline]
> kernel_restart kernel/reboot.c:246 [inline]
> __do_sys_reboot.cold+0x5d/0x97 kernel/reboot.c:347
> do_syscall_64+0x2d/0x40 arch/x86/entry/common.c:46
> entry_SYSCALL_64_after_hwframe+0x44/0xa9
> RIP: 0033:0x7fa389e6c8c6
> Code: Unable to access opcode bytes at RIP 0x7fa389e6c89c.
> RSP: 002b:00007ffe1fb46e18 EFLAGS: 00000206 ORIG_RAX: 00000000000000a9
> RAX: ffffffffffffffda RBX: 0000000000000000 RCX: 00007fa389e6c8c6
> RDX: 0000000001234567 RSI: 0000000028121969 RDI: fffffffffee1dead
> RBP: 00007ffe1fb46ea8 R08: 0000000000002800 R09: 0000000000000005
> R10: 0000000000000002 R11: 0000000000000206 R12: 0000000000000000
> R13: 0000000000000000 R14: 000055c2d05dc150 R15: 00007ffe1fb47198
>
> Showing all locks held in the system:
> 1 lock held by systemd-shutdow/1:
> #0: ffffffff871288a8 (system_transition_mutex){+.+.}-{3:3}, at: __do_sys_reboot+0x1a4/0x3e0 kernel/reboot.c:344
> 5 locks held by kworker/1:0/17:
> 1 lock held by khungtaskd/1253:
> #0: ffffffff872492e0 (rcu_read_lock){....}-{1:2}, at: debug_show_all_locks+0x53/0x269 kernel/locking/lockdep.c:6253
>
> =============================================
>
> NMI backtrace for cpu 1
> CPU: 1 PID: 1253 Comm: khungtaskd Not tainted 5.10.0-rc3-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Call Trace:
> __dump_stack lib/dump_stack.c:77 [inline]
> dump_stack+0x107/0x163 lib/dump_stack.c:118
> nmi_cpu_backtrace.cold+0x46/0xe0 lib/nmi_backtrace.c:105
> nmi_trigger_cpumask_backtrace+0x1da/0x200 lib/nmi_backtrace.c:62
> trigger_all_cpu_backtrace include/linux/nmi.h:146 [inline]
> check_hung_uninterruptible_tasks kernel/hung_task.c:209 [inline]
> watchdog+0xd32/0xf70 kernel/hung_task.c:294
> kthread+0x38c/0x460 kernel/kthread.c:292
> ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:296
> Sending NMI from CPU 1 to CPUs 0:
> NMI backtrace for cpu 0 skipped: idling at native_safe_halt arch/x86/include/asm/irqflags.h:60 [inline]
> NMI backtrace for cpu 0 skipped: idling at arch_safe_halt arch/x86/include/asm/irqflags.h:103 [inline]
> NMI backtrace for cpu 0 skipped: idling at acpi_safe_halt drivers/acpi/processor_idle.c:111 [inline]
> NMI backtrace for cpu 0 skipped: idling at acpi_idle_do_entry+0x1c9/0x250 drivers/acpi/processor_idle.c:517
>
>
> ---
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>
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