INFO: task hung in ret_from_fork

[syzbot]

Hello,

syzbot found the following crash on:

HEAD commit: d1e0b8e0cb7a Add linux-next specific files for 20180725
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=1797c252400000
kernel config: https://syzkaller.appspot.com/x/.config?x=eef3552c897e4d33
dashboard link: https://syzkaller.appspot.com/bug?extid=77cdbd57605c5e6b2e92
compiler: gcc (GCC) 8.0.1 20180413 (experimental)
CC: [gre...@linuxfoundation.org h...@zytor.com
kste...@linuxfoundation.org linux-...@vger.kernel.org mi...@redhat.com
pombr...@nexb.com tg...@linutronix.de x...@kernel.org]

Unfortunately, I don't have any reproducer for this crash yet.

IMPORTANT: if you fix the bug, please add the following tag to the commit:
Reported-by: syzbot+77cdbd...@syzkaller.appspotmail.com

IPVS: stopping backup sync thread 26932 ...
IPVS: stopping backup sync thread 26947 ...
kworker/dying (54) used greatest stack depth: 8704 bytes left
INFO: task kthreadd:26950 blocked for more than 140 seconds.
Not tainted 4.18.0-rc6-next-20180725+ #18
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kthreadd D28056 26950 2 0x80000000
Call Trace:
context_switch kernel/sched/core.c:2820 [inline]
__schedule+0x87c/0x1ed0 kernel/sched/core.c:3468
schedule+0xfb/0x450 kernel/sched/core.c:3512
kthread+0x26a/0x410 kernel/kthread.c:240
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:415
INFO: lockdep is turned off.
NMI backtrace for cpu 1
CPU: 1 PID: 774 Comm: khungtaskd Not tainted 4.18.0-rc6-next-20180725+ #18
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+0x1c9/0x2b4 lib/dump_stack.c:113
nmi_cpu_backtrace.cold.3+0x48/0x88 lib/nmi_backtrace.c:101
nmi_trigger_cpumask_backtrace+0x151/0x192 lib/nmi_backtrace.c:62
arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
trigger_all_cpu_backtrace include/linux/nmi.h:144 [inline]
check_hung_uninterruptible_tasks kernel/hung_task.c:204 [inline]
watchdog+0xb39/0x10b0 kernel/hung_task.c:265
kthread+0x345/0x410 kernel/kthread.c:246
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:415
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at native_safe_halt+0x6/0x10
arch/x86/include/asm/irqflags.h:54
Kernel panic - not syncing: hung_task: blocked tasks
CPU: 1 PID: 774 Comm: khungtaskd Not tainted 4.18.0-rc6-next-20180725+ #18
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+0x1c9/0x2b4 lib/dump_stack.c:113
panic+0x238/0x4e7 kernel/panic.c:184
check_hung_uninterruptible_tasks kernel/hung_task.c:205 [inline]
watchdog+0xb4a/0x10b0 kernel/hung_task.c:265
kthread+0x345/0x410 kernel/kthread.c:246
ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:415
Dumping ftrace buffer:
(ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..


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[syzbot]

Auto-closing this bug as obsolete.
Crashes did not happen for a while, no reproducer and no activity.