unregister_netdevice: waiting for lo to become free. Usage count = 2
INFO: task syz-executor2:22812 blocked for more than 120 seconds.
      Not tainted 4.9.47-g6ec1052 #40
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor2   D29088 22812   3239 0x00000004
 ffff8801a7930000 0000000000000000 ffff8801a7d21a40 ffffffff84426880
 ffff8801db221518 ffff8801c89d79f8 ffffffff8389961b 0000000000000246
 ffff8801a7930000 0000000000000000 ffff8801db221e40 ffff8801db221e68
Call Trace:
 [<ffffffff8389abd2>] schedule+0x92/0x1b0 kernel/sched/core.c:3625
 [<ffffffff8389b543>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3658
 [<ffffffff838a0b52>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff838a0b52>] mutex_lock_nested+0x312/0x870 kernel/locking/mutex.c:621
 [<ffffffff82f15b35>] copy_net_ns+0x155/0x280 net/core/net_namespace.c:387
 [<ffffffff8119e26f>] create_new_namespaces+0x37f/0x730 kernel/nsproxy.c:106
 [<ffffffff8119e8b1>] copy_namespaces+0x291/0x320 kernel/nsproxy.c:164
 [<ffffffff8112b889>] copy_process.part.50+0x1c99/0x5d40 kernel/fork.c:1659
 [<ffffffff8112fdc0>] copy_process kernel/fork.c:1483 [inline]
 [<ffffffff8112fdc0>] _do_fork+0x1c0/0xd70 kernel/fork.c:1941
 [<ffffffff81130a47>] SYSC_clone kernel/fork.c:2051 [inline]
 [<ffffffff81130a47>] SyS_clone+0x37/0x50 kernel/fork.c:2045
 [<ffffffff81006527>] do_syscall_64+0x197/0x490 arch/x86/entry/common.c:280
 [<ffffffff838aae4d>] entry_SYSCALL64_slow_path+0x25/0x25
INFO: lockdep is turned off.
NMI backtrace for cpu 0
CPU: 0 PID: 514 Comm: khungtaskd Not tainted 4.9.47-g6ec1052 #40
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d8907d00 ffffffff81d93049 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810bd020 ffff8801d8907d38
 ffffffff81d9e15d 0000000000000000 0000000000000000 ffff8801a7930418
Call Trace:
 [<ffffffff81d93049>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d93049>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81d9e15d>] nmi_cpu_backtrace+0xfd/0x120 lib/nmi_backtrace.c:99
 [<ffffffff81d9e297>] nmi_trigger_cpumask_backtrace+0x117/0x190 lib/nmi_backtrace.c:60
 [<ffffffff810bd114>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81372820>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81372820>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81372820>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81372820>] watchdog+0x6f0/0xa70 kernel/hung_task.c:239
 [<ffffffff8119acdd>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838ab02a>] ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:433
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1 skipped: idling at pc 0xffffffff838a99f6
Kernel panic - not syncing: hung_task: blocked tasks
CPU: 0 PID: 514 Comm: khungtaskd Not tainted 4.9.47-g6ec1052 #40
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d8907cb8 ffffffff81d93049 ffffffff83a899a0 ffff8801d8907d90
 ffff8801a7930400 dffffc0000000000 ffffffff84409000 ffff8801d8907d80
 ffffffff8142e6d1 0000000041b58ab3 ffffffff84184938 ffffffff8142e515
Call Trace:
 [<ffffffff81d93049>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d93049>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff8142e6d1>] panic+0x1bc/0x3a8 kernel/panic.c:179
 [<ffffffff81372831>] check_hung_task kernel/hung_task.c:126 [inline]
 [<ffffffff81372831>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81372831>] watchdog+0x701/0xa70 kernel/hung_task.c:239
 [<ffffffff8119acdd>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838ab02a>] ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:433
Dumping ftrace buffer:
   (ftrace buffer empty)
Kernel Offset: disabled
Rebooting in 86400 seconds..