unregister_netdevice: waiting for lo to become free. Usage count = 1
INFO: task syz-executor4:17317 blocked for more than 120 seconds.
      Not tainted 4.9.64-gfbb7468 #94
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor4   D28688 17317   3238 0x00000004
 ffff8801cdd80000 ffff8801acdaca80 ffff8801c4e78fc0 ffff8801c9899800
 ffff8801db321418 ffff8801c82ff9f8 ffffffff83897fdb 0000000000000000
 0000000000000007 00ff8801cdd80000 ffff8801db321d40 ffff8801db321d68
Call Trace:
 [<ffffffff8389957f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3540
 [<ffffffff83899f03>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3573
 [<ffffffff8389f512>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff8389f512>] mutex_lock_nested+0x312/0x870 kernel/locking/mutex.c:621
 [<ffffffff82f14af5>] copy_net_ns+0x155/0x280 net/core/net_namespace.c:387
 [<ffffffff8119bb4f>] create_new_namespaces+0x37f/0x730 kernel/nsproxy.c:106
 [<ffffffff8119c191>] copy_namespaces+0x291/0x320 kernel/nsproxy.c:164
 [<ffffffff81128db9>] copy_process.part.51+0x1c99/0x5d40 kernel/fork.c:1667
 [<ffffffff8112d2f0>] copy_process kernel/fork.c:1491 [inline]
 [<ffffffff8112d2f0>] _do_fork+0x1c0/0xd70 kernel/fork.c:1949
 [<ffffffff8112df77>] SYSC_clone kernel/fork.c:2059 [inline]
 [<ffffffff8112df77>] SyS_clone+0x37/0x50 kernel/fork.c:2053
 [<ffffffff81006517>] do_syscall_64+0x197/0x490 arch/x86/entry/common.c:280
 [<ffffffff838a984d>] entry_SYSCALL64_slow_path+0x25/0x25

Showing all locks held in the system:
2 locks held by khungtaskd/514:
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136fed5>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136fed5>] watchdog+0x125/0xa70 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.?..}, at: [<ffffffff81235700>] debug_show_all_locks+0x70/0x280 kernel/locking/lockdep.c:4336
1 lock held by rsyslogd/3121:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<ffffffff815cf99f>] __fdget_pos+0x9f/0xc0 fs/file.c:781
2 locks held by getty/3210:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838a79a2>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff82001b14>] n_tty_read+0x1f4/0x16c0 drivers/tty/n_tty.c:2133
3 locks held by kworker/u4:5/3657:
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff81187719>] __write_once_size include/linux/compiler.h:272 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff81187719>] atomic64_set arch/x86/include/asm/atomic64_64.h:33 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff81187719>] atomic_long_set include/asm-generic/atomic-long.h:56 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff81187719>] set_work_data kernel/workqueue.c:616 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff81187719>] set_work_pool_and_clear_pending kernel/workqueue.c:643 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff81187719>] process_one_work+0x6a9/0x15f0 kernel/workqueue.c:2083
 #1:  (net_cleanup_work){+.+.+.}, at: [<ffffffff8118774b>] process_one_work+0x6db/0x15f0 kernel/workqueue.c:2087
 #2:  (net_mutex){+.+.+.}, at: [<ffffffff82f144cf>] cleanup_net+0x13f/0x610 net/core/net_namespace.c:420
1 lock held by syz-executor4/17317:
 #0:  (net_mutex){+.+.+.}, at: [<ffffffff82f14af5>] copy_net_ns+0x155/0x280 net/core/net_namespace.c:387

=============================================

NMI backtrace for cpu 1
CPU: 1 PID: 514 Comm: khungtaskd Not tainted 4.9.64-gfbb7468 #94
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d882fd00 ffffffff81d90429 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810ba170 ffff8801d882fd38
 ffffffff81d9b54d 0000000000000001 0000000000000000 ffff8801cdd80418
Call Trace:
 [<ffffffff81d90429>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d90429>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81d9b54d>] nmi_cpu_backtrace+0xfd/0x120 lib/nmi_backtrace.c:99
 [<ffffffff81d9b687>] nmi_trigger_cpumask_backtrace+0x117/0x190 lib/nmi_backtrace.c:60
 [<ffffffff810ba264>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff813704a0>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff813704a0>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff813704a0>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff813704a0>] watchdog+0x6f0/0xa70 kernel/hung_task.c:239
 [<ffffffff811985dd>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838a9a2a>] ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:433
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0 skipped: idling at pc 0xffffffff838a8416