unregister_netdevice: waiting for lo to become free. Usage count = 2
INFO: task syz-executor4:13656 blocked for more than 120 seconds.
      Not tainted 4.9.40-ged32335 #10
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor4   D28848 13656   3326 0x00000004
 ffff8801c60baf00 0000000000000000 ffff8801d1d01a40 ffffffff84426880
 ffff8801db221498 ffff8801a8f679f8 ffffffff838a22bb 0000000000000000
 0000000000000007 00ff8801c60baf00 ffff8801db221db0 ffff8801db221dd8
Call Trace:
 [<ffffffff838a3872>] schedule+0x92/0x1b0 kernel/sched/core.c:3624
 [<ffffffff838a41e3>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3657
 [<ffffffff838a97f2>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff838a97f2>] mutex_lock_nested+0x312/0x870 kernel/locking/mutex.c:621
 [<ffffffff82f1eba5>] copy_net_ns+0x155/0x280 net/core/net_namespace.c:387
 [<ffffffff8119e31f>] create_new_namespaces+0x37f/0x730 kernel/nsproxy.c:106
 [<ffffffff8119e961>] copy_namespaces+0x291/0x320 kernel/nsproxy.c:164
 [<ffffffff8112b809>] copy_process.part.50+0x1c99/0x5d40 kernel/fork.c:1658
 [<ffffffff8112fd40>] copy_process kernel/fork.c:1482 [inline]
 [<ffffffff8112fd40>] _do_fork+0x1c0/0xd70 kernel/fork.c:1940
 [<ffffffff811309c7>] SYSC_clone kernel/fork.c:2050 [inline]
 [<ffffffff811309c7>] SyS_clone+0x37/0x50 kernel/fork.c:2044
 [<ffffffff81006527>] do_syscall_64+0x197/0x490 arch/x86/entry/common.c:280
 [<ffffffff838b378d>] entry_SYSCALL64_slow_path+0x25/0x25

Showing all locks held in the system:
2 locks held by khungtaskd/519:
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136d275>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136d275>] watchdog+0x125/0xa70 kernel/hung_task.c:239
 #1:  (tasklist_lock){.?.+..}, at: [<ffffffff81233524>] debug_show_all_locks+0x74/0x290 kernel/locking/lockdep.c:4329
1 lock held by rsyslogd/3204:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<ffffffff815cc97f>] __fdget_pos+0x9f/0xc0 fs/file.c:781
2 locks held by getty/3297:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838b18c2>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff81fff0f4>] n_tty_read+0x1f4/0x16c0 drivers/tty/n_tty.c:2133
3 locks held by kworker/u4:8/4945:
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff81189e29>] __write_once_size include/linux/compiler.h:272 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff81189e29>] atomic64_set arch/x86/include/asm/atomic64_64.h:33 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff81189e29>] atomic_long_set include/asm-generic/atomic-long.h:56 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff81189e29>] set_work_data kernel/workqueue.c:615 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff81189e29>] set_work_pool_and_clear_pending kernel/workqueue.c:642 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff81189e29>] process_one_work+0x6a9/0x15f0 kernel/workqueue.c:2089
 #1:  (net_cleanup_work){+.+.+.}, at: [<ffffffff81189e5b>] process_one_work+0x6db/0x15f0 kernel/workqueue.c:2093
 #2:  (net_mutex){+.+.+.}, at: [<ffffffff82f1e57f>] cleanup_net+0x13f/0x610 net/core/net_namespace.c:420
1 lock held by syz-executor4/13656:
 #0:  (net_mutex){+.+.+.}, at: [<ffffffff82f1eba5>] copy_net_ns+0x155/0x280 net/core/net_namespace.c:387

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

NMI backtrace for cpu 1
CPU: 1 PID: 519 Comm: khungtaskd Not tainted 4.9.40-ged32335 #10
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d893fd00 ffffffff81d8d829 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810bd010 ffff8801d893fd38
 ffffffff81d9893d 0000000000000001 0000000000000000 ffff8801c60bb298
Call Trace:
 [<ffffffff81d8d829>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d8d829>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81d9893d>] nmi_cpu_backtrace+0xfd/0x120 lib/nmi_backtrace.c:99
 [<ffffffff81d98a77>] nmi_trigger_cpumask_backtrace+0x117/0x190 lib/nmi_backtrace.c:60
 [<ffffffff810bd104>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff8136d840>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff8136d840>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff8136d840>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff8136d840>] watchdog+0x6f0/0xa70 kernel/hung_task.c:239
 [<ffffffff8119ad8d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838b396a>] 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 0xffffffff838b2336