unregister_netdevice: waiting for lo to become free. Usage count = 3
INFO: task syz-executor6:24943 blocked for more than 120 seconds.
      Not tainted 4.9.40-ged32335 #11
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor6   D28496 24943   3281 0x00000004
 ffff8801c4a85e00 ffff8801ab71e4c0 ffff8801a4961a40 ffff8801d5bb8000
 ffff8801db221498 ffff8801ab8879f8 ffffffff8388f2bb 0000000000000000
 0000000000000007 00ff8801c4a85e00 ffff8801db221db0 ffff8801db221dd8
Call Trace:
 [<ffffffff83890872>] schedule+0x92/0x1b0 kernel/sched/core.c:3624
 [<ffffffff838911e3>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3657
 [<ffffffff838967f2>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff838967f2>] mutex_lock_nested+0x312/0x870 kernel/locking/mutex.c:621
 [<ffffffff82f0bba5>] 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
 [<ffffffff838a078d>] entry_SYSCALL64_slow_path+0x25/0x25

Showing all locks held in the system:
2 locks held by khungtaskd/513:
 #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/3115:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<ffffffff815cc97f>] __fdget_pos+0x9f/0xc0 fs/file.c:781
2 locks held by getty/3205:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff8389e8c2>] 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/u4:3/3503:
 #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: [<ffffffff82f0b57f>] cleanup_net+0x13f/0x610 net/core/net_namespace.c:420
1 lock held by syz-executor6/24943:
 #0:  (net_mutex){+.+.+.}, at: [<ffffffff82f0bba5>] copy_net_ns+0x155/0x280 net/core/net_namespace.c:387

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

NMI backtrace for cpu 0
CPU: 0 PID: 513 Comm: khungtaskd Not tainted 4.9.40-ged32335 #11
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d893fd00 ffffffff81d8d829 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810bd010 ffff8801d893fd38
 ffffffff81d9893d 0000000000000000 0000000000000000 ffff8801c4a86198
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
 [<ffffffff838a096a>] 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 0xffffffff8389f336