unregister_netdevice: waiting for lo to become free. Usage count = 4
unregister_netdevice: waiting for lo to become free. Usage count = 4
unregister_netdevice: waiting for lo to become free. Usage count = 4
unregister_netdevice: waiting for lo to become free. Usage count = 4
unregister_netdevice: waiting for lo to become free. Usage count = 4
INFO: task syz-executor4:29792 blocked for more than 120 seconds.
      Not tainted 4.9.93-geba1ffe #3
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor4   D28760 29792      1 0x00000004
 ffff8801d6d36000 ffff8801b6164540 ffff880197e924c0 ffff8801adfc3000
 ffff8801db221b98 ffff8801c61a7bc8 ffffffff838c4a7d ffff8801d6d368c0
 ffffed003ada6d17 ffff8801d6d36000 00fffc0000000000 ffff8801db222468
Call Trace:
 [<ffffffff838c607f>] schedule+0x7f/0x1b0 kernel/sched/core.c:3556
 [<ffffffff838c6a03>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3589
 [<ffffffff838cae86>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff838cae86>] mutex_lock_nested+0x326/0x870 kernel/locking/mutex.c:621
 [<ffffffff82f39e15>] copy_net_ns+0x155/0x290 net/core/net_namespace.c:387
 [<ffffffff8119e1bc>] create_new_namespaces+0x51c/0x730 kernel/nsproxy.c:106
 [<ffffffff8119e9b5>] unshare_nsproxy_namespaces+0xa5/0x1d0 kernel/nsproxy.c:205
 [<ffffffff81133289>] SYSC_unshare kernel/fork.c:2244 [inline]
 [<ffffffff81133289>] SyS_unshare+0x319/0x710 kernel/fork.c:2194
 [<ffffffff81006316>] do_syscall_64+0x1a6/0x490 arch/x86/entry/common.c:282
 [<ffffffff838d5953>] entry_SYSCALL_64_after_swapgs+0x5d/0xdb

Showing all locks held in the system:
2 locks held by khungtaskd/514:
 #0:  (rcu_read_lock){......}, at: [<ffffffff813643fc>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff813643fc>] watchdog+0x11c/0xa20 kernel/hung_task.c:239
 #1:  (tasklist_lock){.+.+..}, at: [<ffffffff81423bb0>] debug_show_all_locks+0x79/0x218 kernel/locking/lockdep.c:4336
3 locks held by kworker/u4:2/911:
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8118ab9e>] work_static include/linux/workqueue.h:186 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8118ab9e>] set_work_data kernel/workqueue.c:617 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8118ab9e>] set_work_pool_and_clear_pending kernel/workqueue.c:644 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8118ab9e>] process_one_work+0x6ee/0x1500 kernel/workqueue.c:2085
 #1:  (net_cleanup_work){+.+.+.}, at: [<ffffffff8118abd8>] process_one_work+0x728/0x1500 kernel/workqueue.c:2089
 #2:  (net_mutex){+.+.+.}, at: [<ffffffff82f397cf>] cleanup_net+0x13f/0x630 net/core/net_namespace.c:420
1 lock held by rsyslogd/3651:
 #0:  (&f->f_pos_lock){+.+.+.}, at: [<ffffffff815d562c>] __fdget_pos+0xac/0xd0 fs/file.c:781
2 locks held by getty/3747:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff838d3b22>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff82007e42>] n_tty_read+0x202/0x16b0 drivers/tty/n_tty.c:2133
1 lock held by syz-executor4/29792:
 #0:  (net_mutex){+.+.+.}, at: [<ffffffff82f39e15>] copy_net_ns+0x155/0x290 net/core/net_namespace.c:387

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

NMI backtrace for cpu 0
CPU: 0 PID: 514 Comm: khungtaskd Not tainted 4.9.93-geba1ffe #3
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d863fd08 ffffffff81d9c2b9 0000000000000000 0000000000000000
 0000000000000000 0000000000000001 ffffffff810b7d90 ffff8801d863fd40
 ffffffff81da75f7 0000000000000000 0000000000000000 0000000000000002
Call Trace:
 [<ffffffff81d9c2b9>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81d9c2b9>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81da75f7>] nmi_cpu_backtrace.cold.2+0x48/0x87 lib/nmi_backtrace.c:99
 [<ffffffff81da758a>] nmi_trigger_cpumask_backtrace+0x12a/0x14f lib/nmi_backtrace.c:60
 [<ffffffff810b7e94>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff81364994>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff81364994>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff81364994>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff81364994>] watchdog+0x6b4/0xa20 kernel/hung_task.c:239
 [<ffffffff8119ab4d>] kthread+0x26d/0x300 kernel/kthread.c:211
 [<ffffffff838d5b1c>] ret_from_fork+0x5c/0x70 arch/x86/entry/entry_64.S:373
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.9.93-geba1ffe #3
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d9b73000 task.stack: ffff8801d9b88000
RIP: 0010:[<ffffffff8128848a>] 
c [<ffffffff8128848a>] rcu_irq_enter+0x3a/0x120 kernel/rcu/tree.c:938
RSP: 0018:ffff8801db307fa8  EFLAGS: 00000046
RAX: 0000000000000001 RBX: 000000000001a690 RCX: 1ffffffff084227d
RDX: dffffc0000000000 RSI: ffffffff81e03cbb RDI: ffffffff842113e8
RBP: ffff8801db307fb8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000001 R14: ffffffff84a3a008 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f3ea2f1e140 CR3: 00000001c6e60000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 0000000000000000
c ffffffff84a2ae68
c ffff8801db307fd0
c ffffffff81148bfa
c
 ffffffff84a2ae68
c ffff8801db307fe8
c ffffffff838da07a
c ffffffff84a2ae68
c
 ffff8801d9b8fd98
c ffffffff838d7c50
c ffff8801d9b8fce8
c <EOI> 
c 0000000000000000
c
Call Trace:
 <IRQ> 
d [<ffffffff81148bfa>] irq_enter+0xa/0xd0 kernel/softirq.c:338
 [<ffffffff838da07a>] smp_reschedule_interrupt+0xa/0x90 arch/x86/kernel/smp.c:267
 [<ffffffff838d7c50>] reschedule_interrupt+0xa0/0xb0 arch/x86/entry/entry_64.S:671
 <EOI> 
d [<ffffffff838d4586>] ? native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:53
 [<ffffffff838d3bc5>] arch_safe_halt arch/x86/include/asm/paravirt.h:104 [inline]
 [<ffffffff838d3bc5>] default_idle+0x55/0x360 arch/x86/kernel/process.c:295
 [<ffffffff81069fa0>] arch_cpu_idle+0x10/0x20 arch/x86/kernel/process.c:286
 [<ffffffff838d49e5>] default_idle_call+0x45/0x60 kernel/sched/idle.c:97
 [<ffffffff81220765>] cpuidle_idle_call kernel/sched/idle.c:155 [inline]
 [<ffffffff81220765>] cpu_idle_loop kernel/sched/idle.c:248 [inline]
 [<ffffffff81220765>] cpu_startup_entry+0x2b5/0x380 kernel/sched/idle.c:303
 [<ffffffff810ad203>] start_secondary+0x323/0x400 arch/x86/kernel/smpboot.c:254
Code: 
c08 
ce8 
c8b 
cb9 
cb7 
c00 
c48 
cba 
c00 
c00 
c00 
c00 
c00 
cfc 
cff 
cdf 
c89 
cc0 
c48 
c8d 
c3c 
cc5 
ce0 
c13 
c21 
c84 
c48 
c89 
cf9 
c48 
cc1 
ce9 
c03 
c80 
c3c 
c11 
c00 
c0f 
c85 
cbb 
c00 
c00 
c00 
c<48> 
c03 
c1c 
cc5 
ce0 
c13 
c21 
c84 
c48 
cb8 
c00 
c00 
c00 
c00 
c00 
cfc 
cff 
cdf 
c48 
c8d 
c7b 
c