INFO: task kworker/u4:0:6 blocked for more than 120 seconds.
      Not tainted 4.4.125-g38f41ec #21
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:0    D ffff8801d9b1f908 25064     6      2 0x00000000
Workqueue: netns cleanup_net
 ffff8801d9b1f908 ffff8801d9b10000 0000000000000003 0000000000000007
 ffff8801d9b10000 ffff8801db21fdb8 ffff8801db21fde0 ffff8801db21f4d8
 ffff8801db21f4c0 ffffffff84217840 ffff8801d9b10000 0000000000000000
Call Trace:
 [<ffffffff8376b82a>] schedule+0x7a/0x1b0 kernel/sched/core.c:3359
 [<ffffffff8376c023>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3392
 [<ffffffff837705e6>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff837705e6>] mutex_lock_nested+0x306/0x850 kernel/locking/mutex.c:621
 [<ffffffff82e860b7>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
 [<ffffffff831f4442>] ip_fib_net_exit+0x22/0x430 net/ipv4/fib_frontend.c:1258
 [<ffffffff831f48bb>] fib_net_exit+0x6b/0x90 net/ipv4/fib_frontend.c:1318
 [<ffffffff82e3089e>] ops_exit_list.isra.4+0xae/0x150 net/core/net_namespace.c:134
 [<ffffffff82e3384d>] cleanup_net+0x31d/0x5f0 net/core/net_namespace.c:433
 [<ffffffff811800f7>] process_one_work+0x7d7/0x16e0 kernel/workqueue.c:2064
 [<ffffffff811810d9>] worker_thread+0xd9/0xfc0 kernel/workqueue.c:2196
 [<ffffffff81190b48>] kthread+0x268/0x300 kernel/kthread.c:211
 [<ffffffff83779d95>] ret_from_fork+0x55/0x80 arch/x86/entry/entry_64.S:510
4 locks held by kworker/u4:0/6:
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8117ffdd>] work_static include/linux/workqueue.h:186 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8117ffdd>] set_work_data kernel/workqueue.c:625 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8117ffdd>] set_work_pool_and_clear_pending kernel/workqueue.c:652 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8117ffdd>] process_one_work+0x6bd/0x16e0 kernel/workqueue.c:2057
 #1:  (net_cleanup_work){+.+.+.}, at: [<ffffffff81180017>] process_one_work+0x6f7/0x16e0 kernel/workqueue.c:2061
 #2:  (net_mutex){+.+.+.}, at: [<ffffffff82e3366f>] cleanup_net+0x13f/0x5f0 net/core/net_namespace.c:399
 #3:  (rtnl_mutex){+.+.+.}, at: [<ffffffff82e860b7>] rtnl_lock+0x17/0x20 net/core/rtnetlink.c:70
Sending NMI to all CPUs:
NMI backtrace for cpu 0
CPU: 0 PID: 486 Comm: khungtaskd Not tainted 4.4.125-g38f41ec #21
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8800bac8b000 task.stack: ffff8800bac98000
RIP: 0010:[<ffffffff810c3f87>]  [<ffffffff810c3f87>] native_apic_mem_write arch/x86/include/asm/apic.h:94 [inline]
RIP: 0010:[<ffffffff810c3f87>]  [<ffffffff810c3f87>] __default_send_IPI_dest_field arch/x86/include/asm/ipi.h:119 [inline]
RIP: 0010:[<ffffffff810c3f87>]  [<ffffffff810c3f87>] _flat_send_IPI_mask arch/x86/kernel/apic/apic_flat_64.c:61 [inline]
RIP: 0010:[<ffffffff810c3f87>]  [<ffffffff810c3f87>] flat_send_IPI_mask+0xf7/0x1a0 arch/x86/kernel/apic/apic_flat_64.c:69
RSP: 0018:ffff8800bac9fcb8  EFLAGS: 00000046
RAX: 0000000003000000 RBX: 0000000000000c00 RCX: 0000000000000000
RDX: 0000000000000c00 RSI: 0000000000000000 RDI: ffffffffff5fb300
RBP: ffff8800bac9fce0 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000246
R13: 0000000000000003 R14: ffffffff8426f5a0 R15: 0000000000000002
FS:  0000000000000000(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f4cb1294000 CR3: 00000001c99d4000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff8426f5a0 ffffffff847f0b40 fffffbfff08fdc1c dffffc0000000000
 ffff8801db31bca0 ffff8800bac9fd00 ffffffff810b9abb ffffffff839f6dc0
 0000000000000003 ffff8800bac9fd60 ffffffff81d11764 ffffffff8141b993
Call Trace:
 [<ffffffff810b9abb>] nmi_raise_cpu_backtrace+0x5b/0x70 arch/x86/kernel/apic/hw_nmi.c:33
 [<ffffffff81d11764>] nmi_trigger_all_cpu_backtrace+0x4a4/0x550 lib/nmi_backtrace.c:85
 [<ffffffff810b9b54>] arch_trigger_all_cpu_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
 [<ffffffff813695ca>] trigger_all_cpu_backtrace include/linux/nmi.h:44 [inline]
 [<ffffffff813695ca>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff813695ca>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff813695ca>] watchdog+0x6fa/0xae0 kernel/hung_task.c:238
 [<ffffffff81190b48>] kthread+0x268/0x300 kernel/kthread.c:211
 [<ffffffff83779d95>] ret_from_fork+0x55/0x80 arch/x86/entry/entry_64.S:510
Code: b3 5f ff f6 c4 10 75 e1 44 89 e8 c1 e0 18 89 04 25 10 b3 5f ff 44 89 fa 09 da 80 cf 04 41 83 ff 02 0f 44 d3 89 14 25 00 b3 5f ff <41> f7 c4 00 02 00 00 74 1a e8 2b 33 17 00 4c 89 e7 57 9d 0f 1f 
NMI backtrace for cpu 1
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.4.125-g38f41ec #21
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d9b49800 task.stack: ffff8801d9b58000
RIP: 0010:[<ffffffff81237f16>]  [<ffffffff81237f16>] atomic_inc arch/x86/include/asm/atomic.h:92 [inline]
RIP: 0010:[<ffffffff81237f16>]  [<ffffffff81237f16>] __lock_acquire+0x626/0x4b50 kernel/locking/lockdep.c:3105
RSP: 0018:ffff8801d9b5fb40  EFLAGS: 00000002
RAX: dffffc0000000000 RBX: ffffffff851615a0 RCX: 0000000000000000
RDX: 1ffff1003b663e9c RSI: 0000000000000001 RDI: ffff8801db31f4e0
RBP: ffff8801d9b5fce0 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000000000001 R11: 1ffff1003b36bf7a R12: 0000000000000000
R13: ffff8801d9b49800 R14: ffff8801db31f4d8 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000c420049e80 CR3: 00000001cc746000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffff8801d9b49800 ffff8801d9b4a0e0 0000000000000025 ffff8801d9b49800
 ffffffff842bdbe0 0000000000000000 ffff8801d9b5fd18 ffffffff8123844f
 00000000810b086a 0000000000000046 ffffffff85162b90 ffff8801d9b4a0f8
Call Trace:
 [<ffffffff8123dcae>] lock_acquire+0x15e/0x460 kernel/locking/lockdep.c:3592
 [<ffffffff83778ad6>] __raw_spin_lock include/linux/spinlock_api_smp.h:144 [inline]
 [<ffffffff83778ad6>] _raw_spin_lock+0x36/0x50 kernel/locking/spinlock.c:151
 [<ffffffff811f7bd7>] update_cpu_load_nohz+0xa7/0x140 kernel/sched/fair.c:4998
 [<ffffffff812d8128>] tick_nohz_restart_sched_tick kernel/time/tick-sched.c:716 [inline]
 [<ffffffff812d8128>] tick_nohz_idle_exit+0x1d8/0x3d0 kernel/time/tick-sched.c:946
 [<ffffffff81221cf5>] cpu_idle_loop kernel/sched/idle.c:267 [inline]
 [<ffffffff81221cf5>] cpu_startup_entry+0x2a5/0x8f0 kernel/sched/idle.c:301
 [<ffffffff810adcd4>] start_secondary+0x304/0x3e0 arch/x86/kernel/smpboot.c:242
Code: 49 8d 7c de 08 48 89 fa 48 c1 ea 03 80 3c 02 00 0f 85 b6 37 00 00 49 8b 5c de 08 48 85 db 0f 84 28 fb ff ff f0 ff 83 98 01 00 00 <49> 8d 85 d8 08 00 00 48 89 c2 48 89 44 24 68 48 b8 00 00 00 00