INFO: task kworker/u4:4:2189 blocked for more than 140 seconds.
      Not tainted 4.4.174+ #4
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
kworker/u4:4    D ffff8801c1047968 24624  2189      2 0x80000000
Workqueue: netns cleanup_net
 ffff8801c1047968 ffff8800b9fe5f00 4d727229f92109f2 ffff8800b9fe5f00
 0000000000000002 ffff8800b9fe6700 ffff8801db71f180 ffff8801db71f1a8
 ffff8801db71e898 ffff8800a54baf80 ffff8800b9fe5f00 ffffed0038208001
Call Trace:
 [<ffffffff82709b79>] schedule+0x99/0x1d0 kernel/sched/core.c:3355
 [<ffffffff8270a333>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3388
 [<ffffffff8270c492>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff8270c492>] mutex_lock_nested+0x3c2/0xb80 kernel/locking/mutex.c:621
 [<ffffffff8221a971>] cleanup_net+0x131/0x860 net/core/net_namespace.c:418
 [<ffffffff81122c25>] process_one_work+0x825/0x1720 kernel/workqueue.c:2064
 [<ffffffff81124004>] worker_thread+0x4e4/0xf50 kernel/workqueue.c:2196
 [<ffffffff811342c3>] kthread+0x273/0x310 kernel/kthread.c:211
 [<ffffffff82718fc5>] ret_from_fork+0x55/0x80 arch/x86/entry/entry_64.S:537
3 locks held by kworker/u4:4/2189:
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff81122b0a>] process_one_work+0x70a/0x1720 kernel/workqueue.c:2057
 #1:  (net_cleanup_work){+.+.+.}, at: [<ffffffff81122b42>] process_one_work+0x742/0x1720 kernel/workqueue.c:2061
 #2:  (net_mutex){+.+.+.}, at: [<ffffffff8221a971>] cleanup_net+0x131/0x860 net/core/net_namespace.c:418
Sending NMI to all CPUs:
NMI backtrace for cpu 0
CPU: 0 PID: 31617 Comm: syz-executor.3 Not tainted 4.4.174+ #4
task: ffff88005577df00 task.stack: ffff8800551c8000
RIP: 0010:[<ffffffff81427df6>]  [<ffffffff81427df6>] __anon_vma_interval_tree_insert mm/interval_tree.c:72 [inline]
RIP: 0010:[<ffffffff81427df6>]  [<ffffffff81427df6>] anon_vma_interval_tree_insert+0x186/0x3a0 mm/interval_tree.c:83
RSP: 0018:ffff8800551cfb08  EFLAGS: 00000a02
RAX: 1ffff1002e8e0ecb RBX: ffff880174707640 RCX: 1ffff1000a7d2048
RDX: 0000000000000000 RSI: ffffffff81427deb RDI: ffff880174707658
RBP: ffff8800551cfb40 R08: ffff880053e901d0 R09: 1ffff1000a7d203b
R10: ffffffff814561de R11: 0000000000000000 R12: dffffc0000000000
R13: ffff880053e90230 R14: 0000000000000a56 R15: ffff880059026f78
FS:  00007f7ce481c700(0000) GS:ffff8801db600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000000 CR3: 00000000551d0000 CR4: 00000000001606b0
Stack:
 ffff8801a8a79e98 0000000000000951 ffff880053e901d0 ffff880053e90230
 ffff880053e532d0 ffff880053e53348 ffff880053e90240 ffff8800551cfb80
 ffffffff814525d2 ffff8801a8a79e00 ffff88016084de70 ffff880053e90230
Call Trace:
 [<ffffffff814525d2>] anon_vma_chain_link+0x142/0x1a0 mm/rmap.c:139
 [<ffffffff8145625b>] anon_vma_clone+0x15b/0x4b0 mm/rmap.c:275
 [<ffffffff81456637>] anon_vma_fork+0x87/0x4b0 mm/rmap.c:328
 [<ffffffff810ceccc>] dup_mmap kernel/fork.c:471 [inline]
 [<ffffffff810ceccc>] dup_mm kernel/fork.c:985 [inline]
 [<ffffffff810ceccc>] copy_mm kernel/fork.c:1039 [inline]
 [<ffffffff810ceccc>] copy_process+0x412c/0x68a0 kernel/fork.c:1519
 [<ffffffff810d186e>] _do_fork+0x14e/0xdc0 kernel/fork.c:1806
 [<ffffffff810d253f>] sys_fork+0x1f/0x30 kernel/fork.c:1877
 [<ffffffff82718cb7>] tracesys+0x88/0x8d
Code: 03 42 80 3c 22 00 0f 85 86 01 00 00 49 8b 17 48 85 d2 0f 84 84 00 00 00 48 89 d3 e8 05 18 ee ff 48 8d 7b 18 48 89 f8 48 c1 e8 03 <42> 80 3c 20 00 0f 85 52 01 00 00 4c 3b 73 18 76 09 e8 e4 17 ee 
NMI backtrace for cpu 1
CPU: 1 PID: 20 Comm: khungtaskd Not tainted 4.4.174+ #4
task: ffff8801da6c4740 task.stack: ffff8801d9ed8000
RIP: 0010:[<ffffffff8109b617>]  [<ffffffff8109b617>] _flat_send_IPI_mask arch/x86/kernel/apic/apic_flat_64.c:62 [inline]
RIP: 0010:[<ffffffff8109b617>]  [<ffffffff8109b617>] flat_send_IPI_mask+0xf7/0x1b0 arch/x86/kernel/apic/apic_flat_64.c:69
RSP: 0018:ffff8801d9edfc88  EFLAGS: 00000046
RAX: 0000000000000000 RBX: 0000000000000c00 RCX: 0000000000000000
RDX: 0000000000000c00 RSI: 0000000000000000 RDI: ffffffffff5fc300
RBP: ffff8801d9edfcb8 R08: 0000000000000018 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000001 R12: 0000000000000246
R13: 0000000003000000 R14: ffffffff82e5f2e0 R15: 0000000000000002
FS:  0000000000000000(0000) GS:ffff8801db700000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000000000000007 CR3: 0000000167d72000 CR4: 00000000001606b0
Stack:
 0000000000000001 ffffffff82e5f2e0 ffffffff831a6ac0 fffffbfff0634c34
 000000000001b6c0 0000000000000008 ffff8801d9edfcd8 ffffffff81092bee
 0000000000000008 ffffffff82924260 ffff8801d9edfd30 ffffffff81ab8252
Call Trace:
 [<ffffffff81092bee>] nmi_raise_cpu_backtrace+0x5e/0x80 arch/x86/kernel/apic/hw_nmi.c:33
 [<ffffffff81ab8252>] nmi_trigger_all_cpu_backtrace.cold+0xa1/0xae lib/nmi_backtrace.c:85
 [<ffffffff81092ca4>] arch_trigger_all_cpu_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
 [<ffffffff813b4762>] trigger_all_cpu_backtrace include/linux/nmi.h:44 [inline]
 [<ffffffff813b4762>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff813b4762>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff813b4762>] watchdog.cold+0xd3/0xee kernel/hung_task.c:238
 [<ffffffff811342c3>] kthread+0x273/0x310 kernel/kthread.c:211
 [<ffffffff82718fc5>] ret_from_fork+0x55/0x80 arch/x86/entry/entry_64.S:537
Code: 00 c3 5f ff 80 e6 10 75 e1 41 c1 e5 18 44 89 2c 25 10 c3 5f ff 44 89 fa 09 da 80 cf 04 41 83 ff 02 0f 44 d3 89 14 25 00 c3 5f ff <41> f7 c4 00 02 00 00 75 1e 4c 89 e7 57 9d 0f 1f 44 00 00 e8 f1