INFO: task syz-executor.1:16655 blocked for more than 140 seconds.
      Not tainted 4.4.174+ #4
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor.1  D ffff8800a774fc28 29144 16655      1 0x00000004
 ffff8800a774fc28 ffff8800b3e0c740 0292a03ef8e66925 ffff8800b3e0c740
 0000000000000000 ffff8800b3e0d000 ffff8801db61f180 ffff8801db61f1a8
 ffff8801db61e898 ffffffff82e151c0 ffff8800b3e0c740 ffffed0014ee9001
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
 [<ffffffff8221b16a>] copy_net_ns+0xca/0x250 net/core/net_namespace.c:387
 [<ffffffff81136a90>] create_new_namespaces+0x2f0/0x670 kernel/nsproxy.c:95
 [<ffffffff8113737b>] unshare_nsproxy_namespaces+0xab/0x1e0 kernel/nsproxy.c:190
 [<ffffffff810d28d2>] SYSC_unshare kernel/fork.c:2092 [inline]
 [<ffffffff810d28d2>] SyS_unshare+0x302/0x6f0 kernel/fork.c:2042
 [<ffffffff82718ba1>] entry_SYSCALL_64_fastpath+0x1e/0x9a
1 lock held by syz-executor.1/16655:
 #0:  (net_mutex){+.+.+.}, at: [<ffffffff8221b16a>] copy_net_ns+0xca/0x250 net/core/net_namespace.c:387
Sending NMI to all CPUs:
NMI backtrace for cpu 0
CPU: 0 PID: 2191 Comm: kworker/u4:4 Not tainted 4.4.174+ #4
Workqueue: netns cleanup_net
task: ffff8800b7c78000 task.stack: ffff8801c08c0000
RIP: 0010:[<ffffffff811ff0b1>]  [<ffffffff811ff0b1>] trace_hardirqs_on_caller+0xb1/0x5a0 kernel/locking/lockdep.c:2580
RSP: 0018:ffff8801c08c79a8  EFLAGS: 00000806
RAX: dffffc0000000000 RBX: ffff8800b7c78000 RCX: 1ffffffff05f7178
RDX: 1ffff10016f8f112 RSI: 0000000000000000 RDI: ffff8800b7c78890
RBP: ffff8801c08c79b8 R08: 0000000000000001 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff810e17ba
R13: ffff88009eaaa240 R14: ffff88009eaaa240 R15: 00000000000057c3
FS:  0000000000000000(0000) GS:ffff8801db600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f5f297ab000 CR3: 00000001d7f1a000 CR4: 00000000001606b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Stack:
 0000000000000200 ffffffff8230ed81 ffff8801c08c79c8 ffffffff811ff5ad
 ffff8801c08c79e8 ffffffff810e17ba 000000000000af85 ffffffff82e097b0
 ffff8801c08c7a58 ffffffff8230eda8 ffff88009eaab7b4 0000000000000000
Call Trace:
 [<ffffffff811ff5ad>] trace_hardirqs_on+0xd/0x10 kernel/locking/lockdep.c:2619
 [<ffffffff810e17ba>] __local_bh_enable_ip+0x6a/0xe0 kernel/softirq.c:175
 [<ffffffff8230eda8>] local_bh_enable include/linux/bottom_half.h:31 [inline]
 [<ffffffff8230eda8>] get_next_corpse net/netfilter/nf_conntrack_core.c:1403 [inline]
 [<ffffffff8230eda8>] nf_ct_iterate_cleanup+0x108/0x500 net/netfilter/nf_conntrack_core.c:1432
 [<ffffffff8232392c>] nf_ct_l4proto_pernet_unregister+0xac/0x110 net/netfilter/nf_conntrack_proto.c:473
 [<ffffffff823377bc>] sctp_net_exit+0x2c/0x30 net/netfilter/nf_conntrack_proto_sctp.c:933
 [<ffffffff82217d90>] ops_exit_list.isra.0+0xb0/0x160 net/core/net_namespace.c:134
 [<ffffffff8221ac16>] cleanup_net+0x3d6/0x860 net/core/net_namespace.c:452
 [<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
Code: 00 45 85 db 0f 85 e3 02 00 00 65 48 8b 1c 25 80 67 01 00 48 8d bb 90 08 00 00 48 b8 00 00 00 00 00 fc ff df 48 89 fa 48 c1 ea 03 <0f> b6 04 02 84 c0 74 08 3c 03 0f 8e 4b 03 00 00 44 8b 93 90 08 
NMI backtrace for cpu 1
CPU: 1 PID: 20 Comm: khungtaskd Not tainted 4.4.174+ #4
task: ffff8801da6f4740 task.stack: ffff8800001d0000
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:ffff8800001d7c88  EFLAGS: 00000046
RAX: 0000000000000000 RBX: 0000000000000c00 RCX: 0000000000000000
RDX: 0000000000000c00 RSI: 0000000000000000 RDI: ffffffffff5fc300
RBP: ffff8800001d7cb8 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: 00007f30590f9000 CR3: 00000001d7f1a000 CR4: 00000000001606b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Stack:
 0000000000000001 ffffffff82e5f2e0 ffffffff831a6ac0 fffffbfff0634c34
 000000000001b6c0 0000000000000008 ffff8800001d7cd8 ffffffff81092bee
 0000000000000008 ffffffff82924260 ffff8800001d7d30 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