INFO: task syz-executor.1:11875 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 ffff8800ba3df9d8 29984 11875   2142 0x00000004
 ffff8800ba3df9d8 ffff8801d4548000 a451b526eb7ad05a ffff8801d4548000
 0000000000000000 ffff8801d4548800 ffff8801db61f180 ffff8801db61f1a8
 ffff8801db61e898 ffff8801cfd017c0 ffff8801d4548000 ffffed001747b001
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
 [<ffffffff8113709a>] copy_namespaces+0x28a/0x320 kernel/nsproxy.c:150
 [<ffffffff810cd012>] copy_process+0x2472/0x68a0 kernel/fork.c:1522
 [<ffffffff810d186e>] _do_fork+0x14e/0xdc0 kernel/fork.c:1806
 [<ffffffff810d25b7>] SYSC_clone kernel/fork.c:1917 [inline]
 [<ffffffff810d25b7>] SyS_clone+0x37/0x50 kernel/fork.c:1911
 [<ffffffff82718cb7>] tracesys+0x88/0x8d
1 lock held by syz-executor.1/11875:
 #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: 60 Comm: kworker/u4:1 Not tainted 4.4.174+ #4
Workqueue: netns cleanup_net
task: ffff8801d8ccaf80 task.stack: ffff8801d8d98000
RIP: 0010:[<ffffffff8115d330>]  [<ffffffff8115d330>] preempt_count_add+0x0/0x1d0 kernel/sched/core.c:3069
RSP: 0018:ffff8801d8d9f9d0  EFLAGS: 00000296
RAX: ffffffff8232392c RBX: 000000000000b7c7 RCX: 1ffff1003b199829
RDX: dffffc0000000000 RSI: 0000000000000200 RDI: 0000000000000001
RBP: ffff8801d8d9f9e8 R08: 0000000000000000 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000000 R12: ffffffff82e09820
R13: ffff8800a0eda240 R14: ffff8800a0eda240 R15: 0000000000005be4
FS:  0000000000000000(0000) GS:ffff8801db600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00003ad2ae489d65 CR3: 00000000990d7000 CR4: 00000000001606b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff82717c77 0000000000000004 ffffffff82e09820 ffff8801d8d9fa58
 ffffffff8230ed60 ffff8800a0edb7b4 0000000000000000 ffff8800a0edb7e8
 ffffffff831a9360 ffffffff82321d80 ffffffff82323607 ffffed00141db6f6
Call Trace:
 [<ffffffff8230ed60>] spin_lock include/linux/spinlock.h:302 [inline]
 [<ffffffff8230ed60>] get_next_corpse net/netfilter/nf_conntrack_core.c:1392 [inline]
 [<ffffffff8230ed60>] nf_ct_iterate_cleanup+0xc0/0x500 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: ff ff ff e8 53 7c 32 00 e9 2c fe ff ff e8 49 7c 32 00 e9 4f fc ff ff 48 89 7d e8 e8 3b 7c 32 00 48 8b 7d e8 e9 fc fc ff ff 66 90 <48> b8 00 00 00 00 00 fc ff df 55 48 89 e5 41 54 41 89 fc 53 48 
NMI backtrace for cpu 1
CPU: 1 PID: 20 Comm: khungtaskd Not tainted 4.4.174+ #4
task: ffff8801da6c2f80 task.stack: ffff8800001e8000
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:ffff8800001efc88  EFLAGS: 00000046
RAX: 0000000000000000 RBX: 0000000000000c00 RCX: 0000000000000000
RDX: 0000000000000c00 RSI: 0000000000000000 RDI: ffffffffff5fc300
RBP: ffff8800001efcb8 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: 000000000247e000 CR3: 00000000b9133000 CR4: 00000000001606b0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 0000000000000001 ffffffff82e5f2e0 ffffffff831a6ac0 fffffbfff0634c34
 000000000001b6c0 0000000000000008 ffff8800001efcd8 ffffffff81092bee
 0000000000000008 ffffffff82924260 ffff8800001efd30 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