INFO: task syz-executor.4:20123 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.4  D ffff8800a46f79d8 27648 20123   2138 0x00000004
 ffff8800a46f79d8 ffff8801d288af80 572db28af27b90ad ffff8801d288af80
 0000000000000000 ffff8801d288b800 ffff8801db71f180 ffff8801db71f1a8
 ffff8801db71e898 ffff8801bd3f8000 ffff8801d288af80 ffffed00148de001
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.4/20123:
 #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: 18089 Comm: syz-executor.0 Not tainted 4.4.174+ #4
task: ffff8800a40dc740 task.stack: ffff8801d0808000
RIP: 0010:[<ffffffff814307f3>]  [<ffffffff814307f3>] __might_fault+0x43/0x1d0 mm/memory.c:3860
RSP: 0018:ffff8801d080feb0  EFLAGS: 00000246
RAX: ffff8801d0808018 RBX: ffff8801d0808000 RCX: 1ffff1003a101003
RDX: dffffc0000000000 RSI: ffffffff814307c8 RDI: ffffffff828a7200
RBP: ffff8801d080fed0 R08: 0000000000000005 R09: 0000000000000006
R10: 0000000000000007 R11: 0000000000000293 R12: ffffffff828a7200
R13: 0000000000000422 R14: 8c9ce8e60d60b9c1 R15: 0000000000000007
FS:  00007ff0368f2700(0000) GS:ffff8801db600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fb473404000 CR3: 00000001d0b10000 CR4: 00000000001606b0
Stack:
 0000000000000000 0000000000750003 ffff8800a40dc740 ffff8800003cda40
 ffff8801d080ff08 ffffffff8157e22c ffffffff8157e23f 0000000000000005
 0000000000750003 0000000000000000 8c9ce8e60d60b9c1 ffff8801d080ff48
Call Trace:
 [<ffffffff8157e22c>] lookup_ioctx+0x5c/0x590 fs/aio.c:1058
 [<ffffffff81584f8d>] SYSC_io_getevents fs/aio.c:1754 [inline]
 [<ffffffff81584f8d>] SyS_io_getevents+0x2d/0x260 fs/aio.c:1748
 [<ffffffff82718ba1>] entry_SYSCALL_64_fastpath+0x1e/0x9a
Code: 48 ba 00 00 00 00 00 fc ff df 65 48 8b 04 25 44 88 00 00 48 8d 98 00 80 ff ff 48 2d e8 7f 00 00 48 89 c1 48 c1 e9 03 80 3c 11 00 <0f> 85 5d 01 00 00 48 83 7b 18 ff 74 40 e8 eb 8d ed ff 48 b8 00 
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: 00007fb473404000 CR3: 00000000b7cd7000 CR4: 00000000001606b0
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