INFO: task syz-executor.2:1534 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.2  D ffff880080daf9d8 29384  1534   2157 0x00000004
 ffff880080daf9d8 ffff88007e2e4740 bd5ad0fa25aa91f2 ffff88007e2e4740
 0000000000000000 ffff88007e2e5000 ffff8801db61f180 ffff8801db61f1a8
 ffff8801db61e898 ffff8800836f17c0 ffff88007e2e4740 ffffed00101b5001
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.2/1534:
 #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: 1720 Comm: syz-executor.2 Not tainted 4.4.174+ #4
task: ffff880097ff5f00 task.stack: ffff88019d1c0000
RIP: 0010:[<ffffffff811fc2f8>]  [<ffffffff811fc2f8>] debug_check_no_locks_freed+0x28/0x1b0 kernel/locking/lockdep.c:4117
RSP: 0018:ffff88019d1c75f8  EFLAGS: 00000006
RAX: 0000000000000003 RBX: ffff88009ed69400 RCX: 1ffffffff05f7178
RDX: dffffc0000000000 RSI: 0000000000000200 RDI: ffff88009ed69400
RBP: ffff88019d1c7610 R08: 0000000000000003 R09: 0000000000000001
R10: 0000000000000000 R11: 0000000000000000 R12: ffffea00027b5a00
R13: ffff8801da401280 R14: ffffffff821fd036 R15: 0000000000000282
FS:  00007f6461d4f700(0000) GS:ffff8801db600000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fd9e0d0e000 CR3: 000000019b894000 CR4: 00000000001606b0
Stack:
 ffff8801da401280 ffffffff821fd036 0000000000000282 ffff88019d1c7648
 ffffffff81481c12 0000000000000000 ffff88009ed69400 ffff88009ed694f0
 ffff88007cce3000 dffffc0000000000 ffff88019d1c7698 ffffffff821fd036
Call Trace:
 [<ffffffff81481c12>] slab_free_hook mm/slub.c:1371 [inline]
 [<ffffffff81481c12>] slab_free_freelist_hook mm/slub.c:1405 [inline]
 [<ffffffff81481c12>] slab_free mm/slub.c:2859 [inline]
 [<ffffffff81481c12>] kfree+0xc2/0x310 mm/slub.c:3749
 [<ffffffff821fd036>] skb_free_head net/core/skbuff.c:571 [inline]
 [<ffffffff821fd036>] skb_release_data+0x2e6/0x380 net/core/skbuff.c:602
 [<ffffffff821fd11d>] skb_release_all+0x4d/0x60 net/core/skbuff.c:661
 [<ffffffff821ff4b3>] __kfree_skb net/core/skbuff.c:675 [inline]
 [<ffffffff821ff4b3>] consume_skb+0xf3/0x3f0 net/core/skbuff.c:748
 [<ffffffff822e6961>] netlink_broadcast_filtered+0x2b1/0x9d0 net/netlink/af_netlink.c:1486
 [<ffffffff81ab60d5>] kobject_uevent_env+0x705/0xba0 lib/kobject_uevent.c:316
 [<ffffffff81ab6590>] kobject_uevent+0x20/0x30 lib/kobject_uevent.c:374
 [<ffffffff81cfd02c>] device_add+0xa3c/0x1490 drivers/base/core.c:1141
 [<ffffffff8229462d>] netdev_register_kobject+0x12d/0x300 net/core/net-sysfs.c:1549
 [<ffffffff8224b059>] register_netdevice+0x669/0xcc0 net/core/dev.c:6807
 [<ffffffff8224b6cb>] register_netdev+0x1b/0x30 net/core/dev.c:6919
 [<ffffffff81e115d8>] loopback_net_init+0x78/0x150 drivers/net/loopback.c:203
 [<ffffffff82217370>] ops_init+0xb0/0x3a0 net/core/net_namespace.c:109
 [<ffffffff82219494>] setup_net+0x1b4/0x4e0 net/core/net_namespace.c:289
 [<ffffffff8221b175>] copy_net_ns+0xd5/0x250 net/core/net_namespace.c:388
 [<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
Code: 00 00 00 48 c7 c0 c0 8b fb 82 55 48 ba 00 00 00 00 00 fc ff df 48 89 c1 48 89 e5 41 57 83 e0 07 41 56 48 c1 e9 03 83 c0 03 41 55 <41> 54 49 89 fc 53 48 83 ec 18 0f b6 14 11 65 4c 8b 2c 25 80 67 
NMI backtrace for cpu 1
CPU: 1 PID: 20 Comm: khungtaskd Not tainted 4.4.174+ #4
task: ffff8801da6f2f80 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: 00007fd9e0d0e000 CR3: 00000001d7df9000 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