unregister_netdevice: waiting for lo to become free. Usage count = 4
unregister_netdevice: waiting for lo to become free. Usage count = 4
unregister_netdevice: waiting for lo to become free. Usage count = 4
unregister_netdevice: waiting for lo to become free. Usage count = 4
unregister_netdevice: waiting for lo to become free. Usage count = 4
INFO: task syz-executor1:8489 blocked for more than 120 seconds.
      Not tainted 4.4.125-g38f41ec #63
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor1   D ffff8800a87cfc38 29016  8489      1 0x00000004
 ffff8800a87cfc38 ffff8801cbc26000 0000000000000000 0000000000000007
 ffff8801cbc26000 ffff8801db21fdb8 ffff8801db21fde0 ffff8801db21f4d8
 ffff8801db21f4c0 ffffffff84217840 ffff8801cbc26000 0000000000000000
Call Trace:
 [<ffffffff8376b82a>] schedule+0x7a/0x1b0 kernel/sched/core.c:3359
 [<ffffffff8376c023>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3392
 [<ffffffff837705e6>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff837705e6>] mutex_lock_nested+0x306/0x850 kernel/locking/mutex.c:621
 [<ffffffff82e33be7>] copy_net_ns+0xc7/0x190 net/core/net_namespace.c:368
 [<ffffffff81193166>] create_new_namespaces+0x2f6/0x610 kernel/nsproxy.c:95
 [<ffffffff81193a1e>] unshare_nsproxy_namespaces+0xae/0x1e0 kernel/nsproxy.c:190
 [<ffffffff8112cc8a>] SYSC_unshare kernel/fork.c:2068 [inline]
 [<ffffffff8112cc8a>] SyS_unshare+0x3da/0x700 kernel/fork.c:2018
 [<ffffffff83779965>] entry_SYSCALL_64_fastpath+0x22/0x9e
1 lock held by syz-executor1/8489:
 #0:  (net_mutex){+.+.+.}, at: [<ffffffff82e33be7>] copy_net_ns+0xc7/0x190 net/core/net_namespace.c:368
Sending NMI to all CPUs:
NMI backtrace for cpu 0
CPU: 0 PID: 486 Comm: khungtaskd Not tainted 4.4.125-g38f41ec #63
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8800bb1b4800 task.stack: ffff8800bb170000
RIP: 0010:[<ffffffff810c3f87>]  [<ffffffff810c3f87>] native_apic_mem_write arch/x86/include/asm/apic.h:94 [inline]
RIP: 0010:[<ffffffff810c3f87>]  [<ffffffff810c3f87>] __default_send_IPI_dest_field arch/x86/include/asm/ipi.h:119 [inline]
RIP: 0010:[<ffffffff810c3f87>]  [<ffffffff810c3f87>] _flat_send_IPI_mask arch/x86/kernel/apic/apic_flat_64.c:61 [inline]
RIP: 0010:[<ffffffff810c3f87>]  [<ffffffff810c3f87>] flat_send_IPI_mask+0xf7/0x1a0 arch/x86/kernel/apic/apic_flat_64.c:69
RSP: 0018:ffff8800bb177cb8  EFLAGS: 00000046
RAX: 0000000003000000 RBX: 0000000000000c00 RCX: 0000000000000000
RDX: 0000000000000c00 RSI: 0000000000000000 RDI: ffffffffff5fb300
RBP: ffff8800bb177ce0 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000001 R12: 0000000000000246
R13: 0000000000000003 R14: ffffffff8426f5a0 R15: 0000000000000002
FS:  0000000000000000(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fa9951f6000 CR3: 00000001d3b4c000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 ffffffff8426f5a0 ffffffff847f0b40 fffffbfff08fdc1c dffffc0000000000
 ffff8801db31bca0 ffff8800bb177d00 ffffffff810b9abb ffffffff839f6dc0
 0000000000000003 ffff8800bb177d60 ffffffff81d11764 ffffffff8141b993
Call Trace:
 [<ffffffff810b9abb>] nmi_raise_cpu_backtrace+0x5b/0x70 arch/x86/kernel/apic/hw_nmi.c:33
 [<ffffffff81d11764>] nmi_trigger_all_cpu_backtrace+0x4a4/0x550 lib/nmi_backtrace.c:85
 [<ffffffff810b9b54>] arch_trigger_all_cpu_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38
 [<ffffffff813695ca>] trigger_all_cpu_backtrace include/linux/nmi.h:44 [inline]
 [<ffffffff813695ca>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff813695ca>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff813695ca>] watchdog+0x6fa/0xae0 kernel/hung_task.c:238
 [<ffffffff81190b48>] kthread+0x268/0x300 kernel/kthread.c:211
 [<ffffffff83779d95>] ret_from_fork+0x55/0x80 arch/x86/entry/entry_64.S:510
Code: b3 5f ff f6 c4 10 75 e1 44 89 e8 c1 e0 18 89 04 25 10 b3 5f ff 44 89 fa 09 da 80 cf 04 41 83 ff 02 0f 44 d3 89 14 25 00 b3 5f ff <41> f7 c4 00 02 00 00 74 1a e8 2b 33 17 00 4c 89 e7 57 9d 0f 1f 
NMI backtrace for cpu 1
CPU: 1 PID: 0 Comm: swapper/1 Not tainted 4.4.125-g38f41ec #63
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffff8801d9b49800 task.stack: ffff8801d9b58000
RIP: 0010:[<ffffffff8123878a>]  [<ffffffff8123878a>] __lock_acquire+0xe9a/0x4b50 kernel/locking/lockdep.c:3236
RSP: 0018:ffff8801d9b5fb80  EFLAGS: 00000097
RAX: 0000000000000001 RBX: ffff8801d9b4a0e0 RCX: 1ffff1003b369420
RDX: 1ffff1003b36941b RSI: ffff8801d9b4a0e0 RDI: 0000000000000000
RBP: ffff8801d9b5fd18 R08: 0000000000000001 R09: 0000000000000000
R10: 0000000000000000 R11: 1ffff1003b36bf82 R12: 0000000000000025
R13: ffff8801d9b49800 R14: 0000000000000000 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8801db300000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffb3905b000 CR3: 00000001d3b4c000 CR4: 0000000000160670
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Stack:
 00000000810b086a 0000000000000046 ffff8801d9b4a0e0 ffff8801d9b5fbd8
 ffffffff812af1d7 ffff8801d9b49800 0000000000000046 0000000000000086
 ffff8801db319640 000000382346a180 ffff8801d9b5fbe0 ffff8801d9b4a0f8
Call Trace:
 [<ffffffff8123dcae>] lock_acquire+0x15e/0x460 kernel/locking/lockdep.c:3592
 [<ffffffff811959d8>] rcu_lock_acquire include/linux/rcupdate.h:477 [inline]
 [<ffffffff811959d8>] rcu_read_lock include/linux/rcupdate.h:861 [inline]
 [<ffffffff811959d8>] __atomic_notifier_call_chain kernel/notifier.c:182 [inline]
 [<ffffffff811959d8>] atomic_notifier_call_chain+0x48/0x140 kernel/notifier.c:193
 [<ffffffff8112e20e>] idle_notifier_call_chain+0x1e/0x30 kernel/cpu.c:865
 [<ffffffff8102937f>] __exit_idle arch/x86/kernel/process.c:247 [inline]
 [<ffffffff8102937f>] arch_cpu_idle_exit+0x1f/0x30 arch/x86/kernel/process.c:268
 [<ffffffff81221cb5>] cpu_idle_loop kernel/sched/idle.c:255 [inline]
 [<ffffffff81221cb5>] cpu_startup_entry+0x265/0x8f0 kernel/sched/idle.c:301
 [<ffffffff810adcd4>] start_secondary+0x304/0x3e0 arch/x86/kernel/smpboot.c:242
Code: c0 74 08 3c 03 0f 8e 13 37 00 00 41 8b 85 d8 08 00 00 83 c0 01 83 f8 2f 41 89 85 d8 08 00 00 0f 87 dc 17 00 00 3b 05 16 53 a9 03 <41> b8 01 00 00 00 0f 86 c5 f6 ff ff 89 05 04 53 a9 03 e9 ba f6