unregister_netdevice: waiting for lo to become free. Usage count = 3
INFO: task syz-executor6:11532 blocked for more than 120 seconds.
      Not tainted 4.9.39-ga1e4c795 #8
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor6   D29080 11532   3456 0x00000004
 ffff8801ccbc2f00 ffff8801c7e61b80 ffff8801cfdcac00 ffff8801c7f25e00
 ffff8801db221498 ffff8801960e7a18 ffffffff83954b2b 0000000000000000
 0000000000000007 00ff8801ccbc2f00 ffff8801db221db0 ffff8801db221dd8
Call Trace:
 [<ffffffff839560e2>] schedule+0x92/0x1b0 kernel/sched/core.c:3624
 [<ffffffff83956a53>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3657
 [<ffffffff8395bdaf>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff8395bdaf>] mutex_lock_nested+0x2ff/0x830 kernel/locking/mutex.c:621
 [<ffffffff82f413f5>] copy_net_ns+0x155/0x280 net/core/net_namespace.c:387
 [<ffffffff8119f47f>] create_new_namespaces+0x37f/0x730 kernel/nsproxy.c:106
 [<ffffffff8119fac1>] copy_namespaces+0x291/0x320 kernel/nsproxy.c:164
 [<ffffffff8112d449>] copy_process.part.39+0x1e39/0x5f70 kernel/fork.c:1658
 [<ffffffff81131a78>] copy_process kernel/fork.c:1482 [inline]
 [<ffffffff81131a78>] _do_fork+0x1b8/0xd50 kernel/fork.c:1940
 [<ffffffff811326e7>] SYSC_clone kernel/fork.c:2050 [inline]
 [<ffffffff811326e7>] SyS_clone+0x37/0x50 kernel/fork.c:2044
 [<ffffffff81006437>] do_syscall_64+0x197/0x490 arch/x86/entry/common.c:280
 [<ffffffff83965a4d>] entry_SYSCALL64_slow_path+0x25/0x25

Showing all locks held in the system:
2 locks held by khungtaskd/548:
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136ae05>] check_hung_uninterruptible_tasks kernel/hung_task.c:168 [inline]
 #0:  (rcu_read_lock){......}, at: [<ffffffff8136ae05>] watchdog+0x125/0xa70 kernel/hung_task.c:239
 #1:  (tasklist_lock){.?.+..}, at: [<ffffffff812341f4>] debug_show_all_locks+0x74/0x290 kernel/locking/lockdep.c:4329
2 locks held by getty/3303:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff83963b92>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff8213c2cc>] n_tty_read+0x1ec/0x1680 drivers/tty/n_tty.c:2133
2 locks held by getty/3304:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff83963b92>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff8213c2cc>] n_tty_read+0x1ec/0x1680 drivers/tty/n_tty.c:2133
2 locks held by getty/3305:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff83963b92>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff8213c2cc>] n_tty_read+0x1ec/0x1680 drivers/tty/n_tty.c:2133
2 locks held by getty/3306:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff83963b92>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff8213c2cc>] n_tty_read+0x1ec/0x1680 drivers/tty/n_tty.c:2133
2 locks held by getty/3307:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff83963b92>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff8213c2cc>] n_tty_read+0x1ec/0x1680 drivers/tty/n_tty.c:2133
2 locks held by getty/3308:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff83963b92>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff8213c2cc>] n_tty_read+0x1ec/0x1680 drivers/tty/n_tty.c:2133
2 locks held by getty/20999:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff83963b92>] ldsem_down_read+0x32/0x40 drivers/tty/tty_ldsem.c:367
 #1:  (&ldata->atomic_read_lock){+.+.+.}, at: [<ffffffff8213c2cc>] n_tty_read+0x1ec/0x1680 drivers/tty/n_tty.c:2133
3 locks held by kworker/u4:0/10825:
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8118a321>] __write_once_size include/linux/compiler.h:272 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8118a321>] atomic64_set arch/x86/include/asm/atomic64_64.h:33 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8118a321>] atomic_long_set include/asm-generic/atomic-long.h:56 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8118a321>] set_work_data kernel/workqueue.c:615 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8118a321>] set_work_pool_and_clear_pending kernel/workqueue.c:642 [inline]
 #0:  ("%s""netns"){.+.+.+}, at: [<ffffffff8118a321>] process_one_work+0x691/0x15c0 kernel/workqueue.c:2089
 #1:  (net_cleanup_work){+.+.+.}, at: [<ffffffff8118a353>] process_one_work+0x6c3/0x15c0 kernel/workqueue.c:2093
 #2:  (net_mutex){+.+.+.}, at: [<ffffffff82f40dd7>] cleanup_net+0x137/0x600 net/core/net_namespace.c:420
1 lock held by syz-executor6/11532:
 #0:  (net_mutex){+.+.+.}, at: [<ffffffff82f413f5>] copy_net_ns+0x155/0x280 net/core/net_namespace.c:387

=============================================

NMI backtrace for cpu 1
CPU: 1 PID: 548 Comm: khungtaskd Not tainted 4.9.39-ga1e4c795 #8
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d964fd00 ffffffff81eacd59 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810bf310 ffff8801d964fd38
 ffffffff81eb7cad 0000000000000001 0000000000000000 ffff8801ccbc3298
Call Trace:
 [<ffffffff81eacd59>] __dump_stack lib/dump_stack.c:15 [inline]
 [<ffffffff81eacd59>] dump_stack+0xc1/0x128 lib/dump_stack.c:51
 [<ffffffff81eb7cad>] nmi_cpu_backtrace+0xfd/0x120 lib/nmi_backtrace.c:99
 [<ffffffff81eb7de7>] nmi_trigger_cpumask_backtrace+0x117/0x190 lib/nmi_backtrace.c:60
 [<ffffffff810bf404>] arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:37
 [<ffffffff8136b3d0>] trigger_all_cpu_backtrace include/linux/nmi.h:58 [inline]
 [<ffffffff8136b3d0>] check_hung_task kernel/hung_task.c:125 [inline]
 [<ffffffff8136b3d0>] check_hung_uninterruptible_tasks kernel/hung_task.c:182 [inline]
 [<ffffffff8136b3d0>] watchdog+0x6f0/0xa70 kernel/hung_task.c:239
 [<ffffffff8119be55>] kthread+0x265/0x300 kernel/kthread.c:211
 [<ffffffff83965c1a>] ret_from_fork+0x2a/0x40 arch/x86/entry/entry_64.S:433
Sending NMI from CPU 1 to CPUs 0:
NMI backtrace for cpu 0
CPU: 0 PID: 0 Comm: swapper/0 Not tainted 4.9.39-ga1e4c795 #8
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffffffff844268c0 task.stack: ffffffff84400000
RIP: 0010:[<ffffffff81283077>] 
c [<ffffffff81283077>] debug_lockdep_rcu_enabled kernel/rcu/update.c:264 [inline]
RIP: 0010:[<ffffffff81283077>] 
c [<ffffffff81283077>] rcu_read_lock_sched_held+0x47/0x120 kernel/rcu/update.c:105
RSP: 0018:ffff8801db207f60  EFLAGS: 00000002
RAX: 0000000000000003 RBX: ffffffff84699440 RCX: 0000000000000002
RDX: 0000000000000000 RSI: ffffffff83c3a540 RDI: ffffffff84a59800
RBP: ffff8801db207f68 R08: 0000000000000001 R09: ffff88021fff9008
R10: ffff88021fff9018 R11: ffff88021fff9010 R12: ffffffff844268c0
R13: ffff8801db200000 R14: ffffffff844268c0 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000c448512500 CR3: 00000001d8491000 CR4: 00000000001406f0
DR0: 0000000020000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000600
Stack:
 0000000000000007
c ffff8801db207f98
c ffffffff8114953c
c ffff8801db221480
c
 ffffffff844268c0
c ffff8801db200000
c ffffffff844268c0
c ffff8801db207fd0
c
 ffffffff811cc626
c ffffffff844268c0
c ffffffff841e2840
c 0000000000000000
c
Call Trace:
 <IRQ> 
d [<ffffffff8114953c>] trace_softirq_raise include/trace/events/irq.h:155 [inline]
 <IRQ> 
d [<ffffffff8114953c>] __raise_softirq_irqoff kernel/softirq.c:443 [inline]
 <IRQ> 
d [<ffffffff8114953c>] raise_softirq_irqoff+0x7c/0x1d0 kernel/softirq.c:417
 [<ffffffff811cc626>] scheduler_ipi+0x376/0x4f0 kernel/sched/core.c:1849
 [<ffffffff810b0586>] __smp_reschedule_interrupt arch/x86/kernel/smp.c:259 [inline]
 [<ffffffff810b0586>] smp_reschedule_interrupt+0x66/0x80 arch/x86/kernel/smp.c:266
 [<ffffffff83967a1c>] reschedule_interrupt+0x8c/0xa0 arch/x86/entry/entry_64.S:732
 <EOI> 
d [<ffffffff83964606>] ? native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:53
 [<ffffffff83963c35>] arch_safe_halt arch/x86/include/asm/paravirt.h:103 [inline]
 [<ffffffff83963c35>] default_idle+0x55/0x360 arch/x86/kernel/process.c:295
 [<ffffffff8106e28a>] arch_cpu_idle+0xa/0x10 arch/x86/kernel/process.c:286
 [<ffffffff83964a56>] default_idle_call+0x36/0x60 kernel/sched/idle.c:97
 [<ffffffff8122837e>] cpuidle_idle_call kernel/sched/idle.c:155 [inline]
 [<ffffffff8122837e>] cpu_idle_loop kernel/sched/idle.c:248 [inline]
 [<ffffffff8122837e>] cpu_startup_entry+0x23e/0x2f0 kernel/sched/idle.c:303
 [<ffffffff839515b9>] rest_init+0x189/0x190 init/main.c:408
 [<ffffffff84a927fb>] start_kernel+0x605/0x62b init/main.c:662
 [<ffffffff84a9129d>] x86_64_start_reservations+0x2a/0x2c arch/x86/kernel/head64.c:196
 [<ffffffff84a913d0>] x86_64_start_kernel+0x131/0x140 arch/x86/kernel/head64.c:177
Code: 
c03 
c0f 
cb6 
c14 
c02 
c48 
c89 
cf8 
c83 
ce0 
c07 
c83 
cc0 
c03 
c38 
cd0 
c7c 
c08 
c84 
cd2 
c0f 
c85 
caa 
c00 
c00 
c00 
c8b 
c0d 
c94 
c67 
c7d 
c03 
c85 
cc9 
c74 
c40 
c48 
cc7 
cc3 
c40 
c94 
c69 
c84 
c<48> 
cb8 
c00 
c00 
c00 
c00 
c00 
cfc 
cff 
cdf 
c48 
c89 
cda 
c48 
cc1 
cea 
c03 
c0f 
cb6 
c14 
c02 
c