unregister_netdevice: waiting for lo to become free. Usage count = 3
INFO: task syz-executor4:15707 blocked for more than 120 seconds.
      Not tainted 4.9.39-gf44842e #5
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
syz-executor4   D28912 15707   3447 0x00000004
 ffff8801d0bc5e00 0000000000000000 ffff8801d92cac00 ffffffff844268c0
 ffff8801db221498 ffff8801d446fa18 ffffffff83954a3b 0000000000000000
 0000000000000007 00ff8801d0bc5e00 ffff8801db221db0 ffff8801db221dd8
Call Trace:
 [<ffffffff83955ff2>] schedule+0x92/0x1b0 kernel/sched/core.c:3624
 [<ffffffff83956963>] schedule_preempt_disabled+0x13/0x20 kernel/sched/core.c:3657
 [<ffffffff8395bcbf>] __mutex_lock_common kernel/locking/mutex.c:582 [inline]
 [<ffffffff8395bcbf>] 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
 [<ffffffff8396598d>] entry_SYSCALL64_slow_path+0x25/0x25

Showing all locks held in the system:
3 locks held by kworker/u4:0/6:
 #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
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/3329:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff83963aa2>] 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/3330:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff83963aa2>] 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/3331:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff83963aa2>] 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/3332:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff83963aa2>] 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/3333:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff83963aa2>] 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/3334:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff83963aa2>] 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
1 lock held by syz-executor4/15707:
 #0:  (net_mutex){+.+.+.}, at: [<ffffffff82f413f5>] copy_net_ns+0x155/0x280 net/core/net_namespace.c:387
2 locks held by getty/15708:
 #0:  (&tty->ldisc_sem){++++++}, at: [<ffffffff83963aa2>] 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

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

NMI backtrace for cpu 1
CPU: 1 PID: 548 Comm: khungtaskd Not tainted 4.9.39-gf44842e #5
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
 ffff8801d8a2fd00 ffffffff81eacd59 0000000000000000 0000000000000001
 0000000000000001 0000000000000001 ffffffff810bf310 ffff8801d8a2fd38
 ffffffff81eb7cad 0000000000000001 0000000000000000 ffff8801d0bc6198
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
 [<ffffffff83965b5a>] 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-gf44842e #5
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
task: ffffffff844268c0 task.stack: ffffffff84400000
RIP: 0010:[<ffffffff81f13680>] 
c [<ffffffff81f13680>] debug_smp_processor_id+0x0/0x20 include/linux/bitmap.h:269
RSP: 0018:ffff8801db207fa0  EFLAGS: 00000046
RAX: 0000000000000046 RBX: ffffffff84a48e48 RCX: 0000000000000000
RDX: 0000000000000000 RSI: 0000000000000001 RDI: ffffffff844270fc
RBP: ffff8801db207fb8 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: ffffffff84a596b8 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8801db200000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000c00005f210 CR3: 00000001c9aa6000 CR4: 00000000001406f0
DR0: 0000000020001008 DR1: 0000000020000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Stack:
 ffffffff81291d10
c 0000000000000000
c ffffffff84a48e48
c ffff8801db207fd0
c
 ffffffff8114926a
c ffffffff84a48e48
c ffff8801db207fe8
c ffffffff810b052a
c
 ffffffff84a48e48
c ffffffff84407e28
c ffffffff8396795c
c ffffffff84407d78
c
Call Trace:
 [<ffffffff8114926a>] irq_enter+0xa/0xd0 kernel/softirq.c:338
 [<ffffffff810b052a>] smp_reschedule_interrupt+0xa/0x80 arch/x86/kernel/smp.c:264
 [<ffffffff8396795c>] reschedule_interrupt+0x8c/0xa0 arch/x86/entry/entry_64.S:732
 <EOI> 
d [<ffffffff83964516>] ? native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:53
 [<ffffffff83963b45>] arch_safe_halt arch/x86/include/asm/paravirt.h:103 [inline]
 [<ffffffff83963b45>] default_idle+0x55/0x360 arch/x86/kernel/process.c:295
 [<ffffffff8106e28a>] arch_cpu_idle+0xa/0x10 arch/x86/kernel/process.c:286
 [<ffffffff83964966>] 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
 [<ffffffff839514c9>] 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: 
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c<55> 
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c