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-executor0:15157 blocked for more than 120 seconds. Not tainted 4.16.0-rc7+ #371 "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. syz-executor0 D23360 15157 11491 0x00000004 Call Trace: context_switch kernel/sched/core.c:2862 [inline] __schedule+0x8fb/0x1ec0 kernel/sched/core.c:3440 schedule+0xf5/0x430 kernel/sched/core.c:3499 schedule_preempt_disabled+0x10/0x20 kernel/sched/core.c:3557 __mutex_lock_common kernel/locking/mutex.c:833 [inline] __mutex_lock+0xaad/0x1a80 kernel/locking/mutex.c:893 mutex_lock_nested+0x16/0x20 kernel/locking/mutex.c:908 iterate_bdevs+0xc8/0x260 fs/block_dev.c:2160 sys_sync+0x120/0x1c0 fs/sync.c:117 do_syscall_64+0x281/0x940 arch/x86/entry/common.c:287 entry_SYSCALL_64_after_hwframe+0x42/0xb7 RIP: 0033:0x4548b9 RSP: 002b:00007fc1039dfc68 EFLAGS: 00000246 ORIG_RAX: 00000000000000a2 RAX: ffffffffffffffda RBX: 00007fc1039e06d4 RCX: 00000000004548b9 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 RBP: 000000000072bea0 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00000000ffffffff R13: 000000000000064b R14: 00000000006fb7a8 R15: 0000000000000000 Showing all locks held in the system: 2 locks held by khungtaskd/869: #0: (rcu_read_lock){....}, at: [<0000000014fc6910>] check_hung_uninterruptible_tasks kernel/hung_task.c:175 [inline] #0: (rcu_read_lock){....}, at: [<0000000014fc6910>] watchdog+0x1c5/0xd60 kernel/hung_task.c:249 #1: (tasklist_lock){.+.+}, at: [<00000000e93d37c7>] debug_show_all_locks+0xd3/0x3d0 kernel/locking/lockdep.c:4470 2 locks held by getty/4388: #0: (&tty->ldisc_sem){++++}, at: [<0000000027113621>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365 #1: (&ldata->atomic_read_lock){+.+.}, at: [<0000000060cfcdc9>] n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131 2 locks held by getty/4389: #0: (&tty->ldisc_sem){++++}, at: [<0000000027113621>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365 #1: (&ldata->atomic_read_lock){+.+.}, at: [<0000000060cfcdc9>] n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131 2 locks held by getty/4390: #0: (&tty->ldisc_sem){++++}, at: [<0000000027113621>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365 #1: (&ldata->atomic_read_lock){+.+.}, at: [<0000000060cfcdc9>] n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131 2 locks held by getty/4391: #0: (&tty->ldisc_sem){++++}, at: [<0000000027113621>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365 #1: (&ldata->atomic_read_lock){+.+.}, at: [<0000000060cfcdc9>] n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131 2 locks held by getty/4392: #0: (&tty->ldisc_sem){++++}, at: [<0000000027113621>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365 #1: (&ldata->atomic_read_lock){+.+.}, at: [<0000000060cfcdc9>] n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131 2 locks held by getty/4393: #0: (&tty->ldisc_sem){++++}, at: [<0000000027113621>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365 #1: (&ldata->atomic_read_lock){+.+.}, at: [<0000000060cfcdc9>] n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131 2 locks held by getty/4394: #0: (&tty->ldisc_sem){++++}, at: [<0000000027113621>] ldsem_down_read+0x37/0x40 drivers/tty/tty_ldsem.c:365 #1: (&ldata->atomic_read_lock){+.+.}, at: [<0000000060cfcdc9>] n_tty_read+0x2ef/0x1a40 drivers/tty/n_tty.c:2131 3 locks held by kworker/u4:5/7037: #0: ((wq_completion)"writeback"){+.+.}, at: [<000000002aa4cb8c>] work_static include/linux/workqueue.h:198 [inline] #0: ((wq_completion)"writeback"){+.+.}, at: [<000000002aa4cb8c>] set_work_data kernel/workqueue.c:619 [inline] #0: ((wq_completion)"writeback"){+.+.}, at: [<000000002aa4cb8c>] set_work_pool_and_clear_pending kernel/workqueue.c:646 [inline] #0: ((wq_completion)"writeback"){+.+.}, at: [<000000002aa4cb8c>] process_one_work+0xb12/0x1bb0 kernel/workqueue.c:2084 #1: ((work_completion)(&(&wb->dwork)->work)){+.+.}, at: [<000000006fbdb881>] process_one_work+0xb89/0x1bb0 kernel/workqueue.c:2088 #2: (&type->s_umount_key#33){++++}, at: [<00000000e693be94>] trylock_super+0x20/0x100 fs/super.c:395 1 lock held by blkid/14876: #0: (&bdev->bd_mutex){+.+.}, at: [<00000000287e5820>] blkdev_put+0x2a/0x4f0 fs/block_dev.c:1808 1 lock held by syz-executor0/15157: #0: (&bdev->bd_mutex){+.+.}, at: [<00000000f9824cf0>] iterate_bdevs+0xc8/0x260 fs/block_dev.c:2160 1 lock held by syz-executor0/15180: #0: (&bdev->bd_mutex){+.+.}, at: [<00000000f9824cf0>] iterate_bdevs+0xc8/0x260 fs/block_dev.c:2160 4 locks held by kworker/u4:7/15203: #0: ((wq_completion)"%s""netns"){+.+.}, at: [<000000002aa4cb8c>] work_static include/linux/workqueue.h:198 [inline] #0: ((wq_completion)"%s""netns"){+.+.}, at: [<000000002aa4cb8c>] set_work_data kernel/workqueue.c:619 [inline] #0: ((wq_completion)"%s""netns"){+.+.}, at: [<000000002aa4cb8c>] set_work_pool_and_clear_pending kernel/workqueue.c:646 [inline] #0: ((wq_completion)"%s""netns"){+.+.}, at: [<000000002aa4cb8c>] process_one_work+0xb12/0x1bb0 kernel/workqueue.c:2084 #1: (net_cleanup_work){+.+.}, at: [<000000006fbdb881>] process_one_work+0xb89/0x1bb0 kernel/workqueue.c:2088 #2: (net_mutex){+.+.}, at: [<0000000002a5c8f0>] cleanup_net+0x242/0xcb0 net/core/net_namespace.c:484 #3: (rcu_sched_state.barrier_mutex){+.+.}, at: [<000000005b225be8>] _rcu_barrier+0x142/0x750 kernel/rcu/tree.c:3517 ============================================= NMI backtrace for cpu 1 CPU: 1 PID: 869 Comm: khungtaskd Not tainted 4.16.0-rc7+ #371 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011 Call Trace: __dump_stack lib/dump_stack.c:17 [inline] dump_stack+0x194/0x24d lib/dump_stack.c:53 nmi_cpu_backtrace+0x1d2/0x210 lib/nmi_backtrace.c:103 nmi_trigger_cpumask_backtrace+0x123/0x180 lib/nmi_backtrace.c:62 arch_trigger_cpumask_backtrace+0x14/0x20 arch/x86/kernel/apic/hw_nmi.c:38 trigger_all_cpu_backtrace include/linux/nmi.h:138 [inline] check_hung_task kernel/hung_task.c:132 [inline] check_hung_uninterruptible_tasks kernel/hung_task.c:190 [inline] watchdog+0x90c/0xd60 kernel/hung_task.c:249 kthread+0x33c/0x400 kernel/kthread.c:238 ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:406 Sending NMI from CPU 1 to CPUs 0: NMI backtrace for cpu 0 skipped: idling at native_safe_halt+0x6/0x10 arch/x86/include/asm/irqflags.h:54