INFO: task syz.0.1791:15920 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.0.1791      state:D stack:25968 pid:15920 tgid:15919 ppid:11397  task_flags:0x400140 flags:0x00004004
Call Trace:
 <TASK>
 __schedule+0x1798/0x4cc0
 schedule+0x165/0x360
 schedule_preempt_disabled+0x13/0x30
 __mutex_lock+0x7e6/0x1350
 sync_bdevs+0x1ac/0x340
 ksys_sync+0xb9/0x150
 __ia32_sys_sync+0xe/0x20
 do_syscall_64+0xfa/0x3b0
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f4057d8ebe9
RSP: 002b:00007f4058b31038 EFLAGS: 00000246 ORIG_RAX: 00000000000000a2
RAX: ffffffffffffffda RBX: 00007f4057fc5fa0 RCX: 00007f4057d8ebe9
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00007f4057fc5fa0 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f4057fc6038 R14: 00007f4057fc5fa0 R15: 00007ffebf0ef748
 </TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/34:
 #0: ffffffff8e139f20 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180
5 locks held by kworker/1:2/793:
 #0: ffff88801b771548 ((wq_completion)usb_hub_wq){+.+.}-{0:0}, at: process_scheduled_works+0x9b4/0x17b0
 #1: ffffc90004fd7bc0 ((work_completion)(&hub->events)){+.+.}-{0:0}, at: process_scheduled_works+0x9ef/0x17b0
 #2: ffff888109531198 (&dev->mutex){....}-{4:4}, at: hub_event+0x184/0x4a20
 #3: ffff888036243198 (&dev->mutex){....}-{4:4}, at: __device_attach+0x88/0x400
 #4: ffff888036245160 (&dev->mutex){....}-{4:4}, at: __device_attach+0x88/0x400
2 locks held by getty/5672:
 #0: ffff888106cb10a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70
 #1: ffffc900029062f0 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x43e/0x1400
1 lock held by udevd/6035:
 #0: ffff88802216f358 (&disk->open_mutex){+.+.}-{4:4}, at: bdev_open+0xe0/0xd30
1 lock held by udevd/6806:
 #0: ffff888107d73358 (&disk->open_mutex){+.+.}-{4:4}, at: bdev_open+0xe0/0xd30
1 lock held by syz.0.1791/15920:
 #0: ffff88802216f358 (&disk->open_mutex){+.+.}-{4:4}, at: sync_bdevs+0x1ac/0x340
2 locks held by dhcpcd/18854:
 #0: ffff88803b982258 (sk_lock-AF_PACKET){+.+.}-{0:0}, at: packet_do_bind+0x32/0xcd0
 #1: ffffffff8e13f9b8 (rcu_state.exp_mutex){+.+.}-{4:4}, at: synchronize_rcu_expedited+0x2f6/0x730

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

NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 34 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Call Trace:
 <TASK>
 dump_stack_lvl+0x189/0x250
 nmi_cpu_backtrace+0x39e/0x3d0
 nmi_trigger_cpumask_backtrace+0x17a/0x300
 watchdog+0xf93/0xfe0
 kthread+0x711/0x8a0
 ret_from_fork+0x3fc/0x770
 ret_from_fork_asm+0x1a/0x30
 </TASK>
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 793 Comm: kworker/1:2 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
Workqueue: usb_hub_wq hub_event
RIP: 0010:io_serial_out+0x7c/0xc0
Code: 72 70 fc 44 89 f9 d3 e5 49 83 c6 40 4c 89 f0 48 c1 e8 03 42 80 3c 20 00 74 08 4c 89 f7 e8 bc e0 d3 fc 41 03 2e 89 d8 89 ea ee <5b> 41 5c 41 5e 41 5f 5d e9 97 6f 2d 06 cc 44 89 f9 80 e1 07 38 c1
RSP: 0018:ffffc90004fd6090 EFLAGS: 00000002
RAX: 0000000000000035 RBX: 0000000000000035 RCX: 0000000000000000
RDX: 00000000000003f8 RSI: 000000000002f98f RDI: 000000000002f990
RBP: 00000000000003f8 R08: ffff888020df8237 R09: 1ffff110041bf046
R10: dffffc0000000000 R11: ffffffff854f3b00 R12: dffffc0000000000
R13: ffffffff99afd8c9 R14: ffffffff99df2420 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8881a3c18000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffd2ab7faf8 CR3: 00000000455e8000 CR4: 00000000000006f0
Call Trace:
 <TASK>
 serial8250_console_write+0x1410/0x1ba0
 console_flush_all+0x728/0xc40
 console_unlock+0xc4/0x270
 vprintk_emit+0x5b7/0x7a0
 dev_vprintk_emit+0x337/0x3f0
 dev_printk_emit+0xe0/0x130
 _dev_info+0x10a/0x160
 usb_serial_device_probe+0x2b4/0x2e0
 really_probe+0x26d/0x9e0
 __driver_probe_device+0x18c/0x2f0
 driver_probe_device+0x4f/0x430
 __device_attach_driver+0x2ce/0x530
 bus_for_each_drv+0x251/0x2e0
 __device_attach+0x2b8/0x400
 bus_probe_device+0x185/0x260
 device_add+0x7b6/0xb50
 usb_serial_probe+0x26cb/0x2d20
 usb_probe_interface+0x668/0xc30
 really_probe+0x26d/0x9e0
 __driver_probe_device+0x18c/0x2f0
 driver_probe_device+0x4f/0x430
 __device_attach_driver+0x2ce/0x530
 bus_for_each_drv+0x251/0x2e0
 __device_attach+0x2b8/0x400
 bus_probe_device+0x185/0x260
 device_add+0x7b6/0xb50
 usb_set_configuration+0x1a87/0x20e0
 usb_generic_driver_probe+0x8d/0x150
 usb_probe_device+0x1c4/0x390
 really_probe+0x26d/0x9e0
 __driver_probe_device+0x18c/0x2f0
 driver_probe_device+0x4f/0x430
 __device_attach_driver+0x2ce/0x530
 bus_for_each_drv+0x251/0x2e0
 __device_attach+0x2b8/0x400
 bus_probe_device+0x185/0x260
 device_add+0x7b6/0xb50
 usb_new_device+0xa39/0x16f0
 hub_event+0x2958/0x4a20
 process_scheduled_works+0xae1/0x17b0
 worker_thread+0x8a0/0xda0
 kthread+0x711/0x8a0
 ret_from_fork+0x3fc/0x770
 ret_from_fork_asm+0x1a/0x30
 </TASK>
