INFO: task syz.4.9716:30196 blocked for more than 143 seconds.
      Tainted: G             L      s
      Tainted: G             L      syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.4.9716      state:D stack:27432 pid:30196 tgid:30189 ppid:28418  task_flags:0x400040 flags:0x00080002
Call Trace:
 <TASK>
 __schedule+0x17d4/0x5820
 schedule+0x164/0x2b0
 schedule_preempt_disabled+0x13/0x30
 __mutex_lock+0x7c1/0x1550
 nfsd_nrthreads+0x4c/0xd0
 write_threads+0x216/0x610
 nfsctl_transaction_write+0x10f/0x160
 vfs_write+0x296/0xba0
 ksys_write+0x150/0x270
 do_syscall_64+0x166/0x520
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f9ea939e159
RSP: 002b:00007f9eaa199028 EFLAGS: 00000246 ORIG_RAX: 0000000000000001
RAX: ffffffffffffffda RBX: 00007f9ea9626090 RCX: 00007f9ea939e159
RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000004
RBP: 00007f9ea943506b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9ea9626128 R14: 00007f9ea9626090 R15: 00007ffdc6c129a8
 </TASK>

Showing all locks held in the system:
locks held by pr/ttyS0/16: 2, last CPU#1:
 #0: ffffffff8ec36278 (console_srcu){....}-{0:0}, at: console_srcu_read_lock+0x30/0x60
 #1: ffffffff9ad270d8 (&port_lock_key){-.-.}-{3:3}, at: univ8250_console_device_lock+0x67/0xc0
locks held by khungtaskd/35: 1, last CPU#0:
 #0: ffffffff8ed5c6a0 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180
locks held by kworker/1:3/2015: 4, on CPU#1:
 #0: ffff888161ae4140 ((wq_completion)usb_hub_wq){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630
 #1: ffffc900083f7c40 ((work_completion)(&hub->events)){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630
 #2: ffff88816e5971d8 (&dev->mutex){....}-{4:4}, at: hub_event+0x184/0x4d30
 #3: ffff8881be5861d8 (&dev->mutex){....}-{4:4}, at: __device_attach+0x88/0x450
locks held by kworker/u8:2/5652: 4, last CPU#1:
 #0: ffff8881012d5940 ((wq_completion)netns){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630
 #1: ffffc90004e17c40 (net_cleanup_work){+.+.}-{0:0}, at: process_scheduled_works+0x97a/0x1630
 #2: ffffffff9023eda8 (pernet_ops_rwsem){++++}-{4:4}, at: cleanup_net+0xf5/0x810
 #3: ffffffff9024d600 (rtnl_mutex){+.+.}-{4:4}, at: ops_undo_list+0x28e/0x8d0
locks held by syz.4.9716/30192: 3, on CPU#1:
 #0: ffff8881bdf39cf0 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x246/0x320
 #1: ffff8881927b0460 (sb_writers#32){.+.+}-{0:0}, at: vfs_write+0x22b/0xba0
 #2: ffffffff8f09ba20 (nfsd_mutex){+.+.}-{4:4}, at: write_ports+0xb5/0xd10
locks held by syz.4.9716/30196: 3, on CPU#1:
 #0: ffff8881a375eef0 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x246/0x320
 #1: ffff8881927b0460 (sb_writers#32){.+.+}-{0:0}, at: vfs_write+0x22b/0xba0
 #2: ffffffff8f09ba20 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_nrthreads+0x4c/0xd0
locks held by syz-executor/30649: 2, on CPU#0:
 #0: ffff888115b5a0e8 (&type->s_umount_key#76){++++}-{4:4}, at: deactivate_super+0xac/0xe0
 #1: ffffffff8f09ba20 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_shutdown_threads+0x4e/0xd0
locks held by syz.7.10179/31466: 2, on CPU#1:
 #0: ffff88819679c0e8 (&type->s_umount_key#76){++++}-{4:4}, at: deactivate_super+0xac/0xe0
 #1: ffffffff8f09ba20 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_shutdown_threads+0x4e/0xd0
locks held by syz.6.10843/1116: 3, on CPU#1:
 #0: ffffffff902be2a8 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40
 #1: ffff88819e13d6e8 (nlk_cb_mutex-GENERIC){+.+.}-{4:4}, at: __netlink_dump_start+0xf4/0x7b0
 #2: ffffffff8f09ba20 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_nl_rpc_status_get_dumpit+0xf0/0x1560
locks held by syz.3.10870/1178: 1, on CPU#0:
 #0: ffff88819679c0e8 (&type->s_umount_key#76){++++}-{4:4}, at: super_lock+0x2d6/0x3d0
locks held by udevd/1776: 4, on CPU#0:
 #0: ffff88801edc6bd8 (&p->lock){+.+.}-{4:4}, at: seq_read_iter+0xa4/0xca0
 #1: ffff88810d6ca880 (&of->mutex#2){+.+.}-{4:4}, at: kernfs_seq_start+0x5d/0x420
 #2: ffff888175bfdb48 (kn->active#30){++++}-{0:0}, at: kernfs_seq_start+0xb2/0x420
 #3: ffff8881be5861d8 (&dev->mutex){....}-{4:4}, at: manufacturer_show+0x26/0xa0

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

NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 35 Comm: khungtaskd Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
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+0xe8/0x150
 nmi_cpu_backtrace+0x274/0x2d0
 nmi_trigger_cpumask_backtrace+0x17d/0x390
 sys_info+0x135/0x170
 watchdog+0xfd7/0x1030
 kthread+0x38b/0x480
 ret_from_fork+0x514/0xb70
 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: 16 Comm: pr/ttyS0 Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.2-debian-1.16.2-1 04/01/2014
RIP: 0010:io_serial_out+0x7c/0xc0
Code: 52 57 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 4c 05 c7 fc 41 03 2e 89 d8 89 ea ee <5b> 41 5c 41 5e 41 5f 5d c3 cc cc cc cc cc 44 89 f9 80 e1 07 38 c1
RSP: 0018:ffffc90000157900 EFLAGS: 00000002
RAX: 000000000000000a RBX: 000000000000000a RCX: 0000000000000000
RDX: 00000000000003f8 RSI: 0000000000000000 RDI: 0000000000000020
RBP: 00000000000003f8 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: ffffffff85705b30 R12: dffffc0000000000
R13: 000000000000000a R14: ffffffff9ad27100 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8882a8ce4000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007f7d507eb840 CR3: 000000016b522000 CR4: 00000000000006f0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000600
Call Trace:
 <TASK>
 __serial8250_console_fifo_write+0x1e6/0x3e0
 serial8250_console_write+0xaa1/0x1200
 nbcon_emit_next_record+0xef5/0x1a90
 nbcon_kthread_func+0x679/0x880
 kthread+0x38b/0x480
 ret_from_fork+0x514/0xb70
 ret_from_fork_asm+0x1a/0x30
 </TASK>
