INFO: task syz.6.3971:21166 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.6.3971      state:D stack:28488 pid:21166 tgid:21165 ppid:11977  task_flags:0x400140 flags:0x00080002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5581 [inline]
 __schedule+0x1b47/0x5b40 kernel/sched/core.c:7384
 __schedule_loop kernel/sched/core.c:7461 [inline]
 schedule+0x164/0x2b0 kernel/sched/core.c:7476
 schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7533
 __mutex_lock_common kernel/locking/mutex.c:726 [inline]
 __mutex_lock+0x7c4/0x15a0 kernel/locking/mutex.c:821
 nfsd_shutdown_threads+0x4e/0xd0 fs/nfsd/nfssvc.c:590
 nfsd_umount+0x41/0x60 fs/nfsd/nfsctl.c:1379
 deactivate_locked_super+0xbe/0x110 fs/super.c:586
 cleanup_mnt+0x3d3/0x460 fs/namespace.c:1329
 task_work_run+0x1d9/0x260 kernel/task_work.c:233
 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline]
 __exit_to_user_mode_loop kernel/entry/common.c:70 [inline]
 exit_to_user_mode_loop+0x204/0x770 kernel/entry/common.c:101
 __exit_to_user_mode_prepare include/linux/irq-entry-common.h:207 [inline]
 syscall_exit_to_user_mode_prepare include/linux/irq-entry-common.h:230 [inline]
 syscall_exit_to_user_mode include/linux/entry-common.h:343 [inline]
 do_syscall_64+0x328/0x520 arch/x86/entry/syscall_64.c:89
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f1be819e159
RSP: 002b:00007f1be8fb4028 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
RAX: fffffffffffffffe RBX: 00007f1be8425fa0 RCX: 00007f1be819e159
RDX: 0000200000000080 RSI: 0000200000000040 RDI: 0000000000000000
RBP: 00007f1be823506b R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f1be8426038 R14: 00007f1be8425fa0 R15: 00007fff3db27778
 </TASK>

Showing all locks held in the system:
locks held by khungtaskd/34: 1, last CPU#0:
 #0: ffffffff8ed5c620 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:309 [inline]
 #0: ffffffff8ed5c620 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
 #0: ffffffff8ed5c620 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x2e/0x180 kernel/locking/lockdep.c:6871
locks held by getty/5369: 2, on CPU#1:
 #0: ffff888035f030a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x25/0x70 drivers/tty/tty_ldisc.c:243
 #1: ffffc900032332e8 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x45a/0x1360 drivers/tty/n_tty.c:2211
locks held by syz.9.3945/21070: 3, on CPU#0:
 #0: ffff8880339500f0 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x118/0x160 fs/file.c:1408
 #1: ffff888031742460 (sb_writers#27){.+.+}-{0:0}, at: file_start_write include/linux/fs.h:2753 [inline]
 #1: ffff888031742460 (sb_writers#27){.+.+}-{0:0}, at: vfs_write+0x22b/0xba0 fs/read_write.c:683
 #2: ffffffff8f09fd40 (nfsd_mutex){+.+.}-{4:4}, at: write_ports+0xb5/0xd10 fs/nfsd/nfsctl.c:874
locks held by syz.6.3971/21166: 2, on CPU#0:
 #0: ffff88807fd7c0e8 (&type->s_umount_key#92){+.+.}-{4:4}, at: __super_lock fs/super.c:60 [inline]
 #0: ffff88807fd7c0e8 (&type->s_umount_key#92){+.+.}-{4:4}, at: __super_lock_excl fs/super.c:75 [inline]
 #0: ffff88807fd7c0e8 (&type->s_umount_key#92){+.+.}-{4:4}, at: deactivate_super+0xac/0xe0 fs/super.c:613
 #1: ffffffff8f09fd40 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_shutdown_threads+0x4e/0xd0 fs/nfsd/nfssvc.c:590

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

NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 34 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 nmi_cpu_backtrace+0x274/0x2d0 lib/nmi_backtrace.c:123
 nmi_trigger_cpumask_backtrace+0x17d/0x390 lib/nmi_backtrace.c:66
 trigger_all_cpu_backtrace include/linux/nmi.h:164 [inline]
 __sys_info lib/sys_info.c:157 [inline]
 sys_info+0x135/0x170 lib/sys_info.c:165
 check_hung_uninterruptible_tasks kernel/hung_task.c:377 [inline]
 watchdog+0x1058/0x10d0 kernel/hung_task.c:598
 kthread+0x38b/0x480 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>