syzbot

INFO: task syz-executor:20193 blocked for more than 144 seconds.
      Tainted: G     U       L      syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz-executor    state:D stack:24296 pid:20193 tgid:20193 ppid:1      task_flags:0x400140 flags:0x00080002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5388 [inline]
 __schedule+0x1295/0x67a0 kernel/sched/core.c:7189
 __schedule_loop kernel/sched/core.c:7268 [inline]
 schedule+0xdd/0x390 kernel/sched/core.c:7283
 schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7340
 __mutex_lock_common kernel/locking/mutex.c:726 [inline]
 __mutex_lock+0xced/0x1b10 kernel/locking/mutex.c:820
 nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:576
 nfsd_umount+0x3b/0x60 fs/nfsd/nfsctl.c:1364
 deactivate_locked_super+0xc1/0x1b0 fs/super.c:476
 deactivate_super fs/super.c:509 [inline]
 deactivate_super+0xe7/0x110 fs/super.c:505
 cleanup_mnt+0x21f/0x450 fs/namespace.c:1312
 task_work_run+0x150/0x240 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:67 [inline]
 exit_to_user_mode_loop+0x157/0x670 kernel/entry/common.c:98
 __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:318 [inline]
 do_syscall_64+0x652/0x840 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fe9f199e097
RSP: 002b:00007ffd278dc888 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: 0000000000000000 RBX: 00007fe9f1a321ca RCX: 00007fe9f199e097
RDX: 0000000000000000 RSI: 0000000000000009 RDI: 00007ffd278dc940
RBP: 00007ffd278dc940 R08: 00007ffd278dd940 R09: 00000000ffffffff
R10: 0000000000000000 R11: 0000000000000246 R12: 00007ffd278dd9d0
R13: 00007fe9f1a321ca R14: 00000000001069e3 R15: 00007ffd278dda10
 </TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/31:
 #0: ffffffff8e7e5360 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
 #0: ffffffff8e7e5360 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:838 [inline]
 #0: ffffffff8e7e5360 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x3d/0x184 kernel/locking/lockdep.c:6775
2 locks held by getty/6240:
 #0: ffff8880378c60a0 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_ref_wait+0x24/0x80 drivers/tty/tty_ldisc.c:243
 #1: ffffc900054792e8 (&ldata->atomic_read_lock){+.+.}-{4:4}, at: n_tty_read+0x419/0x14f0 drivers/tty/n_tty.c:2211
1 lock held by syz.0.703/9386:
2 locks held by syz-executor/15704:
 #0: ffff888032ad20d8 (&type->s_umount_key#54){++++}-{4:4}, at: __super_lock fs/super.c:58 [inline]
 #0: ffff888032ad20d8 (&type->s_umount_key#54){++++}-{4:4}, at: __super_lock_excl fs/super.c:73 [inline]
 #0: ffff888032ad20d8 (&type->s_umount_key#54){++++}-{4:4}, at: deactivate_super fs/super.c:508 [inline]
 #0: ffff888032ad20d8 (&type->s_umount_key#54){++++}-{4:4}, at: deactivate_super+0xdf/0x110 fs/super.c:505
 #1: ffffffff8ec621e0 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:576
2 locks held by syz.1.2759/20168:
 #0: ffffffff906b4888 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1217
 #1: ffffffff8ec621e0 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_nl_threads_set_doit+0x8c8/0x1100 fs/nfsd/nfsctl.c:1644
2 locks held by syz-executor/20193:
 #0: ffff8880322b20d8 (&type->s_umount_key#54){++++}-{4:4}, at: __super_lock fs/super.c:58 [inline]
 #0: ffff8880322b20d8 (&type->s_umount_key#54){++++}-{4:4}, at: __super_lock_excl fs/super.c:73 [inline]
 #0: ffff8880322b20d8 (&type->s_umount_key#54){++++}-{4:4}, at: deactivate_super fs/super.c:508 [inline]
 #0: ffff8880322b20d8 (&type->s_umount_key#54){++++}-{4:4}, at: deactivate_super+0xdf/0x110 fs/super.c:505
 #1: ffffffff8ec621e0 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:576
2 locks held by syz-executor/20374:
 #0: ffff88807c86c0d8 (&type->s_umount_key#54){++++}-{4:4}, at: __super_lock fs/super.c:58 [inline]
 #0: ffff88807c86c0d8 (&type->s_umount_key#54){++++}-{4:4}, at: __super_lock_excl fs/super.c:73 [inline]
 #0: ffff88807c86c0d8 (&type->s_umount_key#54){++++}-{4:4}, at: deactivate_super fs/super.c:508 [inline]
 #0: ffff88807c86c0d8 (&type->s_umount_key#54){++++}-{4:4}, at: deactivate_super+0xdf/0x110 fs/super.c:505
 #1: ffffffff8ec621e0 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:576
2 locks held by syz-executor/20889:
 #0: ffff88803534c0d8 (&type->s_umount_key#54){++++}-{4:4}, at: __super_lock fs/super.c:58 [inline]
 #0: ffff88803534c0d8 (&type->s_umount_key#54){++++}-{4:4}, at: __super_lock_excl fs/super.c:73 [inline]
 #0: ffff88803534c0d8 (&type->s_umount_key#54){++++}-{4:4}, at: deactivate_super fs/super.c:508 [inline]
 #0: ffff88803534c0d8 (&type->s_umount_key#54){++++}-{4:4}, at: deactivate_super+0xdf/0x110 fs/super.c:505
 #1: ffffffff8ec621e0 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:576
2 locks held by syz.3.2874/20932:
 #0: ffff88809320c0d8 (&type->s_umount_key#54){++++}-{4:4}, at: __super_lock fs/super.c:58 [inline]
 #0: ffff88809320c0d8 (&type->s_umount_key#54){++++}-{4:4}, at: __super_lock_excl fs/super.c:73 [inline]
 #0: ffff88809320c0d8 (&type->s_umount_key#54){++++}-{4:4}, at: deactivate_super fs/super.c:508 [inline]
 #0: ffff88809320c0d8 (&type->s_umount_key#54){++++}-{4:4}, at: deactivate_super+0xdf/0x110 fs/super.c:505
 #1: ffffffff8ec621e0 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:576
2 locks held by syz-executor/21121:
 #0: ffff88802af200d8 (&type->s_umount_key#54){++++}-{4:4}, at: __super_lock fs/super.c:58 [inline]
 #0: ffff88802af200d8 (&type->s_umount_key#54){++++}-{4:4}, at: __super_lock_excl fs/super.c:73 [inline]
 #0: ffff88802af200d8 (&type->s_umount_key#54){++++}-{4:4}, at: deactivate_super fs/super.c:508 [inline]
 #0: ffff88802af200d8 (&type->s_umount_key#54){++++}-{4:4}, at: deactivate_super+0xdf/0x110 fs/super.c:505
 #1: ffffffff8ec621e0 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:576
4 locks held by syz.2.3121/22490:
2 locks held by syz.2.3121/22496:

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

NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 31 Comm: khungtaskd Tainted: G     U       L      syzkaller #0 PREEMPT(full) 
Tainted: [U]=USER, [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 nmi_cpu_backtrace.cold+0x12d/0x151 lib/nmi_backtrace.c:113
 nmi_trigger_cpumask_backtrace+0x1d7/0x230 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:162 [inline]
 __sys_info lib/sys_info.c:157 [inline]
 sys_info+0x141/0x190 lib/sys_info.c:165
 check_hung_uninterruptible_tasks kernel/hung_task.c:353 [inline]
 watchdog+0xcb1/0x1030 kernel/hung_task.c:561
 kthread+0x370/0x450 kernel/kthread.c:436
 ret_from_fork+0x72b/0xd50 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>