syzbot

INFO: task syz.5.2909:21673 blocked for more than 143 seconds.
      Tainted: G             L      syzkaller #0
      Blocked by coredump.
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:syz.5.2909      state:D stack:25096 pid:21673 tgid:21669 ppid:17483  task_flags:0x40054c flags:0x00080001
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5510 [inline]
 __schedule+0x125c/0x6730 kernel/sched/core.c:7234
 __schedule_loop kernel/sched/core.c:7311 [inline]
 schedule+0xdd/0x2c0 kernel/sched/core.c:7326
 schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7383
 __mutex_lock_common kernel/locking/mutex.c:726 [inline]
 __mutex_lock+0xccc/0x1bd0 kernel/locking/mutex.c:821
 nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:576
 nfsd_umount+0x3b/0x60 fs/nfsd/nfsctl.c:1365
 deactivate_locked_super+0xc1/0x1b0 fs/super.c:477
 deactivate_super fs/super.c:510 [inline]
 deactivate_super+0xe7/0x110 fs/super.c:506
 cleanup_mnt+0x21f/0x450 fs/namespace.c:1317
 task_work_run+0x150/0x240 kernel/task_work.c:233
 exit_task_work include/linux/task_work.h:40 [inline]
 do_exit+0x951/0x2ae0 kernel/exit.c:1009
 do_group_exit+0xd5/0x2a0 kernel/exit.c:1152
 get_signal+0x1ec7/0x21e0 kernel/signal.c:3046
 arch_do_signal_or_restart+0x91/0x7a0 arch/x86/kernel/signal.c:337
 __exit_to_user_mode_loop kernel/entry/common.c:66 [inline]
 exit_to_user_mode_loop+0x139/0x6f0 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:318 [inline]
 do_syscall_64+0x652/0x840 arch/x86/entry/syscall_64.c:100
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f85dfd9de59
RSP: 002b:00007f85e0c07028 EFLAGS: 00000246 ORIG_RAX: 0000000000000117
RAX: fffffffffffffff2 RBX: 00007f85e0026090 RCX: 00007f85dfd9de59
RDX: 0000000000000000 RSI: 0002000000000003 RDI: 0000000000000001
RBP: 00007f85dfe33e6f R08: 0000000000000000 R09: 8000400000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f85e0026128 R14: 00007f85e0026090 R15: 00007ffe471a1468
 </TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/31:
 #0: ffffffff8ebe5f00 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:300 [inline]
 #0: ffffffff8ebe5f00 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:840 [inline]
 #0: ffffffff8ebe5f00 (rcu_read_lock){....}-{1:3}, at: debug_show_all_locks+0x3d/0x184 kernel/locking/lockdep.c:6775
2 locks held by khugepaged/38:
3 locks held by kworker/0:7/5778:
 #0: ffff88801bc07140 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x12b1/0x1940 kernel/workqueue.c:3297
 #1: ffffc9000448fd08 ((fqdir_free_work).work){+.+.}-{0:0}, at: process_one_work+0x988/0x1940 kernel/workqueue.c:3298
 #2: ffffffff8ebf1878 (rcu_state.barrier_mutex){+.+.}-{4:4}, at: rcu_barrier+0x48/0x6d0 kernel/rcu/tree.c:3857
5 locks held by kworker/u10:36/14912:
 #0: ffff88801caf6140 ((wq_completion)netns){+.+.}-{0:0}, at: process_one_work+0x12b1/0x1940 kernel/workqueue.c:3297
 #1: ffffc90004e3fd08 (net_cleanup_work){+.+.}-{0:0}, at: process_one_work+0x988/0x1940 kernel/workqueue.c:3298
 #2: ffffffff90a858a8 (pernet_ops_rwsem){++++}-{4:4}, at: cleanup_net+0xb8/0x920 net/core/net_namespace.c:673
 #3: ffffffff8ebf1878 (rcu_state.barrier_mutex){+.+.}-{4:4}, at: rcu_barrier+0x48/0x6d0 kernel/rcu/tree.c:3857
 #4: ffff8880b843b660 (&rq->__lock){-.-.}-{2:2}, at: raw_spin_rq_lock_nested+0x2c/0x140 kernel/sched/core.c:667
3 locks held by kworker/0:0/17044:
 #0: ffff88801bc07140 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x12b1/0x1940 kernel/workqueue.c:3297
 #1: ffffc9000354fd08 (free_ipc_work){+.+.}-{0:0}, at: process_one_work+0x988/0x1940 kernel/workqueue.c:3298
 #2: ffffffff8ebf19a8 (rcu_state.exp_mutex){+.+.}-{4:4}, at: exp_funnel_lock+0x19e/0x3c0 kernel/rcu/tree_exp.h:343
2 locks held by syz-executor/18745:
 #0: ffff888029a2e0d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: __super_lock fs/super.c:58 [inline]
 #0: ffff888029a2e0d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: __super_lock_excl fs/super.c:73 [inline]
 #0: ffff888029a2e0d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: deactivate_super fs/super.c:509 [inline]
 #0: ffff888029a2e0d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: deactivate_super+0xdf/0x110 fs/super.c:506
 #1: ffffffff8f06f220 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:576
2 locks held by syz.5.2909/21673:
 #0: ffff88807a9fa0d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: __super_lock fs/super.c:58 [inline]
 #0: ffff88807a9fa0d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: __super_lock_excl fs/super.c:73 [inline]
 #0: ffff88807a9fa0d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: deactivate_super fs/super.c:509 [inline]
 #0: ffff88807a9fa0d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: deactivate_super+0xdf/0x110 fs/super.c:506
 #1: ffffffff8f06f220 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:576
2 locks held by syz.4.3048/22438:
 #0: ffffffff90b4d0c8 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1217
 #1: ffffffff8f06f220 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_nl_listener_set_doit+0xd5/0x1a80 fs/nfsd/nfsctl.c:1964
2 locks held by syz-executor/22609:
 #0: ffff888052bc20d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: __super_lock fs/super.c:58 [inline]
 #0: ffff888052bc20d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: __super_lock_excl fs/super.c:73 [inline]
 #0: ffff888052bc20d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: deactivate_super fs/super.c:509 [inline]
 #0: ffff888052bc20d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: deactivate_super+0xdf/0x110 fs/super.c:506
 #1: ffffffff8f06f220 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:576
2 locks held by syz-executor/22832:
 #0: ffff88807a4cc0d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: __super_lock fs/super.c:58 [inline]
 #0: ffff88807a4cc0d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: __super_lock_excl fs/super.c:73 [inline]
 #0: ffff88807a4cc0d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: deactivate_super fs/super.c:509 [inline]
 #0: ffff88807a4cc0d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: deactivate_super+0xdf/0x110 fs/super.c:506
 #1: ffffffff8f06f220 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:576
2 locks held by syz.3.3126/22935:
 #0: ffffffff90b4d0c8 (cb_lock){++++}-{4:4}, at: genl_rcv+0x19/0x40 net/netlink/genetlink.c:1217
 #1: ffffffff8f06f220 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_nl_threads_set_doit+0x8c8/0x1100 fs/nfsd/nfsctl.c:1660
2 locks held by syz-executor/23134:
 #0: ffff8880332160d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: __super_lock fs/super.c:58 [inline]
 #0: ffff8880332160d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: __super_lock_excl fs/super.c:73 [inline]
 #0: ffff8880332160d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: deactivate_super fs/super.c:509 [inline]
 #0: ffff8880332160d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: deactivate_super+0xdf/0x110 fs/super.c:506
 #1: ffffffff8f06f220 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:576
3 locks held by syz.6.3243/23608:
 #0: ffff8880796d7430 (&f->f_pos_lock){+.+.}-{4:4}, at: fdget_pos+0x2aa/0x380 fs/file.c:1259
 #1: ffff888026d12450 (sb_writers#3){.+.+}-{0:0}, at: do_writev+0x13e/0x340 fs/read_write.c:1104
 #2: ffffffff8f06f220 (nfsd_mutex){+.+.}-{4:4}, at: expkey_flush+0x18/0x90 fs/nfsd/export.c:253
2 locks held by syz-executor/23638:
 #0: ffff8880602940d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: __super_lock fs/super.c:58 [inline]
 #0: ffff8880602940d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: __super_lock_excl fs/super.c:73 [inline]
 #0: ffff8880602940d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: deactivate_super fs/super.c:509 [inline]
 #0: ffff8880602940d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: deactivate_super+0xdf/0x110 fs/super.c:506
 #1: ffffffff8f06f220 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:576
2 locks held by syz-executor/23786:
 #0: ffff888023b5e0d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: __super_lock fs/super.c:58 [inline]
 #0: ffff888023b5e0d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: __super_lock_excl fs/super.c:73 [inline]
 #0: ffff888023b5e0d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: deactivate_super fs/super.c:509 [inline]
 #0: ffff888023b5e0d8 (&type->s_umount_key#52){+.+.}-{4:4}, at: deactivate_super+0xdf/0x110 fs/super.c:506
 #1: ffffffff8f06f220 (nfsd_mutex){+.+.}-{4:4}, at: nfsd_shutdown_threads+0x5b/0xf0 fs/nfsd/nfssvc.c:576
1 lock held by syz.4.3338/24381:
 #0: ffff8880531acea0 (&hdev->req_lock){+.+.}-{4:4}, at: hci_dev_do_close+0x26/0xb0 net/bluetooth/hci_core.c:497

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

NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 31 Comm: khungtaskd Tainted: G             L      syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 05/09/2026
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:122
 nmi_trigger_cpumask_backtrace+0x21c/0x2a0 lib/nmi_backtrace.c:65
 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>