INFO: task udevd:2856 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:udevd           state:D
 stack:26736 pid:2856  tgid:2856  ppid:1      task_flags:0x400140 flags:0x00080000
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5295 [inline]
 __schedule+0xeb1/0x41f0 kernel/sched/core.c:6907
 __schedule_loop kernel/sched/core.c:6989 [inline]
 schedule+0xdd/0x390 kernel/sched/core.c:7004
 schedule_preempt_disabled+0x13/0x30 kernel/sched/core.c:7061
 rwsem_down_read_slowpath+0x5dc/0xb30 kernel/locking/rwsem.c:1086
 __down_read_common kernel/locking/rwsem.c:1261 [inline]
 __down_read kernel/locking/rwsem.c:1274 [inline]
 down_read+0xed/0x460 kernel/locking/rwsem.c:1539
 kernfs_dop_revalidate+0xa5/0x740 fs/kernfs/dir.c:1185
 d_revalidate fs/namei.c:1030 [inline]
 d_revalidate fs/namei.c:1026 [inline]
 lookup_fast+0x3c7/0x600 fs/namei.c:1877
 walk_component fs/namei.c:2275 [inline]
 link_path_walk+0x7a8/0x1b30 fs/namei.c:2647
 path_lookupat+0x74/0xc40 fs/namei.c:2803
 filename_lookup+0x202/0x590 fs/namei.c:2833
 do_readlinkat+0xd3/0x370 fs/stat.c:571
 __do_sys_readlink fs/stat.c:605 [inline]
 __se_sys_readlink fs/stat.c:602 [inline]
 __x64_sys_readlink+0x78/0xc0 fs/stat.c:602
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x106/0x7b0 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f05717f03a7
RSP: 002b:00007ffeecbb7978 EFLAGS: 00000246
 ORIG_RAX: 0000000000000059
RAX: ffffffffffffffda RBX: 00007ffeecbb7e50 RCX: 00007f05717f03a7
RDX: 0000000000000400 RSI: 00007ffeecbb7980 RDI: 00007ffeecbb7e50
RBP: 00007ffeecbb7980 R08: 0000000000000075 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000400
R13: 0000559dd4841100 R14: 0000000000000001 R15: 00007ffeecbb9750
 </TASK>

Showing all locks held in the system:
4 locks held by kworker/0:0/9:
 #0: 
ffff88810006b548
 (
(wq_completion)events
){+.+.}-{0:0}
, at: process_one_work+0x1287/0x1920 kernel/workqueue.c:3250
 #1: 
ffffc9000009fd18
 (kernfs_notify_work
){+.+.}-{0:0}
, at: process_one_work+0x93c/0x1920 kernel/workqueue.c:3251
 #2: 
ffff8881012982b8
 (
&root->kernfs_supers_rwsem
){++++}-{4:4}
, at: kernfs_notify_workfn+0xf7/0x5f0 fs/kernfs/file.c:932
 #3: 
ffff888101298188
 (
&root->kernfs_rwsem
){++++}-{4:4}
, at: kernfs_notify_workfn+0xff/0x5f0 fs/kernfs/file.c:933
7 locks held by kworker/0:1/10:
1 lock held by khungtaskd/30:
 #0: 
ffffffff896e05a0
 (
rcu_read_lock
){....}-{1:3}
, at: rcu_lock_acquire include/linux/rcupdate.h:312 [inline]
, at: rcu_read_lock include/linux/rcupdate.h:850 [inline]
, at: debug_show_all_locks+0x3d/0x184 kernel/locking/lockdep.c:6775
5 locks held by kworker/u8:6/91:
 #0: 
ffff888101299148
 (
(wq_completion)netns
){+.+.}-{0:0}
, at: process_one_work+0x1287/0x1920 kernel/workqueue.c:3250
 #1: 
ffffc90001477d18
 (
net_cleanup_work
){+.+.}-{0:0}
, at: process_one_work+0x93c/0x1920 kernel/workqueue.c:3251
 #2: 
ffffffff8aae0830
 (
pernet_ops_rwsem
){++++}-{4:4}
, at: cleanup_net+0xb8/0x9e0 net/core/net_namespace.c:675
 #3: 
ffffffff8aaf8e68
 (
rtnl_mutex
){+.+.}-{4:4}
, at: ops_exit_rtnl_list net/core/net_namespace.c:173 [inline]
, at: ops_undo_list+0x7ec/0xab0 net/core/net_namespace.c:248
 #4: 
ffffffff896ec1b8
 (
rcu_state.exp_mutex
){+.+.}-{4:4}
, at: exp_funnel_lock+0x27f/0x3c0 kernel/rcu/tree_exp.h:311
5 locks held by kworker/0:3/2815:
1 lock held by udevd/2856:
 #0: 
ffff888101298188
 (
&root->kernfs_rwsem
){++++}-{4:4}
, at: kernfs_dop_revalidate+0xa5/0x740 fs/kernfs/dir.c:1185
2 locks held by getty/2918:
 #0: 
ffff888115c0b0a0
 (
&tty->ldisc_sem
){++++}-{0:0}
, at: tty_ldisc_ref_wait+0x24/0x80 drivers/tty/tty_ldisc.c:243
 #1: 
ffffc900000432f0
 (
&ldata->atomic_read_lock
){+.+.}-{4:4}
, at: n_tty_read+0x419/0x1500 drivers/tty/n_tty.c:2211
1 lock held by syz-executor/3053:
 #0: 
ffff888101298188
 (
&root->kernfs_rwsem
){++++}-{4:4}
, at: kernfs_dop_revalidate+0x397/0x740 fs/kernfs/dir.c:1167
1 lock held by syz-executor/3055:
 #0: 
ffff888101298188
 (
&root->kernfs_rwsem
){++++}-{4:4}
, at: kernfs_dop_revalidate+0x397/0x740 fs/kernfs/dir.c:1167
1 lock held by syz-executor/3057:
 #0: 
ffff888101298188
 (
&root->kernfs_rwsem
){++++}-{4:4}
, at: kernfs_dop_revalidate+0x397/0x740 fs/kernfs/dir.c:1167
1 lock held by syz-executor/3064:
 #0: 
ffff888101298188
 (
&root->kernfs_rwsem
){++++}-{4:4}
, at: kernfs_dop_revalidate+0x397/0x740 fs/kernfs/dir.c:1167
4 locks held by udevd/5272:
 #0: 
ffff88811aade0a0
 (
&p->lock
){+.+.}-{4:4}
, at: seq_read_iter+0xe1/0x1270 fs/seq_file.c:183
 #1: 
ffff88811de92088
 (
&of->mutex
#2
){+.+.}-{4:4}
, at: kernfs_seq_start+0x4f/0x2a0 fs/kernfs/file.c:172
 #2: 
ffff888113580878
 (
kn->active
#18
){.+.+}-{0:0}
, at: kernfs_get_active_of fs/kernfs/file.c:80 [inline]
, at: kernfs_seq_start+0xbc/0x2a0 fs/kernfs/file.c:173
 #3: 
ffff88810ffb3198
 (
&dev->mutex
){....}-{4:4}
, at: device_lock_interruptible include/linux/device.h:900 [inline]
, at: manufacturer_show+0x26/0xa0 drivers/usb/core/sysfs.c:142
8 locks held by kworker/0:4/5314:
1 lock held by syz-executor/5326:
 #0: 
ffff888101298188
 (
&root->kernfs_rwsem
){++++}-{4:4}
, at: kernfs_dop_revalidate+0xa5/0x740 fs/kernfs/dir.c:1185
1 lock held by syz-executor/5327:
 #0: 
ffff888101298188
 (
&root->kernfs_rwsem
){++++}-{4:4}
, at: kernfs_dop_revalidate+0xa5/0x740 fs/kernfs/dir.c:1185
1 lock held by syz-executor/5328:
 #0: 
ffff888101298188
 (
&root->kernfs_rwsem
){++++}-{4:4}
, at: kernfs_dop_revalidate+0xa5/0x740 fs/kernfs/dir.c:1185
1 lock held by syz-executor/5329:
 #0: 
ffff888101298188
 (
&root->kernfs_rwsem
){++++}-{4:4}
, at: kernfs_dop_revalidate+0xa5/0x740 fs/kernfs/dir.c:1185
1 lock held by syz-executor/5330:
 #0: 
ffff888101298188
 (
&root->kernfs_rwsem
){++++}-{4:4}
, at: kernfs_dop_revalidate+0xa5/0x740 fs/kernfs/dir.c:1185

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

NMI backtrace for cpu 1
CPU: 1 UID: 0 PID: 30 Comm: khungtaskd Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
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:161 [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:346 [inline]
 watchdog+0xd25/0x1050 kernel/hung_task.c:515
 kthread+0x370/0x450 kernel/kthread.c:467
 ret_from_fork+0x6c3/0xcb0 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Sending NMI from CPU 1 to CPUs 0:
yealink 4-1:36.0: unexpected response 0
NMI backtrace for cpu 0
CPU: 0 UID: 0 PID: 5314 Comm: kworker/0:4 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Workqueue: events_power_efficient gc_worker
RIP: 0010:io_serial_out+0x8f/0xb0 drivers/tty/serial/8250/8250_port.c:407
Code: 48 8d 7d 40 44 89 e1 48 b8 00 00 00 00 00 fc ff df 48 89 fa d3 e3 48 c1 ea 03 80 3c 02 00 75 1c 66 03 5d 40 44 89 e8 89 da ee <5b> 5d 41 5c 41 5d c3 cc cc cc cc e8 31 24 f6 fe eb a0 e8 ba 24 f6
RSP: 0018:ffffc90000007430 EFLAGS: 00000006
RAX: 0000000000000000 RBX: 00000000000003f9 RCX: 0000000000000000
RDX: 00000000000003f9 RSI: ffffffff831f6585 RDI: ffffffff941ae5c0
RBP: ffffffff941ae580 R08: 0000000000000001 R09: 000000000000001f
R10: 0000000000000000 R11: 0000000000000000 R12: 0000000000000000
R13: 0000000000000000 R14: ffffffff941ae5d0 R15: 0000000000000000
FS:  0000000000000000(0000) GS:ffff8882686d3000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000000110c2f23ea CR3: 00000000094ae000 CR4: 00000000003506f0
Call Trace:
 <IRQ>
 serial_out drivers/tty/serial/8250/8250.h:133 [inline]
 serial8250_clear_IER+0xa7/0xd0 drivers/tty/serial/8250/8250_port.c:714
 serial8250_console_write+0x252/0x1900 drivers/tty/serial/8250/8250_port.c:3307
 console_emit_next_record kernel/printk/printk.c:3183 [inline]
 console_flush_one_record+0x790/0xe50 kernel/printk/printk.c:3269
 console_flush_all kernel/printk/printk.c:3343 [inline]
 __console_flush_and_unlock kernel/printk/printk.c:3373 [inline]
 console_unlock+0x103/0x260 kernel/printk/printk.c:3413
 vprintk_emit+0x407/0x6b0 kernel/printk/printk.c:2479
 dev_vprintk_emit+0x394/0x3e0 drivers/base/core.c:4913
 dev_printk_emit+0xd2/0x10d drivers/base/core.c:4924
 __dev_printk+0xcb/0x100 drivers/base/core.c:4936
 _dev_err+0xef/0x127 drivers/base/core.c:4979
 urb_irq_callback.cold+0x81/0xfd drivers/input/misc/yealink.c:435
 __usb_hcd_giveback_urb+0x38d/0x610 drivers/usb/core/hcd.c:1657
 usb_hcd_giveback_urb+0x3ca/0x4a0 drivers/usb/core/hcd.c:1741
 dummy_timer+0xd85/0x3670 drivers/usb/gadget/udc/dummy_hcd.c:1995
 __run_hrtimer kernel/time/hrtimer.c:1785 [inline]
 __hrtimer_run_queues+0x50e/0xa70 kernel/time/hrtimer.c:1849
 hrtimer_run_softirq+0x17d/0x350 kernel/time/hrtimer.c:1866
 handle_softirqs+0x1de/0x9d0 kernel/softirq.c:622
 __do_softirq kernel/softirq.c:656 [inline]
 invoke_softirq kernel/softirq.c:496 [inline]
 __irq_exit_rcu+0xed/0x150 kernel/softirq.c:723
 irq_exit_rcu+0x9/0x30 kernel/softirq.c:739
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1056 [inline]
 sysvec_apic_timer_interrupt+0x8f/0xb0 arch/x86/kernel/apic/apic.c:1056
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x1a/0x20 arch/x86/include/asm/idtentry.h:697
RIP: 0010:check_preemption_disabled+0x23/0xe0 lib/smp_processor_id.c:54
Code: 90 90 90 90 90 90 90 41 54 55 53 48 83 ec 08 65 8b 1d d5 2f 8c 05 65 f7 05 c6 2f 8c 05 ff ff ff 7f 74 0f 48 83 c4 08 89 d8 5b <5d> 41 5c c3 cc cc cc cc 9c 58 f6 c4 02 74 ea 65 4c 8b 25 8e 2f 8c
RSP: 0018:ffffc90002a2fb28 EFLAGS: 00000292
RAX: 0000000000000000 RBX: 0000000000000001 RCX: ffffffff8679194a
RDX: ffff88811a545700 RSI: ffffffff87afa3a0 RDI: ffffffff87afa3e0
RBP: 00000000000076dd R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000001 R11: 0000000000000000 R12: dffffc0000000000
R13: 0000000000040000 R14: 0000000000003b6e R15: 0000000000001770
 rcu_is_watching_curr_cpu include/linux/context_tracking.h:128 [inline]
 rcu_is_watching+0x12/0xc0 kernel/rcu/tree.c:752
 rcu_read_unlock include/linux/rcupdate.h:879 [inline]
 gc_worker+0xf4e/0x1630 net/netfilter/nf_conntrack_core.c:1617
 process_one_work+0x9d7/0x1920 kernel/workqueue.c:3275
 process_scheduled_works kernel/workqueue.c:3358 [inline]
 worker_thread+0x5da/0xe40 kernel/workqueue.c:3439
 kthread+0x370/0x450 kernel/kthread.c:467
 ret_from_fork+0x6c3/0xcb0 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>