INFO: task hung in hci_unregister_dev

Status: upstream: reported on 2026/08/05 07:37
Reported-by: syzbot+7bd1e41e53a7d70b3df7@syzkaller.appspotmail.com
First crash: 2d20h, last: 1d06h
Similar bugs (3)
Kernel Title Rank 🛈 Repro Cause bisect Fix bisect Count Last Reported Patched Status
upstream INFO: task hung in hci_unregister_dev bluetooth 1 1 576d 576d 0/29 auto-obsoleted due to no activity on 2025/04/08 16:17
linux-6.1 INFO: task hung in hci_unregister_dev 1 1 3d02h 3d02h 0/3 upstream: reported on 2026/08/05 00:46
upstream INFO: task can't die in hci_unregister_dev bluetooth 1 1 1698d 1694d 0/29 auto-closed as invalid on 2022/02/11 04:46

Sample crash report:
INFO: task getty:3945 blocked for more than 143 seconds.
      Not tainted syzkaller #0
"echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
task:getty           state:D stack:22288 pid: 3945 ppid:     1 flags:0x00004002
Call Trace:
 <TASK>
 context_switch kernel/sched/core.c:5049 [inline]
 __schedule+0x11c3/0x4350 kernel/sched/core.c:6395
 schedule+0x11b/0x1e0 kernel/sched/core.c:6478
 schedule_timeout+0xbd/0x2d0 kernel/time/timer.c:2093
 do_wait_for_common+0x295/0x460 kernel/sched/completion.c:85
 __wait_for_common kernel/sched/completion.c:106 [inline]
 wait_for_common kernel/sched/completion.c:117 [inline]
 wait_for_completion+0x48/0x60 kernel/sched/completion.c:138
 __flush_work+0x15a/0x210 kernel/workqueue.c:3094
 __cancel_work_timer+0x3f4/0x560 kernel/workqueue.c:3181
 hci_unregister_dev+0x163/0x590 net/bluetooth/hci_core.c:4061
 hci_uart_tty_close+0x268/0x330 drivers/bluetooth/hci_ldisc.c:575
 tty_ldisc_reinit+0xe4/0x460 drivers/tty/tty_ldisc.c:679
 tty_ldisc_hangup+0x360/0x4a0 drivers/tty/tty_ldisc.c:745
 __tty_hangup+0x44e/0x670 drivers/tty/tty_io.c:639
 disassociate_ctty+0x38d/0x860 drivers/tty/tty_jobctrl.c:275
 do_exit+0x5f9/0x2110 kernel/exit.c:888
 do_group_exit+0x12c/0x2f0 kernel/exit.c:1004
 __do_sys_exit_group kernel/exit.c:1015 [inline]
 __se_sys_exit_group kernel/exit.c:1013 [inline]
 __x64_sys_exit_group+0x3b/0x40 kernel/exit.c:1013
 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
 do_syscall_64+0x4c/0xa0 arch/x86/entry/common.c:80
 entry_SYSCALL_64_after_hwframe+0x66/0xd0
RIP: 0033:0x7f7e959a06c5
RSP: 002b:00007fffa05c6dc8 EFLAGS: 00000202 ORIG_RAX: 00000000000000e7
RAX: ffffffffffffffda RBX: 00007f7e95aa1fe8 RCX: 00007f7e959a06c5
RDX: 00000000000000e7 RSI: ffffffffffffff88 RDI: 0000000000000001
RBP: 0000000000000001 R08: 00007fffa05c6d58 R09: 0000000000000000
R10: 00007fffa05c6bf0 R11: 0000000000000202 R12: 0000000000000000
R13: 0000000000000001 R14: 00007f7e95aa0680 R15: 00007f7e95aa2000
 </TASK>

Showing all locks held in the system:
1 lock held by khungtaskd/27:
 #0: ffffffff8c31ef60 (rcu_read_lock){....}-{1:2}, at: rcu_lock_acquire+0x0/0x30
2 locks held by getty/3945:
 #0: ffff88802bea31c0 (&tty->legacy_mutex){+.+.}-{3:3}, at: __tty_hangup+0xc0/0x670 drivers/tty/tty_io.c:599
 #1: ffff88802bea3098 (&tty->ldisc_sem){++++}-{0:0}, at: __tty_ldisc_lock drivers/tty/tty_ldisc.c:300 [inline]
 #1: ffff88802bea3098 (&tty->ldisc_sem){++++}-{0:0}, at: tty_ldisc_lock+0x68/0xb0 drivers/tty/tty_ldisc.c:324
3 locks held by kworker/u5:7/4202:
 #0: ffff88807831d138 ((wq_completion)hci5){+.+.}-{0:0}, at: process_one_work+0x75c/0xff0 kernel/workqueue.c:-1
 #1: ffffc90002f3fd00 ((work_completion)(&hdev->power_on)){+.+.}-{0:0}, at: process_one_work+0x79e/0xff0 kernel/workqueue.c:2285
 #2: ffff88805faa13f0 (&hdev->req_lock){+.+.}-{3:3}, at: hci_dev_do_open+0xa4/0x12a0 net/bluetooth/hci_core.c:1464
4 locks held by kworker/1:4/4231:
 #0: ffff888141dc6938 ((wq_completion)infiniband){+.+.}-{0:0}, at: process_one_work+0x75c/0xff0 kernel/workqueue.c:-1
 #1: ffffc900030bfd00 ((work_completion)(&work->work)#3){+.+.}-{0:0}, at: process_one_work+0x79e/0xff0 kernel/workqueue.c:2285
 #2: ffff88802df41218 (&rxe->usdev_lock){+.+.}-{3:3}, at: rxe_query_port+0x46/0x190 drivers/infiniband/sw/rxe/rxe_verbs.c:40
 #3: ffffffff8d44d488 (rtnl_mutex){+.+.}-{3:3}, at: ib_get_eth_speed+0x16b/0x500 drivers/infiniband/core/verbs.c:1905
2 locks held by kworker/u4:9/6527:
3 locks held by kworker/1:15/7839:
 #0: ffff888016c70938 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work+0x75c/0xff0 kernel/workqueue.c:-1
 #1: ffffc9000376fd00 (deferred_process_work){+.+.}-{0:0}, at: process_one_work+0x79e/0xff0 kernel/workqueue.c:2285
 #2: ffffffff8d44d488 (rtnl_mutex){+.+.}-{3:3}, at: switchdev_deferred_process_work+0xa/0x20 net/switchdev/switchdev.c:74
2 locks held by syz.4.1226/8890:
 #0: ffffffff8d44d488 (rtnl_mutex){+.+.}-{3:3}, at: rtnl_lock net/core/rtnetlink.c:72 [inline]
 #0: ffffffff8d44d488 (rtnl_mutex){+.+.}-{3:3}, at: rtnetlink_rcv_msg+0x79f/0xf10 net/core/rtnetlink.c:5695
 #1: ffffffff8c3239e8 (rcu_state.exp_mutex){+.+.}-{3:3}, at: exp_funnel_lock kernel/rcu/tree_exp.h:290 [inline]
 #1: ffffffff8c3239e8 (rcu_state.exp_mutex){+.+.}-{3:3}, at: synchronize_rcu_expedited+0x2d1/0x750 kernel/rcu/tree_exp.h:845
3 locks held by syz.4.1226/8893:
 #0: ffffffff8d4aa0b0 (cb_lock){++++}-{3:3}, at: genl_rcv+0x15/0x40 net/netlink/genetlink.c:802
 #1: ffffffff8d4a9f08 (genl_mutex){+.+.}-{3:3}, at: genl_lock net/netlink/genetlink.c:33 [inline]
 #1: ffffffff8d4a9f08 (genl_mutex){+.+.}-{3:3}, at: genl_rcv_msg+0x161/0xfa0 net/netlink/genetlink.c:790
 #2: ffffffff8d44d488 (rtnl_mutex){+.+.}-{3:3}, at: team_nl_cmd_options_set+0xab/0xe70 drivers/net/team/team.c:2573

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

NMI backtrace for cpu 0
CPU: 0 PID: 27 Comm: khungtaskd Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0x188/0x250 lib/dump_stack.c:106
 nmi_cpu_backtrace+0x3a2/0x3d0 lib/nmi_backtrace.c:111
 nmi_trigger_cpumask_backtrace+0x163/0x280 lib/nmi_backtrace.c:62
 trigger_all_cpu_backtrace include/linux/nmi.h:148 [inline]
 check_hung_uninterruptible_tasks kernel/hung_task.c:212 [inline]
 watchdog+0xe1b/0xe60 kernel/hung_task.c:369
 kthread+0x42e/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>
Sending NMI from CPU 0 to CPUs 1:
NMI backtrace for cpu 1
CPU: 1 PID: 4234 Comm: kworker/1:6 Not tainted syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
Workqueue: events nsim_dev_trap_report_work
RIP: 0010:check_kcov_mode kernel/kcov.c:172 [inline]
RIP: 0010:write_comp_data kernel/kcov.c:227 [inline]
RIP: 0010:__sanitizer_cov_trace_const_cmp8+0x2a/0x80 kernel/kcov.c:300
Code: 48 8b 04 24 65 48 8b 0d 24 6f 89 7e 65 8b 15 25 6f 89 7e 81 e2 00 01 ff 00 74 11 81 fa 00 01 00 00 75 57 83 b9 34 16 00 00 00 <74> 4e 8b 91 10 16 00 00 83 fa 03 75 43 48 8b 91 18 16 00 00 44 8b
RSP: 0018:ffffc90000dd0a78 EFLAGS: 00000246
RAX: ffffffff8818cb1c RBX: 000000a7c5ac471b RCX: ffff888061aebb80
RDX: 0000000000000100 RSI: 0000000000000000 RDI: 000000a7c5ac471b
RBP: 0000000000000000 R08: 0000000000000003 R09: 0000000000000004
R10: dffffc0000000000 R11: fffff520001ba150 R12: ffff88801abac300
R13: 0019999999999998 R14: 0000000225c17d04 R15: 0000001cfdb417b6
FS:  0000000000000000(0000) GS:ffff8880b9100000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 0000001b32b12ff8 CR3: 0000000077b26000 CR4: 00000000003506e0
DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
Call Trace:
 <IRQ>
 pie_calculate_probability+0x24c/0x7f0 net/sched/sch_pie.c:346
 fq_pie_timer+0x17f/0x3c0 net/sched/sch_fq_pie.c:393
 call_timer_fn+0x17b/0x540 kernel/time/timer.c:1648
 expire_timers kernel/time/timer.c:1699 [inline]
 __run_timers+0x56c/0x810 kernel/time/timer.c:1970
 run_timer_softirq+0x63/0xf0 kernel/time/timer.c:1983
 handle_softirqs+0x336/0x830 kernel/softirq.c:576
 __do_softirq kernel/softirq.c:610 [inline]
 invoke_softirq kernel/softirq.c:450 [inline]
 __irq_exit_rcu+0x13b/0x230 kernel/softirq.c:659
 irq_exit_rcu+0x5/0x20 kernel/softirq.c:671
 instr_sysvec_apic_timer_interrupt arch/x86/kernel/apic/apic.c:1108 [inline]
 sysvec_apic_timer_interrupt+0xa0/0xc0 arch/x86/kernel/apic/apic.c:1108
 </IRQ>
 <TASK>
 asm_sysvec_apic_timer_interrupt+0x16/0x20 arch/x86/include/asm/idtentry.h:676
RIP: 0010:orc_find arch/x86/kernel/unwind_orc.c:171 [inline]
RIP: 0010:unwind_next_frame+0x1d9/0x1cf0 arch/x86/kernel/unwind_orc.c:448
Code: 8b 24 24 89 e8 ff c0 4c 8d 2c 85 00 e3 9e 8e 4c 89 e8 48 c1 e8 03 42 0f b6 04 38 84 c0 0f 85 dd 15 00 00 45 8b 45 00 41 ff c0 <4b> 8d 04 64 48 8d 94 00 b4 f6 ff 8d 4b 8d 04 40 48 8d 84 00 b4 f6
RSP: 0018:ffffc900030ff670 EFLAGS: 00000202
RAX: 0000000000000000 RBX: ffffc900030ff708 RCX: ffffffff962f4f00
RDX: dffffc0000000000 RSI: 0000000000090081 RDI: 0000000000000001
RBP: 0000000000000047 R08: 0000000000000131 R09: 0000000000000009
R10: dffffc0000000000 R11: fffff5200061feed R12: 0000000000000115
R13: ffffffff8e9ee420 R14: ffffffff810047fe R15: dffffc0000000000
 arch_stack_walk+0x10c/0x140 arch/x86/kernel/stacktrace.c:25
 stack_trace_save+0xa6/0xf0 kernel/stacktrace.c:122
 kasan_save_stack mm/kasan/common.c:38 [inline]
 kasan_set_track+0x4b/0x70 mm/kasan/common.c:46
 kasan_set_free_info+0x1f/0x40 mm/kasan/generic.c:360
 ____kasan_slab_free+0xd5/0x110 mm/kasan/common.c:366
 kasan_slab_free include/linux/kasan.h:230 [inline]
 slab_free_hook mm/slub.c:1710 [inline]
 slab_free_freelist_hook+0xec/0x170 mm/slub.c:1736
 slab_free mm/slub.c:3504 [inline]
 kmem_cache_free+0x8f/0x210 mm/slub.c:3520
 nsim_dev_trap_report drivers/net/netdevsim/dev.c:737 [inline]
 nsim_dev_trap_report_work+0x771/0xab0 drivers/net/netdevsim/dev.c:762
 process_one_work+0x867/0xff0 kernel/workqueue.c:2310
 worker_thread+0xad7/0x12a0 kernel/workqueue.c:2457
 kthread+0x42e/0x520 kernel/kthread.c:334
 ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:287
 </TASK>

Crashes (3):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/08/06 21:27 linux-5.15.y 9c7634c60784 c38879ea .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: task hung in hci_unregister_dev
2026/08/05 07:37 linux-5.15.y 6e2fd6534337 52aa2820 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: task hung in hci_unregister_dev
2026/08/05 07:37 linux-5.15.y 6e2fd6534337 52aa2820 .config console log report info [disk image] [vmlinux] [kernel image] ci2-linux-5-15-kasan INFO: task hung in hci_unregister_dev
* Struck through repros no longer work on HEAD.