possible deadlock in rfcomm_process_sessions

Status: upstream: reported on 2026/10/15 03:45
Subsystems: bluetooth
Labels: prio:low
[Documentation on labels]
Reported-by: syzbot+c8793045f4776ea20bc6@syzkaller.appspotmail.com
First crash: 4d10h, last: 1d17h
▶ ▼ ✨ AI Jobs (3)
ID Workflow Result Correct Bug Created Started Finished Revision
99323f39 repro-c 💥 possible deadlock in rfcomm_process_sessions 2026/10/15 00:01 2026/10/15 00:01 2026/10/15 03:21 8fb0ae89
3ff8f585 repro-c 💥 possible deadlock in rfcomm_process_sessions 2026/10/13 09:48 2026/10/13 09:48 2026/10/13 11:41 745a967f
889cb6d6 assessment-security DenialOfService: ❌ Exploitable: ❌ FilesystemTrigger: ❌ NetworkTrigger: ❌ PeripheralTrigger: ❌ RemoteTrigger: ❌ Unprivileged: ❌ UserNamespace: ❌ VMGuestTrigger: ❌ VMHostTrigger: ❌ ❓ possible deadlock in rfcomm_process_sessions 2026/10/13 05:16 2026/10/13 05:16 2026/10/13 06:17 745a967f
▶ ▼ Discussions (1)
Title Replies (including bot) Last reply
[syzbot] [bluetooth?] possible deadlock in rfcomm_process_sessions 0 (1) 2026/10/15 03:45

Sample crash report:
======================================================
WARNING: possible circular locking dependency detected
syzkaller #0 Tainted: G             L      
------------------------------------------------------
krfcommd/3206 is trying to acquire lock:
ffff888037d3d948 ((wq_completion)hci2#2){+.+.}-{0:0}, at: touch_wq_lockdep_map+0xb5/0x180 kernel/workqueue.c:4272

but task is already holding lock:
ffffffff91825f00 (rfcomm_mutex){+.+.}-{4:4}, at: rfcomm_process_sessions+0x2c6/0x9690 net/bluetooth/rfcomm/core.c:2150

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #4 (rfcomm_mutex){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x197/0x15a0 kernel/locking/mutex.c:821
       rfcomm_security_cfm+0x90/0x820 net/bluetooth/rfcomm/core.c:2277
       hci_auth_cfm include/net/bluetooth/hci_core.h:2250 [inline]
       hci_auth_complete_evt+0x39f/0xc80 net/bluetooth/hci_event.c:3635
       hci_event_func net/bluetooth/hci_event.c:8021 [inline]
       hci_event_packet+0x6cd/0xf10 net/bluetooth/hci_event.c:8072
       hci_rx_work+0x2b4/0x1110 net/bluetooth/hci_core.c:4124
       process_one_work kernel/workqueue.c:3495 [inline]
       process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3578
       worker_thread+0xa47/0xfb0 kernel/workqueue.c:3659
       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

-> #3 (hci_cb_list_lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x197/0x15a0 kernel/locking/mutex.c:821
       hci_connect_cfm include/net/bluetooth/hci_core.h:2211 [inline]
       hci_remote_features_evt+0x53d/0x950 net/bluetooth/hci_event.c:3892
       hci_event_func net/bluetooth/hci_event.c:8021 [inline]
       hci_event_packet+0x6cd/0xf10 net/bluetooth/hci_event.c:8072
       hci_rx_work+0x2b4/0x1110 net/bluetooth/hci_core.c:4124
       process_one_work kernel/workqueue.c:3495 [inline]
       process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3578
       worker_thread+0xa47/0xfb0 kernel/workqueue.c:3659
       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

-> #2 (&hdev->lock){+.+.}-{4:4}:
       __mutex_lock_common kernel/locking/mutex.c:646 [inline]
       __mutex_lock+0x197/0x15a0 kernel/locking/mutex.c:821
       hci_send_cmd_sync net/bluetooth/hci_core.c:4163 [inline]
       hci_cmd_work+0xa0/0x850 net/bluetooth/hci_core.c:4212
       process_one_work kernel/workqueue.c:3495 [inline]
       process_scheduled_works+0xc3d/0x1630 kernel/workqueue.c:3578
       worker_thread+0xa47/0xfb0 kernel/workqueue.c:3659
       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

-> #1 ((work_completion)(&hdev->cmd_work)){+.+.}-{0:0}:
       process_one_work kernel/workqueue.c:3471 [inline]
       process_scheduled_works+0xc03/0x1630 kernel/workqueue.c:3578
       worker_thread+0xa47/0xfb0 kernel/workqueue.c:3659
       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

-> #0 ((wq_completion)hci2#2){+.+.}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3209 [inline]
       check_prevs_add kernel/locking/lockdep.c:3328 [inline]
       validate_chain kernel/locking/lockdep.c:3952 [inline]
       __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
       lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
       touch_wq_lockdep_map+0xcb/0x180 kernel/workqueue.c:4272
       __flush_workqueue+0x148/0x10b0 kernel/workqueue.c:4314
       drain_workqueue+0xce/0x380 kernel/workqueue.c:4478
       destroy_workqueue+0xbe/0x7b0 kernel/workqueue.c:6372
       hci_release_dev+0xe3/0x1510 net/bluetooth/hci_core.c:2728
       bt_host_release+0x93/0xa0 net/bluetooth/hci_sysfs.c:100
       device_release+0xc4/0x1f0 drivers/base/core.c:-1
       kobject_cleanup lib/kobject.c:689 [inline]
       kobject_release lib/kobject.c:720 [inline]
       kref_put include/linux/kref.h:65 [inline]
       kobject_put+0x222/0x550 lib/kobject.c:737
       device_release+0xc4/0x1f0 drivers/base/core.c:-1
       kobject_cleanup lib/kobject.c:689 [inline]
       kobject_release lib/kobject.c:720 [inline]
       kref_put include/linux/kref.h:65 [inline]
       kobject_put+0x222/0x550 lib/kobject.c:737
       hci_conn_put include/net/bluetooth/hci_core.h:1737 [inline]
       l2cap_conn_free net/bluetooth/l2cap_core.c:1933 [inline]
       kref_put include/linux/kref.h:65 [inline]
       l2cap_conn_put net/bluetooth/l2cap_core.c:1946 [inline]
       l2cap_chan_destroy net/bluetooth/l2cap_core.c:495 [inline]
       kref_put include/linux/kref.h:65 [inline]
       l2cap_chan_put+0x1fd/0x350 net/bluetooth/l2cap_core.c:522
       l2cap_sock_release+0x1a2/0x230 net/bluetooth/l2cap_sock.c:1536
       __sock_release net/socket.c:735 [inline]
       sock_release+0x85/0x150 net/socket.c:763
       rfcomm_session_del+0x14b/0x270 net/bluetooth/rfcomm/core.c:782
       rfcomm_process_sessions+0x7456/0x9690 net/bluetooth/rfcomm/core.c:-1
       rfcomm_run+0x3f5/0x620 net/bluetooth/rfcomm/core.c:2259
       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

other info that might help us debug this:

Chain exists of:
  (wq_completion)hci2#2 --> hci_cb_list_lock --> rfcomm_mutex

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(rfcomm_mutex);
                               lock(hci_cb_list_lock);
                               lock(rfcomm_mutex);
  lock((wq_completion)hci2#2);

 *** DEADLOCK ***

locks held by krfcommd/3206: 1, last CPU#1:
 #0: ffffffff91825f00 (rfcomm_mutex){+.+.}-{4:4}, at: rfcomm_process_sessions+0x2c6/0x9690 net/bluetooth/rfcomm/core.c:2150

stack backtrace:
CPU: 1 UID: 0 PID: 3206 Comm: krfcommd Tainted: G             L       syzkaller #0 PREEMPT(full) 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/07/2026
Call Trace:
 <TASK>
 dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120
 print_circular_bug+0x2e2/0x300 kernel/locking/lockdep.c:2087
 check_noncircular+0x12f/0x150 kernel/locking/lockdep.c:2219
 check_prev_add kernel/locking/lockdep.c:3209 [inline]
 check_prevs_add kernel/locking/lockdep.c:3328 [inline]
 validate_chain kernel/locking/lockdep.c:3952 [inline]
 __lock_acquire+0x164c/0x2de0 kernel/locking/lockdep.c:5288
 lock_acquire+0x115/0x350 kernel/locking/lockdep.c:5942
 touch_wq_lockdep_map+0xcb/0x180 kernel/workqueue.c:4272
 __flush_workqueue+0x148/0x10b0 kernel/workqueue.c:4314
 drain_workqueue+0xce/0x380 kernel/workqueue.c:4478
 destroy_workqueue+0xbe/0x7b0 kernel/workqueue.c:6372
 hci_release_dev+0xe3/0x1510 net/bluetooth/hci_core.c:2728
 bt_host_release+0x93/0xa0 net/bluetooth/hci_sysfs.c:100
 device_release+0xc4/0x1f0 drivers/base/core.c:-1
 kobject_cleanup lib/kobject.c:689 [inline]
 kobject_release lib/kobject.c:720 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x222/0x550 lib/kobject.c:737
 device_release+0xc4/0x1f0 drivers/base/core.c:-1
 kobject_cleanup lib/kobject.c:689 [inline]
 kobject_release lib/kobject.c:720 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x222/0x550 lib/kobject.c:737
 hci_conn_put include/net/bluetooth/hci_core.h:1737 [inline]
 l2cap_conn_free net/bluetooth/l2cap_core.c:1933 [inline]
 kref_put include/linux/kref.h:65 [inline]
 l2cap_conn_put net/bluetooth/l2cap_core.c:1946 [inline]
 l2cap_chan_destroy net/bluetooth/l2cap_core.c:495 [inline]
 kref_put include/linux/kref.h:65 [inline]
 l2cap_chan_put+0x1fd/0x350 net/bluetooth/l2cap_core.c:522
 l2cap_sock_release+0x1a2/0x230 net/bluetooth/l2cap_sock.c:1536
 __sock_release net/socket.c:735 [inline]
 sock_release+0x85/0x150 net/socket.c:763
 rfcomm_session_del+0x14b/0x270 net/bluetooth/rfcomm/core.c:782
 rfcomm_process_sessions+0x7456/0x9690 net/bluetooth/rfcomm/core.c:-1
 rfcomm_run+0x3f5/0x620 net/bluetooth/rfcomm/core.c:2259
 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>

Crashes (2):
Time Kernel Commit Syzkaller Config Log Report Syz repro C repro VM info Assets (help?) Manager Title
2026/10/13 21:05 linux-next 4eb2586bd40d 7321cd29 .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-rust-kasan-gce possible deadlock in rfcomm_process_sessions
2026/10/11 03:41 linux-next becb95e45ef0 4f92358f .config console log report info [disk image] [vmlinux] [kernel image] ci-upstream-linux-next-kasan-gce-root possible deadlock in rfcomm_process_sessions
* Struck through repros no longer work on HEAD.