Kernel bug: possible deadlock in l2cap_conn_del
Subsystem: bluetooth
Status: open

Crash report:
======================================================
WARNING: possible circular locking dependency detected
6.14.0-rc3-syzkaller-00060-g6537cfb395f3 #0 Not tainted
------------------------------------------------------
kworker/u9:0/53 is trying to acquire lock:
ffff888035a42840 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: rcu_lock_acquire include/linux/rcupdate.h:337 [inline]
ffff888035a42840 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
ffff888035a42840 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: start_flush_work kernel/workqueue.c:4148 [inline]
ffff888035a42840 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: __flush_work+0xe9/0xc60 kernel/workqueue.c:4206

but task is already holding lock:
ffff888035a42b38 (&conn->lock#2){+.+.}-{4:4}, at: l2cap_conn_del+0x71/0x690 net/bluetooth/l2cap_core.c:1760

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 (&conn->lock#2){+.+.}-{4:4}:
       lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5851
       __mutex_lock_common kernel/locking/mutex.c:585 [inline]
       __mutex_lock+0x19c/0x1010 kernel/locking/mutex.c:730
       l2cap_info_timeout+0x60/0xa0 net/bluetooth/l2cap_core.c:1666
       process_one_work kernel/workqueue.c:3236 [inline]
       process_scheduled_works+0xabe/0x18e0 kernel/workqueue.c:3317
       worker_thread+0x870/0xd30 kernel/workqueue.c:3398
       kthread+0x7a9/0x920 kernel/kthread.c:464
       ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:148
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

-> #0 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3163 [inline]
       check_prevs_add kernel/locking/lockdep.c:3282 [inline]
       validate_chain+0x18ef/0x5920 kernel/locking/lockdep.c:3906
       __lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5228
       lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5851
       touch_work_lockdep_map kernel/workqueue.c:3920 [inline]
       start_flush_work kernel/workqueue.c:4174 [inline]
       __flush_work+0x739/0xc60 kernel/workqueue.c:4206
       __cancel_work_sync+0xbc/0x110 kernel/workqueue.c:4362
       l2cap_conn_del+0x507/0x690 net/bluetooth/l2cap_core.c:1794
       l2cap_connect_cfm+0xcc/0x1090 net/bluetooth/l2cap_core.c:7195
       hci_connect_cfm include/net/bluetooth/hci_core.h:2051 [inline]
       hci_conn_failed+0x287/0x400 net/bluetooth/hci_conn.c:1266
       hci_abort_conn_sync+0xd27/0x1340 net/bluetooth/hci_sync.c:5588
       hci_cmd_sync_work+0x22b/0x400 net/bluetooth/hci_sync.c:332
       process_one_work kernel/workqueue.c:3236 [inline]
       process_scheduled_works+0xabe/0x18e0 kernel/workqueue.c:3317
       worker_thread+0x870/0xd30 kernel/workqueue.c:3398
       kthread+0x7a9/0x920 kernel/kthread.c:464
       ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:148
       ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&conn->lock#2);
                               lock((work_completion)(&(&conn->info_timer)->work));
                               lock(&conn->lock#2);
  lock((work_completion)(&(&conn->info_timer)->work));

 *** DEADLOCK ***

6 locks held by kworker/u9:0/53:
 #0: ffff888024bc9148 ((wq_completion)hci5){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3211 [inline]
 #0: ffff888024bc9148 ((wq_completion)hci5){+.+.}-{0:0}, at: process_scheduled_works+0x98b/0x18e0 kernel/workqueue.c:3317
 #1: ffffc90000bd7c60 ((work_completion)(&hdev->cmd_sync_work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3212 [inline]
 #1: ffffc90000bd7c60 ((work_completion)(&hdev->cmd_sync_work)){+.+.}-{0:0}, at: process_scheduled_works+0x9c6/0x18e0 kernel/workqueue.c:3317
 #2: ffff88805cf6cd80 (&hdev->req_lock){+.+.}-{4:4}, at: hci_cmd_sync_work+0x1ec/0x400 net/bluetooth/hci_sync.c:331
 #3: ffff88805cf6c078 (&hdev->lock){+.+.}-{4:4}, at: hci_abort_conn_sync+0x9ee/0x1340 net/bluetooth/hci_sync.c:5569
 #4: ffff888035a42b38 (&conn->lock#2){+.+.}-{4:4}, at: l2cap_conn_del+0x71/0x690 net/bluetooth/l2cap_core.c:1760
 #5: ffffffff8eb38f60 (rcu_read_lock){....}-{1:3}, at: rcu_lock_acquire include/linux/rcupdate.h:337 [inline]
 #5: ffffffff8eb38f60 (rcu_read_lock){....}-{1:3}, at: rcu_read_lock include/linux/rcupdate.h:849 [inline]
 #5: ffffffff8eb38f60 (rcu_read_lock){....}-{1:3}, at: start_flush_work kernel/workqueue.c:4148 [inline]
 #5: ffffffff8eb38f60 (rcu_read_lock){....}-{1:3}, at: __flush_work+0xe9/0xc60 kernel/workqueue.c:4206

stack backtrace:
CPU: 1 UID: 0 PID: 53 Comm: kworker/u9:0 Not tainted 6.14.0-rc3-syzkaller-00060-g6537cfb395f3 #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 12/27/2024
Workqueue: hci5 hci_cmd_sync_work
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120
 print_circular_bug+0x13a/0x1b0 kernel/locking/lockdep.c:2076
 check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2208
 check_prev_add kernel/locking/lockdep.c:3163 [inline]
 check_prevs_add kernel/locking/lockdep.c:3282 [inline]
 validate_chain+0x18ef/0x5920 kernel/locking/lockdep.c:3906
 __lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5228
 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5851
 touch_work_lockdep_map kernel/workqueue.c:3920 [inline]
 start_flush_work kernel/workqueue.c:4174 [inline]
 __flush_work+0x739/0xc60 kernel/workqueue.c:4206
 __cancel_work_sync+0xbc/0x110 kernel/workqueue.c:4362
 l2cap_conn_del+0x507/0x690 net/bluetooth/l2cap_core.c:1794
 l2cap_connect_cfm+0xcc/0x1090 net/bluetooth/l2cap_core.c:7195
 hci_connect_cfm include/net/bluetooth/hci_core.h:2051 [inline]
 hci_conn_failed+0x287/0x400 net/bluetooth/hci_conn.c:1266
 hci_abort_conn_sync+0xd27/0x1340 net/bluetooth/hci_sync.c:5588
 hci_cmd_sync_work+0x22b/0x400 net/bluetooth/hci_sync.c:332
 process_one_work kernel/workqueue.c:3236 [inline]
 process_scheduled_works+0xabe/0x18e0 kernel/workqueue.c:3317
 worker_thread+0x870/0xd30 kernel/workqueue.c:3398
 kthread+0x7a9/0x920 kernel/kthread.c:464
 ret_from_fork+0x4b/0x80 arch/x86/kernel/process.c:148
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:244
 </TASK>