[syzbot] [bluetooth?] possible deadlock in l2cap_info_timeout

[syzbot <syzbot+d8bca25877c7eda36f5b@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    8a61cb6e150e Merge tag 'block-6.14-20250221' of git://git...
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17261fdf980000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b7bde34acd8f53b1
dashboard link: https://syzkaller.appspot.com/bug?extid=d8bca25877c7eda36f5b
compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40

Unfortunately, I don't have any reproducer for this issue yet.

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/7feb34a89c2a/non_bootable_disk-8a61cb6e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/420db9e4c0d8/vmlinux-8a61cb6e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/6ce6feff857d/bzImage-8a61cb6e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+d8bca25877c7eda36f5b@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
6.14.0-rc3-syzkaller-00213-g8a61cb6e150e #0 Not tainted
------------------------------------------------------
kworker/0:2/56 is trying to acquire lock:
ffff888042bae338 (&conn->lock#2){+.+.}-{4:4}, at: l2cap_info_timeout+0x60/0xa0 net/bluetooth/l2cap_core.c:1666

but task is already holding lock:
ffffc9000103fc60 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3212 [inline]
ffffc9000103fc60 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: process_scheduled_works+0x9c6/0x18e0 kernel/workqueue.c:3317

which lock already depends on the new lock.


the existing dependency chain (in reverse order) is:

-> #1 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}:
       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
       hci_disconn_cfm include/net/bluetooth/hci_core.h:2069 [inline]
       hci_conn_hash_flush+0x1be/0x350 net/bluetooth/hci_conn.c:2698
       hci_dev_do_reset net/bluetooth/hci_core.c:547 [inline]
       hci_dev_reset+0x3ed/0x5d0 net/bluetooth/hci_core.c:591
       sock_do_ioctl+0x158/0x460 net/socket.c:1199
       sock_ioctl+0x626/0x8e0 net/socket.c:1318
       vfs_ioctl fs/ioctl.c:51 [inline]
       __do_sys_ioctl fs/ioctl.c:906 [inline]
       __se_sys_ioctl+0xf5/0x170 fs/ioctl.c:892
       do_syscall_x64 arch/x86/entry/common.c:52 [inline]
       do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83
       entry_SYSCALL_64_after_hwframe+0x77/0x7f

-> #0 (&conn->lock#2){+.+.}-{4:4}:
       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
       __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

other info that might help us debug this:

 Possible unsafe locking scenario:

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

 *** DEADLOCK ***

2 locks held by kworker/0:2/56:
 #0: ffff88801b074d48 ((wq_completion)events){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3211 [inline]
 #0: ffff88801b074d48 ((wq_completion)events){+.+.}-{0:0}, at: process_scheduled_works+0x98b/0x18e0 kernel/workqueue.c:3317
 #1: ffffc9000103fc60 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: process_one_work kernel/workqueue.c:3212 [inline]
 #1: ffffc9000103fc60 ((work_completion)(&(&conn->info_timer)->work)){+.+.}-{0:0}, at: process_scheduled_works+0x9c6/0x18e0 kernel/workqueue.c:3317

stack backtrace:
CPU: 0 UID: 0 PID: 56 Comm: kworker/0:2 Not tainted 6.14.0-rc3-syzkaller-00213-g8a61cb6e150e #0
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
Workqueue: events l2cap_info_timeout
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
 __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
 </TASK>


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