[syzbot] [bluetooth?] possible deadlock in __flush_workqueue

[syzbot <syzbot+da0a9c9721e36db712e8@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    943b9f0ab2cf Add linux-next specific files for 20240117
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=121de2fbe80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=12af1d067b6a6d19
dashboard link: https://syzkaller.appspot.com/bug?extid=da0a9c9721e36db712e8
compiler:       gcc (Debian 12.2.0-14) 12.2.0, GNU ld (GNU Binutils for Debian) 2.40

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/9c032ce79e0f/disk-943b9f0a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/93163e287878/vmlinux-943b9f0a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/512cc2e14a4b/bzImage-943b9f0a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+da0a9c9721e36db712e8@syzkaller.appspotmail.com

Bluetooth: hci2: Opcode 0x0c03 failed: -110
============================================
WARNING: possible recursive locking detected
6.7.0-next-20240117-syzkaller #0 Not tainted
--------------------------------------------
kworker/u5:1/21244 is trying to acquire lock:
ffff88802e0a2538 ((wq_completion)hci2){+.+.}-{0:0}, at: __flush_workqueue+0x141/0x1340 kernel/workqueue.c:3147

but task is already holding lock:
ffff88802e0a2538 ((wq_completion)hci2){+.+.}-{0:0}, at: process_one_work+0x7ba/0x16e0 kernel/workqueue.c:2608

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock((wq_completion)hci2);
  lock((wq_completion)hci2);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by kworker/u5:1/21244:
 #0: ffff88802e0a2538 ((wq_completion)hci2){+.+.}-{0:0}, at: process_one_work+0x7ba/0x16e0 kernel/workqueue.c:2608
 #1: ffffc9000dc27d80 ((work_completion)(&hdev->error_reset)){+.+.}-{0:0}, at: process_one_work+0x824/0x16e0 kernel/workqueue.c:2609

stack backtrace:
CPU: 1 PID: 21244 Comm: kworker/u5:1 Not tainted 6.7.0-next-20240117-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 11/17/2023
Workqueue: hci2 hci_error_reset
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xd9/0x1b0 lib/dump_stack.c:106
 check_deadlock kernel/locking/lockdep.c:3062 [inline]
 validate_chain kernel/locking/lockdep.c:3856 [inline]
 __lock_acquire+0x20e6/0x3b30 kernel/locking/lockdep.c:5137
 lock_acquire kernel/locking/lockdep.c:5754 [inline]
 lock_acquire+0x1b1/0x540 kernel/locking/lockdep.c:5719
 __flush_workqueue+0x14b/0x1340 kernel/workqueue.c:3147
 drain_workqueue+0x18f/0x3d0 kernel/workqueue.c:3312
 destroy_workqueue+0xc3/0xb10 kernel/workqueue.c:4801
 hci_release_dev+0x14e/0x620 net/bluetooth/hci_core.c:2808
 bt_host_release+0x6a/0xb0 net/bluetooth/hci_sysfs.c:94
 device_release+0xa1/0x240 drivers/base/core.c:2485
 kobject_cleanup lib/kobject.c:682 [inline]
 kobject_release lib/kobject.c:716 [inline]
 kref_put include/linux/kref.h:65 [inline]
 kobject_put+0x1d0/0x440 lib/kobject.c:733
 put_device+0x1f/0x30 drivers/base/core.c:3733
 process_one_work+0x8d5/0x16e0 kernel/workqueue.c:2633
 process_scheduled_works kernel/workqueue.c:2707 [inline]
 worker_thread+0x8b6/0x1290 kernel/workqueue.c:2788
 kthread+0x2c1/0x3a0 kernel/kthread.c:388
 ret_from_fork+0x45/0x80 arch/x86/kernel/process.c:147
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:242
 </TASK>


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