Subject: [syzbot] linux-next test error: possible deadlock in hci_cmd_sync_clear

From: syzbot <[email-masked]>
Date: Fri, 24 Feb 2023 00:41:54 -0800

Hello,

syzbot found the following issue on:

HEAD commit:    4d6d7ce9baaf Add linux-next specific files for 20230224
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=159b1e44c80000
kernel config:  https://syzkaller.appspot.com/x/.config?x=4fe68735401a6111
dashboard link: https://syzkaller.appspot.com/bug?extid=0dc69aab0bf17cdd4092
compiler:       gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/f73e26755a73/disk-4d6d7ce9.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/e8a9e1fdaa91/vmlinux-4d6d7ce9.xz
kernel image: https://storage.googleapis.com/syzbot-assets/ad213a829368/bzImage-4d6d7ce9.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: [email-masked]

======================================================
WARNING: possible circular locking dependency detected
6.2.0-next-20230224-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.0/5079 is trying to acquire lock:
ffff888022388880 ((work_completion)(&hdev->cmd_sync_work)){+.+.}-{0:0}, at: __flush_work+0xdd/0xb60 kernel/workqueue.c:3167

but task is already holding lock:
ffff888022388920 (&hdev->cmd_sync_work_lock){+.+.}-{3:3}, at: hci_cmd_sync_clear+0x3c/0x2a0 net/bluetooth/hci_sync.c:653

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&hdev->cmd_sync_work_lock){+.+.}-{3:3}:
       __mutex_lock_common kernel/locking/mutex.c:603 [inline]
       __mutex_lock+0x12f/0x1350 kernel/locking/mutex.c:747
       hci_cmd_sync_work+0x26f/0x450 net/bluetooth/hci_sync.c:287
       process_one_work+0x9bf/0x1820 kernel/workqueue.c:2390
       worker_thread+0x669/0x1090 kernel/workqueue.c:2537
       kthread+0x2e8/0x3a0 kernel/kthread.c:376
       ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:308

-> #0 ((work_completion)(&hdev->cmd_sync_work)){+.+.}-{0:0}:
       check_prev_add kernel/locking/lockdep.c:3098 [inline]
       check_prevs_add kernel/locking/lockdep.c:3217 [inline]
       validate_chain kernel/locking/lockdep.c:3832 [inline]
       __lock_acquire+0x2ec7/0x5d40 kernel/locking/lockdep.c:5056
       lock_acquire.part.0+0x11a/0x370 kernel/locking/lockdep.c:5669
       __flush_work+0x109/0xb60 kernel/workqueue.c:3170
       __cancel_work_timer+0x3f9/0x570 kernel/workqueue.c:3261
       hci_cmd_sync_clear+0x48/0x2a0 net/bluetooth/hci_sync.c:654
       hci_unregister_dev+0x16b/0x580 net/bluetooth/hci_core.c:2696
       vhci_release+0x80/0xf0 drivers/bluetooth/hci_vhci.c:568
       __fput+0x27c/0xa90 fs/file_table.c:321
       task_work_run+0x16f/0x270 kernel/task_work.c:179
       exit_task_work include/linux/task_work.h:38 [inline]
       do_exit+0xb42/0x2b60 kernel/exit.c:869
       do_group_exit+0xd4/0x2a0 kernel/exit.c:1019
       get_signal+0x2315/0x25b0 kernel/signal.c:2859
       arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306
       exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
       exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203
       __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
       syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
       do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
       entry_SYSCALL_64_after_hwframe+0x63/0xcd

other info that might help us debug this:

 Possible unsafe locking scenario:

       CPU0                    CPU1
       ----                    ----
  lock(&hdev->cmd_sync_work_lock);
                               lock((work_completion)(&hdev->cmd_sync_work));
                               lock(&hdev->cmd_sync_work_lock);
  lock((work_completion)(&hdev->cmd_sync_work));

 *** DEADLOCK ***

1 lock held by syz-executor.0/5079:
 #0: ffff888022388920 (&hdev->cmd_sync_work_lock){+.+.}-{3:3}, at: hci_cmd_sync_clear+0x3c/0x2a0 net/bluetooth/hci_sync.c:653

stack backtrace:
CPU: 0 PID: 5079 Comm: syz-executor.0 Not tainted 6.2.0-next-20230224-syzkaller #0
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/16/2023
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:88 [inline]
 dump_stack_lvl+0xd9/0x150 lib/dump_stack.c:106
 check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2178
 check_prev_add kernel/locking/lockdep.c:3098 [inline]
 check_prevs_add kernel/locking/lockdep.c:3217 [inline]
 validate_chain kernel/locking/lockdep.c:3832 [inline]
 __lock_acquire+0x2ec7/0x5d40 kernel/locking/lockdep.c:5056
 lock_acquire.part.0+0x11a/0x370 kernel/locking/lockdep.c:5669
 __flush_work+0x109/0xb60 kernel/workqueue.c:3170
 __cancel_work_timer+0x3f9/0x570 kernel/workqueue.c:3261
 hci_cmd_sync_clear+0x48/0x2a0 net/bluetooth/hci_sync.c:654
 hci_unregister_dev+0x16b/0x580 net/bluetooth/hci_core.c:2696
 vhci_release+0x80/0xf0 drivers/bluetooth/hci_vhci.c:568
 __fput+0x27c/0xa90 fs/file_table.c:321
 task_work_run+0x16f/0x270 kernel/task_work.c:179
 exit_task_work include/linux/task_work.h:38 [inline]
 do_exit+0xb42/0x2b60 kernel/exit.c:869
 do_group_exit+0xd4/0x2a0 kernel/exit.c:1019
 get_signal+0x2315/0x25b0 kernel/signal.c:2859
 arch_do_signal_or_restart+0x79/0x5c0 arch/x86/kernel/signal.c:306
 exit_to_user_mode_loop kernel/entry/common.c:168 [inline]
 exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:203
 __syscall_exit_to_user_mode_work kernel/entry/common.c:285 [inline]
 syscall_exit_to_user_mode+0x1d/0x50 kernel/entry/common.c:296
 do_syscall_64+0x46/0xb0 arch/x86/entry/common.c:86
 entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7ff20608d567
Code: Unable to access opcode bytes at 0x7ff20608d53d.
RSP: 002b:00007fffc36b4528 EFLAGS: 00000246 ORIG_RAX: 00000000000000a6
RAX: fffffffffffffffe RBX: 0000000000000003 RCX: 00007ff20608d567
RDX: 00007fffc36b45fc RSI: 000000000000000a RDI: 00007fffc36b45f0
RBP: 00007fffc36b45f0 R08: 00000000ffffffff R09: 00007fffc36b43c0
R10: 0000555555e77853 R11: 0000000000000246 R12: 00007ff2060e6b24
R13: 00007fffc36b56b0 R14: 0000555555e77810 R15: 00007fffc36b56f0
 </TASK>

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