[syzbot] possible deadlock in hci_unregister_dev

syzbot
2022-08-22T09:31:19Z

Hello,

syzbot found the following issue on:

HEAD commit: 5b6a4bf680d6 Add linux-next specific files for 20220818
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=10ea94b5080000
kernel config: https://syzkaller.appspot.com/x/.config?x=ead6107a3bbe3c62
dashboard link: https://syzkaller.appspot.com/bug?extid=c933391d8e4089f1f53e
compiler: gcc (Debian 10.2.1-6) 10.2.1 20210110, GNU ld (GNU Binutils for Debian) 2.35.2

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

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c933391d8e4089f1f53e@syzkaller.appspotmail.com

======================================================
WARNING: possible circular locking dependency detected
6.0.0-rc1-next-20220818-syzkaller #0 Not tainted
------------------------------------------------------
syz-executor.5/21304 is trying to acquire lock:
ffff8880751049a8 ((work_completion)(&(&hdev->discov_off)->work)){+.+.}-{0:0}, at: __flush_work+0xdd/0xae0 kernel/workqueue.c:3066

but task is already holding lock:
ffff888075104078 (&hdev->lock){+.+.}-{3:3}, at: hci_unregister_dev+0x347/0x4e0 net/bluetooth/hci_core.c:2687

which lock already depends on the new lock.

the existing dependency chain (in reverse order) is:

-> #1 (&hdev->lock){+.+.}-{3:3}:
__mutex_lock_common kernel/locking/mutex.c:603 [inline]
__mutex_lock+0x12f/0x1350 kernel/locking/mutex.c:747
discov_off+0x88/0x1a0 net/bluetooth/mgmt.c:1033
process_one_work+0x991/0x1610 kernel/workqueue.c:2289
worker_thread+0x665/0x1080 kernel/workqueue.c:2436
kthread+0x2e4/0x3a0 kernel/kthread.c:376
ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:306

-> #0 ((work_completion)(&(&hdev->discov_off)->work)){+.+.}-{0:0}:
check_prev_add kernel/locking/lockdep.c:3095 [inline]
check_prevs_add kernel/locking/lockdep.c:3214 [inline]
validate_chain kernel/locking/lockdep.c:3829 [inline]
__lock_acquire+0x2a43/0x56d0 kernel/locking/lockdep.c:5053
lock_acquire kernel/locking/lockdep.c:5666 [inline]
lock_acquire+0x1ab/0x570 kernel/locking/lockdep.c:5631
__flush_work+0x105/0xae0 kernel/workqueue.c:3069
__cancel_work_timer+0x3f9/0x570 kernel/workqueue.c:3160
mgmt_index_removed+0x218/0x340 net/bluetooth/mgmt.c:8951
hci_unregister_dev+0x34f/0x4e0 net/bluetooth/hci_core.c:2688
vhci_release+0x7c/0xf0 drivers/bluetooth/hci_vhci.c:568
__fput+0x27c/0xa90 fs/file_table.c:320
task_work_run+0xdd/0x1a0 kernel/task_work.c:177
exit_task_work include/linux/task_work.h:38 [inline]
do_exit+0xc39/0x2b60 kernel/exit.c:814
do_group_exit+0xd0/0x2a0 kernel/exit.c:944
get_signal+0x238c/0x2610 kernel/signal.c:2858
arch_do_signal_or_restart+0x82/0x2300 arch/x86/kernel/signal.c:869
exit_to_user_mode_loop kernel/entry/common.c:166 [inline]
exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:201
__syscall_exit_to_user_mode_work kernel/entry/common.c:283 [inline]
syscall_exit_to_user_mode+0x19/0x50 kernel/entry/common.c:294
do_syscall_64+0x42/0xb0 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->lock);
lock((work_completion)(&(&hdev->discov_off)->work));
lock(&hdev->lock);
lock((work_completion)(&(&hdev->discov_off)->work));

*** DEADLOCK ***

1 lock held by syz-executor.5/21304:
#0: ffff888075104078 (&hdev->lock){+.+.}-{3:3}, at: hci_unregister_dev+0x347/0x4e0 net/bluetooth/hci_core.c:2687

stack backtrace:
CPU: 1 PID: 21304 Comm: syz-executor.5 Not tainted 6.0.0-rc1-next-20220818-syzkaller #0
syz-executor.5[21304] cmdline: ��a�����\x01
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/22/2022
Call Trace:
<TASK>
__dump_stack lib/dump_stack.c:122 [inline]
dump_stack_lvl+0xcd/0x134 lib/dump_stack.c:140
check_noncircular+0x25f/0x2e0 kernel/locking/lockdep.c:2175
check_prev_add kernel/locking/lockdep.c:3095 [inline]
check_prevs_add kernel/locking/lockdep.c:3214 [inline]
validate_chain kernel/locking/lockdep.c:3829 [inline]
__lock_acquire+0x2a43/0x56d0 kernel/locking/lockdep.c:5053
lock_acquire kernel/locking/lockdep.c:5666 [inline]
lock_acquire+0x1ab/0x570 kernel/locking/lockdep.c:5631
__flush_work+0x105/0xae0 kernel/workqueue.c:3069
__cancel_work_timer+0x3f9/0x570 kernel/workqueue.c:3160
mgmt_index_removed+0x218/0x340 net/bluetooth/mgmt.c:8951
hci_unregister_dev+0x34f/0x4e0 net/bluetooth/hci_core.c:2688
vhci_release+0x7c/0xf0 drivers/bluetooth/hci_vhci.c:568
__fput+0x27c/0xa90 fs/file_table.c:320
task_work_run+0xdd/0x1a0 kernel/task_work.c:177
exit_task_work include/linux/task_work.h:38 [inline]
do_exit+0xc39/0x2b60 kernel/exit.c:814
do_group_exit+0xd0/0x2a0 kernel/exit.c:944
get_signal+0x238c/0x2610 kernel/signal.c:2858
arch_do_signal_or_restart+0x82/0x2300 arch/x86/kernel/signal.c:869
exit_to_user_mode_loop kernel/entry/common.c:166 [inline]
exit_to_user_mode_prepare+0x15f/0x250 kernel/entry/common.c:201
__syscall_exit_to_user_mode_work kernel/entry/common.c:283 [inline]
syscall_exit_to_user_mode+0x19/0x50 kernel/entry/common.c:294
do_syscall_64+0x42/0xb0 arch/x86/entry/common.c:86
entry_SYSCALL_64_after_hwframe+0x63/0xcd
RIP: 0033:0x7fce942adfa1
Code: Unable to access opcode bytes at RIP 0x7fce942adf77.
RSP: 002b:00007fce954540b0 EFLAGS: 00000293 ORIG_RAX: 00000000000000e6
RAX: fffffffffffffdfc RBX: 00007fce9439bf80 RCX: 00007fce942adfa1
RDX: 00007fce954540f0 RSI: 0000000000000000 RDI: 0000000000000000
RBP: 00007fce942e3189 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000000
R13: 00007fff7d48034f R14: 00007fce95454300 R15: 0000000000022000
</TASK>

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