Re: [syzbot] [wireless?] WARNING in rfkill_unregister

On 01/01/2026 13:07, Johannes Berg wrote:

Hi,

quoted

------------[ cut here ]------------
rtmutex deadlock detected
WARNING: kernel/locking/rtmutex.c:1674 at rt_mutex_handle_deadlock+0x21/0xb0 kernel/locking/rtmutex.c:1674, CPU#0: syz.7.2908/15923
Modules linked in:
CPU: 0 UID: 0 PID: 15923 Comm: syz.7.2908 Not tainted syzkaller #0 PREEMPT_{RT,(full)} 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
RIP: 0010:rt_mutex_handle_deadlock+0x21/0xb0 kernel/locking/rtmutex.c:1674
Code: 90 90 90 90 90 90 90 90 90 41 57 41 56 41 55 41 54 53 83 ff dd 0f 85 86 00 00 00 48 89 f7 e8 a6 39 01 00 48 8d 3d af 7c 0a 04 <67> 48 0f b9 3a 4c 8d 3d 00 00 00 00 65 48 8b 1c 25 08 10 b3 91 4c
RSP: 0018:ffffc90004617710 EFLAGS: 00010286
RAX: 0000000080000000 RBX: ffffc900046177a0 RCX: 0000000000000000
RDX: 0000000000000006 RSI: ffffffff8ce0bbf9 RDI: ffffffff8ede5760
RBP: ffffc900046178c0 R08: ffffffff8edb3477 R09: 1ffffffff1db668e
R10: dffffc0000000000 R11: fffffbfff1db668f R12: 1ffff920008c2ef0
R13: ffffffff8ad3d599 R14: ffffffff8eb910e0 R15: dffffc0000000000
FS:  0000000000000000(0000) GS:ffff888126cef000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000056422df5abe0 CR3: 000000005929c000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 __rt_mutex_slowlock kernel/locking/rtmutex.c:1734 [inline]
 __rt_mutex_slowlock_locked kernel/locking/rtmutex.c:1760 [inline]
 rt_mutex_slowlock+0x666/0x6b0 kernel/locking/rtmutex.c:1800
 __rt_mutex_lock kernel/locking/rtmutex.c:1815 [inline]
 __mutex_lock_common kernel/locking/rtmutex_api.c:534 [inline]
 mutex_lock_nested+0x16a/0x1d0 kernel/locking/rtmutex_api.c:552
 rfkill_unregister+0xd1/0x230 net/rfkill/core.c:1145
 nfc_unregister_device+0x96/0x300 net/nfc/core.c:1167
 virtual_ncidev_close+0x59/0x90 drivers/nfc/virtual_ncidev.c:172

NFC has been issues with this for *years*. Technically, Krzysztof is
listed as a maintainer but I suspect that's mostly dead.

And I have little time nowadays to do any real maintenance. I am
thinking that NFC should be marked Odd Fixes.

Is there a way you could route rfkill issues to NFC (and have them
ignored there) if NFC is involved?

Clearly they're not useful if nobody is interested in fixing NFC, so
maybe we should just disable the virtual NFC driver completely and just
not have syzbot run on anything there...

Great benefit of virtual NFC driver was to show how buggy the NFC stack
is :)

Best regards,
Krzysztof