linux-kernel - [syzbot] [bluetooth?] WARNING: locking bug in l2cap_unregister

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Message-ID: <694cb223.050a0220.35954c.0032.GAE@google.com>
Date: Wed, 24 Dec 2025 19:40:19 -0800
From: syzbot <syzbot+a97711deac466a4afeac@...kaller.appspotmail.com>
To: johan.hedberg@...il.com, linux-bluetooth@...r.kernel.org, 
	linux-kernel@...r.kernel.org, luiz.dentz@...il.com, marcel@...tmann.org, 
	syzkaller-bugs@...glegroups.com
Subject: [syzbot] [bluetooth?] WARNING: locking bug in l2cap_unregister_user

Hello,

syzbot found the following issue on:

HEAD commit:    8f0b4cce4481 Linux 6.19-rc1
git tree:       git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git for-kernelci
console output: https://syzkaller.appspot.com/x/log.txt?x=14520b1a580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=8a8594efdc14f07a
dashboard link: https://syzkaller.appspot.com/bug?extid=a97711deac466a4afeac
compiler:       Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
userspace arch: arm64

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/cd4f5f43efc8/disk-8f0b4cce.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/aafb35ac3a3c/vmlinux-8f0b4cce.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d221fae4ab17/Image-8f0b4cce.gz.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+a97711deac466a4afeac@...kaller.appspotmail.com

------------[ cut here ]------------
DEBUG_LOCKS_WARN_ON(1)
WARNING: kernel/locking/lockdep.c:238 at hlock_class kernel/locking/lockdep.c:-1 [inline], CPU#1: khidpd_10cf5502/6710
WARNING: kernel/locking/lockdep.c:238 at check_wait_context kernel/locking/lockdep.c:4854 [inline], CPU#1: khidpd_10cf5502/6710
WARNING: kernel/locking/lockdep.c:238 at __lock_acquire+0x384/0x30a4 kernel/locking/lockdep.c:5187, CPU#1: khidpd_10cf5502/6710
Modules linked in:
CPU: 1 UID: 0 PID: 6710 Comm: khidpd_10cf5502 Tainted: G             L      syzkaller #0 PREEMPT 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/03/2025
pstate: 634000c5 (nZCv daIF +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : hlock_class kernel/locking/lockdep.c:-1 [inline]
pc : check_wait_context kernel/locking/lockdep.c:4854 [inline]
pc : __lock_acquire+0x384/0x30a4 kernel/locking/lockdep.c:5187
lr : hlock_class kernel/locking/lockdep.c:238 [inline]
lr : check_wait_context kernel/locking/lockdep.c:4854 [inline]
lr : __lock_acquire+0x378/0x30a4 kernel/locking/lockdep.c:5187
sp : ffff80009f727820
x29: ffff80009f727900 x28: 0000000000000001 x27: ffff0000cfc46078
x26: ffff80008afa88d4 x25: 0000000000000000 x24: 0000000000000001
x23: 0000000000000000 x22: 0000000000000000 x21: ffff0000cfc45580
x20: ffff8000975d0000 x19: 0000000000000000 x18: 1fffe00033781890
x17: ffff80008f86e000 x16: ffff800082e5c71c x15: 0000000000000001
x14: 1fffe000337818fa x13: 0000000000000000 x12: 0000000000000000
x11: ffff800093397d48 x10: 0000000000ff0100 x9 : 910d7cd7a1feeb00
x8 : 0000000000000000 x7 : 4e5241575f534b43 x6 : ffff800080575c38
x5 : 0000000000000000 x4 : 0000000000000000 x3 : ffff8000807f0908
x2 : 0000000000000001 x1 : 0000000100000002 x0 : 0000000000000000
Call trace:
 hlock_class kernel/locking/lockdep.c:-1 [inline] (P)
 check_wait_context kernel/locking/lockdep.c:4854 [inline] (P)
 __lock_acquire+0x384/0x30a4 kernel/locking/lockdep.c:5187 (P)
 lock_acquire+0x140/0x2e0 kernel/locking/lockdep.c:5868
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0x5c/0x7c kernel/locking/spinlock.c:162
 class_raw_spinlock_irqsave_constructor include/linux/spinlock.h:557 [inline]
 set_task_blocked_on include/linux/sched.h:2165 [inline]
 __mutex_lock_common+0xd24/0x2678 kernel/locking/mutex.c:701
 __mutex_lock kernel/locking/mutex.c:776 [inline]
 mutex_lock_nested+0x2c/0x38 kernel/locking/mutex.c:828
 l2cap_unregister_user+0x74/0x190 net/bluetooth/l2cap_core.c:1729
 hidp_session_thread+0x3d0/0x490 net/bluetooth/hidp/core.c:1304
 kthread+0x5fc/0x75c kernel/kthread.c:463
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:844
irq event stamp: 60
hardirqs last  enabled at (59): [<ffff80008049e5a4>] raw_spin_rq_unlock_irq kernel/sched/sched.h:1570 [inline]
hardirqs last  enabled at (59): [<ffff80008049e5a4>] finish_lock_switch+0xb0/0x1c0 kernel/sched/core.c:4995
hardirqs last disabled at (60): [<ffff80008afb8d40>] __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:108 [inline]
hardirqs last disabled at (60): [<ffff80008afb8d40>] _raw_spin_lock_irqsave+0x2c/0x7c kernel/locking/spinlock.c:162
softirqs last  enabled at (0): [<ffff8000803bf2b4>] copy_process+0x10a8/0x32fc kernel/fork.c:2167
softirqs last disabled at (0): [<0000000000000000>] 0x0
---[ end trace 0000000000000000 ]---
Unable to handle kernel NULL pointer dereference at virtual address 00000000000000c4
Mem abort info:
  ESR = 0x0000000096000006
  EC = 0x25: DABT (current EL), IL = 32 bits
  SET = 0, FnV = 0
  EA = 0, S1PTW = 0
  FSC = 0x06: level 2 translation fault
Data abort info:
  ISV = 0, ISS = 0x00000006, ISS2 = 0x00000000
  CM = 0, WnR = 0, TnD = 0, TagAccess = 0
  GCS = 0, Overlay = 0, DirtyBit = 0, Xs = 0
user pgtable: 4k pages, 48-bit VAs, pgdp=0000000117997000
[00000000000000c4] pgd=08000001229a2403, p4d=08000001229a2403, pud=080000010828f403, pmd=0000000000000000
Internal error: Oops: 0000000096000006 [#1]  SMP
Modules linked in:
CPU: 1 UID: 0 PID: 6710 Comm: khidpd_10cf5502 Tainted: G        W    L      syzkaller #0 PREEMPT 
Tainted: [W]=WARN, [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/03/2025
pstate: 634000c5 (nZCv daIF +PAN -UAO +TCO +DIT -SSBS BTYPE=--)
pc : check_wait_context kernel/locking/lockdep.c:4854 [inline]
pc : __lock_acquire+0x398/0x30a4 kernel/locking/lockdep.c:5187
lr : hlock_class kernel/locking/lockdep.c:238 [inline]
lr : check_wait_context kernel/locking/lockdep.c:4854 [inline]
lr : __lock_acquire+0x378/0x30a4 kernel/locking/lockdep.c:5187
sp : ffff80009f727820
x29: ffff80009f727900 x28: 0000000000000001 x27: ffff0000cfc46078
x26: ffff80008afa88d4 x25: 0000000000000000 x24: 0000000000000001
x23: 0000000000000000 x22: 0000000000000000 x21: ffff0000cfc45580
x20: ffff8000975d0000 x19: 0000000000000000 x18: 1fffe00033781890
x17: ffff80008f86e000 x16: ffff800082e5c71c x15: 0000000000000001
x14: 1fffe000337818fa x13: 0000000000000000 x12: 0000000000000000
x11: ffff800093397d48 x10: 0000000000ff0100 x9 : 00000000000c1e77
x8 : 0000000000000000 x7 : 4e5241575f534b43 x6 : ffff800080575c38
x5 : 0000000000000000 x4 : 0000000000000000 x3 : ffff8000807f0908
x2 : 0000000000000001 x1 : 0000000100000002 x0 : 0000000000000000
Call trace:
 hlock_class kernel/locking/lockdep.c:229 [inline] (P)
 check_wait_context kernel/locking/lockdep.c:4855 [inline] (P)
 __lock_acquire+0x398/0x30a4 kernel/locking/lockdep.c:5187 (P)
 lock_acquire+0x140/0x2e0 kernel/locking/lockdep.c:5868
 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
 _raw_spin_lock_irqsave+0x5c/0x7c kernel/locking/spinlock.c:162
 class_raw_spinlock_irqsave_constructor include/linux/spinlock.h:557 [inline]
 set_task_blocked_on include/linux/sched.h:2165 [inline]
 __mutex_lock_common+0xd24/0x2678 kernel/locking/mutex.c:701
 __mutex_lock kernel/locking/mutex.c:776 [inline]
 mutex_lock_nested+0x2c/0x38 kernel/locking/mutex.c:828
 l2cap_unregister_user+0x74/0x190 net/bluetooth/l2cap_core.c:1729
 hidp_session_thread+0x3d0/0x490 net/bluetooth/hidp/core.c:1304
 kthread+0x5fc/0x75c kernel/kthread.c:463
 ret_from_fork+0x10/0x20 arch/arm64/kernel/entry.S:844
Code: 14000003 d00972eb 9135216b b9402369 (39431113) 
---[ end trace 0000000000000000 ]---
----------------
Code disassembly (best guess):
   0:	14000003 	b	0xc
   4:	d00972eb 	adrp	x11, 0x12e5e000
   8:	9135216b 	add	x11, x11, #0xd48
   c:	b9402369 	ldr	w9, [x27, #32]
* 10:	39431113 	ldrb	w19, [x8, #196] <-- trapping instruction


---
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