[syzbot] [bluetooth?] WARNING in hci_connect_sco

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: d8ba32c5a460 Merge tag 'block-6.19-20251218' of git://git...
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=179a83c2580000
kernel config: https://syzkaller.appspot.com/x/.config?x=513255d80ab78f2b
dashboard link: https://syzkaller.appspot.com/bug?extid=5897b3c764f5989ea942
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8

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

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-d8ba32c5.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/ce9be55c4ca6/vmlinux-d8ba32c5.xz
kernel image: https://storage.googleapis.com/syzbot-assets/0a47a6667df3/bzImage-d8ba32c5.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5897b3...@syzkaller.appspotmail.com

------------[ cut here ]------------
workqueue: cannot queue hci_conn_timeout on wq hci0
WARNING: kernel/workqueue.c:2252 at __queue_work+0xd20/0xf90 kernel/workqueue.c:2250, CPU#0: syz.0.0/5341
Modules linked in:
CPU: 0 UID: 0 PID: 5341 Comm: syz.0.0 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014
RIP: 0010:__queue_work+0xd4b/0xf90 kernel/workqueue.c:2250
Code: 83 c5 18 4c 89 e8 48 c1 e8 03 42 80 3c 20 00 74 08 4c 89 ef e8 86 f8 9e 00 49 8b 75 00 49 81 c7 78 01 00 00 4c 89 f7 4c 89 fa <67> 48 0f b9 3a 48 83 c4 58 5b 41 5c 41 5d 41 5e 41 5f 5d e9 8d fb
RSP: 0018:ffffc9000bd4fb10 EFLAGS: 00010086
RAX: 1ffff11006c5114b RBX: 0000000000000008 RCX: 0000000000100000
RDX: ffff88801168a178 RSI: ffffffff8a596e20 RDI: ffffffff8fa52910
RBP: 0000000000000000 R08: ffff888036288a47 R09: 1ffff11006c51148
R10: dffffc0000000000 R11: ffffed1006c51149 R12: dffffc0000000000
R13: ffff888036288a58 R14: ffffffff8fa52910 R15: ffff88801168a178
FS: 00007f3f80e366c0(0000) GS:ffff88808d22a000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fff38bb2f52 CR3: 00000000419d7000 CR4: 0000000000352ef0
Call Trace:
<TASK>
queue_delayed_work_on+0x18b/0x280 kernel/workqueue.c:2555
hci_connect_sco+0xe9/0x3a0 net/bluetooth/hci_conn.c:1767
sco_connect net/bluetooth/sco.c:339 [inline]
sco_sock_connect+0x308/0xad0 net/bluetooth/sco.c:665
__sys_connect_file net/socket.c:2089 [inline]
__sys_connect+0x316/0x440 net/socket.c:2108
__do_sys_connect net/socket.c:2114 [inline]
__se_sys_connect net/socket.c:2111 [inline]
__x64_sys_connect+0x7a/0x90 net/socket.c:2111
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xfa/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f3f7ff8f7c9
Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007f3f80e36038 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 00007f3f801e6090 RCX: 00007f3f7ff8f7c9
RDX: 0000000000000008 RSI: 0000200000000100 RDI: 0000000000000006
RBP: 00007f3f80013f91 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f3f801e6128 R14: 00007f3f801e6090 R15: 00007ffdb2852538
</TASK>
----------------
Code disassembly (best guess):
0: 83 c5 18 add $0x18,%ebp
3: 4c 89 e8 mov %r13,%rax
6: 48 c1 e8 03 shr $0x3,%rax
a: 42 80 3c 20 00 cmpb $0x0,(%rax,%r12,1)
f: 74 08 je 0x19
11: 4c 89 ef mov %r13,%rdi
14: e8 86 f8 9e 00 call 0x9ef89f
19: 49 8b 75 00 mov 0x0(%r13),%rsi
1d: 49 81 c7 78 01 00 00 add $0x178,%r15
24: 4c 89 f7 mov %r14,%rdi
27: 4c 89 fa mov %r15,%rdx
* 2a: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction
2f: 48 83 c4 58 add $0x58,%rsp
33: 5b pop %rbx
34: 41 5c pop %r12
36: 41 5d pop %r13
38: 41 5e pop %r14
3a: 41 5f pop %r15
3c: 5d pop %rbp
3d: e9 .byte 0xe9
3e: 8d (bad)
3f: fb sti


---
This report is generated by a bot. It may contain errors.
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#syz fix: exact-commit-title

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If the report is a duplicate of another one, reply with:
#syz dup: exact-subject-of-another-report

If you want to undo deduplication, reply with:
#syz undup

[syzbot]

syzbot has found a reproducer for the following issue on:

HEAD commit: ad9a728a3388 Merge tag 'for-linus-iommufd' of git://git.ke..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=15513c5a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f1fac0919970b671
dashboard link: https://syzkaller.appspot.com/bug?extid=5897b3c764f5989ea942
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17b45322580000

Downloadable assets:
disk image (non-bootable): https://storage.googleapis.com/syzbot-assets/d900f083ada3/non_bootable_disk-ad9a728a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/bad71633ff53/vmlinux-ad9a728a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/7cac661e37c7/bzImage-ad9a728a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+5897b3...@syzkaller.appspotmail.com

------------[ cut here ]------------

workqueue: cannot queue hci_conn_timeout on wq hci1
WARNING: kernel/workqueue.c:2251 at __queue_work+0xcbb/0x10f0 kernel/workqueue.c:2250, CPU#1: syz.0.8416/24058
Modules linked in:
CPU: 1 UID: 0 PID: 24058 Comm: syz.0.8416 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:__queue_work+0xcbf/0x10f0 kernel/workqueue.c:2250
Code: 00 00 00 fc ff df 49 8d 94 24 78 01 00 00 48 89 f9 48 c1 e9 03 80 3c 01 00 0f 85 15 04 00 00 48 8d 3d 95 f5 eb 0e 48 8b 75 18 <67> 48 0f b9 3a e9 77 f7 ff ff e8 a2 b0 38 00 90 0f 0b 90 e9 ff f5
RSP: 0018:ffffc90005f2fbf8 EFLAGS: 00010046
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 1ffff11006ee094b
RDX: ffff888027001178 RSI: ffffffff8a71b840 RDI: ffffffff90ba4040
RBP: ffff888037704a40 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff888027001000
R13: ffff888048858000 R14: ffff888037704a88 R15: ffff888037704a48
FS: 00007fa16e9826c0(0000) GS:ffff8880d66d9000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00002000000000c0 CR3: 00000000523e6000 CR4: 0000000000352ef0
Call Trace:
<TASK>
__queue_delayed_work+0x365/0x470 kernel/workqueue.c:2503
queue_delayed_work_on+0x180/0x1e0 kernel/workqueue.c:2555
queue_delayed_work include/linux/workqueue.h:684 [inline]
hci_conn_drop include/net/bluetooth/hci_core.h:1710 [inline]
hci_conn_drop include/net/bluetooth/hci_core.h:1684 [inline]
hci_connect_sco+0x4d2/0xef0 net/bluetooth/hci_conn.c:1767
sco_connect net/bluetooth/sco.c:339 [inline]
sco_sock_connect+0x303/0xcb0 net/bluetooth/sco.c:665
__sys_connect_file+0x141/0x1a0 net/socket.c:2089
__sys_connect+0x141/0x170 net/socket.c:2108

__do_sys_connect net/socket.c:2114 [inline]
__se_sys_connect net/socket.c:2111 [inline]

__x64_sys_connect+0x72/0xb0 net/socket.c:2111
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xc9/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fa16db9aeb9
Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fa16e982028 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 00007fa16de15fa0 RCX: 00007fa16db9aeb9
RDX: 0000000000000008 RSI: 00002000000000c0 RDI: 0000000000000004
RBP: 00007fa16dc08c1f R08: 0000000000000000 R09: 0000000000000000

R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000

R13: 00007fa16de16038 R14: 00007fa16de15fa0 R15: 00007ffcb1740998

</TASK>
----------------
Code disassembly (best guess):

0: 00 00 add %al,(%rax)
2: 00 fc add %bh,%ah
4: ff lcall (bad)
5: df 49 8d fisttps -0x73(%rcx)
8: 94 xchg %eax,%esp
9: 24 78 and $0x78,%al
b: 01 00 add %eax,(%rax)
d: 00 48 89 add %cl,-0x77(%rax)
10: f9 stc
11: 48 c1 e9 03 shr $0x3,%rcx
15: 80 3c 01 00 cmpb $0x0,(%rcx,%rax,1)
19: 0f 85 15 04 00 00 jne 0x434
1f: 48 8d 3d 95 f5 eb 0e lea 0xeebf595(%rip),%rdi # 0xeebf5bb
26: 48 8b 75 18 mov 0x18(%rbp),%rsi

* 2a: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction

2f: e9 77 f7 ff ff jmp 0xfffff7ab
34: e8 a2 b0 38 00 call 0x38b0db
39: 90 nop
3a: 0f 0b ud2
3c: 90 nop
3d: e9 .byte 0xe9
3e: ff f5 push %rbp


---
If you want syzbot to run the reproducer, reply with:
#syz test: git://repo/address.git branch-or-commit-hash
If you attach or paste a git patch, syzbot will apply it before testing.

[Hillf Danton]

> Date: Sat, 31 Jan 2026 05:50:28 -0800

> syzbot has found a reproducer for the following issue on:
>
> HEAD commit: ad9a728a3388 Merge tag 'for-linus-iommufd' of git://git.ke..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=15513c5a580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=f1fac0919970b671
> dashboard link: https://syzkaller.appspot.com/bug?extid=5897b3c764f5989ea942
> compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17b45322580000

#syz test

--- x/include/net/bluetooth/hci_core.h
+++ y/include/net/bluetooth/hci_core.h
@@ -1687,6 +1687,7 @@ static inline void hci_conn_drop(struct

if (atomic_dec_and_test(&conn->refcnt)) {
unsigned long timeo;
+ struct hci_dev *hdev;

switch (conn->type) {
case ACL_LINK:
@@ -1707,8 +1708,14 @@ static inline void hci_conn_drop(struct
}

cancel_delayed_work(&conn->disc_work);
- queue_delayed_work(conn->hdev->workqueue,
- &conn->disc_work, timeo);
+ hdev = conn->hdev;
+ rcu_read_lock();
+ if (test_bit(HCI_RESET, &hdev->flags) ||
+ hci_dev_test_flag(hdev, HCI_CMD_DRAIN_WORKQUEUE))
+ ;
+ else
+ queue_delayed_work(hdev->workqueue, &conn->disc_work, timeo);
+ rcu_read_unlock();
}
}

--

[syzbot]

Hello,

syzbot has tested the proposed patch but the reproducer is still triggering an issue:
WARNING in hci_conn_drop

------------[ cut here ]------------
workqueue: cannot queue hci_conn_timeout on wq hci0
WARNING: kernel/workqueue.c:2251 at __queue_work+0xcbb/0x10f0 kernel/workqueue.c:2250, CPU#0: syz.1.10090/27807
Modules linked in:
CPU: 0 UID: 0 PID: 27807 Comm: syz.1.10090 Not tainted syzkaller #0 PREEMPT(full)

Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2 04/01/2014
RIP: 0010:__queue_work+0xcbf/0x10f0 kernel/workqueue.c:2250

Code: 00 00 00 fc ff df 49 8d 94 24 78 01 00 00 48 89 f9 48 c1 e9 03 80 3c 01 00 0f 85 15 04 00 00 48 8d 3d 95 e7 eb 0e 48 8b 75 18 <67> 48 0f b9 3a e9 77 f7 ff ff e8 a2 b0 38 00 90 0f 0b 90 e9 ff f5
RSP: 0018:ffffc9000351fbd0 EFLAGS: 00010046
RAX: dffffc0000000000 RBX: 0000000000000000 RCX: 1ffff1100765514b
RDX: ffff88802a0ab178 RSI: ffffffff8a71aaf0 RDI: ffffffff90ba3240
RBP: ffff88803b2a8a40 R08: 0000000000000005 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000000 R12: ffff88802a0ab000
R13: ffff8880375b8000 R14: ffff88803b2a8a88 R15: ffff88803b2a8a48
FS: 00007f7ed548e6c0(0000) GS:ffff8880d65dc000(0000) knlGS:0000000000000000

CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033

CR2: 00007f7ed548dff8 CR3: 00000000568a8000 CR4: 0000000000352ef0

Call Trace:
<TASK>
__queue_delayed_work+0x365/0x470 kernel/workqueue.c:2503
queue_delayed_work_on+0x180/0x1e0 kernel/workqueue.c:2555
queue_delayed_work include/linux/workqueue.h:684 [inline]

hci_conn_drop.part.0+0x3c9/0x430 include/net/bluetooth/hci_core.h:1717
hci_conn_drop include/net/bluetooth/hci_core.h:1688 [inline]
hci_connect_sco+0x420/0x980 net/bluetooth/hci_conn.c:1767
sco_connect net/bluetooth/sco.c:339 [inline]
sco_sock_connect+0x303/0xac0 net/bluetooth/sco.c:665

__sys_connect_file+0x141/0x1a0 net/socket.c:2089
__sys_connect+0x141/0x170 net/socket.c:2108
__do_sys_connect net/socket.c:2114 [inline]
__se_sys_connect net/socket.c:2111 [inline]
__x64_sys_connect+0x72/0xb0 net/socket.c:2111
do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
do_syscall_64+0xc9/0xf80 arch/x86/entry/syscall_64.c:94
entry_SYSCALL_64_after_hwframe+0x77/0x7f

RIP: 0033:0x7f7ed459aeb9

Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48

RSP: 002b:00007f7ed548e028 EFLAGS: 00000246 ORIG_RAX: 000000000000002a
RAX: ffffffffffffffda RBX: 00007f7ed4815fa0 RCX: 00007f7ed459aeb9

RDX: 0000000000000008 RSI: 00002000000000c0 RDI: 0000000000000004

RBP: 00007f7ed4608c1f R08: 0000000000000000 R09: 0000000000000000

R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000

R13: 00007f7ed4816038 R14: 00007f7ed4815fa0 R15: 00007ffdf46ed6a8

</TASK>
----------------
Code disassembly (best guess):
0: 00 00 add %al,(%rax)
2: 00 fc add %bh,%ah
4: ff lcall (bad)
5: df 49 8d fisttps -0x73(%rcx)
8: 94 xchg %eax,%esp
9: 24 78 and $0x78,%al
b: 01 00 add %eax,(%rax)
d: 00 48 89 add %cl,-0x77(%rax)
10: f9 stc
11: 48 c1 e9 03 shr $0x3,%rcx
15: 80 3c 01 00 cmpb $0x0,(%rcx,%rax,1)
19: 0f 85 15 04 00 00 jne 0x434

1f: 48 8d 3d 95 e7 eb 0e lea 0xeebe795(%rip),%rdi # 0xeebe7bb

26: 48 8b 75 18 mov 0x18(%rbp),%rsi
* 2a: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction
2f: e9 77 f7 ff ff jmp 0xfffff7ab
34: e8 a2 b0 38 00 call 0x38b0db
39: 90 nop
3a: 0f 0b ud2
3c: 90 nop
3d: e9 .byte 0xe9
3e: ff f5 push %rbp

Tested on:

commit: 162b4244 Merge tag 'iommu-fixes-v6.19-rc7' of git://gi..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=175ce45a580000

kernel config: https://syzkaller.appspot.com/x/.config?x=f1fac0919970b671
dashboard link: https://syzkaller.appspot.com/bug?extid=5897b3c764f5989ea942
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

patch: https://syzkaller.appspot.com/x/patch.diff?x=122b972a580000

[Hillf Danton]

> Date: Sat, 31 Jan 2026 05:50:28 -0800

> syzbot has found a reproducer for the following issue on:
>
> HEAD commit: ad9a728a3388 Merge tag 'for-linus-iommufd' of git://git.ke..
> git tree: upstream
> console output: https://syzkaller.appspot.com/x/log.txt?x=15513c5a580000
> kernel config: https://syzkaller.appspot.com/x/.config?x=f1fac0919970b671
> dashboard link: https://syzkaller.appspot.com/bug?extid=5897b3c764f5989ea942
> compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44
> syz repro: https://syzkaller.appspot.com/x/repro.syz?x=17b45322580000

#syz test

--- x/include/net/bluetooth/hci_core.h
+++ y/include/net/bluetooth/hci_core.h
@@ -1687,6 +1687,7 @@ static inline void hci_conn_drop(struct

if (atomic_dec_and_test(&conn->refcnt)) {
unsigned long timeo;
+ struct hci_dev *hdev;

switch (conn->type) {
case ACL_LINK:
@@ -1707,8 +1708,14 @@ static inline void hci_conn_drop(struct
}

cancel_delayed_work(&conn->disc_work);
- queue_delayed_work(conn->hdev->workqueue,
- &conn->disc_work, timeo);
+ hdev = conn->hdev;
+ rcu_read_lock();
+ if (test_bit(HCI_RESET, &hdev->flags) ||
+ hci_dev_test_flag(hdev, HCI_CMD_DRAIN_WORKQUEUE))
+ ;
+ else
+ queue_delayed_work(hdev->workqueue, &conn->disc_work, timeo);
+ rcu_read_unlock();
}
}

--- x/net/bluetooth/hci_sync.c
+++ y/net/bluetooth/hci_sync.c
@@ -5307,10 +5307,13 @@ int hci_dev_close_sync(struct hci_dev *h
cancel_delayed_work_sync(&adv_instance->rpa_expired_cb);
}

+ hci_dev_set_flag(hdev, HCI_CMD_DRAIN_WORKQUEUE);
+ synchronize_rcu();
/* Avoid potential lockdep warnings from the *_flush() calls by
* ensuring the workqueue is empty up front.
*/
drain_workqueue(hdev->workqueue);
+ hci_dev_clear_flag(hdev, HCI_CMD_DRAIN_WORKQUEUE);

hci_dev_lock(hdev);

--

[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+5897b3...@syzkaller.appspotmail.com
Tested-by: syzbot+5897b3...@syzkaller.appspotmail.com

Tested on:

commit: 18f7fcd5 Linux 6.19-rc8
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=13ad5644580000

kernel config: https://syzkaller.appspot.com/x/.config?x=f1fac0919970b671
dashboard link: https://syzkaller.appspot.com/bug?extid=5897b3c764f5989ea942
compiler: gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

patch: https://syzkaller.appspot.com/x/patch.diff?x=155f445a580000

Note: testing is done by a robot and is best-effort only.