Re: [syzbot] [bluetooth?] WARNING in l2cap_chan_send

[syzbot <syzbot+b6919040d9958e2fc1ae@syzkaller.appspotmail.com>]

syzbot has found a reproducer for the following issue on:

HEAD commit:    a7c7074b58d2 Merge tag 'fbdev-for-7.2-rc7' of git://git.ke..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=171c0149580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=b924ab49cf8bae2a
dashboard link: https://syzkaller.appspot.com/bug?extid=b6919040d9958e2fc1ae
compiler:       Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8
C reproducer:   https://syzkaller.appspot.com/x/repro.c?x=109c0149580000

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+b6919040d9958e2fc1ae@syzkaller.appspotmail.com

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workqueue: cannot queue hci_tx_work on wq hci0
WARNING: kernel/workqueue.c:2306 at __queue_work+0xd4a/0x1090 kernel/workqueue.c:2305, CPU#1: syz-executor109/5985
Modules linked in:
CPU: 1 UID: 0 PID: 5985 Comm: syz-executor109 Not tainted syzkaller #0 PREEMPT(full) 
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 07/24/2026
RIP: 0010:__queue_work+0xd66/0x1090 kernel/workqueue.c:2305
Code: 49 81 c7 70 01 00 00 4c 8d 35 86 dd 5b 0e 48 89 f8 48 c1 e8 03 80 3c 18 00 74 05 e8 a4 20 a5 00 49 8b 75 18 4c 89 f7 4c 89 fa <67> 48 0f b9 3a 4c 89 e8 48 c1 e8 03 80 3c 18 00 74 08 4c 89 ef e8
RSP: 0018:ffffc900032d7510 EFLAGS: 00010046
RAX: 1ffff11004fd798a RBX: dffffc0000000000 RCX: ffff8880308b1f00
RDX: ffff88807d1c0970 RSI: ffffffff8a85e850 RDI: ffffffff8fe7e260
RBP: 0000000000000000 R08: ffff888027ebcc3f R09: 1ffff11004fd7987
R10: dffffc0000000000 R11: ffffed1004fd7988 R12: 0000000000000008
R13: ffff888027ebcc38 R14: ffffffff8fe7e260 R15: ffff88807d1c0970
FS:  00007fed8a7926c0(0000) GS:ffff888125866000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007fed8c796d58 CR3: 00000000739ba000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 queue_work_on+0x106/0x1c0 kernel/workqueue.c:2452
 l2cap_chan_send+0x168a/0x22f0 net/bluetooth/l2cap_core.c:-1
 l2cap_sock_sendmsg+0x33a/0x4d0 net/bluetooth/l2cap_sock.c:1180
 sock_sendmsg_nosec+0x13a/0x180 net/socket.c:775
 __sock_sendmsg net/socket.c:790 [inline]
 ____sys_sendmsg+0x54e/0x850 net/socket.c:2684
 ___sys_sendmsg+0x2a5/0x360 net/socket.c:2738
 __sys_sendmmsg+0x273/0x4d0 net/socket.c:2827
 __do_sys_sendmmsg net/socket.c:2854 [inline]
 __se_sys_sendmmsg net/socket.c:2851 [inline]
 __x64_sys_sendmmsg+0xa0/0xc0 net/socket.c:2851
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x15f/0x560 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7fed8cfcb649
Code: c0 79 93 eb d5 48 8d 7c 1d 00 eb 99 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 d0 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007fed8a791f58 EFLAGS: 00000246 ORIG_RAX: 0000000000000133
RAX: ffffffffffffffda RBX: 00000000000001f2 RCX: 00007fed8cfcb649
RDX: 000000000000000a RSI: 00007fed8a791f80 RDI: 0000000000000006
RBP: 00007fed8a791f80 R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000040 R11: 0000000000000246 R12: 0000000000000006
R13: 0000000000000000 R14: 00007ffed10ed450 R15: 00007ffed10ed538
 </TASK>
----------------
Code disassembly (best guess):
   0:	49 81 c7 70 01 00 00 	add    $0x170,%r15
   7:	4c 8d 35 86 dd 5b 0e 	lea    0xe5bdd86(%rip),%r14        # 0xe5bdd94
   e:	48 89 f8             	mov    %rdi,%rax
  11:	48 c1 e8 03          	shr    $0x3,%rax
  15:	80 3c 18 00          	cmpb   $0x0,(%rax,%rbx,1)
  19:	74 05                	je     0x20
  1b:	e8 a4 20 a5 00       	call   0xa520c4
  20:	49 8b 75 18          	mov    0x18(%r13),%rsi
  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:	4c 89 e8             	mov    %r13,%rax
  32:	48 c1 e8 03          	shr    $0x3,%rax
  36:	80 3c 18 00          	cmpb   $0x0,(%rax,%rbx,1)
  3a:	74 08                	je     0x44
  3c:	4c 89 ef             	mov    %r13,%rdi
  3f:	e8                   	.byte 0xe8


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