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* [syzbot] [comedi?] possible deadlock in comedi_do_insn (2)
@ 2026-07-01 22:14 syzbot
  2026-09-14 19:58 ` syzbot
  0 siblings, 1 reply; 2+ messages in thread
From: syzbot @ 2026-07-01 22:14 UTC (permalink / raw)
  To: abbotti, hsweeten, linux-kernel, syzkaller-bugs

Hello,

syzbot found the following issue on:

HEAD commit:    780d569e6c4b Merge tag 'pwm/for-7.2-rc1-2' of git://git.ke..
git tree:       upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=131b4176580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=f9bf5d2bfae96234
dashboard link: https://syzkaller.appspot.com/bug?extid=acd959f649966559199c
compiler:       gcc (Debian 14.2.0-19) 14.2.0, GNU ld (GNU Binutils for Debian) 2.44

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-780d569e.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/944d8beefedc/vmlinux-780d569e.xz
kernel image: https://storage.googleapis.com/syzbot-assets/615f6b8a2abd/bzImage-780d569e.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+acd959f649966559199c@syzkaller.appspotmail.com

============================================
WARNING: possible recursive locking detected
syzkaller #0 Not tainted
--------------------------------------------
syz.4.6324/17474 is trying to acquire lock:
ffff88803435a0f0 (&dev->mutex#4){+.+.}-{4:4}, at: comedi_do_insn+0x2e/0x360 drivers/comedi/kcomedilib/kcomedilib_main.c:183

but task is already holding lock:
ffff88803435c8f0 (&dev->mutex#4){+.+.}-{4:4}, at: comedi_unlocked_ioctl+0x180/0x3310 drivers/comedi/comedi_fops.c:2290

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(&dev->mutex#4);
  lock(&dev->mutex#4);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

1 lock held by syz.4.6324/17474:
 #0: ffff88803435c8f0 (&dev->mutex#4){+.+.}-{4:4}, at: comedi_unlocked_ioctl+0x180/0x3310 drivers/comedi/comedi_fops.c:2290

stack backtrace:
CPU: 2 UID: 0 PID: 17474 Comm: syz.4.6324 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
Call Trace:
 <TASK>
 __dump_stack lib/dump_stack.c:94 [inline]
 dump_stack_lvl+0x100/0x190 lib/dump_stack.c:120
 print_deadlock_bug.cold+0xbd/0xca kernel/locking/lockdep.c:3041
 check_deadlock kernel/locking/lockdep.c:3093 [inline]
 validate_chain kernel/locking/lockdep.c:3895 [inline]
 __lock_acquire+0x1256/0x1a40 kernel/locking/lockdep.c:5237
 lock_acquire kernel/locking/lockdep.c:5868 [inline]
 lock_acquire+0x1b9/0x370 kernel/locking/lockdep.c:5825
 __mutex_lock_common kernel/locking/mutex.c:646 [inline]
 __mutex_lock+0x1a4/0x1bd0 kernel/locking/mutex.c:821
 comedi_do_insn+0x2e/0x360 drivers/comedi/kcomedilib/kcomedilib_main.c:183
 comedi_dio_bitfield2+0x3c0/0x420 drivers/comedi/kcomedilib/kcomedilib_main.c:314
 bonding_dio_insn_bits+0x2b9/0x570 drivers/comedi/drivers/comedi_bond.c:100
 insn_rw_emulate_bits+0x2a2/0x5e0 drivers/comedi/drivers.c:703
 parse_insn+0x83f/0x19f0 drivers/comedi/comedi_fops.c:1565
 do_insn_ioctl+0x152/0x4e0 drivers/comedi/comedi_fops.c:1790
 comedi_unlocked_ioctl+0xf68/0x3310 drivers/comedi/comedi_fops.c:2422
 vfs_ioctl fs/ioctl.c:51 [inline]
 __do_sys_ioctl fs/ioctl.c:597 [inline]
 __se_sys_ioctl fs/ioctl.c:583 [inline]
 __x64_sys_ioctl+0x18e/0x210 fs/ioctl.c:583
 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline]
 do_syscall_64+0x115/0x870 arch/x86/entry/syscall_64.c:94
 entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f9a0d59ce59
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:00007f9a0e40e028 EFLAGS: 00000246 ORIG_RAX: 0000000000000010
RAX: ffffffffffffffda RBX: 00007f9a0d815fa0 RCX: 00007f9a0d59ce59
RDX: 0000200000000000 RSI: 000000008028640c RDI: 0000000000000003
RBP: 00007f9a0d632e6f R08: 0000000000000000 R09: 0000000000000000
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
R13: 00007f9a0d816038 R14: 00007f9a0d815fa0 R15: 00007fff138218d8
 </TASK>


---
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^ permalink raw reply	[flat|nested] 2+ messages in thread
end of thread, other threads:[~2026-09-14 19:58 UTC | newest]

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2026-07-01 22:14 [syzbot] [comedi?] possible deadlock in comedi_do_insn (2) syzbot
2026-09-14 19:58 ` syzbot

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