[syzbot] [comedi?] general protection fault in comedi_get_is_subdevice_running

[syzbot <syzbot+f24c3d5d316011bacc70@syzkaller.appspotmail.com>]

Hello,

syzbot found the following issue on:

HEAD commit:    e98d21c170b0 Add linux-next specific files for 20260508
git tree:       linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=13321306580000
kernel config:  https://syzkaller.appspot.com/x/.config?x=59b98218d9b2edf4
dashboard link: https://syzkaller.appspot.com/bug?extid=f24c3d5d316011bacc70
compiler:       Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8

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

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/66f2a00ee290/disk-e98d21c1.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/6b982257ce9e/vmlinux-e98d21c1.xz
kernel image: https://storage.googleapis.com/syzbot-assets/a73fbea43e1a/bzImage-e98d21c1.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f24c3d5d316011bacc70@syzkaller.appspotmail.com

Oops: general protection fault, probably for non-canonical address 0xdffffc0000000014: 0000 [#1] SMP KASAN PTI
KASAN: null-ptr-deref in range [0x00000000000000a0-0x00000000000000a7]
CPU: 0 UID: 0 PID: 18526 Comm: irq/7-comedi_pa Tainted: G             L      syzkaller #0 PREEMPT_{RT,(full)} 
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 04/18/2026
RIP: 0010:kasan_byte_accessible+0x12/0x30 mm/kasan/generic.c:210
Code: 79 ff ff ff 0f 1f 40 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 40 d6 48 c1 ef 03 48 b8 00 00 00 00 00 fc ff df <0f> b6 04 07 3c 08 0f 92 c0 e9 80 cc 08 09 cc 66 66 66 66 66 66 2e
RSP: 0018:ffffc9000477f9a0 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: ffffffff8b35f873 RCX: 0000000080000001
RDX: 0000000000000000 RSI: ffffffff8b35f873 RDI: 0000000000000014
RBP: ffffffff888f752a R08: 0000000000000001 R09: 0000000000000000
R10: dffffc0000000000 R11: ffffffff88920660 R12: 0000000000000000
R13: 00000000000000a0 R14: 00000000000000a0 R15: 0000000000000001
FS:  0000000000000000(0000) GS:ffff888125cc7000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ff47d8456b8 CR3: 0000000029342000 CR4: 00000000003526f0
Call Trace:
 <TASK>
 __kasan_check_byte+0x12/0x40 mm/kasan/common.c:573
 kasan_check_byte include/linux/kasan.h:402 [inline]
 lock_acquire+0x84/0x350 kernel/locking/lockdep.c:5844
 rt_spin_lock+0x83/0x400 kernel/locking/spinlock_rt.c:56
 spin_lock include/linux/spinlock_rt.h:45 [inline]
 comedi_get_is_subdevice_running+0x2a/0x130 drivers/comedi/comedi_fops.c:715
 comedi_buf_write_samples+0x29/0x5f0 drivers/comedi/comedi_buf.c:676
 parport_interrupt+0x105/0x160 drivers/comedi/drivers/comedi_parport.c:218
 irq_thread_fn kernel/irq/manage.c:1143 [inline]
 irq_forced_thread_fn+0x98/0x120 kernel/irq/manage.c:1165
 irq_thread+0x47e/0x6e0 kernel/irq/manage.c:1271
 kthread+0x388/0x470 kernel/kthread.c:436
 ret_from_fork+0x514/0xb70 arch/x86/kernel/process.c:158
 ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245
 </TASK>
Modules linked in:
---[ end trace 0000000000000000 ]---
RIP: 0010:kasan_byte_accessible+0x12/0x30 mm/kasan/generic.c:210
Code: 79 ff ff ff 0f 1f 40 00 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 90 0f 1f 40 d6 48 c1 ef 03 48 b8 00 00 00 00 00 fc ff df <0f> b6 04 07 3c 08 0f 92 c0 e9 80 cc 08 09 cc 66 66 66 66 66 66 2e
RSP: 0018:ffffc9000477f9a0 EFLAGS: 00010206
RAX: dffffc0000000000 RBX: ffffffff8b35f873 RCX: 0000000080000001
RDX: 0000000000000000 RSI: ffffffff8b35f873 RDI: 0000000000000014
RBP: ffffffff888f752a R08: 0000000000000001 R09: 0000000000000000
R10: dffffc0000000000 R11: ffffffff88920660 R12: 0000000000000000
R13: 00000000000000a0 R14: 00000000000000a0 R15: 0000000000000001
FS:  0000000000000000(0000) GS:ffff888125cc7000(0000) knlGS:0000000000000000
CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ff47d8456b8 CR3: 0000000029342000 CR4: 00000000003526f0
----------------
Code disassembly (best guess), 4 bytes skipped:
   0:	0f 1f 40 00          	nopl   0x0(%rax)
   4:	90                   	nop
   5:	90                   	nop
   6:	90                   	nop
   7:	90                   	nop
   8:	90                   	nop
   9:	90                   	nop
   a:	90                   	nop
   b:	90                   	nop
   c:	90                   	nop
   d:	90                   	nop
   e:	90                   	nop
   f:	90                   	nop
  10:	90                   	nop
  11:	90                   	nop
  12:	90                   	nop
  13:	90                   	nop
  14:	0f 1f 40 d6          	nopl   -0x2a(%rax)
  18:	48 c1 ef 03          	shr    $0x3,%rdi
  1c:	48 b8 00 00 00 00 00 	movabs $0xdffffc0000000000,%rax
  23:	fc ff df
* 26:	0f b6 04 07          	movzbl (%rdi,%rax,1),%eax <-- trapping instruction
  2a:	3c 08                	cmp    $0x8,%al
  2c:	0f 92 c0             	setb   %al
  2f:	e9 80 cc 08 09       	jmp    0x908ccb4
  34:	cc                   	int3
  35:	66                   	data16
  36:	66                   	data16
  37:	66                   	data16
  38:	66                   	data16
  39:	66                   	data16
  3a:	66                   	data16
  3b:	2e                   	cs


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