[syzbot] [dri?] WARNING in drm_crtc_wait_one_vblank

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: cc3aa43b44bd Add linux-next specific files for 20251219
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=175fb77c580000
kernel config: https://syzkaller.appspot.com/x/.config?x=f7a09bf3b9133d9d
dashboard link: https://syzkaller.appspot.com/bug?extid=c9f3062e1f1e68af836a
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: https://storage.googleapis.com/syzbot-assets/b1b23d9783ee/disk-cc3aa43b.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/07451939cf74/vmlinux-cc3aa43b.xz
kernel image: https://storage.googleapis.com/syzbot-assets/e5ddf385746f/bzImage-cc3aa43b.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c9f306...@syzkaller.appspotmail.com

------------[ cut here ]------------
faux_driver vkms: [drm] vblank wait timed out on crtc 0
WARNING: drivers/gpu/drm/drm_vblank.c:1320 at drm_crtc_wait_one_vblank+0x33a/0x4f0 drivers/gpu/drm/drm_vblank.c:1320, CPU#1: kworker/1:2/19751
Modules linked in:
CPU: 1 UID: 0 PID: 19751 Comm: kworker/1:2 Tainted: G L syzkaller #0 PREEMPT(full)
Tainted: [L]=SOFTLOCKUP
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: events drm_fb_helper_damage_work
RIP: 0010:drm_crtc_wait_one_vblank+0x4a3/0x4f0 drivers/gpu/drm/drm_vblank.c:1320
Code: 48 b9 00 00 00 00 00 fc ff df 80 3c 08 00 74 08 4c 89 ef e8 ff ee e1 fc 4d 8b 7d 00 4c 89 e7 48 8b 74 24 18 4c 89 fa 44 89 f1 <67> 48 0f b9 3a 48 8b 7c 24 28 44 89 f6 e8 8b f6 ff ff b8 92 ff ff
RSP: 0018:ffffc9000bc1f840 EFLAGS: 00010246
RAX: 1ffff11004a3da00 RBX: 1ffff92001783f10 RCX: 0000000000000000
RDX: ffffffff8c08f7a0 RSI: ffffffff8c0aa5c0 RDI: ffffffff8fced610
RBP: ffffc9000bc1f948 R08: ffffffff8fc3d077 R09: 1ffffffff1f87a0e
R10: dffffc0000000000 R11: fffffbfff1f87a0f R12: ffffffff8fced610
R13: ffff8880251ed000 R14: 0000000000000000 R15: ffffffff8c08f7a0
FS: 0000000000000000(0000) GS:ffff888125adc000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00005627ed0d9b20 CR3: 000000002e21a000 CR4: 00000000003526f0
DR0: ffffffffffffffff DR1: 00000000000001f8 DR2: 0000000000000083
DR3: ffffffffefffff15 DR6: 00000000ffff0ff0 DR7: 0000000000000400
Call Trace:
<TASK>
drm_client_modeset_wait_for_vblank+0xc5/0xf0 drivers/gpu/drm/drm_client_modeset.c:1330
drm_fb_helper_fb_dirty drivers/gpu/drm/drm_fb_helper.c:236 [inline]
drm_fb_helper_damage_work+0xc9/0x710 drivers/gpu/drm/drm_fb_helper.c:271
process_one_work+0x93a/0x15a0 kernel/workqueue.c:3279
process_scheduled_works kernel/workqueue.c:3362 [inline]
worker_thread+0x9b0/0xee0 kernel/workqueue.c:3443
kthread+0x711/0x8a0 kernel/kthread.c:463
ret_from_fork+0x599/0xb30 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
</TASK>
----------------
Code disassembly (best guess):
0: 48 b9 00 00 00 00 00 movabs $0xdffffc0000000000,%rcx
7: fc ff df
a: 80 3c 08 00 cmpb $0x0,(%rax,%rcx,1)
e: 74 08 je 0x18
10: 4c 89 ef mov %r13,%rdi
13: e8 ff ee e1 fc call 0xfce1ef17
18: 4d 8b 7d 00 mov 0x0(%r13),%r15
1c: 4c 89 e7 mov %r12,%rdi
1f: 48 8b 74 24 18 mov 0x18(%rsp),%rsi
24: 4c 89 fa mov %r15,%rdx
27: 44 89 f1 mov %r14d,%ecx
* 2a: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction
2f: 48 8b 7c 24 28 mov 0x28(%rsp),%rdi
34: 44 89 f6 mov %r14d,%esi
37: e8 8b f6 ff ff call 0xfffff6c7
3c: b8 .byte 0xb8
3d: 92 xchg %eax,%edx
3e: ff (bad)
3f: ff .byte 0xff


---
This report is generated by a bot. It may contain errors.
See https://goo.gl/tpsmEJ for more information about syzbot.
syzbot engineers can be reached at syzk...@googlegroups.com.

syzbot will keep track of this issue. See:
https://goo.gl/tpsmEJ#status for how to communicate with syzbot.

If the report is already addressed, let syzbot know by replying with:
#syz fix: exact-commit-title

If you want to overwrite report's subsystems, reply with:
#syz set subsystems: new-subsystem
(See the list of subsystem names on the web dashboard)

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: 6de23f81a5e0 Linux 7.0-rc1
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=1240455a580000
kernel config: https://syzkaller.appspot.com/x/.config?x=d91443204e48b7a1
dashboard link: https://syzkaller.appspot.com/bug?extid=c9f3062e1f1e68af836a
compiler: Debian clang version 21.1.8 (++20251221033036+2078da43e25a-1~exp1~20251221153213.50), Debian LLD 21.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=14ffc152580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=147dd9e6580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/8c986068e2b3/disk-6de23f81.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/15bbf2602cdc/vmlinux-6de23f81.xz
kernel image: https://storage.googleapis.com/syzbot-assets/5e9cae7959ff/bzImage-6de23f81.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+c9f306...@syzkaller.appspotmail.com

------------[ cut here ]------------
faux_driver vkms: [drm] vblank wait timed out on crtc 0

WARNING: drivers/gpu/drm/drm_vblank.c:1320 at drm_crtc_wait_one_vblank+0x357/0x500 drivers/gpu/drm/drm_vblank.c:1320, CPU#0: kworker/0:4/5856
Modules linked in:
CPU: 0 UID: 0 PID: 5856 Comm: kworker/0:4 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 02/12/2026
Workqueue: events drm_fb_helper_damage_work
RIP: 0010:drm_crtc_wait_one_vblank+0x4b6/0x500 drivers/gpu/drm/drm_vblank.c:1320
Code: e8 03 48 b9 00 00 00 00 00 fc ff df 80 3c 08 00 74 08 4c 89 ef e8 8a d9 d4 fc 4d 8b 7d 00 48 89 df 4c 89 e6 4c 89 fa 44 89 f1 <67> 48 0f b9 3a 48 8b 3c 24 44 89 f6 e8 e9 f4 ff ff b8 92 ff ff ff
RSP: 0018:ffffc90004b878e0 EFLAGS: 00010246
RAX: 1ffff11004a21800 RBX: ffffffff8f7504f0 RCX: 0000000000000000
RDX: ffffffff8bbf2ce0 RSI: ffffffff8bc0ebe0 RDI: ffffffff8f7504f0
RBP: ffffc90004b879c8 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: fffffbfff1ed44b7 R12: ffffffff8bc0ebe0
R13: ffff88802510c000 R14: 0000000000000000 R15: ffffffff8bbf2ce0
FS: 0000000000000000(0000) GS:ffff888126343000(0000) knlGS:0000000000000000

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

CR2: 00007f3c5d8c9d40 CR3: 00000000247e0000 CR4: 00000000003526f0

Call Trace:
<TASK>
drm_client_modeset_wait_for_vblank+0xc5/0xf0 drivers/gpu/drm/drm_client_modeset.c:1330
drm_fb_helper_fb_dirty drivers/gpu/drm/drm_fb_helper.c:236 [inline]

drm_fb_helper_damage_work+0x131/0x6f0 drivers/gpu/drm/drm_fb_helper.c:274
process_one_work kernel/workqueue.c:3275 [inline]
process_scheduled_works+0xb02/0x1830 kernel/workqueue.c:3358
worker_thread+0xa50/0xfc0 kernel/workqueue.c:3439
kthread+0x388/0x470 kernel/kthread.c:467
ret_from_fork+0x51e/0xb90 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:245

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

0: e8 03 48 b9 00 call 0xb94808
5: 00 00 add %al,(%rax)
7: 00 00 add %al,(%rax)
9: fc cld
a: ff lcall (bad)
b: df 80 3c 08 00 74 filds 0x7400083c(%rax)
11: 08 4c 89 ef or %cl,-0x11(%rcx,%rcx,4)
15: e8 8a d9 d4 fc call 0xfcd4d9a4
1a: 4d 8b 7d 00 mov 0x0(%r13),%r15
1e: 48 89 df mov %rbx,%rdi
21: 4c 89 e6 mov %r12,%rsi

24: 4c 89 fa mov %r15,%rdx
27: 44 89 f1 mov %r14d,%ecx
* 2a: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction

2f: 48 8b 3c 24 mov (%rsp),%rdi
33: 44 89 f6 mov %r14d,%esi
36: e8 e9 f4 ff ff call 0xfffff524
3b: b8 92 ff ff ff mov $0xffffff92,%eax


---
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.