[syzbot] [dri?] WARNING in drm_wait_one_vblank (3)

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: f0b9d8eb98df Merge tag 'nfsd-6.19-3' of git://git.kernel.o..
git tree: upstream
console output: https://syzkaller.appspot.com/x/log.txt?x=17ea1074580000
kernel config: https://syzkaller.appspot.com/x/.config?x=1f2b6fe1fdf1a00b
dashboard link: https://syzkaller.appspot.com/bug?extid=f59157955aba9d0cb43b
compiler: Debian clang version 20.1.8 (++20250708063551+0c9f909b7976-1~exp1~20250708183702.136), Debian LLD 20.1.8
syz repro: https://syzkaller.appspot.com/x/repro.syz?x=10706922580000
C reproducer: https://syzkaller.appspot.com/x/repro.c?x=17f89f92580000

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/200586687016/disk-f0b9d8eb.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/d56481335522/vmlinux-f0b9d8eb.xz
kernel image: https://storage.googleapis.com/syzbot-assets/12cfd8855d89/bzImage-f0b9d8eb.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+f59157...@syzkaller.appspotmail.com

------------[ cut here ]------------
faux_driver vkms: [drm] vblank wait timed out on crtc 0
WARNING: drivers/gpu/drm/drm_vblank.c:1318 at drm_wait_one_vblank+0x39a/0x5c0 drivers/gpu/drm/drm_vblank.c:1318, CPU#0: kworker/0:0/9
Modules linked in:
CPU: 0 UID: 0 PID: 9 Comm: kworker/0:0 Not tainted syzkaller #0 PREEMPT_{RT,(full)}
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 10/25/2025
Workqueue: events drm_fb_helper_damage_work
RIP: 0010:drm_wait_one_vblank+0x587/0x5c0 drivers/gpu/drm/drm_vblank.c:1318
Code: 03 48 b9 00 00 00 00 00 fc ff df 80 3c 08 00 74 08 4c 89 ef e8 ba c8 f6 fc 4d 8b 7d 00 48 89 df 4c 89 e6 4c 89 fa 8b 4c 24 04 <67> 48 0f b9 3a e9 d5 fc ff ff 44 89 f9 80 e1 07 80 c1 03 38 c1 0f
RSP: 0018:ffffc900000e7860 EFLAGS: 00010246
RAX: 1ffff110281e8400 RBX: ffffffff8ee5ae70 RCX: 0000000000000000
RDX: ffffffff8b569b80 RSI: ffffffff8b584ca0 RDI: ffffffff8ee5ae70
RBP: ffffc900000e7948 R08: 0000000000000000 R09: 0000000000000000
R10: dffffc0000000000 R11: fffffbfff1db66af R12: ffffffff8b584ca0
R13: ffff888140f42000 R14: 1ffff9200001cf10 R15: ffffffff8b569b80
FS: 0000000000000000(0000) GS:ffff888126cef000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 000055557a9da5c8 CR3: 0000000043562000 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:334 [inline]
drm_fb_helper_damage_work+0xc9/0x650 drivers/gpu/drm/drm_fb_helper.c:369
process_one_work kernel/workqueue.c:3257 [inline]
process_scheduled_works+0xad1/0x1770 kernel/workqueue.c:3340
worker_thread+0x8a0/0xda0 kernel/workqueue.c:3421
kthread+0x711/0x8a0 kernel/kthread.c:463
ret_from_fork+0x510/0xa50 arch/x86/kernel/process.c:158
ret_from_fork_asm+0x1a/0x30 arch/x86/entry/entry_64.S:246
</TASK>
----------------
Code disassembly (best guess), 1 bytes skipped:
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 ba c8 f6 fc call 0xfcf6c8d2
18: 4d 8b 7d 00 mov 0x0(%r13),%r15
1c: 48 89 df mov %rbx,%rdi
1f: 4c 89 e6 mov %r12,%rsi
22: 4c 89 fa mov %r15,%rdx
25: 8b 4c 24 04 mov 0x4(%rsp),%ecx
* 29: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction
2e: e9 d5 fc ff ff jmp 0xfffffd08
33: 44 89 f9 mov %r15d,%ecx
36: 80 e1 07 and $0x7,%cl
39: 80 c1 03 add $0x3,%cl
3c: 38 c1 cmp %al,%cl
3e: 0f .byte 0xf


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