[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


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