Re: [syzbot] [dri?] WARNING in drm_crtc_wait_one_vblank

[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+c9f3062e1f1e68af836a@xxxxxxxxxxxxxxxxxxxxxxxxx

------------[ 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


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