[syzbot] [dri?] linux-next test error: WARNING in drm_mode_config_validate

[syzbot]

Hello,

syzbot found the following issue on:

HEAD commit: 0718283ab28b Add linux-next specific files for 20260717
git tree: linux-next
console output: https://syzkaller.appspot.com/x/log.txt?x=16351c32580000
kernel config: https://syzkaller.appspot.com/x/.config?x=2f6d4fd2982f9977
dashboard link: https://syzkaller.appspot.com/bug?extid=6245cb95ae707991bffa
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

Downloadable assets:
disk image: https://storage.googleapis.com/syzbot-assets/83fbf4236ddb/disk-0718283a.raw.xz
vmlinux: https://storage.googleapis.com/syzbot-assets/53d15a8f3db7/vmlinux-0718283a.xz
kernel image: https://storage.googleapis.com/syzbot-assets/d826bc7a4a27/bzImage-0718283a.xz

IMPORTANT: if you fix the issue, please add the following tag to the commit:
Reported-by: syzbot+6245cb...@syzkaller.appspotmail.com

smbdirect: subsystem loaded
Key type cifs.spnego registered
Key type cifs.idmap registered
ntfs3: Enabled Linux POSIX ACLs support
ntfs3: Read-only LZX/Xpress compression included
jffs2: version 2.2. (NAND) (SUMMARY) © 2001-2006 Red Hat, Inc.
romfs: ROMFS MTD (C) 2007 Red Hat, Inc.
QNX4 filesystem 0.2.3 registered.
qnx6: QNX6 filesystem 1.0.0 registered.
fuse: init (API version 7.45)
orangefs_debugfs_init: called with debug mask: :none: :0:
orangefs_init: module version upstream loaded
JFS: nTxBlock = 8192, nTxLock = 65536
SGI XFS with ACLs, security attributes, realtime, scrub, repair, quota, no debug enabled
9p: Installing v9fs 9p2000 file system support
NILFS version 2 loaded
befs: version: 0.9.3
ocfs2: Registered cluster interface o2cb
ocfs2: Registered cluster interface user
OCFS2 User DLM kernel interface loaded
gfs2: GFS2 installed
ceph: loaded (mds proto 32)
NET: Registered PF_ALG protocol family
async_tx: api initialized (async)
Key type asymmetric registered
Asymmetric key parser 'x509' registered
Asymmetric key parser 'pkcs8' registered
Key type pkcs7_test registered
Block layer SCSI generic (bsg) driver version 0.4 loaded (major 239)
io scheduler mq-deadline registered
io scheduler kyber registered
io scheduler bfq registered
raid6: skipped pq benchmark and selected avx2x4
input: Power Button as /devices/platform/LNXPWRBN:00/input/input0
ACPI: button: Power Button [PWRF]
input: Sleep Button as /devices/platform/LNXSLPBN:00/input/input1
ACPI: button: Sleep Button [SLPF]
ioatdma: Intel(R) QuickData Technology Driver 5.00
N_HDLC line discipline registered with maxframe=4096
Serial: 8250/16550 driver, 4 ports, IRQ sharing enabled
00:02: ttyS0 I/O:0x3f8 (irq = 4, base_baud = 115200) is a 16550A
00:03: ttyS1 I/O:0x2f8 (irq = 3, base_baud = 115200) is a 16550A
00:04: ttyS2 I/O:0x3e8 (irq = 6, base_baud = 115200) is a 16550A
00:05: ttyS3 I/O:0x2e8 (irq = 7, base_baud = 115200) is a 16550A
Non-volatile memory driver v1.3
usbcore: registered new interface driver xillyusb
ACPI: bus type drm_connector registered
[drm] Initialized vgem 1.0.0 for vgem on minor 0
------------[ cut here ]------------
[PLANE:35:plane-0] pixel format with alpha exposed but blend mode not setup
WARNING: drivers/gpu/drm/drm_mode_config.c:873 at validate_blend_mode_for_alpha_formats drivers/gpu/drm/drm_mode_config.c:872 [inline], CPU#0: swapper/0/1
WARNING: drivers/gpu/drm/drm_mode_config.c:873 at drm_mode_config_validate+0x1c6a/0x1e60 drivers/gpu/drm/drm_mode_config.c:938, CPU#0: swapper/0/1
Modules linked in:
CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Not tainted syzkaller #0 PREEMPT(full)
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 06/25/2026
RIP: 0010:validate_blend_mode_for_alpha_formats drivers/gpu/drm/drm_mode_config.c:872 [inline]
RIP: 0010:drm_mode_config_validate+0x1cab/0x1e60 drivers/gpu/drm/drm_mode_config.c:938
Code: 0f 85 ae 00 00 00 4d 8d 77 10 8b 6d 00 4c 89 f0 48 c1 e8 03 80 3c 18 00 74 08 4c 89 f7 e8 4d 08 a9 fc 49 8b 16 4c 89 ef 89 ee <67> 48 0f b9 3a eb 05 e8 39 fe 3a fc 49 bd 00 00 00 00 00 fc ff df
RSP: 0000:ffffc90000067810 EFLAGS: 00010246
RAX: 1ffff11004d63408 RBX: dffffc0000000000 RCX: ffff88801daeddc0
RDX: ffff8880268100e0 RSI: 0000000000000023 RDI: ffffffff9063bf50
RBP: 0000000000000023 R08: ffff888023a4e3ab R09: 1ffff11004749c75
R10: dffffc0000000000 R11: ffffed1004749c76 R12: dffffc0000000000
R13: ffffffff9063bf50 R14: ffff888026b1a040 R15: ffff888026b1a030
FS: 0000000000000000(0000) GS:ffff888124f37000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: ffff88823ffff000 CR3: 000000000e946000 CR4: 00000000003526f0
Call Trace:
<TASK>
drm_dev_register+0x7c/0xd80 drivers/gpu/drm/drm_drv.c:1075
vkms_create+0x40d/0x4f0 drivers/gpu/drm/vkms/vkms_drv.c:208
vkms_init+0x57/0x80 drivers/gpu/drm/vkms/vkms_drv.c:240
do_one_initcall+0x250/0x870 init/main.c:1357
do_initcall_level+0x10a/0x1a0 init/main.c:1419
do_initcalls+0x59/0xa0 init/main.c:1435
kernel_init_freeable+0x29d/0x3e0 init/main.c:1670
kernel_init+0x22/0x1d0 init/main.c:1560
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>
----------------
Code disassembly (best guess):
0: 0f 85 ae 00 00 00 jne 0xb4
6: 4d 8d 77 10 lea 0x10(%r15),%r14
a: 8b 6d 00 mov 0x0(%rbp),%ebp
d: 4c 89 f0 mov %r14,%rax
10: 48 c1 e8 03 shr $0x3,%rax
14: 80 3c 18 00 cmpb $0x0,(%rax,%rbx,1)
18: 74 08 je 0x22
1a: 4c 89 f7 mov %r14,%rdi
1d: e8 4d 08 a9 fc call 0xfca9086f
22: 49 8b 16 mov (%r14),%rdx
25: 4c 89 ef mov %r13,%rdi
28: 89 ee mov %ebp,%esi
* 2a: 67 48 0f b9 3a ud1 (%edx),%rdi <-- trapping instruction
2f: eb 05 jmp 0x36
31: e8 39 fe 3a fc call 0xfc3afe6f
36: 49 bd 00 00 00 00 00 movabs $0xdffffc0000000000,%r13
3d: fc ff df


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[syzbot]

Hello,

syzbot has tested the proposed patch and the reproducer did not trigger any issue:

Reported-by: syzbot+6245cb...@syzkaller.appspotmail.com
Tested-by: syzbot+6245cb...@syzkaller.appspotmail.com

Tested on:

commit: 0718283a Add linux-next specific files for 20260717
git tree: linux-next

kernel config: https://syzkaller.appspot.com/x/.config?x=2f6d4fd2982f9977
dashboard link: https://syzkaller.appspot.com/bug?extid=6245cb95ae707991bffa
compiler: Debian clang version 22.1.8 (++20260613092233+e80beda6e255-1~exp1~20260613092250.77), Debian LLD 22.1.8

patch: https://syzkaller.appspot.com/x/patch.diff?x=111b02b9580000

Note: testing is done by a robot and is best-effort only.