Hi
Am 06.02.26 um 12:18 schrieb 王志:
Hi,
Just a gentle follow-up on this bug report. Since it's been about three weeks,
we wanted to check the status and see if this is something you’d like us to
pursue further.
We don’t want to let this slip if it’s a valid issue, but we also understand if
it’s not a priority. Could you let us know if we should provide more data (like
the QEMU DRM model or a further reduced reproducer), or if we can close this on
our end?
Thanks for your time!
Honestly speaking, no one will look at these bug reports if they require
your customization to qemu. If the bug doesn't happen with the upstream
code, then it's not a problem of upstream.
Best regards
Thomas
-----原始邮件-----
发件人: 王志 <[email protected]>
发送时间:2026-01-16 23:33:04 (星期五)
收件人: "Thomas Zimmermann" <[email protected]>
主题: Re: Re: [BUG] WARNING in drm_gem_object_handle_put_unlocked during
drm_release on Linux 6.18
Hi,
thank you very much for testing the reproducer and for the detailed feedback.
-----原始邮件-----
发件人: "Thomas Zimmermann" <[email protected]>
发送时间:2026-01-16 17:38:57 (星期五)
收件人: 王志 <[email protected]>, "Maarten Lankhorst"
<[email protected]>, "Maxime Ripard" <[email protected]>
主题: Re: [BUG] WARNING in drm_gem_object_handle_put_unlocked during drm_release
on Linux 6.18
Hi
Am 16.01.26 um 09:44 schrieb 王志:
Dear Maintainers,
I hope you are doing well. I am following up on the DRM warning in
drm_gem_object_handle_put_unlocked that I reported on January 10. I wanted to
check whether there has been any progress in investigating this issue.
If you encounter any difficulties reproducing the bug or need additional
reproducer tests, logs, or QEMU device modeling files, we would be happy to
provide assistance.
I'm running the reproducer in a qemu guest with bochs. There's no error
so far. Do I need any special parameter?
This issue depends on a custom DRM device model that we added to QEMU, so it
will not reproduce on a vanilla QEMU setup with only bochs or virtio-gpu
enabled. To reproduce the warning, the following steps are required:
1. Build QEMU with our provided device model
Please first build QEMU with the DRM device modeling code we provided (the
custom PCI device).
2. Start QEMU with the custom DRM device enabled
In the QEMU command line, add the device:
-device bochs_drm_pci
3. Verify the device inside the guest
After booting the guest, please check:
ls /dev/dri
On our setup, the custom device appears as card2.
Adjust the reproducer if needed
If card2 does not appear and the device is enumerated with a different index
(for example card0), please update the reproducer accordingly.
In the reproducer, at around line 300:
res = syz_open_dev(/*dev=*/0x200000000000, /*id=*/2,
/*flags=*/0x20001);
Please change the id value to match the actual DRM device index present in
/dev/dri (e.g. 0 if the device is card0), then rebuild and rerun the reproducer.
With the above setup, the WARNING in drm_gem_object_handle_put_unlocked can be
triggered reliably. On our machines, this reproduces the issue consistently.
Thank you very much for your time and support.
Best regards,
Zhi Wang
-----原始邮件-----
发件人: 王志 <[email protected]>
发送时间:2026-01-10 19:25:04 (星期六)
收件人: "Maarten Lankhorst" <[email protected]>, "Maxime Ripard"
<[email protected]>, "Thomas Zimmermann" <[email protected]>
抄送: [email protected], [email protected]
主题: [BUG] WARNING in drm_gem_object_handle_put_unlocked during drm_release on
Linux 6.18
Dear Maintainers,
When using our customized Syzkaller to fuzz the latest Linux kernel, the
following crash was triggered.
HEAD commit:7d0a66e4bb9081d75c82ec4957c50034cb0ea449
git tree: upstream
Output:https://github.com/manual0/crash/blob/main/report1.txt
This report says:
SYZFAIL: failed to recv rpc
fd=3 want=4 recv=0 n=0 (errno 9: Bad file descriptor)
If the DRM report a result of this problem?
Best regards
Thomas
Kernel config: https://github.com/manual0/crash/blob/main/config.txt
C reproducer:https://github.com/manual0/crash/blob/main/repro1.c
drm_gem_object_handle_put_unlocked within drivers/gpu/drm/drm_gem.c which was
identified during fuzzing on a Linux 6.18 kernel. This warning indicates a
reference counting inconsistency when releasing a GEM object handle during the
process exit path.The issue consistently occurs during the resource cleanup
sequence where drm_release calls drm_file_free and subsequently
drm_gem_release, which then iterates through GEM handles via idr_for_each. We
noticed that syzbot has previously reported a similar warning in
drm_gem_object_handle_put_unlocked under extid ef3256a360c02207a4cb, but our
finding is distinct because the syzbot report is triggered during the creation
path via drm_mode_create_dumb_ioctl whereas our trace proves the issue persists
in the cleanup path even on the newer 6.18.0 upstream tree. We have searched
for existing patches but found none that address this specific release-side
inconsistency. This bug was reproduced in a specialized environment using a
custom-modeled device added to QEMU to simulate specific hardware-driver
interactions. To assist in your analysis, we have provided our QEMU device
modeling file in the appendix as the bug may not be triggerable on standard
emulated hardware.
If you fix this issue, please add the following tag to the commit:
Reported-by: Zhi Wang <[email protected]>, Bin Yu<[email protected]>, MingYu
Wang<[email protected]>, WenJian Lu<[email protected]>, KeFeng Gao<[email protected]>,
thank you!
WARNING: CPU: 1 PID: 108806 at drivers/gpu/drm/drm_gem.c:300
drm_gem_object_handle_put_unlocked+0x30e/0x3e0
Modules linked in:
CPU: 1 UID: 0 PID: 108806 Comm: syz.1.31978 Not tainted 6.18.0 #1 PREEMPT(full)
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS
rel-1.16.3-0-ga6ed6b701f0a-prebuilt.qemu.org 04/01/2014
RIP: 0010:drm_gem_object_handle_put_unlocked+0x30e/0x3e0
Code: ed 74 61 e8 74 a8 84 fc 4c 89 e7 e8 2c 9e 94 00 48 c7 c1 60 09 ea 8b 4c 89 ea
48 c7 c7 40 05 ea 8b 48 89 c6 e8 e3 3b 44 fc 90 <0f> 0b 90 90 5b 5d 41 5c 41 5d
41 5e 41 5f e9 3f a8 84 fc 4c 89 ff
RSP: 0018:ffffc90002d27b80 EFLAGS: 00010286
RAX: 0000000000000000 RBX: ffff88811ac0fbe0 RCX: ffffffff8179ed09
RDX: ffff888124a2ba00 RSI: ffffffff8179ed16 RDI: 0000000000000001
RBP: ffff888107df1000 R08: 0000000000000001 R09: ffffed1026bc4841
R10: 0000000000000001 R11: 0000000000139fc0 R12: ffff8881001ec0c8
R13: ffff88801c71bd60 R14: 0000000000000000 R15: ffff888107df1004
FS: 000055557ced1500(0000) GS:ffff8881a2601000(0000) knlGS:0000000000000000
CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033
CR2: 00007ffe5646ff00 CR3: 000000012fba2000 CR4: 00000000000006f0
Call Trace:
<TASK>
drm_gem_object_release_handle+0xc7/0x200
idr_for_each+0x119/0x230 home/wmy/Fuzzer/third_tool/linux-6.18/lib/idr.c:208
drm_gem_release+0x29/0x40
drm_file_free.part.0+0x724/0xcf0
drm_close_helper.isra.0+0x183/0x1f0
drm_release+0x1ab/0x360
__fput+0x402/0xb50 home/wmy/Fuzzer/third_tool/linux-6.18/fs/file_table.c:468
task_work_run+0x16b/0x260
home/wmy/Fuzzer/third_tool/linux-6.18/kernel/task_work.c:227
exit_to_user_mode_loop+0xf9/0x130
do_syscall_64+0x424/0xfa0
home/wmy/Fuzzer/third_tool/linux-6.18/arch/x86/entry/syscall_32.c:308
entry_SYSCALL_64_after_hwframe+0x77/0x7f
RIP: 0033:0x7f5f9d3b059d
Code: 02 b8 ff ff ff ff c3 66 0f 1f 44 00 00 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6
48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48
c7 c1 a8 ff ff ff f7 d8 64 89 01 48
RSP: 002b:00007ffeb85fc6d8 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4
RAX: 0000000000000000 RBX: 00007f5f9d627da0 RCX: 00007f5f9d3b059d
RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003
RBP: 00007ffeb85fc778 R08: 0000001b3292016a R09: 0000000000000000
R10: 0000001b32d20000 R11: 0000000000000246 R12: ffffffffffffffff
R13: 00007f5f9d62609c R14: 00007f5f9d627da0 R15: 00007ffeb85fc7a0
</TASK>
Thanks,
Zhi Wang
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)
--
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstr. 146, 90461 Nürnberg, Germany, www.suse.com
GF: Jochen Jaser, Andrew McDonald, Werner Knoblich, (HRB 36809, AG Nürnberg)
