REGRESSION on linux-next (next-20251125)

["Borah, Chaitanya Kumar" <chaitanya.kumar.borah@intel.com>]

Hello Christian,

Hope you are doing well. I am Chaitanya from the linux graphics team in 
Intel.

This mail is regarding a regression we are seeing in our CI runs[1] on
linux-next repository.

Since the version next-20251125 [2], we are seeing the following regression

`````````````````````````````````````````````````````````````````````````````````
(kms_busy:5818) sw_sync-CRITICAL: Test assertion failure function 
sw_sync_timeline_create_fence, file ../lib/sw_sync.c:117:
(kms_busy:5818) sw_sync-CRITICAL: Failed assertion: 
sw_sync_fd_is_valid(fence)
(kms_busy:5818) sw_sync-CRITICAL: Last errno: 2, No such file or directory
(kms_busy:5818) sw_sync-CRITICAL: Created invalid fence
(kms_busy:5818) igt_core-INFO: Stack trace:
(kms_busy:5818) igt_core-INFO:   #0 ../lib/igt_core.c:2075 
__igt_fail_assert()
(kms_busy:5818) igt_core-INFO:   #1 [sw_sync_timeline_create_fence+0x5f]
(kms_busy:5818) igt_core-INFO:   #2 ../tests/intel/kms_busy.c:122 
flip_to_fb()
(kms_busy:5818) igt_core-INFO:   #3 ../tests/intel/kms_busy.c:220 
test_flip()
(kms_busy:5818) igt_core-INFO:   #4 ../tests/intel/kms_busy.c:459 
__igt_unique____real_main411()
(kms_busy:5818) igt_core-INFO:   #5 ../tests/intel/kms_busy.c:411 main()
(kms_busy:5818) igt_core-INFO:   #6 [__libc_init_first+0x8a]
(kms_busy:5818) igt_core-INFO:   #7 [__libc_start_main+0x8b]
(kms_busy:5818) igt_core-INFO:   #8 [_start+0x25]
`````````````````````````````````````````````````````````````````````````````````
Details log can be found in [3].

After bisecting the tree, the following patch [4] seems to be the first 
"bad" commit

`````````````````````````````````````````````````````````````````````````````````````````````````````````
commit 8459303c886151b71e8de08b73e384fd2bb7499c
Author: Christian Brauner brauner@kernel.org
Date:   Sun Nov 23 17:33:55 2025 +0100

     dma: port sw_sync_ioctl_create_fence() to FD_PREPARE()
`````````````````````````````````````````````````````````````````````````````````````````````````````````

We also verified that if we revert the patch the issue is not seen.

Could you please check why the patch causes this regression and provide 
a fix if necessary?

Thank you.

Regards

Chaitanya

[1]
https://intel-gfx-ci.01.org/tree/linux-next/combined-alt.html?
[2] 
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?h=next-20251125
[3]
https://intel-gfx-ci.01.org/tree/linux-next/next-20251125/bat-arls-6/igt@kms_busy@basic.html
[4] 
https://git.kernel.org/pub/scm/linux/kernel/git/next/linux-next.git/commit/?h=next-20251125&id=8459303c886151b71e8de08b73e384fd2bb7499c