Re: [PATCH v2] selftests/mm: add folio_split() and filemap_get_entry() race test

[Zi Yan]

On 18 Mar 2026, at 22:21, Zi Yan wrote:

> The added folio_split_race_test is a modified C port of the race condition
> test from [1]. The test creates shmem huge pages shared by both a parent
> and a child processes, where the parent process punches holes in the shmem
> to cause folio_split() in the kernel and the child process reads the shmem
> in 16 threads to cause filemap_get_entry() in the kernel.
> filemap_get_entry() reads the folio and xarray split by folio_split()
> locklessly. The original test[2] is written in rust and uses memfd (shmem
> backed). This C port uses shmem directly.
>
> Note: the initial rust to C conversion is done by Cursor.
>
> Link: https://lore.kernel.org/all/CAKNNEtw5_kZomhkugedKMPOG-sxs5Q5OLumWJdiWXv+C9Yct0w@xxxxxxxxxxxxxx/ [1]
> Link: https://github.com/dfinity/thp-madv-remove-test [2]
> Signed-off-by: Bas van Dijk <bas@xxxxxxxxxxx>
> Signed-off-by: Adam Bratschi-Kaye <adam.bratschikaye@xxxxxxxxxxx>
> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
> ---
> From V1:
> 1. added prctl(PR_SET_PDEATHSIG, SIGTERM) to avoid child looping
>    forever.
> 2. removed page_idx % PUNCH_INTERVAL >= 0, since it is a nop. Added a
>    comment.
> 3. added a child process status check to prevent parent looping forever
>    and record that as a failure.
> 4. used ksft_exit_skip() instead of ksft_finished() when the program is
>    not running as root.
> 5. restored THP settings properly when the program exits abnormally.
>
>  tools/testing/selftests/mm/Makefile           |   1 +
>  .../selftests/mm/folio_split_race_test.c      | 431 ++++++++++++++++++
>  tools/testing/selftests/mm/run_vmtests.sh     |   2 +
>  3 files changed, 434 insertions(+)
>  create mode 100644 tools/testing/selftests/mm/folio_split_race_test.c
>

It seems that I sent a stale version. Will update it. Sorry for the noise.

Best Regards,
Yan, Zi