Re: [PATCH v3] selftests/mm: add folio_split() and filemap_get_entry() race test

[Lorenzo Stoakes (Oracle)]

On Fri, Mar 20, 2026 at 01:58:18PM -0400, Zi Yan wrote:
> On 20 Mar 2026, at 13:53, Lorenzo Stoakes (Oracle) wrote:
>
> > (-cc old email)
> >
> > On Thu, Mar 19, 2026 at 03:04:08PM -0400, 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, where the main thread
> >> punches holes in the shmem to cause folio_split() in the kernel and
> >> a set of 16 threads reads the shmem 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 and use a single
> >> process.
> >>
> >> 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>
> >
> > No .gitignore entry? :)
> >
> > (Just saw it flag up locally in git status)
> >
> > Linus says don't remove, but he doesn't say don't add :P
>
> I did not know about that. The fixup is below. Thank you for pointing it out.

To be clear I'm referencing this re: the .gitignore _removals_ ;)

https://lore.kernel.org/linux-mm/CAHk-=wiHK5_oBUdUiNAaevmN9f-ORe+QBqbRefAZaw-RbgEn3w@xxxxxxxxxxxxxx/

Thanks! :)

>
> From bd164a7090c0e8b6e3013502c64c161214e38714 Mon Sep 17 00:00:00 2001
> From: Zi Yan <ziy@xxxxxxxxxx>
> Date: Fri, 20 Mar 2026 13:56:04 -0400
> Subject: [PATCH] git: add generated binary into gitignore
>
> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
> ---
>  tools/testing/selftests/mm/.gitignore | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/tools/testing/selftests/mm/.gitignore b/tools/testing/selftests/mm/.gitignore
> index 83ad9454dd9d1..b0c30c5ee9e30 100644
> --- a/tools/testing/selftests/mm/.gitignore
> +++ b/tools/testing/selftests/mm/.gitignore
> @@ -61,3 +61,4 @@ guard-regions
>  merge
>  prctl_thp_disable
>  rmap
> +folio_split_race_test
> --
> 2.51.0
>
>
>
> Best Regards,
> Yan, Zi

Cheers, Lorenzo