Re: [PATCH v3 1/2] kselftest: mm: return fail when child test result is fail in khugepaged

[Gregory Price]

On Wed, Sep 23, 2026 at 04:29:51PM +0100, Yeoreum Yun wrote:
> Although the child process in collapse_fork*() or collapse_max_ptes_shared()
> reports `KSFT_FAIL`, the result is ignored because the test only checks
> whether the parent’s page was collapsed into a huge page.
> 
> As a result, the test is considered successful whenever the parent’s page
> is a huge page, even if the child test fails, as shown below:
> 
>   #
>   # Run test: collapse_max_ptes_shared (khugepaged:anon)
>   # Allocate huge page... OK
>   # Share huge page over fork()... OK
>   # Trigger CoW on page 1023 of 2048... OK
>   # Maybe collapse with max_ptes_shared exceeded.... OK
>   # Trigger CoW on page 1024 of 2048... Fail
>   Bail out! Unexpected huge page
>   # Planned tests != run tests (26 != 23)
>   # Totals: pass:23 fail:0 xfail:0 xpass:0 skip:0 error:0  // child failed.
>   # Check if parent still has huge page... OK              // parent hpage success
>   ok 24 collapse_max_ptes_shared                           // considered as success
>   ...
>   # Totals: pass:26 fail:0 xfail:0 xpass:0 skip:0 error:0
> 
> To address this, propagate the child’s failure and skip the subsequent
> check in the parent.
> 
> Reviewed-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> Signed-off-by: Yeoreum Yun <yeoreum.yun@xxxxxxx>

Reviewed-by: Gregory Price (Meta) <gourry@xxxxxxxxxx>