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

["Lorenzo Stoakes (ARM)" <ljs@kernel.org>]

On Tue, Sep 29, 2026 at 10:21:53AM +0200, David Hildenbrand (Arm) wrote:
> On 9/23/26 17:29, 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@linux.alibaba.com>
> > Signed-off-by: Yeoreum Yun <yeoreum.yun@arm.com>
> > ---
>
> That test implementation is rather messy ... :)

Yeah, I wish we could just convert more and more tests to the harness. Makes
everything easier...!

>
> Acked-by: David Hildenbrand (Arm) <david@kernel.org>

Patch LGTM so:

Reviewed-by: Lorenzo Stoakes (ARM) <ljs@kernel.org>

>
> --
> Cheers,
>
> David

--
Cheers, Lorenzo