Re: [PATCH 2/2] selftests/mm: add hugetlb_region_cache_race regression test

[蔡翔峰]

> > On Jul 14, 2026, at 01:14, Xiangfeng Cai <caixiangfeng@xxxxxxxxxxxxx> wrote:
> > 
> > Add a regression test for the list corruption in
> > allocate_file_region_entries() fixed by the previous patch
> > ("mm/hugetlb: fix list corruption in allocate_file_region_entries()").
> > 
> > Triggering the bug requires a concurrent reservation operation to drain
> > resv->region_cache while allocate_file_region_entries() has dropped
> > resv->lock for its GFP_KERNEL allocation, forcing its retry loop to run
> > again.  As the mmap() and fallocate(PUNCH_HOLE) paths serialise on
> > inode_lock, the cache has to be drained by faults from a separate address
> > space.  The test forks several processes sharing one hugetlb inode via
> > memfd_create(MFD_HUGETLB); each mmap()s and faults ranges and punches holes
> > to keep the shared resv_map fragmented.
> > 
> > Two modes are provided:
> > 
> > - default: a safe single-process functional check that exercises the buggy
> >   line without forcing a second loop iteration; safe on any kernel.
> > 
> > - --trigger: the concurrent reproducer, which panics a vulnerable
> >   CONFIG_DEBUG_LIST=y kernel and is therefore opt-in.  It faults pages in,
> >   so it needs as many free huge pages as the file is large.
> > 
> > Assisted-by: Claude:claude-opus-4-8
> > Signed-off-by: Xiangfeng Cai <caixiangfeng@xxxxxxxxxxxxx>
> 
> It looks like this is a regression test case for a very specific instance of
> list corruption.
> 
> In my opinion, selftests should focus more on functional testing with clear
> expected behaviors and results to users. I don't think it's worth maintaining
> a test case for a minor issue like this, especially since code changes happen
> so quickly. Once the code evolves, this specific list corruption might never
> occur again, and the function itself could even be deleted during a refactor.
> 
> Therefore, I wouldn't recommend adding this as a selftest.

That makes sense to me.  This test is quite specific to the previous internal
list corruption, so I agree it is probably not a good fit for selftests.
I'll drop it.

Thanks for the review.

Xiangfeng