Re: [PATCH v4 1/3] mm: pagewalk: simplify hugepage boundary

[Sahil Chandna]

On Wed, Dec 24, 2025 at 05:23:32PM +0800, Lance Yang wrote:
> From: Lance Yang <lance.yang@xxxxxxxxx>
>
>
> On Wed, 24 Dec 2025 15:50:34 +0800, Baolin Wang wrote:
> > Hi Andrew,
> >
> > On 2025/11/28 15:01, Sahil Chandna wrote:
> > > Replace hugepage boundary computation with ALIGN() helper instead of
> > > an open coded expression. This helps to improves code readability.
> > >
> > > This was flagged by Coccinelle (misc/minmax.cocci) as an opportunity
> > > to use min(), after which the boundary computation was updated following
> > > review suggestions.
> > >
> > > Found by: make coccicheck MODE=report M=mm/
> > > No functional change intended.
> > >
> > > Acked-by: David Hildenbrand (Red Hat) <david@xxxxxxxxxx>
> > > Suggested-by: David Hildenbrand (Red Hat) <david@xxxxxxxxxx>
> > > Suggested-by: Matthew Wilcox <willy@xxxxxxxxxxxxx>
> > > Suggested-by: David Laight <david.laight.linux@xxxxxxxxx>
> > > Signed-off-by: Sahil Chandna <chandna.sahil@xxxxxxxxx>
> > > ---
> > >   mm/pagewalk.c | 3 +--
> > >   1 file changed, 1 insertion(+), 2 deletions(-)
> > >
> > > diff --git a/mm/pagewalk.c b/mm/pagewalk.c
> > > index 9f91cf85a5be..9fd59d517f37 100644
> > > --- a/mm/pagewalk.c
> > > +++ b/mm/pagewalk.c
> > > @@ -312,8 +312,7 @@ static int walk_pgd_range(unsigned long addr, unsigned long end,
> > >   static unsigned long hugetlb_entry_end(struct hstate *h, unsigned long addr,
> > >   				       unsigned long end)
> > >   {
> > > -	unsigned long boundary = (addr & huge_page_mask(h)) + huge_page_size(h);
> > > -	return boundary < end ? boundary : end;
> > > +	return min(ALIGN(addr, huge_page_size(h)), end);
> > >   }
> >
> > Please drop this patch from the mm-new branch, as it causes
> > 'run_vmtests.sh' to hang. Specifically, it leads to the system hanging
> > when executing hugepage-vmemmap test, because the program falls into an
> > infinite loop in walk_hugetlb_range() and cannot break out.
>
> Good catch! The problem is that ALIGN() returns addr itself when already
> aligned, causing the infinite loop ...
>
> > This patch does introduce functional changes and makes an incorrect
> > assumption that the 'end' must be aligned to the hugepage size. However,
>
> Yep. This patch is not equivalent to the original code when addr is
> already aligned :)
>
> > this is not necessarily the case. For example, see how pagemap_read()
> > calculates the 'end':
> >
> > "
> > end = start_vaddr + ((count / PM_ENTRY_BYTES) << PAGE_SHIFT);
> > "
> >
> > Revert this patch, mm selftests work well.
Hi Baolin, Lance, Andrew,
Thanks for catching this, I understand why ALIGN() caused an infinite loop.
Please drop this patch, or shall I submit the revert ? 
Apologies for this, I am setting up environment for running the selftest
and will send out corrected patch once it successfully pass mm selftests.

Regards,
Sahil