Re: [PATCH] mm/memory_failure: reject unsupported non-folio compound page

[Harry Yoo]

On Wed, Feb 04, 2026 at 10:40:22PM -0500, Zi Yan wrote:
> On 4 Feb 2026, at 22:25, Miaohe Lin wrote:
> 
> > On 2026/2/5 8:56, Zi Yan wrote:
> >> When !CONFIG_TRANSPARENT_HUGEPAGE, a non-folio compound page can appear in
> >> a userspace mapping via either vm_insert_*() functions or
> >> vm_operatios_struct->fault(). They are not folios, thus should not be
> >> considered for folio operations like split. Change memory_failure() and
> >> soft_offline_page() to reject these non-folio compound pages as
> >> EOPNOTSUPP.
> >>
> >> Add PageNonFolioCompound() helper function. This function is functionally
> >> equivalent to folio_test_large() && !folio_test_large_rmappable(), but it
> >> is supposed to be used on struct page. So open code it instead.
> >>
> >> Fixes: 689b8986776c ("mm/memory-failure: improve large block size folio handling")
> >> Reported-by: 是参差 <shicenci@xxxxxxxxx>
> >> Closes: https://lore.kernel.org/all/PS1PPF7E1D7501F1E4F4441E7ECD056DEADAB98A@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx/
> >> Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
> >> ---
> >>  include/linux/page-flags.h | 16 ++++++++++++++++
> >>  mm/memory-failure.c        |  9 ++++++---
> >>  2 files changed, 22 insertions(+), 3 deletions(-)
> >>
> >> diff --git a/include/linux/page-flags.h b/include/linux/page-flags.h
> >> index f7a0e4af0c73..2fe8047f42a3 100644
> >> --- a/include/linux/page-flags.h
> >> +++ b/include/linux/page-flags.h
> >> @@ -1102,6 +1102,22 @@ static inline bool folio_contain_hwpoisoned_page(struct folio *folio)
> >>
> >>  bool is_free_buddy_page(const struct page *page);
> >>
> >> +static inline bool PageNonFolioCompound(const struct page *page)
> >> +{
> >> +	if (PageCompound(page)) {
> >> +		const struct page *head = compound_head(page);
> >> +
> >> +		/*
> >> +		 * Without CONFIG_TRANSPARENT_HUGEPAGE, PG_large_rmappable
> >> +		 * should not be set/used.
> >> +		 */
> >> +		return !IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE) ||
> >> +		       !test_bit(PG_large_rmappable, &head[1].flags.f);
> >> +	}
> >> +
> >> +	return false;
> >> +}
> >> +
> >>  #ifdef CONFIG_MIGRATION
> >>  /*
> >>   * This page is migratable through movable_ops (for selected typed pages
> >> diff --git a/mm/memory-failure.c b/mm/memory-failure.c
> >> index cf0d526e6d41..8b6b5950bb66 100644
> >> --- a/mm/memory-failure.c
> >> +++ b/mm/memory-failure.c
> >> @@ -2440,9 +2440,12 @@ int memory_failure(unsigned long pfn, int flags)
> >>
> >>  	folio = page_folio(p);
> >>
> >> -	/* filter pages that are protected from hwpoison test by users */
> >> +	/*
> >> +	 * filter pages that are protected from hwpoison test by users or
> >> +	 * unsupported non folio compound ones
> >> +	 */
> >>  	folio_lock(folio);
> >> -	if (hwpoison_filter(p)) {
> >> +	if (hwpoison_filter(p) || PageNonFolioCompound(p)) {
> >>  		ClearPageHWPoison(p);
> >>  		folio_unlock(folio);
> >>  		folio_put(folio);
> >> @@ -2945,7 +2948,7 @@ int soft_offline_page(unsigned long pfn, int flags)
> >>  	ret = get_hwpoison_page(page, flags | MF_SOFT_OFFLINE);
> >>  	put_online_mems();
> >>
> >> -	if (hwpoison_filter(page)) {
> >> +	if (hwpoison_filter(page) || PageNonFolioCompound(page)) {
> >
> > There should be no problem in soft_offline_page(). HWPoisonHandlable() check will be used
> > by get_hwpoison_page() to reject PageNonFolioCompound folios. Or am I miss something?

Oops, I missed Miohe's email.
So it's rejected because it's not on LRU.

> I did not know that. Why does memory_failure() not call HWPosonHandlable() to check the input
> page? It looks to me that HWPosonHandlable() is more appropriate than PageNonFolioCompound()
> here.

soft_offline_page() unconditionally calls get_hwpoison_page(), but
memory_failure() doesn't call it if MF_COUNT_INCREASED is set.

(MF_COUNT_INCREASED set by madvise_inject_error(), in this case)

-- 
Cheers,
Harry / Hyeonggon