mm-huge_memory-set-pg_has_hwpoisoned-only-after-new-folio-head-is-established.patch removed from -mm tree

The quilt patch titled
Subject: mm/huge_memory: set PG_has_hwpoisoned only after new folio head is established
has been removed from the -mm tree. Its filename was
mm-huge_memory-set-pg_has_hwpoisoned-only-after-new-folio-head-is-established.patch

This patch was dropped because it was merged into the mm-hotfixes-stable branch of git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

------------------------------------------------------
From: Rik van Riel <[email protected]>
Subject: mm/huge_memory: set PG_has_hwpoisoned only after new folio head is established
Date: Wed, 1 Jul 2026 13:42:34 -0400

__split_folio_to_order() copies the hwpoison state onto each new sub-folio while splitting a folio to a non-zero order. It does so via

	if (handle_hwpoison && page_range_has_hwpoisoned(new_head, new_nr_pages))
		folio_set_has_hwpoisoned(new_folio);

*before* clear_compound_head(new_head)/prep_compound_page(new_head, ...) turns @new_head from a tail page into a proper folio head.

PG_has_hwpoisoned is a FOLIO_SECOND_PAGE flag, so folio_set_has_hwpoisoned() resolves to folio_flags(folio, 1). With the new compound_info-based page-flags layout, folio_flags() asserts the page is not a tail:

	VM_BUG_ON_PGFLAGS(page->compound_info & 1, page);
	VM_BUG_ON_PGFLAGS(n > 0 && !test_bit(PG_head, &page->flags.f), page);

At the current call site @new_head still has the tail marker (compound_info bit 0 set, PG_head clear), so on CONFIG_DEBUG_VM kernels this hits:

kernel BUG at include/linux/page-flags.h:354 folio_flags+0x82
folio_set_has_hwpoisoned
__split_folio_to_order
__split_unmapped_folio
__folio_split
truncate_inode_partial_folio (shmem hole-punch / MADV_REMOVE)

Reproduced by syzkaller: hwpoison-inject a few subpages of a large shmem folio, then MADV_REMOVE (fallocate punch hole) on the same range, which splits the partial folio to a non-zero order.

memory_failure() tries to split the poisoned folio to order 0 first, but that split is best-effort; when it fails the folio is left large with PG_has_hwpoisoned set, the case fa5a06170036 added this hwpoison copying for.

Move the folio_set_has_hwpoisoned() call to after clear_compound_head()/prep_compound_page(), where @new_folio is a real order-new_order head folio (handle_hwpoison implies new_order != 0, so a second page always exists). The flag still lands on the same struct page (page[1] of the new folio); only the ordering relative to compound-head setup changes, satisfying the FOLIO_SECOND_PAGE precondition.

---

 mm/huge_memory.c |   12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

@@ -3587,10 +3587,6 @@ static void __split_folio_to_order(struc
 				 (1L << PG_dropbehind) |
 				 LRU_GEN_MASK | LRU_REFS_MASK));
 
-		if (handle_hwpoison &&
-		    page_range_has_hwpoisoned(new_head, new_nr_pages))
-			folio_set_has_hwpoisoned(new_folio);
-
 		new_folio->mapping = folio->mapping;
 		new_folio->index = folio->index + i;
 

@@ -3612,6 +3608,14 @@ static void __split_folio_to_order(struc
 			folio_set_large_rmappable(new_folio);
 		}
 
+		/*
+		 * PG_has_hwpoisoned is on the 2nd page, so set it after
+		 * the compound head is prepped.
+		 */
+		if (handle_hwpoison &&
+		    page_range_has_hwpoisoned(new_head, new_nr_pages))
+			folio_set_has_hwpoisoned(new_folio);
+
 		if (folio_test_young(folio))
 			folio_set_young(new_folio);
 		if (folio_test_idle(folio))

_

Patches currently in -mm which might be from [email protected] are