FAILED: Patch "mm: allow set/clear page_type again" failed to apply to v6.6-stable tree

The patch below does not apply to the v6.6-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

Thanks,
Sasha

------------------ original commit in Linus's tree ------------------

From 9d08ec41a0645283d79a2e642205d488feaceacf Mon Sep 17 00:00:00 2001
From: Yu Zhao <[email protected]>
Date: Sat, 19 Oct 2024 22:22:12 -0600
Subject: [PATCH] mm: allow set/clear page_type again

Some page flags (page->flags) were converted to page types (page->page_types). A recent example is PG_hugetlb.

From the exclusive writer's perspective, e.g., a thread doing __folio_set_hugetlb(), there is a difference between the page flag and type APIs: the former allows the same non-atomic operation to be repeated whereas the latter does not. For example, calling __folio_set_hugetlb() twice triggers VM_BUG_ON_FOLIO(), since the second call expects the type (PG_hugetlb) not to be set previously.

Using add_hugetlb_folio() as an example, it calls __folio_set_hugetlb() in the following error-handling path. And when that happens, it triggers the aforementioned VM_BUG_ON_FOLIO().

  if (folio_test_hugetlb(folio)) {
    rc = hugetlb_vmemmap_restore_folio(h, folio);
    if (rc) {
      spin_lock_irq(&hugetlb_lock);
      add_hugetlb_folio(h, folio, false);
      ...

It is possible to make hugeTLB comply with the new requirements from the page type API. However, a straightforward fix would be to just allow the same page type to be set or cleared again inside the API, to avoid any changes to its callers.

---
 include/linux/page-flags.h | 8 ++++++++
 1 file changed, 8 insertions(+)

index 1b3a767104878..cc839e4365c18 100644
@@ -975,12 +975,16 @@ static __always_inline bool folio_test_##fname(const struct folio *folio) \
 }									\
 static __always_inline void __folio_set_##fname(struct folio *folio)	\
 {									\
+	if (folio_test_##fname(folio))					\
+		return;							\
 	VM_BUG_ON_FOLIO(data_race(folio->page.page_type) != UINT_MAX,	\
 			folio);						\
 	folio->page.page_type = (unsigned int)PGTY_##lname << 24;	\
 }									\
 static __always_inline void __folio_clear_##fname(struct folio *folio)	\
 {									\
+	if (folio->page.page_type == UINT_MAX)				\
+		return;							\
 	VM_BUG_ON_FOLIO(!folio_test_##fname(folio), folio);		\
 	folio->page.page_type = UINT_MAX;				\
 }

@@ -993,11 +997,15 @@ static __always_inline int Page##uname(const struct page *page)		\
 }									\
 static __always_inline void __SetPage##uname(struct page *page)		\
 {									\
+	if (Page##uname(page))						\
+		return;							\
 	VM_BUG_ON_PAGE(data_race(page->page_type) != UINT_MAX, page);	\
 	page->page_type = (unsigned int)PGTY_##lname << 24;		\
 }									\
 static __always_inline void __ClearPage##uname(struct page *page)	\
 {									\
+	if (page->page_type == UINT_MAX)				\
+		return;							\
 	VM_BUG_ON_PAGE(!Page##uname(page), page);			\
 	page->page_type = UINT_MAX;					\
 }

2.43.0