mm: fix ASSERT_EXCLUSIVE_BITS by passing memdesc_flags_t by pointer

From: Hui Zhu <[email protected]>

KCSAN reports a data race between page_to_nid()/folio_pgdat() reading page->flags and folio_trylock()/folio_lock() concurrently doing test_and_set_bit_lock(PG_locked, ...) on the same word, e.g.:

  BUG: KCSAN: data-race in __lruvec_stat_mod_folio / shmem_get_folio_gfp

The race is benign: nid/zone bits are set once at page init and never overlap with PG_locked. However, ASSERT_EXCLUSIVE_BITS() inside memdesc_nid/zonenum() was checking a by-value copy of the flags word, not the live page->flags, so it failed to annotate the real access.

Change memdesc_nid(), memdesc_zonenum(), memdesc_section(), and memdesc_is_zone_device() to take a const memdesc_flags_t * and update all callers to pass &page->flags / &folio->flags, so ASSERT_EXCLUSIVE_BITS() operates on the actual shared word.

Guard the ASSERT_EXCLUSIVE_BITS() calls in memdesc_zonenum() and memdesc_section() under ZONES_WIDTH != 0 / SECTIONS_WIDTH != 0 to avoid a zero-mask check on configs where the corresponding field is absent. Under CONFIG_NUMA=n, stub out page_to_nid() and folio_nid() as plain "return 0" instead of reading page->flags when NODES_MASK is 0 and the check can never fire.

Signed-off-by Hui Zhu <[email protected]>

Co-developed-by David Hildenbrand (Arm) <[email protected]>

Signed-off-by David Hildenbrand (Arm) <[email protected]>

Signed-off-by Hui Zhu <[email protected]>

---
Changelog:
v9:
Add the SECTIONS_WIDTH check to memdesc_section.
v8:
According to the comments of Andrew, include kcsan-checks.h in mm.h. Incorporate David's patch that switch memdesc_nid(), memdesc_zonenum(), memdesc_section() and memdesc_is_zone_device() to take a const memdesc_flags_t * instead of using a per-accessor macro/call-site hack. Update all callers accordingly and extend the same exclusive-bits check to memdesc_section() and memdesc_is_zone_device(), guarded by SECTIONS_WIDTH != 0 / reusing ZONES_WIDTH != 0 to avoid zero-mask checks on configs without the corresponding field.
v7:
According to the comments of Sashiko, restrict the memdesc_nid() macro to CONFIG_NUMA, keeping a plain "return 0" static inline stub otherwise, and re-add a local page pointer in page_to_nid() to avoid evaluating PF_POISONED_CHECK(page) twice.
v6:
According to the comments of David, turn memdesc_nid() from a static inline function into a macro so ASSERT_EXCLUSIVE_BITS() can check the caller's page->flags/folio->flags directly.
v5:
According to the comments of Sashiko, guard the ASSERT_EXCLUSIVE_BITS() calls with #ifndef NODE_NOT_IN_PAGE_FLAGS (for nid) and #if ZONES_WIDTH != 0 (for zonenum).
According to the comments of David, avoid calling PF_POISONED_CHECK(page) twice in page_to_nid().
According to the warning of lkp, switch the CONFIG_NUMA=n page_to_nid()/folio_nid() stubs from macros to static inline functions. v4:
According to the comments of Andrew and Sashiko, set page_to_nid()/folio_nid() as static inline stubs returning 0 under CONFIG_NUMA=n.
v3:
According to the comments of Andrew and Sashiko, move ASSERT_EXCLUSIVE_BITS out of memdesc_nid()/memdesc_zonenum() into the page/folio call sites.
v2:
According to the comments of David, remove useless comments and use ASSERT_EXCLUSIVE_BITS() in memdesc_nid() instead of data_race() in page_to_nid().

 include/asm-generic/memory_model.h |  2 +-
 include/linux/mm.h                 | 42 ++++++++++++++++++++++++------
 include/linux/mm_inline.h          |  4 +--
 include/linux/mmzone.h             | 26 +++++++++---------
 mm/page_alloc.c                    |  6 ++---
 mm/slab.h                          |  2 +-
 mm/sparse.c                        |  2 +-
 7 files changed, 56 insertions(+), 28 deletions(-)

include/asm-generic/memory_model.h +1 -1

index efa6610acbc7..f8404bc7773c 100644
@@ -53,7 +53,7 @@ static inline int pfn_valid(unsigned long pfn)
  */
 #define __page_to_pfn(pg)					\
 ({	const struct page *__pg = (pg);				\
-	int __sec = memdesc_section(__pg->flags);		\
+	int __sec = memdesc_section(&__pg->flags);		\
 	(unsigned long)(__pg - __section_mem_map_addr(__nr_to_section(__sec)));	\
 })
 

include/linux/mm.h +25 -3

index 485df9c2dbdd..60722c42a622 100644
@@ -37,6 +37,7 @@
 #include <linux/bitmap.h>
 #include <linux/bitops.h>
 #include <linux/iommu-debug-pagealloc.h>
+#include <linux/kcsan-checks.h>
 
 struct mempolicy;
 struct anon_vma;

@@ -2286,23 +2287,45 @@ static inline int page_zone_id(struct page *page)
 }
 
 #ifdef NODE_NOT_IN_PAGE_FLAGS
-int memdesc_nid(memdesc_flags_t mdf);
+int memdesc_nid(const memdesc_flags_t *mdf);
 #else
-static inline int memdesc_nid(memdesc_flags_t mdf)
+#ifdef CONFIG_NUMA
+static inline int memdesc_nid(const memdesc_flags_t *mdf)
 {
-	return (mdf.f >> NODES_PGSHIFT) & NODES_MASK;
+	ASSERT_EXCLUSIVE_BITS(mdf->f, NODES_MASK << NODES_PGSHIFT);
+	return (mdf->f >> NODES_PGSHIFT) & NODES_MASK;
+}
+#else
+static inline int memdesc_nid(const memdesc_flags_t *mdf)
+{
+	return 0;
 }
 #endif
+#endif
+
+#ifdef CONFIG_NUMA
+static inline int page_to_nid(const struct page *page)
+{
+	const struct page *p = PF_POISONED_CHECK(page);
 
+	return memdesc_nid(&p->flags);
+}
+
+static inline int folio_nid(const struct folio *folio)
+{
+	return memdesc_nid(&folio->flags);
+}
+#else
 static inline int page_to_nid(const struct page *page)

include/linux/mm.h +4 -1

+	ASSERT_EXCLUSIVE_BITS(mdf->f, SECTIONS_MASK << SECTIONS_PGSHIFT);
+#endif
+	return (mdf->f >> SECTIONS_PGSHIFT) & SECTIONS_MASK;
 }
 #else /* !SECTION_IN_PAGE_FLAGS */
-static inline unsigned long memdesc_section(memdesc_flags_t mdf)
+static inline unsigned long memdesc_section(const memdesc_flags_t *mdf)
 {
 	return 0;
 }

include/linux/mm_inline.h +2 -2

index a8430a7ae054..efcddb9925ad 100644
@@ -650,7 +650,7 @@ static inline bool vma_has_recency(const struct vm_area_struct *vma)
 static inline size_t num_pages_contiguous(struct page **pages, size_t nr_pages)
 {
 	struct page *cur_page = pages[0];
-	unsigned long section = memdesc_section(cur_page->flags);
+	unsigned long section = memdesc_section(&cur_page->flags);
 	size_t i;
 
 	for (i = 1; i < nr_pages; i++) {

@@ -660,7 +660,7 @@ static inline size_t num_pages_contiguous(struct page **pages, size_t nr_pages)
 		 * In unproblematic kernel configs, page_to_section() == 0 and
 		 * the whole check will get optimized out.
 		 */
-		if (memdesc_section(cur_page->flags) != section)
+		if (memdesc_section(&cur_page->flags) != section)
 			break;
 	}
 

include/linux/mmzone.h +0 -0

index ca2712187147..e60dad546ca6 100644
@@ -1272,31 +1272,33 @@ static inline bool zone_is_empty(const struct zone *zone)
 #define KASAN_TAG_MASK		((1UL << KASAN_TAG_WIDTH) - 1)
 #define ZONEID_MASK		((1UL << ZONEID_SHIFT) - 1)