1 files changed, 53 insertions, 26 deletions

diff --git a/mm/rmap.c b/mm/rmap.c
index 0f760b93fc0a..3da1ca49881c 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -2614,35 +2614,37 @@ static void rmap_walk_anon(struct folio *folio,
 		anon_vma_unlock_read(anon_vma);
 }
 
-/*
- * rmap_walk_file - do something to file page using the object-based rmap method
- * @folio: the folio to be handled
- * @rwc: control variable according to each walk type
- * @locked: caller holds relevant rmap lock
+/**
+ * __rmap_walk_file() - Traverse the reverse mapping for a file-backed mapping
+ * of a page mapped within a specified page cache object at a specified offset.
  *
- * Find all the mappings of a folio using the mapping pointer and the vma chains
- * contained in the address_space struct it points to.
+ * @folio: 		Either the folio whose mappings to traverse, or if NULL,
+ * 			the callbacks specified in @rwc will be configured such
+ * 			as to be able to look up mappings correctly.
+ * @mapping: 		The page cache object whose mapping VMAs we intend to
+ * 			traverse. If @folio is non-NULL, this should be equal to
+ *			folio_mapping(folio).
+ * @pgoff_start:	The offset within @mapping of the page which we are
+ * 			looking up. If @folio is non-NULL, this should be equal
+ * 			to folio_pgoff(folio).
+ * @nr_pages:		The number of pages mapped by the mapping. If @folio is
+ *			non-NULL, this should be equal to folio_nr_pages(folio).
+ * @rwc:		The reverse mapping walk control object describing how
+ *			the traversal should proceed.
+ * @locked:		Is the @mapping already locked? If not, we acquire the
+ *			lock.
  */
-static void rmap_walk_file(struct folio *folio,
-		struct rmap_walk_control *rwc, bool locked)
+static void __rmap_walk_file(struct folio *folio, struct address_space *mapping,
+			     pgoff_t pgoff_start, unsigned long nr_pages,
+			     struct rmap_walk_control *rwc, bool locked)
 {
-	struct address_space *mapping = folio_mapping(folio);
-	pgoff_t pgoff_start, pgoff_end;
+	pgoff_t pgoff_end = pgoff_start + nr_pages - 1;
 	struct vm_area_struct *vma;
 
-	/*
-	 * The page lock not only makes sure that page->mapping cannot
-	 * suddenly be NULLified by truncation, it makes sure that the
-	 * structure at mapping cannot be freed and reused yet,
-	 * so we can safely take mapping->i_mmap_rwsem.
-	 */
-	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
-
-	if (!mapping)
-		return;
+	VM_WARN_ON_FOLIO(folio && mapping != folio_mapping(folio), folio);
+	VM_WARN_ON_FOLIO(folio && pgoff_start != folio_pgoff(folio), folio);
+	VM_WARN_ON_FOLIO(folio && nr_pages != folio_nr_pages(folio), folio);
 
-	pgoff_start = folio_pgoff(folio);
-	pgoff_end = pgoff_start + folio_nr_pages(folio) - 1;
 	if (!locked) {
 		if (i_mmap_trylock_read(mapping))
 			goto lookup;
@@ -2657,8 +2659,7 @@ static void rmap_walk_file(struct folio *folio,
 lookup:
 	vma_interval_tree_foreach(vma, &mapping->i_mmap,
 			pgoff_start, pgoff_end) {
-		unsigned long address = vma_address(vma, pgoff_start,
-			       folio_nr_pages(folio));
+		unsigned long address = vma_address(vma, pgoff_start, nr_pages);
 
 		VM_BUG_ON_VMA(address == -EFAULT, vma);
 		cond_resched();
@@ -2671,12 +2672,38 @@ lookup:
 		if (rwc->done && rwc->done(folio))
 			goto done;
 	}
-
 done:
 	if (!locked)
 		i_mmap_unlock_read(mapping);
 }
 
+/*
+ * rmap_walk_file - do something to file page using the object-based rmap method
+ * @folio: the folio to be handled
+ * @rwc: control variable according to each walk type
+ * @locked: caller holds relevant rmap lock
+ *
+ * Find all the mappings of a folio using the mapping pointer and the vma chains
+ * contained in the address_space struct it points to.
+ */
+static void rmap_walk_file(struct folio *folio,
+		struct rmap_walk_control *rwc, bool locked)
+{
+	/*
+	 * The folio lock not only makes sure that folio->mapping cannot
+	 * suddenly be NULLified by truncation, it makes sure that the structure
+	 * at mapping cannot be freed and reused yet, so we can safely take
+	 * mapping->i_mmap_rwsem.
+	 */
+	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
+
+	if (!folio->mapping)
+		return;
+
+	__rmap_walk_file(folio, folio->mapping, folio->index,
+			 folio_nr_pages(folio), rwc, locked);
+}
+
 void rmap_walk(struct folio *folio, struct rmap_walk_control *rwc)
 {
 	if (unlikely(folio_test_ksm(folio)))