1 files changed, 26 insertions, 25 deletions

diff --git a/mm/filemap.c b/mm/filemap.c
index ad5b4aa049..5be7887957 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -4108,28 +4108,40 @@ static void filemap_cachestat(struct address_space *mapping,
 
 	rcu_read_lock();
 	xas_for_each(&xas, folio, last_index) {
+		int order;
 		unsigned long nr_pages;
 		pgoff_t folio_first_index, folio_last_index;
 
+		/*
+		 * Don't deref the folio. It is not pinned, and might
+		 * get freed (and reused) underneath us.
+		 *
+		 * We *could* pin it, but that would be expensive for
+		 * what should be a fast and lightweight syscall.
+		 *
+		 * Instead, derive all information of interest from
+		 * the rcu-protected xarray.
+		 */
+
 		if (xas_retry(&xas, folio))
 			continue;
 
+		order = xa_get_order(xas.xa, xas.xa_index);
+		nr_pages = 1 << order;
+		folio_first_index = round_down(xas.xa_index, 1 << order);
+		folio_last_index = folio_first_index + nr_pages - 1;
+
+		/* Folios might straddle the range boundaries, only count covered pages */
+		if (folio_first_index < first_index)
+			nr_pages -= first_index - folio_first_index;
+
+		if (folio_last_index > last_index)
+			nr_pages -= folio_last_index - last_index;
+
 		if (xa_is_value(folio)) {
 			/* page is evicted */
 			void *shadow = (void *)folio;
 			bool workingset; /* not used */
-			int order = xa_get_order(xas.xa, xas.xa_index);
-
-			nr_pages = 1 << order;
-			folio_first_index = round_down(xas.xa_index, 1 << order);
-			folio_last_index = folio_first_index + nr_pages - 1;
-
-			/* Folios might straddle the range boundaries, only count covered pages */
-			if (folio_first_index < first_index)
-				nr_pages -= first_index - folio_first_index;
-
-			if (folio_last_index > last_index)
-				nr_pages -= folio_last_index - last_index;
 
 			cs->nr_evicted += nr_pages;
 
@@ -4147,24 +4159,13 @@ static void filemap_cachestat(struct address_space *mapping,
 			goto resched;
 		}
 
-		nr_pages = folio_nr_pages(folio);
-		folio_first_index = folio_pgoff(folio);
-		folio_last_index = folio_first_index + nr_pages - 1;
-
-		/* Folios might straddle the range boundaries, only count covered pages */
-		if (folio_first_index < first_index)
-			nr_pages -= first_index - folio_first_index;
-
-		if (folio_last_index > last_index)
-			nr_pages -= folio_last_index - last_index;
-
 		/* page is in cache */
 		cs->nr_cache += nr_pages;
 
-		if (folio_test_dirty(folio))
+		if (xas_get_mark(&xas, PAGECACHE_TAG_DIRTY))
 			cs->nr_dirty += nr_pages;
 
-		if (folio_test_writeback(folio))
+		if (xas_get_mark(&xas, PAGECACHE_TAG_WRITEBACK))
 			cs->nr_writeback += nr_pages;
 
 resched: