Merge branch 'slab/for-6.2/fit_rcu_head' into slab/for-next

A series by myself to reorder fields in struct slab to allow the
embedded rcu_head to grow (for debugging purposes). Requires changes to
isolate_movable_page() to skip slab pages which can otherwise become
false-positive __PageMovable due to its use of low bits in
page->mapping.

1 files changed, 15 insertions, 11 deletions

diff --git a/mm/slub.c b/mm/slub.c
index 1ff5319c0ea8..0a14e7bc278c 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -1800,6 +1800,8 @@ static inline struct slab *alloc_slab_page(gfp_t flags, int node,
 
 	slab = folio_slab(folio);
 	__folio_set_slab(folio);
+	/* Make the flag visible before any changes to folio->mapping */
+	smp_wmb();
 	if (page_is_pfmemalloc(folio_page(folio, 0)))
 		slab_set_pfmemalloc(slab);
 
@@ -1999,17 +2001,11 @@ static void __free_slab(struct kmem_cache *s, struct slab *slab)
 	int order = folio_order(folio);
 	int pages = 1 << order;
 
-	if (kmem_cache_debug_flags(s, SLAB_CONSISTENCY_CHECKS)) {
-		void *p;
-
-		slab_pad_check(s, slab);
-		for_each_object(p, s, slab_address(slab), slab->objects)
-			check_object(s, slab, p, SLUB_RED_INACTIVE);
-	}
-
 	__slab_clear_pfmemalloc(slab);
-	__folio_clear_slab(folio);
 	folio->mapping = NULL;
+	/* Make the mapping reset visible before clearing the flag */
+	smp_wmb();
+	__folio_clear_slab(folio);
 	if (current->reclaim_state)
 		current->reclaim_state->reclaimed_slab += pages;
 	unaccount_slab(slab, order, s);
@@ -2025,9 +2021,17 @@ static void rcu_free_slab(struct rcu_head *h)
 
 static void free_slab(struct kmem_cache *s, struct slab *slab)
 {
-	if (unlikely(s->flags & SLAB_TYPESAFE_BY_RCU)) {
+	if (kmem_cache_debug_flags(s, SLAB_CONSISTENCY_CHECKS)) {
+		void *p;
+
+		slab_pad_check(s, slab);
+		for_each_object(p, s, slab_address(slab), slab->objects)
+			check_object(s, slab, p, SLUB_RED_INACTIVE);
+	}
+
+	if (unlikely(s->flags & SLAB_TYPESAFE_BY_RCU))
 		call_rcu(&slab->rcu_head, rcu_free_slab);
-	} else
+	else
 		__free_slab(s, slab);
 }