mm/slab: abstract slabobj_ext.ref access

In preparation for changes to the structure, abstract access to the ref
field with a slab_obj_ext_codetag_ref() function. Rename the field to
_ctref to make an unexpected direct access a compile error.

No functional change intended.

Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Hao Li <hao.li@linux.dev>
Reviewed-by: Harry Yoo (Oracle) <harry@kernel.org>
Link: https://patch.msgid.link/20260727-b4-objext_split-v3-6-c29ef0f1f257@kernel.org
Signed-off-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>

2 files changed, 37 insertions, 15 deletions

diff --git a/mm/slab.h b/mm/slab.h
index ea014311e29f..c806afdef2ee 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -558,7 +558,7 @@ struct slabobj_ext {
 	struct obj_cgroup *_objcg;
 #endif
 #ifdef CONFIG_MEM_ALLOC_PROFILING
-	union codetag_ref ref;
+	union codetag_ref _ctref;
 #endif
 } __aligned(8);
 
@@ -677,6 +677,14 @@ slab_obj_ext_set_objcg(struct slab *slab, struct slabobj_ext *obj_ext,
 }
 #endif
 
+#ifdef CONFIG_MEM_ALLOC_PROFILING
+static inline union codetag_ref *
+slab_obj_ext_codetag_ref(struct slab *slab, struct slabobj_ext *obj_ext)
+{
+	return &obj_ext->_ctref;
+}
+#endif
+
 int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
 			gfp_t gfp, unsigned int alloc_flags);
 
diff --git a/mm/slub.c b/mm/slub.c
index ed18860fa0fd..9d60d192737c 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2074,18 +2074,20 @@ static inline void mark_obj_codetag_empty(const void *obj)
 	slab_exts = slab_obj_exts(obj_slab);
 	if (slab_exts) {
 		struct slabobj_ext *ext;
+		union codetag_ref *ref;
 
 		get_slab_obj_exts(slab_exts);
 		ext = slab_obj_ext(obj_slab->slab_cache, obj_slab, slab_exts, obj);
+		ref = slab_obj_ext_codetag_ref(obj_slab, ext);
 
-		if (unlikely(is_codetag_empty(&ext->ref))) {
+		if (unlikely(is_codetag_empty(ref))) {
 			put_slab_obj_exts(slab_exts);
 			return;
 		}
 
 		/* codetag should be NULL here */
-		WARN_ON(ext->ref.ct);
-		set_codetag_empty(&ext->ref);
+		WARN_ON(ref->ct);
+		set_codetag_empty(ref);
 		put_slab_obj_exts(slab_exts);
 	}
 }
@@ -2095,19 +2097,22 @@ static inline bool mark_failed_objexts_alloc(struct slab *slab)
 	return cmpxchg(&slab->obj_exts, 0, OBJEXTS_ALLOC_FAIL) == 0;
 }
 
-static inline void handle_failed_objexts_alloc(unsigned long obj_exts,
-			struct slabobj_ext *vec, unsigned int objects)
+static inline void handle_failed_objexts_alloc(struct slab *slab,
+		unsigned long obj_exts, struct slabobj_ext *vec)
 {
 	/*
 	 * If vector previously failed to allocate then we have live
 	 * objects with no tag reference. Mark all references in this
 	 * vector as empty to avoid warnings later on.
 	 */
-	if (obj_exts == OBJEXTS_ALLOC_FAIL) {
-		unsigned int i;
+	if (obj_exts != OBJEXTS_ALLOC_FAIL)
+		return;
+
+	for (unsigned int i = 0; i < slab->objects; i++) {
+		union codetag_ref *ref = slab_obj_ext_codetag_ref(slab, vec);
 
-		for (i = 0; i < objects; i++)
-			set_codetag_empty(&vec[i].ref);
+		set_codetag_empty(ref);
+		vec++;
 	}
 }
 
@@ -2115,8 +2120,8 @@ static inline void handle_failed_objexts_alloc(unsigned long obj_exts,
 
 static inline void mark_obj_codetag_empty(const void *obj) {}
 static inline bool mark_failed_objexts_alloc(struct slab *slab) { return false; }
-static inline void handle_failed_objexts_alloc(unsigned long obj_exts,
-			struct slabobj_ext *vec, unsigned int objects) {}
+static inline void handle_failed_objexts_alloc(struct slab *slab,
+		unsigned long obj_exts, struct slabobj_ext *vec) {}
 
 #endif /* CONFIG_MEM_ALLOC_PROFILING_DEBUG */
 
@@ -2184,7 +2189,7 @@ int alloc_slab_obj_exts(struct slab *slab, struct kmem_cache *s,
 #endif
 retry:
 	old_exts = READ_ONCE(slab->obj_exts);
-	handle_failed_objexts_alloc(old_exts, vec, slab->objects);
+	handle_failed_objexts_alloc(slab, old_exts, vec);
 
 	if (new_slab) {
 		/*
@@ -2364,9 +2369,15 @@ __alloc_tagging_slab_alloc_hook(struct kmem_cache *s, void *object, gfp_t flags,
 	 * check should be added before alloc_tag_add().
 	 */
 	if (obj_exts) {
+		union codetag_ref *ref;
+
 		get_slab_obj_exts(obj_exts);
+
 		obj_ext = slab_obj_ext(s, slab, obj_exts, object);
-		alloc_tag_add(&obj_ext->ref, current->alloc_tag, s->size);
+		ref = slab_obj_ext_codetag_ref(slab, obj_ext);
+
+		alloc_tag_add(ref, current->alloc_tag, s->size);
+
 		put_slab_obj_exts(obj_exts);
 	} else {
 		alloc_tag_set_inaccurate(current->alloc_tag);
@@ -2398,10 +2409,13 @@ __alloc_tagging_slab_free_hook(struct kmem_cache *s, struct slab *slab, void **p
 
 	get_slab_obj_exts(obj_exts);
 	for (int i = 0; i < objects; i++) {
+		struct slabobj_ext *ext;
+
 		if (is_kfence_address(p[i]))
 			continue;
 
-		alloc_tag_sub(&slab_obj_ext(s, slab, obj_exts, p[i])->ref, s->size);
+		ext = slab_obj_ext(s, slab, obj_exts, p[i]);
+		alloc_tag_sub(slab_obj_ext_codetag_ref(slab, ext), s->size);
 	}
 	put_slab_obj_exts(obj_exts);
 }