[PATCH RFC 05/12] mm/slab: abstract slabobj_ext.objcg access

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

No functional change intended.

Signed-off-by: Vlastimil Babka (SUSE) <[email protected]>
---
 mm/kfence/core.c |  2 +-
 mm/memcontrol.c  | 23 +++++++++++++++--------
 mm/slab.h        |  9 ++++++++-
 mm/slub.c        |  2 +-
 4 files changed, 25 insertions(+), 11 deletions(-)

diff --git a/mm/kfence/core.c b/mm/kfence/core.c
index 6577bd76954e..717e8baf7e5d 100644
--- a/mm/kfence/core.c
+++ b/mm/kfence/core.c
@@ -1249,7 +1249,7 @@ void __kfence_free(void *addr)
 	struct kfence_metadata *meta = addr_to_metadata((unsigned long)addr);
 
 #ifdef CONFIG_MEMCG
-	KFENCE_WARN_ON(meta->obj_exts.objcg);
+	KFENCE_WARN_ON(*slab_obj_ext_objcgp(&meta->obj_exts));
 #endif
 	/*
 	 * If the objects of the cache are SLAB_TYPESAFE_BY_RCU, defer freeing
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 4e427286a88a..6303a2b1a9d0 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -2865,6 +2865,7 @@ struct mem_cgroup *mem_cgroup_from_obj_slab(struct slab *slab, void *p)
 	 */
 	unsigned long obj_exts;
 	struct slabobj_ext *obj_ext;
+	struct obj_cgroup *objcg;
 
 	obj_exts = slab_obj_exts(slab);
 	if (!obj_exts)
@@ -2872,9 +2873,8 @@ struct mem_cgroup *mem_cgroup_from_obj_slab(struct slab *slab, void *p)
 
 	get_slab_obj_exts(obj_exts);
 	obj_ext = slab_obj_ext(slab->slab_cache, slab, obj_exts, p);
-	if (obj_ext->objcg) {
-		struct obj_cgroup *objcg = obj_ext->objcg;
-
+	objcg = *slab_obj_ext_objcgp(obj_ext);
+	if (objcg) {
 		put_slab_obj_exts(obj_exts);
 		return obj_cgroup_memcg(objcg);
 	}
@@ -3577,6 +3577,7 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,
 		unsigned long obj_exts;
 		struct slabobj_ext *obj_ext;
 		struct obj_stock_pcp *stock;
+		struct obj_cgroup **objcgp;
 
 		slab = virt_to_slab(p[i]);
 
@@ -3612,10 +3613,15 @@ bool __memcg_slab_post_alloc_hook(struct kmem_cache *s, struct list_lru *lru,
 		unlock_stock(stock);
 
 		obj_exts = slab_obj_exts(slab);
+
 		get_slab_obj_exts(obj_exts);
+
 		obj_ext = slab_obj_ext(s, slab, obj_exts, p[i]);
+		objcgp = slab_obj_ext_objcgp(obj_ext);
+
 		obj_cgroup_get(objcg);
-		obj_ext->objcg = objcg;
+		*objcgp = objcg;
+
 		put_slab_obj_exts(obj_exts);
 	}
 
@@ -3628,16 +3634,17 @@ void __memcg_slab_free_hook(struct kmem_cache *s, struct slab *slab,
 	size_t obj_size = obj_full_size(s);
 
 	for (int i = 0; i < objects; i++) {
-		struct obj_cgroup *objcg;
+		struct obj_cgroup **objcgp, *objcg;
 		struct slabobj_ext *obj_ext;
 		struct obj_stock_pcp *stock;
 
 		obj_ext = slab_obj_ext(s, slab, obj_exts, p[i]);
-		objcg = obj_ext->objcg;
-		if (!objcg)
+		objcgp = slab_obj_ext_objcgp(obj_ext);
+		if (!*objcgp)
 			continue;
 
-		obj_ext->objcg = NULL;
+		objcg = *objcgp;
+		*objcgp = NULL;
 
 		stock = trylock_stock();
 		__refill_obj_stock(objcg, stock, obj_size, true);
diff --git a/mm/slab.h b/mm/slab.h
index 36d067d6e7c0..789bd292075f 100644
--- a/mm/slab.h
+++ b/mm/slab.h
@@ -555,7 +555,7 @@ static inline bool need_kmalloc_no_objext(void)
  */
 struct slabobj_ext {
 #ifdef CONFIG_MEMCG
-	struct obj_cgroup *objcg;
+	struct obj_cgroup *_objcg;
 #endif
 #ifdef CONFIG_MEM_ALLOC_PROFILING
 	union codetag_ref ref;
@@ -661,6 +661,13 @@ slab_obj_ext(struct kmem_cache *s, struct slab *slab, unsigned long obj_exts,
 	return kasan_reset_tag(obj_ext);
 }
 
+#ifdef CONFIG_MEMCG
+static inline struct obj_cgroup **slab_obj_ext_objcgp(struct slabobj_ext *obj_ext)
+{
+	return &obj_ext->_objcg;
+}
+#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 5e3f53bcd0d3..48e10198a3ce 100644
--- a/mm/slub.c
+++ b/mm/slub.c
@@ -2523,7 +2523,7 @@ bool memcg_slab_post_charge(void *p, gfp_t flags)
 	if (obj_exts) {
 		get_slab_obj_exts(obj_exts);
 		obj_ext = slab_obj_ext(s, slab, obj_exts, p);
-		if (unlikely(obj_ext->objcg)) {
+		if (unlikely(*slab_obj_ext_objcgp(obj_ext))) {
 			put_slab_obj_exts(obj_exts);
 			return true;
 		}

-- 
2.55.0