slab: create kmem_cache_create() compatibility layer

Use _Generic() to create a compatibility layer that type switches on the
third argument to either call __kmem_cache_create() or
__kmem_cache_create_args(). If NULL is passed for the struct
kmem_cache_args argument use default args making porting for callers
that don't care about additional arguments easy.

Reviewed-by: Kees Cook <kees@kernel.org>
Reviewed-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Christian Brauner <brauner@kernel.org>
Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Roman Gushchin <roman.gushchin@linux.dev>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

include/linux/slab.h

@@ -262,9 +262,10 @@ struct kmem_cache *__kmem_cache_create_args(const char *name,
 					    unsigned int object_size,
 					    struct kmem_cache_args *args,
 					    slab_flags_t flags);
-struct kmem_cache *kmem_cache_create(const char *name, unsigned int size,
-			unsigned int align, slab_flags_t flags,
-			void (*ctor)(void *));
+
+struct kmem_cache *__kmem_cache_create(const char *name, unsigned int size,
+				       unsigned int align, slab_flags_t flags,
+				       void (*ctor)(void *));
 struct kmem_cache *kmem_cache_create_usercopy(const char *name,
 			unsigned int size, unsigned int align,
 			slab_flags_t flags,
@@ -273,6 +274,28 @@ struct kmem_cache *kmem_cache_create_usercopy(const char *name,
 struct kmem_cache *kmem_cache_create_rcu(const char *name, unsigned int size,
 					 unsigned int freeptr_offset,
 					 slab_flags_t flags);
+
+/* If NULL is passed for @args, use this variant with default arguments. */
+static inline struct kmem_cache *
+__kmem_cache_default_args(const char *name, unsigned int size,
+			  struct kmem_cache_args *args,
+			  slab_flags_t flags)
+{
+	struct kmem_cache_args kmem_default_args = {};
+
+	/* Make sure we don't get passed garbage. */
+	if (WARN_ON_ONCE(args))
+		return ERR_PTR(-EINVAL);
+
+	return __kmem_cache_create_args(name, size, &kmem_default_args, flags);
+}
+
+#define kmem_cache_create(__name, __object_size, __args, ...)           \
+	_Generic((__args),                                              \
+		struct kmem_cache_args *: __kmem_cache_create_args,	\
+		void *: __kmem_cache_default_args,			\
+		default: __kmem_cache_create)(__name, __object_size, __args, __VA_ARGS__)
+
 void kmem_cache_destroy(struct kmem_cache *s);
 int kmem_cache_shrink(struct kmem_cache *s);
 

mm/slab_common.c

@@ -383,7 +383,7 @@ kmem_cache_create_usercopy(const char *name, unsigned int size,
 EXPORT_SYMBOL(kmem_cache_create_usercopy);
 
 /**
- * kmem_cache_create - Create a cache.
+ * __kmem_cache_create - Create a cache.
  * @name: A string which is used in /proc/slabinfo to identify this cache.
  * @size: The size of objects to be created in this cache.
  * @align: The required alignment for the objects.
@@ -407,9 +407,9 @@ EXPORT_SYMBOL(kmem_cache_create_usercopy);
  *
  * Return: a pointer to the cache on success, NULL on failure.
  */
-struct kmem_cache *
-kmem_cache_create(const char *name, unsigned int size, unsigned int align,
-		slab_flags_t flags, void (*ctor)(void *))
+struct kmem_cache *__kmem_cache_create(const char *name, unsigned int size,
+				       unsigned int align, slab_flags_t flags,
+				       void (*ctor)(void *))
 {
 	struct kmem_cache_args kmem_args = {
 		.align	= align,
@@ -418,7 +418,7 @@ kmem_cache_create(const char *name, unsigned int size, unsigned int align,
 
 	return __kmem_cache_create_args(name, size, &kmem_args, flags);
 }
-EXPORT_SYMBOL(kmem_cache_create);
+EXPORT_SYMBOL(__kmem_cache_create);
 
 /**
  * kmem_cache_create_rcu - Create a SLAB_TYPESAFE_BY_RCU cache.