mm/slab: Move kvfree_rcu() into SLAB

Move kvfree_rcu() functionality to the slab_common.c file.

The reason to have kvfree_rcu() functionality as part of SLAB is that
there is a clear trend and need of closer integration. One of the recent
example is creating a barrier function for SLAB caches.

Another reason is to prevent of having several implementations of RCU
machinery for reclaiming objects after a GP. As future steps, it can be
more integrated(easier) with SLAB internals.

Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Acked-by: Hyeonggon Yoo <hyeonggon.yoo@sk.com>
Tested-by: Hyeonggon Yoo <hyeonggon.yoo@sk.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

include/linux/rcupdate.h

@@ -118,7 +118,6 @@ static inline void call_rcu_hurry(struct rcu_head *head, rcu_callback_t func)
 
 /* Internal to kernel */
 void rcu_init(void);
-void __init kvfree_rcu_init(void);
 extern int rcu_scheduler_active;
 void rcu_sched_clock_irq(int user);
 

include/linux/slab.h

@@ -1099,5 +1099,6 @@ unsigned int kmem_cache_size(struct kmem_cache *s);
 size_t kmalloc_size_roundup(size_t size);
 
 void __init kmem_cache_init_late(void);
+void __init kvfree_rcu_init(void);
 
 #endif	/* _LINUX_SLAB_H */