slab: remove unused PREEMPT_RT specific macros

The macros slub_get_cpu_ptr()/slub_put_cpu_ptr() are now unused, remove
them. USE_LOCKLESS_FAST_PATH() has lost its true meaning with the code
being removed. The only remaining usage is in fact testing whether we
can assert irqs disabled, because spin_lock_irqsave() only does that on
!RT. Test for CONFIG_PREEMPT_RT instead.

Reviewed-by: Hao Li <hao.li@linux.dev>
Reviewed-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Harry Yoo <harry.yoo@oracle.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

Author: tehcaster

mm/slub.c

@@ -201,28 +201,6 @@ enum slab_flags {
 	SL_pfmemalloc = PG_active,	/* Historical reasons for this bit */
 };
 
-/*
- * We could simply use migrate_disable()/enable() but as long as it's a
- * function call even on !PREEMPT_RT, use inline preempt_disable() there.
- */
-#ifndef CONFIG_PREEMPT_RT
-#define slub_get_cpu_ptr(var)		get_cpu_ptr(var)
-#define slub_put_cpu_ptr(var)		put_cpu_ptr(var)
-#define USE_LOCKLESS_FAST_PATH()	(true)
-#else
-#define slub_get_cpu_ptr(var)		\
-({					\
-	migrate_disable();		\
-	this_cpu_ptr(var);		\
-})
-#define slub_put_cpu_ptr(var)		\
-do {					\
-	(void)(var);			\
-	migrate_enable();		\
-} while (0)
-#define USE_LOCKLESS_FAST_PATH()	(false)
-#endif
-
 #ifndef CONFIG_SLUB_TINY
 #define __fastpath_inline __always_inline
 #else
@@ -713,7 +691,7 @@ static inline bool __slab_update_freelist(struct kmem_cache *s, struct slab *sla
 {
 	bool ret;
 
-	if (USE_LOCKLESS_FAST_PATH())
+	if (!IS_ENABLED(CONFIG_PREEMPT_RT))
 		lockdep_assert_irqs_disabled();
 
 	if (s->flags & __CMPXCHG_DOUBLE)