random: use IS_ENABLED(CONFIG_NUMA) instead of ifdefs

Rather than an awkward combination of ifdefs and __maybe_unused, we can
ensure more source gets parsed, regardless of the configuration, by
using IS_ENABLED for the CONFIG_NUMA conditional code. This makes things
cleaner and easier to follow.

I've confirmed that on !CONFIG_NUMA, we don't wind up with excess code
by accident; the generated object file is the same.

Reviewed-by: Dominik Brodowski <linux@dominikbrodowski.net>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>

drivers/char/random.c

@@ -759,15 +759,13 @@ static int credit_entropy_bits_safe(struct entropy_store *r, int nbits)
 
 static DECLARE_WAIT_QUEUE_HEAD(crng_init_wait);
 
-#ifdef CONFIG_NUMA
 /*
  * Hack to deal with crazy userspace progams when they are all trying
  * to access /dev/urandom in parallel.  The programs are almost
  * certainly doing something terribly wrong, but we'll work around
  * their brain damage.
  */
 static struct crng_state **crng_node_pool __read_mostly;
-#endif
 
 static void invalidate_batched_entropy(void);
 static void numa_crng_init(void);
@@ -815,7 +813,7 @@ static bool __init crng_init_try_arch_early(struct crng_state *crng)
 	return arch_init;
 }
 
-static void __maybe_unused crng_initialize_secondary(struct crng_state *crng)
+static void crng_initialize_secondary(struct crng_state *crng)
 {
 	chacha_init_consts(crng->state);
 	_get_random_bytes(&crng->state[4], sizeof(__u32) * 12);
@@ -866,7 +864,6 @@ static void crng_finalize_init(struct crng_state *crng)
 	}
 }
 
-#ifdef CONFIG_NUMA
 static void do_numa_crng_init(struct work_struct *work)
 {
 	int i;
@@ -893,29 +890,24 @@ static DECLARE_WORK(numa_crng_init_work, do_numa_crng_init);
 
 static void numa_crng_init(void)
 {
-	schedule_work(&numa_crng_init_work);
+	if (IS_ENABLED(CONFIG_NUMA))
+		schedule_work(&numa_crng_init_work);
 }
 
 static struct crng_state *select_crng(void)
 {
-	struct crng_state **pool;
-	int nid = numa_node_id();
-
-	/* pairs with cmpxchg_release() in do_numa_crng_init() */
-	pool = READ_ONCE(crng_node_pool);
-	if (pool && pool[nid])
-		return pool[nid];
+	if (IS_ENABLED(CONFIG_NUMA)) {
+		struct crng_state **pool;
+		int nid = numa_node_id();
 
-	return &primary_crng;
-}
-#else
-static void numa_crng_init(void) {}
+		/* pairs with cmpxchg_release() in do_numa_crng_init() */
+		pool = READ_ONCE(crng_node_pool);
+		if (pool && pool[nid])
+			return pool[nid];
+	}
 
-static struct crng_state *select_crng(void)
-{
 	return &primary_crng;
 }
-#endif
 
 /*
  * crng_fast_load() can be called by code in the interrupt service