rcu: Shrink TINY_RCU by reworking CPU-stall ifdefs

TINY_RCU's reset_cpu_stall_ticks() and check_cpu_stalls() functions
are defined unconditionally, and are empty functions if CONFIG_RCU_TRACE
is disabled (which in turns disables detection of RCU CPU stalls).
This commit saves a few lines of source code by defining these functions
only if CONFIG_RCU_TRACE=y.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>

kernel/rcutiny.c

@@ -204,7 +204,7 @@ static int rcu_is_cpu_rrupt_from_idle(void)
  */
 static int rcu_qsctr_help(struct rcu_ctrlblk *rcp)
 {
-	reset_cpu_stall_ticks(rcp);
+	RCU_TRACE(reset_cpu_stall_ticks(rcp));
 	if (rcp->rcucblist != NULL &&
 	    rcp->donetail != rcp->curtail) {
 		rcp->donetail = rcp->curtail;
@@ -251,7 +251,7 @@ void rcu_bh_qs(int cpu)
  */
 void rcu_check_callbacks(int cpu, int user)
 {
-	check_cpu_stalls();
+	RCU_TRACE(check_cpu_stalls());
 	if (user || rcu_is_cpu_rrupt_from_idle())
 		rcu_sched_qs(cpu);
 	else if (!in_softirq())

kernel/rcutiny_plugin.h

@@ -158,15 +158,11 @@ static void check_cpu_stall(struct rcu_ctrlblk *rcp)
 		rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check();
 }
 
-#endif /* #ifdef CONFIG_RCU_TRACE */
-
 static void reset_cpu_stall_ticks(struct rcu_ctrlblk *rcp)
 {
-#ifdef CONFIG_RCU_TRACE
 	rcp->ticks_this_gp = 0;
 	rcp->gp_start = jiffies;
 	rcp->jiffies_stall = jiffies + rcu_jiffies_till_stall_check();
-#endif /* #ifdef CONFIG_RCU_TRACE */
 }
 
 static void check_cpu_stalls(void)
@@ -174,3 +170,5 @@ static void check_cpu_stalls(void)
 	RCU_TRACE(check_cpu_stall(&rcu_bh_ctrlblk));
 	RCU_TRACE(check_cpu_stall(&rcu_sched_ctrlblk));
 }
+
+#endif /* #ifdef CONFIG_RCU_TRACE */