rcutorture: Consolidate rcu_torture_boost() timing and statistics

This commit consolidates two loops in rcu_torture_boost(), one of which
counts the number of boost-test episodes and the other of which computes
the start time of the next episode, into one loop that does both with but
a single acquisition of boost_mutex.  This means that the count of the
number of boost-test episodes is incremented after an episode completes
rather than before it starts, but it also avoids the over-counting that
was possible previously.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

kernel/rcu/rcutorture.c

@@ -956,15 +956,6 @@ static int rcu_torture_boost(void *arg)
 		bool failed = false; // Test failed already in this test interval
 		bool gp_initiated = false;
 
-		/* Increment n_rcu_torture_boosts once per boost-test */
-		while (!kthread_should_stop()) {
-			if (mutex_trylock(&boost_mutex)) {
-				n_rcu_torture_boosts++;
-				mutex_unlock(&boost_mutex);
-				break;
-			}
-			schedule_timeout_uninterruptible(1);
-		}
 		if (kthread_should_stop())
 			goto checkwait;
 
@@ -1015,7 +1006,10 @@ static int rcu_torture_boost(void *arg)
 		 */
 		while (oldstarttime == boost_starttime && !kthread_should_stop()) {
 			if (mutex_trylock(&boost_mutex)) {
-				boost_starttime = jiffies + test_boost_interval * HZ;
+				if (oldstarttime == boost_starttime) {
+					boost_starttime = jiffies + test_boost_interval * HZ;
+					n_rcu_torture_boosts++;
+				}
 				mutex_unlock(&boost_mutex);
 				break;
 			}