rcu-tasks: Convert sleeps to idle priority

This commit converts the long-standing schedule_timeout_interruptible()
and schedule_timeout_uninterruptible() calls used by the various Tasks
RCU's grace-period kthreads to schedule_timeout_idle().  This conversion
avoids polluting the load-average with Tasks-RCU-related sleeping.
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

kernel/rcu/tasks.h

@@ -205,7 +205,7 @@ static int __noreturn rcu_tasks_kthread(void *arg)
 			if (!rtp->cbs_head) {
 				WARN_ON(signal_pending(current));
 				set_tasks_gp_state(rtp, RTGS_WAIT_WAIT_CBS);
-				schedule_timeout_interruptible(HZ/10);
+				schedule_timeout_idle(HZ/10);
 			}
 			continue;
 		}
@@ -227,7 +227,7 @@ static int __noreturn rcu_tasks_kthread(void *arg)
 			cond_resched();
 		}
 		/* Paranoid sleep to keep this from entering a tight loop */
-		schedule_timeout_uninterruptible(HZ/10);
+		schedule_timeout_idle(HZ/10);
 
 		set_tasks_gp_state(rtp, RTGS_WAIT_CBS);
 	}
@@ -336,7 +336,7 @@ static void rcu_tasks_wait_gp(struct rcu_tasks *rtp)
 
 		/* Slowly back off waiting for holdouts */
 		set_tasks_gp_state(rtp, RTGS_WAIT_SCAN_HOLDOUTS);
-		schedule_timeout_interruptible(HZ/fract);
+		schedule_timeout_idle(HZ/fract);
 
 		if (fract > 1)
 			fract--;