sched: Extend activate_task to allow queueing to the head of a list

The ability of enqueueing a task to the head of a SCHED_FIFO priority
list is required to fix some violations of POSIX scheduling policy.

Extend activate_task with a "head" argument and fix up all callers.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

2 files changed, 14 insertions, 12 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 83b9c3230632..1ca987256375 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1500,7 +1500,8 @@ static const u32 prio_to_wmult[40] = {
  /*  15 */ 119304647, 148102320, 186737708, 238609294, 286331153,
 };
 
-static void activate_task(struct rq *rq, struct task_struct *p, int wakeup);
+static void activate_task(struct rq *rq, struct task_struct *p, int wakeup,
+			  bool head);
 
 /*
  * runqueue iterator, to support SMP load-balancing between different
@@ -1967,12 +1968,13 @@ static int effective_prio(struct task_struct *p)
 /*
  * activate_task - move a task to the runqueue.
  */
-static void activate_task(struct rq *rq, struct task_struct *p, int wakeup)
+static void
+activate_task(struct rq *rq, struct task_struct *p, int wakeup, bool head)
 {
 	if (task_contributes_to_load(p))
 		rq->nr_uninterruptible--;
 
-	enqueue_task(rq, p, wakeup, false);
+	enqueue_task(rq, p, wakeup, head);
 	inc_nr_running(rq);
 }
 
@@ -2617,7 +2619,7 @@ out_activate:
 		schedstat_inc(p, se.nr_wakeups_local);
 	else
 		schedstat_inc(p, se.nr_wakeups_remote);
-	activate_task(rq, p, 1);
+	activate_task(rq, p, 1, false);
 	success = 1;
 
 	/*
@@ -2826,7 +2828,7 @@ void wake_up_new_task(struct task_struct *p, unsigned long clone_flags)
 	p->prio = effective_prio(p);
 
 	if (!p->sched_class->task_new || !current->se.on_rq) {
-		activate_task(rq, p, 0);
+		activate_task(rq, p, 0, false);
 	} else {
 		/*
 		 * Let the scheduling class do new task startup
@@ -3362,7 +3364,7 @@ static void pull_task(struct rq *src_rq, struct task_struct *p,
 {
 	deactivate_task(src_rq, p, 0);
 	set_task_cpu(p, this_cpu);
-	activate_task(this_rq, p, 0);
+	activate_task(this_rq, p, 0, false);
 	/*
 	 * Note that idle threads have a prio of MAX_PRIO, for this test
 	 * to be always true for them.
@@ -6651,7 +6653,7 @@ recheck:
 	if (running)
 		p->sched_class->set_curr_task(rq);
 	if (on_rq) {
-		activate_task(rq, p, 0);
+		activate_task(rq, p, 0, false);
 
 		check_class_changed(rq, p, prev_class, oldprio, running);
 	}
@@ -7578,7 +7580,7 @@ static int __migrate_task(struct task_struct *p, int src_cpu, int dest_cpu)
 
 	set_task_cpu(p, dest_cpu);
 	if (on_rq) {
-		activate_task(rq_dest, p, 0);
+		activate_task(rq_dest, p, 0, false);
 		check_preempt_curr(rq_dest, p, 0);
 	}
 done:
@@ -7758,7 +7760,7 @@ void sched_idle_next(void)
 	__setscheduler(rq, p, SCHED_FIFO, MAX_RT_PRIO-1);
 
 	update_rq_clock(rq);
-	activate_task(rq, p, 0);
+	activate_task(rq, p, 0, false);
 
 	atomic_spin_unlock_irqrestore(&rq->lock, flags);
 }
@@ -9959,7 +9961,7 @@ static void normalize_task(struct rq *rq, struct task_struct *p)
 		deactivate_task(rq, p, 0);
 	__setscheduler(rq, p, SCHED_NORMAL, 0);
 	if (on_rq) {
-		activate_task(rq, p, 0);
+		activate_task(rq, p, 0, false);
 		resched_task(rq->curr);
 	}
 }
diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 0f1aba273f92..60efb82dc5eb 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -1419,7 +1419,7 @@ static int push_rt_task(struct rq *rq)
 
 	deactivate_task(rq, next_task, 0);
 	set_task_cpu(next_task, lowest_rq->cpu);
-	activate_task(lowest_rq, next_task, 0);
+	activate_task(lowest_rq, next_task, 0, false);
 
 	resched_task(lowest_rq->curr);
 
@@ -1502,7 +1502,7 @@ static int pull_rt_task(struct rq *this_rq)
 
 			deactivate_task(src_rq, p, 0);
 			set_task_cpu(p, this_cpu);
-			activate_task(this_rq, p, 0);
+			activate_task(this_rq, p, 0, false);
 			/*
 			 * We continue with the search, just in
 			 * case there's an even higher prio task