sched/rtmutex: Refactor rt_mutex_setprio()

With the introduction of SCHED_DEADLINE the whole notion that priority
is a single number is gone, therefore the @prio argument to
rt_mutex_setprio() doesn't make sense anymore.

So rework the code to pass a pi_task instead.

Note this also fixes a problem with pi_top_task caching; previously we
would not set the pointer (call rt_mutex_update_top_task) if the
priority didn't change, this could lead to a stale pointer.

As for the XXX, I think its fine to use pi_task->prio, because if it
differs from waiter->prio, a PI chain update is immenent.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: juri.lelli@arm.com
Cc: bigeasy@linutronix.de
Cc: xlpang@redhat.com
Cc: rostedt@goodmis.org
Cc: mathieu.desnoyers@efficios.com
Cc: jdesfossez@efficios.com
Cc: bristot@redhat.com
Link: http://lkml.kernel.org/r/20170323150216.303827095@infradead.org
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

1 files changed, 8 insertions, 16 deletions

diff --git a/include/linux/sched/rt.h b/include/linux/sched/rt.h
index 10ee7eeb0ee2..f93329aba31a 100644
--- a/include/linux/sched/rt.h
+++ b/include/linux/sched/rt.h
@@ -18,28 +18,20 @@ static inline int rt_task(struct task_struct *p)
 }
 
 #ifdef CONFIG_RT_MUTEXES
-extern int rt_mutex_getprio(struct task_struct *p);
-extern void rt_mutex_setprio(struct task_struct *p, int prio);
-extern int rt_mutex_get_effective_prio(struct task_struct *task, int newprio);
-extern void rt_mutex_update_top_task(struct task_struct *p);
-extern struct task_struct *rt_mutex_get_top_task(struct task_struct *task);
+/*
+ * Must hold either p->pi_lock or task_rq(p)->lock.
+ */
+static inline struct task_struct *rt_mutex_get_top_task(struct task_struct *p)
+{
+	return p->pi_top_task;
+}
+extern void rt_mutex_setprio(struct task_struct *p, struct task_struct *pi_task);
 extern void rt_mutex_adjust_pi(struct task_struct *p);
 static inline bool tsk_is_pi_blocked(struct task_struct *tsk)
 {
 	return tsk->pi_blocked_on != NULL;
 }
 #else
-static inline int rt_mutex_getprio(struct task_struct *p)
-{
-	return p->normal_prio;
-}
-
-static inline int rt_mutex_get_effective_prio(struct task_struct *task,
-					      int newprio)
-{
-	return newprio;
-}
-
 static inline struct task_struct *rt_mutex_get_top_task(struct task_struct *task)
 {
 	return NULL;