3 files changed, 24 insertions, 8 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 6c463c80e93d..b30196a00b0d 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1438,6 +1438,7 @@ static void rt_mutex_init_task(struct task_struct *p)
 #ifdef CONFIG_RT_MUTEXES
         p->pi_waiters = RB_ROOT;
         p->pi_waiters_leftmost = NULL;
+        p->pi_top_task = NULL;
         p->pi_blocked_on = NULL;
 #endif
 }
diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 71ecf0624410..bc05b104eaed 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -323,6 +323,19 @@ rt_mutex_dequeue_pi(struct task_struct *task, struct rt_mutex_waiter *waiter)
 }
 
 /*
+ * Must hold both p->pi_lock and task_rq(p)->lock.
+ */
+void rt_mutex_update_top_task(struct task_struct *p)
+{
+        if (!task_has_pi_waiters(p)) {
+                p->pi_top_task = NULL;
+                return;
+        }
+
+        p->pi_top_task = task_top_pi_waiter(p)->task;
+}
+
+/*
  * Calculate task priority from the waiter tree priority
  *
  * Return task->normal_prio when the waiter tree is empty or when
@@ -337,12 +350,12 @@ int rt_mutex_getprio(struct task_struct *task)
                    task->normal_prio);
 }
 
+/*
+ * Must hold either p->pi_lock or task_rq(p)->lock.
+ */
 struct task_struct *rt_mutex_get_top_task(struct task_struct *task)
 {
-        if (likely(!task_has_pi_waiters(task)))
-                return NULL;
-
-        return task_top_pi_waiter(task)->task;
+        return task->pi_top_task;
 }
 
 /*
@@ -351,12 +364,12 @@ struct task_struct *rt_mutex_get_top_task(struct task_struct *task)
  */
 int rt_mutex_get_effective_prio(struct task_struct *task, int newprio)
 {
-        if (!task_has_pi_waiters(task))
+        struct task_struct *top_task = rt_mutex_get_top_task(task);
+
+        if (!top_task)
                 return newprio;
 
-        if (task_top_pi_waiter(task)->task->prio <= newprio)
-                return task_top_pi_waiter(task)->task->prio;
-        return newprio;
+        return min(top_task->prio, newprio);
 }
 
 /*
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ab9f6ac099a7..e1f44ec701c8 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3713,6 +3713,8 @@ void rt_mutex_setprio(struct task_struct *p, int prio)
                 goto out_unlock;
         }
 
+        rt_mutex_update_top_task(p);
+
         trace_sched_pi_setprio(p, prio);
         oldprio = p->prio;