2 files changed, 42 insertions, 11 deletions

diff --git a/kernel/locking/rtmutex.c b/kernel/locking/rtmutex.c
index 2e960a2bab81..aa4dff04b594 100644
--- a/kernel/locking/rtmutex.c
+++ b/kernel/locking/rtmutex.c
@@ -213,6 +213,18 @@ struct task_struct *rt_mutex_get_top_task(struct task_struct *task)
 }
 
 /*
+ * Called by sched_setscheduler() to check whether the priority change
+ * is overruled by a possible priority boosting.
+ */
+int rt_mutex_check_prio(struct task_struct *task, int newprio)
+{
+        if (!task_has_pi_waiters(task))
+                return 0;
+
+        return task_top_pi_waiter(task)->task->prio <= newprio;
+}
+
+/*
  * Adjust the priority of a task, after its pi_waiters got modified.
  *
  * This can be both boosting and unboosting. task->pi_lock must be held.
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 9c2fcbf9a266..003263b3b05c 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -2902,7 +2902,8 @@ EXPORT_SYMBOL(sleep_on_timeout);
  * This function changes the 'effective' priority of a task. It does
  * not touch ->normal_prio like __setscheduler().
  *
- * Used by the rt_mutex code to implement priority inheritance logic.
+ * Used by the rt_mutex code to implement priority inheritance
+ * logic. Call site only calls if the priority of the task changed.
  */
 void rt_mutex_setprio(struct task_struct *p, int prio)
 {
@@ -3171,9 +3172,8 @@ __setparam_dl(struct task_struct *p, const struct sched_attr *attr)
         dl_se->dl_new = 1;
 }
 
-/* Actually do priority change: must hold pi & rq lock. */
-static void __setscheduler(struct rq *rq, struct task_struct *p,
-                           const struct sched_attr *attr)
+static void __setscheduler_params(struct task_struct *p,
+                const struct sched_attr *attr)
 {
         int policy = attr->sched_policy;
 
@@ -3193,9 +3193,14 @@ static void __setscheduler(struct rq *rq, struct task_struct *p,
          * getparam()/getattr() don't report silly values for !rt tasks.
          */
         p->rt_priority = attr->sched_priority;
+        set_load_weight(p);
+}
 
-        p->normal_prio = normal_prio(p);
-        p->prio = rt_mutex_getprio(p);
+/* Actually do priority change: must hold pi & rq lock. */
+static void __setscheduler(struct rq *rq, struct task_struct *p,
+                           const struct sched_attr *attr)
+{
+        __setscheduler_params(p, attr);
 
         if (dl_prio(p->prio))
                 p->sched_class = &dl_sched_class;
@@ -3203,8 +3208,6 @@ static void __setscheduler(struct rq *rq, struct task_struct *p,
                 p->sched_class = &rt_sched_class;
         else
                 p->sched_class = &fair_sched_class;
-
-        set_load_weight(p);
 }
 
 static void
@@ -3257,6 +3260,7 @@ static int __sched_setscheduler(struct task_struct *p,
                                 const struct sched_attr *attr,
                                 bool user)
 {
+        int newprio = MAX_RT_PRIO - 1 - attr->sched_priority;
         int retval, oldprio, oldpolicy = -1, on_rq, running;
         int policy = attr->sched_policy;
         unsigned long flags;
@@ -3427,6 +3431,24 @@ change:
                 return -EBUSY;
         }
 
+        p->sched_reset_on_fork = reset_on_fork;
+        oldprio = p->prio;
+
+        /*
+         * Special case for priority boosted tasks.
+         *
+         * If the new priority is lower or equal (user space view)
+         * than the current (boosted) priority, we just store the new
+         * normal parameters and do not touch the scheduler class and
+         * the runqueue. This will be done when the task deboost
+         * itself.
+         */
+        if (rt_mutex_check_prio(p, newprio)) {
+                __setscheduler_params(p, attr);
+                task_rq_unlock(rq, p, &flags);
+                return 0;
+        }
+
         on_rq = p->on_rq;
         running = task_current(rq, p);
         if (on_rq)
@@ -3434,9 +3456,6 @@ change:
         if (running)
                 p->sched_class->put_prev_task(rq, p);
 
-        p->sched_reset_on_fork = reset_on_fork;
-
-        oldprio = p->prio;
         prev_class = p->sched_class;
         __setscheduler(rq, p, attr);