1 files changed, 45 insertions, 9 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index 7f522832250c..5f64fed56a44 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -486,7 +486,7 @@ struct rq {
          */
         unsigned long nr_uninterruptible;
 
-        struct task_struct *curr, *idle;
+        struct task_struct *curr, *idle, *stop;
         unsigned long next_balance;
         struct mm_struct *prev_mm;
 
@@ -1837,7 +1837,7 @@ static inline void __set_task_cpu(struct task_struct *p, unsigned int cpu)
 
 static const struct sched_class rt_sched_class;
 
-#define sched_class_highest (&rt_sched_class)
+#define sched_class_highest (&stop_sched_class)
 #define for_each_class(class) \
    for (class = sched_class_highest; class; class = class->next)
 
@@ -1917,10 +1917,41 @@ static void deactivate_task(struct rq *rq, struct task_struct *p, int flags)
 #include "sched_idletask.c"
 #include "sched_fair.c"
 #include "sched_rt.c"
+#include "sched_stoptask.c"
 #ifdef CONFIG_SCHED_DEBUG
 # include "sched_debug.c"
 #endif
 
+void sched_set_stop_task(int cpu, struct task_struct *stop)
+{
+        struct sched_param param = { .sched_priority = MAX_RT_PRIO - 1 };
+        struct task_struct *old_stop = cpu_rq(cpu)->stop;
+
+        if (stop) {
+                /*
+                 * Make it appear like a SCHED_FIFO task, its something
+                 * userspace knows about and won't get confused about.
+                 *
+                 * Also, it will make PI more or less work without too
+                 * much confusion -- but then, stop work should not
+                 * rely on PI working anyway.
+                 */
+                sched_setscheduler_nocheck(stop, SCHED_FIFO, &param);
+
+                stop->sched_class = &stop_sched_class;
+        }
+
+        cpu_rq(cpu)->stop = stop;
+
+        if (old_stop) {
+                /*
+                 * Reset it back to a normal scheduling class so that
+                 * it can die in pieces.
+                 */
+                old_stop->sched_class = &rt_sched_class;
+        }
+}
+
 /*
  * __normal_prio - return the priority that is based on the static prio
  */
@@ -3720,17 +3751,13 @@ pick_next_task(struct rq *rq)
                         return p;
         }
 
-        class = sched_class_highest;
-        for ( ; ; ) {
+        for_each_class(class) {
                 p = class->pick_next_task(rq);
                 if (p)
                         return p;
-                /*
-                 * Will never be NULL as the idle class always
-                 * returns a non-NULL p:
-                 */
-                class = class->next;
         }
+
+        BUG(); /* the idle class will always have a runnable task */
 }
 
 /*
@@ -4659,6 +4686,15 @@ recheck:
          */
         rq = __task_rq_lock(p);
 
+        /*
+         * Changing the policy of the stop threads its a very bad idea
+         */
+        if (p == rq->stop) {
+                __task_rq_unlock(rq);
+                raw_spin_unlock_irqrestore(&p->pi_lock, flags);
+                return -EINVAL;
+        }
+
 #ifdef CONFIG_RT_GROUP_SCHED
         if (user) {
                 /*