1 files changed, 85 insertions, 0 deletions

diff --git a/kernel/sched.c b/kernel/sched.c
index ae5e1a19b9d6..2effcb71a478 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -1686,6 +1686,39 @@ static void double_rq_unlock(struct rq *rq1, struct rq *rq2)
                 __release(rq2->lock);
 }
 
+#else /* CONFIG_SMP */
+
+/*
+ * double_rq_lock - safely lock two runqueues
+ *
+ * Note this does not disable interrupts like task_rq_lock,
+ * you need to do so manually before calling.
+ */
+static void double_rq_lock(struct rq *rq1, struct rq *rq2)
+        __acquires(rq1->lock)
+        __acquires(rq2->lock)
+{
+        BUG_ON(!irqs_disabled());
+        BUG_ON(rq1 != rq2);
+        raw_spin_lock(&rq1->lock);
+        __acquire(rq2->lock);   /* Fake it out ;) */
+}
+
+/*
+ * double_rq_unlock - safely unlock two runqueues
+ *
+ * Note this does not restore interrupts like task_rq_unlock,
+ * you need to do so manually after calling.
+ */
+static void double_rq_unlock(struct rq *rq1, struct rq *rq2)
+        __releases(rq1->lock)
+        __releases(rq2->lock)
+{
+        BUG_ON(rq1 != rq2);
+        raw_spin_unlock(&rq1->lock);
+        __release(rq2->lock);
+}
+
 #endif
 
 static void calc_load_account_idle(struct rq *this_rq);
@@ -5448,6 +5481,58 @@ void __sched yield(void)
 }
 EXPORT_SYMBOL(yield);
 
+/**
+ * yield_to - yield the current processor to another thread in
+ * your thread group, or accelerate that thread toward the
+ * processor it's on.
+ *
+ * It's the caller's job to ensure that the target task struct
+ * can't go away on us before we can do any checks.
+ *
+ * Returns true if we indeed boosted the target task.
+ */
+bool __sched yield_to(struct task_struct *p, bool preempt)
+{
+        struct task_struct *curr = current;
+        struct rq *rq, *p_rq;
+        unsigned long flags;
+        bool yielded = 0;
+
+        local_irq_save(flags);
+        rq = this_rq();
+
+again:
+        p_rq = task_rq(p);
+        double_rq_lock(rq, p_rq);
+        while (task_rq(p) != p_rq) {
+                double_rq_unlock(rq, p_rq);
+                goto again;
+        }
+
+        if (!curr->sched_class->yield_to_task)
+                goto out;
+
+        if (curr->sched_class != p->sched_class)
+                goto out;
+
+        if (task_running(p_rq, p) || p->state)
+                goto out;
+
+        yielded = curr->sched_class->yield_to_task(rq, p, preempt);
+        if (yielded)
+                schedstat_inc(rq, yld_count);
+
+out:
+        double_rq_unlock(rq, p_rq);
+        local_irq_restore(flags);
+
+        if (yielded)
+                schedule();
+
+        return yielded;
+}
+EXPORT_SYMBOL_GPL(yield_to);
+
 /*
  * This task is about to go to sleep on IO. Increment rq->nr_iowait so
  * that process accounting knows that this is a task in IO wait state.