Merge commit 'v2.6.30-rc3' into tracing/hw-branch-tracing

[~andy/linux] / kernel / sched.c

diff --git a/kernel/sched.c b/kernel/sched.c
index b902e587a3a03e32a3e26f676e419f692ba79145..36322e8682c70f56e23a4612993057b19f69cadd 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -2014,6 +2014,49 @@ migrate_task(struct task_struct *p, int dest_cpu, struct migration_req *req)
        return 1;
 }
 
+/*
+ * wait_task_context_switch -  wait for a thread to complete at least one
+ *                             context switch.
+ *
+ * @p must not be current.
+ */
+void wait_task_context_switch(struct task_struct *p)
+{
+       unsigned long nvcsw, nivcsw, flags;
+       int running;
+       struct rq *rq;
+
+       nvcsw   = p->nvcsw;
+       nivcsw  = p->nivcsw;
+       for (;;) {
+               /*
+                * The runqueue is assigned before the actual context
+                * switch. We need to take the runqueue lock.
+                *
+                * We could check initially without the lock but it is
+                * very likely that we need to take the lock in every
+                * iteration.
+                */
+               rq = task_rq_lock(p, &flags);
+               running = task_running(rq, p);
+               task_rq_unlock(rq, &flags);
+
+               if (likely(!running))
+                       break;
+               /*
+                * The switch count is incremented before the actual
+                * context switch. We thus wait for two switches to be
+                * sure at least one completed.
+                */
+               if ((p->nvcsw - nvcsw) > 1)
+                       break;
+               if ((p->nivcsw - nivcsw) > 1)
+                       break;
+
+               cpu_relax();
+       }
+}
+
 /*
  * wait_task_inactive - wait for a thread to unschedule.
  *