sched, rt: Fix rq->rt.pushable_tasks bug in push_rt_task()

Do not call dequeue_pushable_task() when failing to push an eligible
task, as it remains pushable, merely not at this particular moment.

Signed-off-by: Hillf Danton <dhillf@gmail.com>
Signed-off-by: Mike Galbraith <mgalbraith@gmx.de>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Yong Zhang <yong.zhang0@gmail.com>
Link: http://lkml.kernel.org/r/1306895385.4791.26.camel@marge.simson.net
Signed-off-by: Ingo Molnar <mingo@elte.hu>

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index e2698c0fc697fefcb13944e15bbcbadb742fcd42..8e189455ed1270eb1e980d9cefebb4474934cacb 100644 (file)
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -1394,6 +1394,7 @@ static int push_rt_task(struct rq *rq)
 {
        struct task_struct *next_task;
        struct rq *lowest_rq;
+       int ret = 0;
 
        if (!rq->rt.overloaded)
                return 0;
@@ -1426,7 +1427,7 @@ retry:
        if (!lowest_rq) {
                struct task_struct *task;
                /*
-                * find lock_lowest_rq releases rq->lock
+                * find_lock_lowest_rq releases rq->lock
                 * so it is possible that next_task has migrated.
                 *
                 * We need to make sure that the task is still on the same
@@ -1436,12 +1437,11 @@ retry:
                task = pick_next_pushable_task(rq);
                if (task_cpu(next_task) == rq->cpu && task == next_task) {
                        /*
-                        * If we get here, the task hasn't moved at all, but
-                        * it has failed to push.  We will not try again,
-                        * since the other cpus will pull from us when they
-                        * are ready.
+                        * The task hasn't migrated, and is still the next
+                        * eligible task, but we failed to find a run-queue
+                        * to push it to.  Do not retry in this case, since
+                        * other cpus will pull from us when ready.
                         */
-                       dequeue_pushable_task(rq, next_task);
                        goto out;
                }
 
@@ -1460,6 +1460,7 @@ retry:
        deactivate_task(rq, next_task, 0);
        set_task_cpu(next_task, lowest_rq->cpu);
        activate_task(lowest_rq, next_task, 0);
+       ret = 1;
 
        resched_task(lowest_rq->curr);
 
@@ -1468,7 +1469,7 @@ retry:
 out:
        put_task_struct(next_task);
 
-       return 1;
+       return ret;
 }
 
 static void push_rt_tasks(struct rq *rq)