[RFC][PATCH 4/7] sched, rt: Fix rq->rt.pushable_tasks bug in push_rt_task()

[Steven Rostedt <rostedt@goodmis.org>]

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From: Hillf Danton <dhillf@gmail.com>

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

Cc: Yong Zhang <yong.zhang0@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Hillf Danton <dhillf@gmail.com>
Signed-off-by: Mike Galbraith <mgalbraith@gmx.de>
Link: http://lkml.kernel.org/r/1306895385.4791.26.camel@marge.simson.net
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/sched_rt.c |   15 ++++++++-------
 1 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index a6f1f64..7737d41 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -1378,6 +1378,7 @@ 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;
@@ -1410,7 +1411,7 @@ 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
@@ -1420,12 +1421,11 @@ 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;
 		}
 
@@ -1444,6 +1444,7 @@ 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);
 
@@ -1452,7 +1453,7 @@ retry:
 out:
 	put_task_struct(next_task);
 
-	return 1;
+	return ret;
 }
 
 static void push_rt_tasks(struct rq *rq)
-- 
1.7.4.4