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Subject[PATCH] sched, rt: fix rq->rt.pushable_tasks bug in push_rt_task()
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On Tue, 2011-05-31 at 11:08 -0400, Steven Rostedt wrote:
> On Tue, 2011-05-31 at 21:56 +0800, Hillf Danton wrote:
> > On Tue, May 31, 2011 at 3:36 PM, Mike Galbraith <efault@gmx.de> wrote:
> > > On Mon, 2011-05-30 at 21:39 +0800, Hillf Danton wrote:
> > >> When pushing, if a pushable task could not be pushed, it is dequeued with no
> > >> updating the rt_nr_migratory element of RT run-queue, then rt_nr_migratory is
> > >> corrupted, which is fixed by removing the dequeue operation.
> > >
> > > Hm. I think you're right that this dequeue_pushable_task() call can be
> > > removed, at least I didn't see it's reason for existing. I'd word it a
> > > bit differently though, and not return 1 unless we really did push.
> > >
> >
> > Hi Mike
> >
> > Your message shows what is called professional work, but something lost,
> >
> > > From: Hillf Danton <dhillf@gmail.com>
> > >
> > > 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 <efault@gmx.de>
> >
>
> Yeah, Mike, can you remail this adding your SOB too. You can keep
> Hillf's SOB as well, since both of you made changes.

From: Hillf Danton <dhillf@gmail.com>
AuthorDate: Mon, 30 May 2011 21:39:50 +0800

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 until either it's cpumask says otherwise,
or is selected. It is merely not pushable at this particular moment.

Signed-off-by: Hillf Danton <dhillf@gmail.com>
Signed-off-by: Mike Galbraith <efault@gmx.de>
---
kernel/sched_rt.c | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)
Index: linux-2.6.40.git/kernel/sched_rt.c
===================================================================
--- linux-2.6.40.git.orig/kernel/sched_rt.c
+++ linux-2.6.40.git/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)



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