linux-kernel - Re: [PATCH][GIT PULL] tracing: Fix compile issue for trace_sched

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Date:	Fri, 22 Oct 2010 10:14:31 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Jason Baron <jbaron@...hat.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Arnaldo Carvalho de Melo <acme@...hat.com>, tj@...nel.org
Subject: Re: [PATCH][GIT PULL] tracing: Fix compile issue for
 trace_sched_wakeup.c

On Thu, 2010-10-21 at 21:44 -0400, Jason Baron wrote:

> I finally found that we actually continue to run after the above
> apparent 'hang'. That is, we continue to make progress updating the jump
> labels. And doing a dump of all the system tasks at the time of the hang
> showed the processes in various places besides the stop machine threads.
> Thus, I thought that perhaps, for some reason the stop machine threads
> weren't being scheduled.
> 
> Thus, I tried commenting out the special scheduling that is set up for
> stop machine threads, and that fixed the hang. I haven't yet looked into
> what might be going wrong with that scheduling...but maybe somebody else
> knows...

Hrmm, so are you saying rq->stop was runnable but not running?

That would imply broken wakeup-preemption, does something like the below
cure that?


---
 kernel/sched_stoptask.c |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/kernel/sched_stoptask.c b/kernel/sched_stoptask.c
index 45bddc0..50ad10f 100644
--- a/kernel/sched_stoptask.c
+++ b/kernel/sched_stoptask.c
@@ -35,6 +35,7 @@ static struct task_struct *pick_next_task_stop(struct rq *rq)
 static void
 enqueue_task_stop(struct rq *rq, struct task_struct *p, int flags)
 {
+	resched_cpu(cpu_of(rq));
 }
 
 static void


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