linux-kernel - Re: CFS and suspend2: hang in atomic copy

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Date:	Thu, 19 Apr 2007 08:29:36 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Bob Picco <bob.picco@...com>
Cc:	Christian Hesse <mail@...thworm.de>, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Con Kolivas <kernel@...ivas.org>,
	Nick Piggin <npiggin@...e.de>, Mike Galbraith <efault@....de>,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	suspend2-devel@...ts.suspend2.net
Subject: Re: CFS and suspend2: hang in atomic copy


* Bob Picco <bob.picco@...com> wrote:

> I had hoped to collect more data with CFS V2. It crashes in 
> scale_nice_down for s2ram when attempting to disable_nonboot_cpus. So 
> part of traceback looks like (typed by hand with obvious omissions):
> 
> scale_nice_down
> update_stats_wait_end - not shown in traceback because inlined
> pick_next_task_fair
> migration_call
> task_rq_lock
> notifier_call_chain
> _cpu_down
> disable_nonboot_cpus

ok, this looks similar to the jpeg Christian did. Does the patch below 
fix the crash for you?

	Ingo

---
 kernel/sched.c |    2 ++
 1 file changed, 2 insertions(+)

Index: linux/kernel/sched.c
===================================================================
--- linux.orig/kernel/sched.c
+++ linux/kernel/sched.c
@@ -4425,6 +4425,8 @@ static void migrate_dead_tasks(unsigned 
 	struct task_struct *next;
 
 	for (;;) {
+		if (!rq->nr_running)
+			break;
 		next = pick_next_task(rq, rq->curr);
 		if (!next)
 			break;
-
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