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

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Message-ID: <20070419062832.GD18894@elte.hu>
Date:	Thu, 19 Apr 2007 08:28:32 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Christian Hesse <mail@...thworm.de>
Cc:	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


* Christian Hesse <mail@...thworm.de> wrote:

> I now got some error message from my system:
> 
> http://www.eworm.de/tmp/cfs-suspend.jpg

ah, this pinpoints a bug: for performance reasons pick_next_task() 
assumes that the runqueue is not empty - which is true for schedule(), 
but not in migrate_dead_tasks(). 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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