linux-kernel - Re: [patch] sched: fix SysRq-N (normalize RT tasks)

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Message-Id: <200706141012.31048.gene.heskett@gmail.com>
Date:	Thu, 14 Jun 2007 10:12:30 -0400
From:	Gene Heskett <gene.heskett@...il.com>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Chris Wright <chrisw@...s-sol.org>
Subject: Re: [patch] sched: fix SysRq-N (normalize RT tasks)

On Thursday 14 June 2007, Ingo Molnar wrote:
>From: Ingo Molnar <mingo@...e.hu>
>Subject: [patch] sched: fix SysRq-N (normalize RT tasks)
>
>Gene Heskett reported the following problem while testing CFS: SysRq-N
>is not always effective in normalizing tasks back to SCHED_OTHER.
>
>the reason for that turns out to be the following bug:
>normalize_rt_tasks() uses for_each_process() to iterate through all
>tasks in the system. The problem is, this method does not iterate
>through all tasks, it iterates through all thread groups. The proper
>mechanism to enumerate all tasks is to use a do_each_thread() +
>while_each_thread() loop.
>
>obvious bugfix for v2.6.22 inclusion. -stable candidate as well.
>
>Reported-by: Gene Heskett <gene.heskett@...il.com>
>Signed-off-by: Ingo Molnar <mingo@...e.hu>
>---
> kernel/sched.c |    8 +++++---
> 1 file changed, 5 insertions(+), 3 deletions(-)
>
>Index: linux/kernel/sched.c
>===================================================================
>--- linux/kernel/sched.c
>+++ linux/kernel/sched.c
>@@ -7071,12 +7071,13 @@ EXPORT_SYMBOL(__might_sleep);
> void normalize_rt_tasks(void)
> {
> 	struct prio_array *array;
>-	struct task_struct *p;
>+	struct task_struct *g, *p;
> 	unsigned long flags;
> 	struct rq *rq;
>
> 	read_lock_irq(&tasklist_lock);
>-	for_each_process(p) {
>+
>+	do_each_thread(g, p) {
> 		if (!rt_task(p))
> 			continue;
>
>@@ -7094,7 +7095,8 @@ void normalize_rt_tasks(void)
>
> 		__task_rq_unlock(rq);
> 		spin_unlock_irqrestore(&p->pi_lock, flags);
>-	}
>+	} while_each_thread(g, p);
>+
> 	read_unlock_irq(&tasklist_lock);
> }

When I looked at sched.c, I found it about 1000 lines shorter than the offsets 
listed above.  So I took it back out and will test the plain 
2.6.22-rc4-cfs-v16 shortly.

-- 
Cheers, Gene
"There are four boxes to be used in defense of liberty:
 soap, ballot, jury, and ammo. Please use in that order."
-Ed Howdershelt (Author)
To save a single life is better than to build a seven story pagoda.
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