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

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Message-ID: <20070614094830.GA494@elte.hu>
Date:	Thu, 14 Jun 2007 11:48:30 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Gene Heskett <gene.heskett@...il.com>,
	linux-kernel@...r.kernel.org, Chris Wright <chrisw@...s-sol.org>
Subject: [patch] sched: fix SysRq-N (normalize RT tasks)

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);
 }
 
-
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