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

[Gene Heskett <gene.heskett@gmail.com>]

On Thursday 14 June 2007, Ingo Molnar wrote:
>From: Ingo Molnar <mingo@elte.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@gmail.com>
>Signed-off-by: Ingo Molnar <mingo@elte.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);
> }

Ingo:  I appended this patch to the cfs-v16 patch for 2.6.22-rc4, and got this 
while applying it:

patching file kernel/sched.c
Hunk #1 FAILED at 7071.
Hunk #2 FAILED at 7095.
2 out of 2 hunks FAILED -- saving rejects to file kernel/sched.c.rej
done

-- 
Cheers, Gene
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