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

From: Gene Heskett
Date: Thu Jun 14 2007 - 10:12:49 EST

On Thursday 14 June 2007, Ingo Molnar wrote:
>From: Ingo Molnar <mingo@xxxxxxx>
>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@xxxxxxxxx>
>Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
> 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)
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