Re: [PATCH] [5/6] scheduler: Protect important kernel threads against normalize_rt

Ingo Molnar
2007-10-08T12:44:04Z

* Andi Kleen <ak@suse.de> wrote:

> softlockup is the same. Just think about it.
>
> If you ever renormalize it and then run a fifo thread it will starve
> and then eventually kill the box.
>
> And starving CPU unplug is also equally bad.

yeah, agreed. I ended up doing the change below.

Ingo

------------------->
Subject: sched: do not normalize kernel threads via SysRq-N
From: Ingo Molnar <mingo@elte.hu>

do not normalize kernel threads via SysRq-N: the migration threads,
softlockup threads, etc. might be essential for the system to
function properly. So only zap user tasks.

pointed out by Andi Kleen.

Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
kernel/sched.c | 18 +++++++-----------
1 file changed, 7 insertions(+), 11 deletions(-)

Index: linux/kernel/sched.c
===================================================================
--- linux.orig/kernel/sched.c
+++ linux/kernel/sched.c
@@ -362,15 +362,6 @@ static inline int cpu_of(struct rq *rq)
#endif
}

-static inline int is_migration_thread(struct task_struct *p, struct rq *rq)
-{
-#ifdef CONFIG_SMP
- return p == rq->migration_thread;
-#else
- return 0;
-#endif
-}
-
/*
* Update the per-runqueue clock, as finegrained as the platform can give
* us, but without assuming monotonicity, etc.:
@@ -6557,6 +6548,12 @@ void normalize_rt_tasks(void)

read_lock_irq(&tasklist_lock);
do_each_thread(g, p) {
+ /*
+ * Only normalize user tasks:
+ */
+ if (!p->mm)
+ continue;
+
p->se.exec_start = 0;
#ifdef CONFIG_SCHEDSTATS
p->se.wait_start = 0;
@@ -6578,8 +6575,7 @@ void normalize_rt_tasks(void)
spin_lock_irqsave(&p->pi_lock, flags);
rq = __task_rq_lock(p);

- if (!is_migration_thread(p, rq))
- normalize_task(rq, p);
+ normalize_task(rq, p);

__task_rq_unlock(rq);
spin_unlock_irqrestore(&p->pi_lock, flags);