linux-kernel - Re: [PATCH/RFC] sched: Remove SYSTEM_RUNNING checks from cond

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Date:	Wed, 8 Jul 2009 16:03:02 +0400
From:	Anton Vorontsov <avorontsov@...mvista.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Oleg Nesterov <oleg@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH/RFC] sched: Remove SYSTEM_RUNNING checks from
 cond_resched*()

On Wed, Jul 08, 2009 at 08:24:23AM +0200, Peter Zijlstra wrote:
> On Wed, 2009-07-08 at 02:50 +0200, Oleg Nesterov wrote:
> 
> > 	/*
> > 	 * It is valid to assume CPU-locality during early bootup:
> > 	 */
> > 	if (system_state != SYSTEM_RUNNING)
> > 		goto out;
> > 
> > this doesn't look right, smp_init() is called before we set
> > SYSTEM_RUNNING.
> 
> The thing is, there's also ton's of code that might end up calling
> cond_resched() and co before the scheduler is fully initialized.

Hm. Speaking of cond_resched*() only, then it should be pretty
safe to convert the SYSTEM_RUNNING checks to scheduler_running,
no? scheduler_running is set after sched_init().

Something like this

diff --git a/kernel/sched.c b/kernel/sched.c
index 7c9098d..555360b 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -6561,7 +6561,7 @@ static void __cond_resched(void)
 int __sched _cond_resched(void)
 {
 	if (need_resched() && !(preempt_count() & PREEMPT_ACTIVE) &&
-					system_state == SYSTEM_RUNNING) {
+					scheduler_running) {
 		__cond_resched();
 		return 1;
 	}
@@ -6579,7 +6579,7 @@ EXPORT_SYMBOL(_cond_resched);
  */
 int cond_resched_lock(spinlock_t *lock)
 {
-	int resched = need_resched() && system_state == SYSTEM_RUNNING;
+	int resched = need_resched() && scheduler_running;
 	int ret = 0;
 
 	if (spin_needbreak(lock) || resched) {
@@ -6599,7 +6599,7 @@ int __sched cond_resched_softirq(void)
 {
 	BUG_ON(!in_softirq());
 
-	if (need_resched() && system_state == SYSTEM_RUNNING) {
+	if (need_resched() && scheduler_running) {
 		local_bh_enable();
 		__cond_resched();
 		local_bh_disable();
--
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