linux-kernel - [29/30] sched: Fix task priority bug

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Date:	Wed, 20 Jan 2010 20:15:50 -0800
From:	Greg KH <gregkh@...e.de>
To:	linux-kernel@...r.kernel.org, stable@...nel.org
Cc:	stable-review@...nel.org, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, alan@...rguk.ukuu.org.uk,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Ingo Molnar <mingo@...e.hu>
Subject: [29/30] sched: Fix task priority bug

2.6.32-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Peter Zijlstra <a.p.zijlstra@...llo.nl>

commit 57785df5ac53c70da9fb53696130f3c551bfe1f9 upstream.

83f9ac removed a call to effective_prio() in wake_up_new_task(), which
leads to tasks running at MAX_PRIO.

This is caused by the idle thread being set to MAX_PRIO before forking
off init. O(1) used that to make sure idle was always preempted, CFS
uses check_preempt_curr_idle() for that so we can savely remove this bit
of legacy code.

Reported-by: Mike Galbraith <efault@....de>
Tested-by: Mike Galbraith <efault@....de>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl>
LKML-Reference: <1259754383.4003.610.camel@...top>
Signed-off-by: Ingo Molnar <mingo@...e.hu>
Signed-off-by: Greg Kroah-Hartman <gregkh@...e.de>

---
 kernel/sched.c |    6 ------
 1 file changed, 6 deletions(-)

--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -3177,10 +3177,6 @@ static void pull_task(struct rq *src_rq,
 	deactivate_task(src_rq, p, 0);
 	set_task_cpu(p, this_cpu);
 	activate_task(this_rq, p, 0);
-	/*
-	 * Note that idle threads have a prio of MAX_PRIO, for this test
-	 * to be always true for them.
-	 */
 	check_preempt_curr(this_rq, p, 0);
 }
 
@@ -6982,7 +6978,6 @@ void __cpuinit init_idle(struct task_str
 	__sched_fork(idle);
 	idle->se.exec_start = sched_clock();
 
-	idle->prio = idle->normal_prio = MAX_PRIO;
 	cpumask_copy(&idle->cpus_allowed, cpumask_of(cpu));
 	__set_task_cpu(idle, cpu);
 
@@ -7686,7 +7681,6 @@ migration_call(struct notifier_block *nf
 		spin_lock_irq(&rq->lock);
 		update_rq_clock(rq);
 		deactivate_task(rq, rq->idle, 0);
-		rq->idle->static_prio = MAX_PRIO;
 		__setscheduler(rq, rq->idle, SCHED_NORMAL, 0);
 		rq->idle->sched_class = &idle_sched_class;
 		migrate_dead_tasks(cpu);


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