linux-kernel - Re: sched: BUG in load

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Message-ID: <1361237185.23152.174.camel@gandalf.local.home>
Date:	Mon, 18 Feb 2013 20:26:25 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	Ingo Molnar <mingo@...e.hu>, Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Dave Jones <davej@...hat.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: sched: BUG in load_balance

On Mon, 2013-02-18 at 19:55 -0500, Sasha Levin wrote:
> Hi all,
> 
> While fuzzing with trinity inside a KVM tools guest, running today's -next,
> I've stumbled on the following spew.
> 
> I've cc'ed Steven Rostedt since the culprit looks like "sched: Enable
> interrupts in idle_balance()".

You're correct. Interrupts are ok but softirqs must still be disabled.

The following patch should work.

-- Steve

Only compiled tested:

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 0fcdbff..a31174c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5222,9 +5222,9 @@ void idle_balance(int this_cpu, struct rq *this_rq)
 	update_rq_runnable_avg(this_rq, 1);
 
 	/*
-	 * Drop the rq->lock, but keep preempt disabled.
+	 * Drop the rq->lock, but keep softirqs disabled.
 	 */
-	preempt_disable();
+	local_bh_disable();
 	raw_spin_unlock_irq(&this_rq->lock);
 
 	update_blocked_averages(this_cpu);
@@ -5253,7 +5253,7 @@ void idle_balance(int this_cpu, struct rq *this_rq)
 	rcu_read_unlock();
 
 	raw_spin_lock_irq(&this_rq->lock);
-	preempt_enable();
+	local_bh_enable();
 
 	if (pulled_task || time_after(jiffies, this_rq->next_balance)) {
 		/*


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