Commit d7ea17a7 authored Sep 04, 2009 by Ingo Molnar

sched: Fix dynamic power-balancing crash



This crash:

[ 1774.088275] divide error: 0000 [#1] SMP
[ 1774.100355] CPU 13
[ 1774.102498] Modules linked in:
[ 1774.105631] Pid: 30881, comm: hackbench Not tainted 2.6.31-rc8-tip-01308-g484d664-dirty #1629 X8DTN
[ 1774.114807] RIP: 0010:[<ffffffff81041c38>]  [<ffffffff81041c38>]
sched_balance_self+0x19b/0x2d4

Triggers because update_group_power() modifies the sd tree and does
temporary calculations there - not considering that other CPUs
could observe intermediate values, such as the zero initial value.

Calculate it in a temporary variable instead. (we need no memory
barrier as these are all statistical values anyway)

Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
LKML-Reference: <20090904092742.GA11014@elte.hu>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

parent 18a3885f

kernel/sched.c

+5 −2

Original line number	Original line	Diff line number	Diff line
	@@ -3765,19 +3765,22 @@ static void update_group_power(struct sched_domain *sd, int cpu)
	{		{
	struct sched_domain *child = sd->child;		struct sched_domain *child = sd->child;
	struct sched_group group, sdg = sd->groups;		struct sched_group group, sdg = sd->groups;
			unsigned long power;

	if (!child) {		if (!child) {
	update_cpu_power(sd, cpu);		update_cpu_power(sd, cpu);
	return;		return;
	}		}

	sdg->cpu_power = 0;		power = 0;

	group = child->groups;		group = child->groups;
	do {		do {
	sdg->cpu_power += group->cpu_power;		power += group->cpu_power;
	group = group->next;		group = group->next;
	} while (group != child->groups);		} while (group != child->groups);

			sdg->cpu_power = power;
	}		}

	/**		/**