From d7ea17a76916e456fcc78e45142c66f7fb875e3d Mon Sep 17 00:00:00 2001 From: Ingo Molnar Date: Fri, 4 Sep 2009 11:49:25 +0200 Subject: [PATCH] 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:[] [] 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 Cc: Mike Galbraith Cc: Paul Mackerras Cc: Arnaldo Carvalho de Melo Cc: Frederic Weisbecker LKML-Reference: <20090904092742.GA11014@elte.hu> Signed-off-by: Ingo Molnar --- kernel/sched.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-) diff --git a/kernel/sched.c b/kernel/sched.c index b537853..796baf7 100644 --- a/kernel/sched.c +++ b/kernel/sched.c @@ -3765,19 +3765,22 @@ static void update_group_power(struct sched_domain *sd, int cpu) { struct sched_domain *child = sd->child; struct sched_group *group, *sdg = sd->groups; + unsigned long power; if (!child) { update_cpu_power(sd, cpu); return; } - sdg->cpu_power = 0; + power = 0; group = child->groups; do { - sdg->cpu_power += group->cpu_power; + power += group->cpu_power; group = group->next; } while (group != child->groups); + + sdg->cpu_power = power; } /** -- 2.7.4