sched: Always initialize cpu-power

Often when we run into mis-shapen topologies the balance iteration
fails to update the cpu power properly and we'll end up in /0 traps.

Always initialize the cpu-power to a semi-sane value so that we can
at least boot the machine, even if the load-balancer might not
function correctly.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/n/tip-3lbhyj25sr169ha7z3qht5na@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

2 files changed, 13 insertions, 2 deletions

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 781acb91a50a..725ee7c1c8cf 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5604,7 +5604,12 @@ static int sched_domain_debug_one(struct sched_domain *sd, int cpu, int level,
                         break;
                 }
 
-                if (!group->sgp->power) {
+                /*
+                 * Even though we initialize ->power to something semi-sane,
+                 * we leave power_orig unset. This allows us to detect if
+                 * domain iteration is still funny without causing /0 traps.
+                 */
+                if (!group->sgp->power_orig) {
                         printk(KERN_CONT "\n");
                         printk(KERN_ERR "ERROR: domain->cpu_power not "
                                         "set\n");
@@ -6075,6 +6080,12 @@ build_overlap_sched_groups(struct sched_domain *sd, int cpu)
                 if (atomic_inc_return(&sg->sgp->ref) == 1)
                         build_group_mask(sd, sg);
 
+                /*
+                 * Initialize sgp->power such that even if we mess up the
+                 * domains and no possible iteration will get us here, we won't
+                 * die on a /0 trap.
+                 */
+                sg->sgp->power = SCHED_POWER_SCALE * cpumask_weight(sg_span);
 
                 /*
                  * Make sure the first group of this domain contains the
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 54cbaa4e7b37..c9fd6d673d05 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -3602,7 +3602,7 @@ void update_group_power(struct sched_domain *sd, int cpu)
                 } while (group != child->groups);
         }
 
-        sdg->sgp->power = power;
+        sdg->sgp->power_orig = sdg->sgp->power = power;
 }
 
 /*