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sched: Check sched_domain before computing group power 

After commit 863bffc808 ("sched/fair: Fix group power_orig
computation"), we can dereference rq->sd before it is set.

Fix this by falling back to power_of() in this case and add a comment
explaining things.

Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
[ Added comment and tweaked patch. ]
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: mikey@neuling.org
Link: http://lkml.kernel.org/r/20131113151718.GN21461@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Srikar Dronamraju 2013-11-12 22:11:26 +05:30 committed by Ingo Molnar
parent 7486d6da09
commit 9abf24d465
1 changed files with 24 additions and 3 deletions
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27
kernel/sched/fair.c
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@ -5379,10 +5379,31 @@ void update_group_power(struct sched_domain *sd, int cpu)
*/
for_each_cpu(cpu, sched_group_cpus(sdg)) {
struct sched_group *sg = cpu_rq(cpu)->sd->groups;
struct sched_group_power *sgp;
struct rq *rq = cpu_rq(cpu);
power_orig += sg->sgp->power_orig;
power += sg->sgp->power;
/*
* build_sched_domains() -> init_sched_groups_power()
* gets here before we've attached the domains to the
* runqueues.
*
* Use power_of(), which is set irrespective of domains
* in update_cpu_power().
*
* This avoids power/power_orig from being 0 and
* causing divide-by-zero issues on boot.
*
* Runtime updates will correct power_orig.
*/
if (unlikely(!rq->sd)) {
power_orig += power_of(cpu);
power += power_of(cpu);
continue;
}
sgp = rq->sd->groups->sgp;
power_orig += sgp->power_orig;
power += sgp->power;
}
} else {
/*