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sched/numa: Cure update_numa_stats() vs. hotplug 

Because we're completely unserialized against hotplug its well
possible to try and generate numa stats for an offlined node.

Bail out early (and avoid a /0) in this case. The resulting stats are
all 0 which should result in an undesirable balance target -- not to
mention that actually trying to migrate to an offline CPU will fail.

Reported-by: Prarit Bhargava <prarit@redhat.com>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Cc: Mel Gorman <mgorman@suse.de>
Link: http://lkml.kernel.org/n/tip-orja0qylcvyhxfsuebcyL5sI@git.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2013-11-06 18:47:57 +01:00 committed by Ingo Molnar
parent 46a73e8a1c
commit 5eca82a9ac
1 changed files with 14 additions and 1 deletions
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15
kernel/sched/fair.c
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@ -1000,7 +1000,7 @@ struct numa_stats {
*/ */
static void update_numa_stats(struct numa_stats *ns, int nid) static void update_numa_stats(struct numa_stats *ns, int nid)
{ {
int cpu; int cpu, cpus = 0;
memset(ns, 0, sizeof(*ns)); memset(ns, 0, sizeof(*ns));
for_each_cpu(cpu, cpumask_of_node(nid)) { for_each_cpu(cpu, cpumask_of_node(nid)) {
@ -1009,8 +1009,21 @@ static void update_numa_stats(struct numa_stats *ns, int nid)
ns->nr_running += rq->nr_running; ns->nr_running += rq->nr_running;
ns->load += weighted_cpuload(cpu); ns->load += weighted_cpuload(cpu);
ns->power += power_of(cpu); ns->power += power_of(cpu);
cpus++;
} }
/*
* If we raced with hotplug and there are no CPUs left in our mask
* the @ns structure is NULL'ed and task_numa_compare() will
* not find this node attractive.
*
* We'll either bail at !has_capacity, or we'll detect a huge imbalance
* and bail there.
*/
if (!cpus)
return;
ns->load = (ns->load * SCHED_POWER_SCALE) / ns->power; ns->load = (ns->load * SCHED_POWER_SCALE) / ns->power;
ns->capacity = DIV_ROUND_CLOSEST(ns->power, SCHED_POWER_SCALE); ns->capacity = DIV_ROUND_CLOSEST(ns->power, SCHED_POWER_SCALE);
ns->has_capacity = (ns->nr_running < ns->capacity); ns->has_capacity = (ns->nr_running < ns->capacity);