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>
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index c11e36f..201be78 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1000,7 +1000,7 @@
*/
static void update_numa_stats(struct numa_stats *ns, int nid)
{
- int cpu;
+ int cpu, cpus = 0;
memset(ns, 0, sizeof(*ns));
for_each_cpu(cpu, cpumask_of_node(nid)) {
@@ -1009,8 +1009,21 @@
ns->nr_running += rq->nr_running;
ns->load += weighted_cpuload(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->capacity = DIV_ROUND_CLOSEST(ns->power, SCHED_POWER_SCALE);
ns->has_capacity = (ns->nr_running < ns->capacity);