for_each_online_cpu() needs the protection of {get,put}_online_cpus() so
cpu_online_mask doesn't change during the iteration.

Signed-off-by: David Rientjes <rient...@google.com>
---
 mm/memcontrol.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -866,6 +866,7 @@ static unsigned long mem_cgroup_read_events(struct 
mem_cgroup *memcg,
        unsigned long val = 0;
        int cpu;
 
+       get_online_cpus();
        for_each_online_cpu(cpu)
                val += per_cpu(memcg->stat->events[idx], cpu);
 #ifdef CONFIG_HOTPLUG_CPU
@@ -873,6 +874,7 @@ static unsigned long mem_cgroup_read_events(struct 
mem_cgroup *memcg,
        val += memcg->nocpu_base.events[idx];
        spin_unlock(&memcg->pcp_counter_lock);
 #endif
+       put_online_cpus();
        return val;
 }
 
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