diff options
authorDavid Rientjes <rientjes@google.com>2013-10-16 13:46:43 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2013-10-16 21:35:52 -0700
commit9c56751271e7a917783fb57ec49fe8382e0dc867 (patch)
parent34ec4de42be5006abdd8d0c08b306ffaa64d0d5d (diff)
mm, memcg: protect mem_cgroup_read_events for cpu hotplug
for_each_online_cpu() needs the protection of {get,put}_online_cpus() so cpu_online_mask doesn't change during the iteration. cpu_hotplug.lock is held while a cpu is going down, it's a coarse lock that is used kernel-wide to synchronize cpu hotplug activity. Memcg has a cpu hotplug notifier, called while there may not be any cpu hotplug refcounts, which drains per-cpu event counts to memcg->nocpu_base.events to maintain a cumulative event count as cpus disappear. Without get_online_cpus() in mem_cgroup_read_events(), it's possible to account for the event count on a dying cpu twice, and this value may be significantly large. In fact, all memcg->pcp_counter_lock use should be nested by {get,put}_online_cpus(). This fixes that issue and ensures the reported statistics are not vastly over-reported during cpu hotplug. Signed-off-by: David Rientjes <rientjes@google.com> Cc: Johannes Weiner <hannes@cmpxchg.org> Cc: Michal Hocko <mhocko@suse.cz> Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> Acked-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 files changed, 2 insertions, 0 deletions
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 1c52ddbc839..5335b2b6be7 100644
--- 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();
val += per_cpu(memcg->stat->events[idx], cpu);
@@ -873,6 +874,7 @@ static unsigned long mem_cgroup_read_events(struct mem_cgroup *memcg,
val += memcg->nocpu_base.events[idx];
+ put_online_cpus();
return val;