[RFC][PATCH 3/5] memcg: Disable preemption in memcg_check_events()

[Steven Rostedt <rostedt@goodmis.org>]

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From: Steven Rostedt <srostedt@redhat.com>

The code in memcg_check_events() calls this_cpu_read() on
different variables without disabling preemption, and can cause
the calculations to be done from two different CPU variables.

Disable preemption throughout the check to keep apples and oranges
from becoming a mixed drink.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Greg Thelen <gthelen@google.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
---
 mm/memcontrol.c |    2 ++
 1 files changed, 2 insertions(+), 0 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 3508777..a164c93 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -718,6 +718,7 @@ static void __mem_cgroup_target_update(struct mem_cgroup *mem, int target)
  */
 static void memcg_check_events(struct mem_cgroup *mem, struct page *page)
 {
+	preempt_disable();
 	/* threshold event is triggered in finer grain than soft limit */
 	if (unlikely(__memcg_event_check(mem, MEM_CGROUP_TARGET_THRESH))) {
 		mem_cgroup_threshold(mem);
@@ -737,6 +738,7 @@ static void memcg_check_events(struct mem_cgroup *mem, struct page *page)
 		}
 #endif
 	}
+	preempt_enable();
 }
 
 static struct mem_cgroup *mem_cgroup_from_cont(struct cgroup *cont)
-- 
1.7.5.4