memcg: Fix race condition in memcg_check_events() with this_cpu usage

Various code in memcontrol.c () calls this_cpu_read() on the calculations
to be done from two different percpu variables, or does an open-coded
read-modify-write on a single percpu variable.

Disable preemption throughout these operations so that the writes go to
the correct palces.

[hannes@cmpxchg.org: added this_cpu to __this_cpu conversion]
Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Cc: Greg Thelen <gthelen@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Christoph Lameter <cl@linux.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/memcontrol.c

@@ -686,8 +686,8 @@ static bool __memcg_event_check(struct mem_cgroup *memcg, int target)
 {
 	unsigned long val, next;
 
-	val = this_cpu_read(memcg->stat->events[MEM_CGROUP_EVENTS_COUNT]);
-	next = this_cpu_read(memcg->stat->targets[target]);
+	val = __this_cpu_read(memcg->stat->events[MEM_CGROUP_EVENTS_COUNT]);
+	next = __this_cpu_read(memcg->stat->targets[target]);
 	/* from time_after() in jiffies.h */
 	return ((long)next - (long)val < 0);
 }
@@ -696,7 +696,7 @@ static void __mem_cgroup_target_update(struct mem_cgroup *memcg, int target)
 {
 	unsigned long val, next;
 
-	val = this_cpu_read(memcg->stat->events[MEM_CGROUP_EVENTS_COUNT]);
+	val = __this_cpu_read(memcg->stat->events[MEM_CGROUP_EVENTS_COUNT]);
 
 	switch (target) {
 	case MEM_CGROUP_TARGET_THRESH:
@@ -712,7 +712,7 @@ static void __mem_cgroup_target_update(struct mem_cgroup *memcg, int target)
 		return;
 	}
 
-	this_cpu_write(memcg->stat->targets[target], next);
+	__this_cpu_write(memcg->stat->targets[target], next);
 }
 
 /*
@@ -721,6 +721,7 @@ static void __mem_cgroup_target_update(struct mem_cgroup *memcg, int target)
  */
 static void memcg_check_events(struct mem_cgroup *memcg, struct page *page)
 {
+	preempt_disable();
 	/* threshold event is triggered in finer grain than soft limit */
 	if (unlikely(__memcg_event_check(memcg, MEM_CGROUP_TARGET_THRESH))) {
 		mem_cgroup_threshold(memcg);
@@ -740,6 +741,7 @@ static void memcg_check_events(struct mem_cgroup *memcg, struct page *page)
 		}
 #endif
 	}
+	preempt_enable();
 }
 
 static struct mem_cgroup *mem_cgroup_from_cont(struct cgroup *cont)