memcg: protect prev_priority

Currently, mem_cgroup doesn't have own lock and almost its member doesn't
need.  (e.g.  mem_cgroup->info is protected by zone lock, mem_cgroup->stat
is per cpu variable)

However, there is one explict exception.  mem_cgroup->prev_priorit need
lock, but doesn't protect.  Luckly, this is NOT bug because prev_priority
isn't used for current reclaim code.

However, we plan to use prev_priority future again.  Therefore, fixing is
better.

In addition, we plan to reuse this lock for another member.  Then
"reclaim_param_lock" name is better than "prev_priority_lock".

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Balbir Singh <balbir@in.ibm.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: 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, 17 insertions, 1 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index af28e128b749..027c0dd7a83e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -144,6 +144,11 @@ struct mem_cgroup {
          */
         struct mem_cgroup_lru_info info;
 
+        /*
+          protect against reclaim related member.
+        */
+        spinlock_t reclaim_param_lock;
+
         int     prev_priority;  /* for recording reclaim priority */
 
         /*
@@ -400,18 +405,28 @@ int mem_cgroup_calc_mapped_ratio(struct mem_cgroup *mem)
  */
 int mem_cgroup_get_reclaim_priority(struct mem_cgroup *mem)
 {
-        return mem->prev_priority;
+        int prev_priority;
+
+        spin_lock(&mem->reclaim_param_lock);
+        prev_priority = mem->prev_priority;
+        spin_unlock(&mem->reclaim_param_lock);
+
+        return prev_priority;
 }
 
 void mem_cgroup_note_reclaim_priority(struct mem_cgroup *mem, int priority)
 {
+        spin_lock(&mem->reclaim_param_lock);
         if (priority < mem->prev_priority)
                 mem->prev_priority = priority;
+        spin_unlock(&mem->reclaim_param_lock);
 }
 
 void mem_cgroup_record_reclaim_priority(struct mem_cgroup *mem, int priority)
 {
+        spin_lock(&mem->reclaim_param_lock);
         mem->prev_priority = priority;
+        spin_unlock(&mem->reclaim_param_lock);
 }
 
 int mem_cgroup_inactive_anon_is_low(struct mem_cgroup *memcg, struct zone *zone)
@@ -2076,6 +2091,7 @@ mem_cgroup_create(struct cgroup_subsys *ss, struct cgroup *cont)
         }
         mem_cgroup_set_inactive_ratio(mem);
         mem->last_scanned_child = NULL;
+        spin_lock_init(&mem->reclaim_param_lock);
 
         return &mem->css;
 free_out: