[PATCH 1/2] memcg: mem_cgroup->prev_priority protected by lock. take2

[KOSAKI Motohiro]

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



Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
---
 mm/memcontrol.c |   18 +++++++++++++++++-
 1 file changed, 17 insertions(+), 1 deletion(-)

Index: b/mm/memcontrol.c
===================================================================
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -142,6 +142,11 @@ 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 */
 
 	/*
@@ -393,18 +398,28 @@ int mem_cgroup_calc_mapped_ratio(struct 
  */
 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);
 }
 
 /*
@@ -1967,6 +1982,7 @@ mem_cgroup_create(struct cgroup_subsys *
 	}
 
 	mem->last_scanned_child = NULL;
+	spin_lock_init(&mem->reclaim_param_lock);
 
 	return &mem->css;
 free_out:


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