[RFC][PATCH 5/4] memcg: don't call res_counter_uncharge whenobsolete

[Daisuke Nishimura]

This is a new one. Please review.

===
From: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>

mem_cgroup_get ensures that the memcg that has been got can be accessed
even after the directory has been removed, but it doesn't ensure that parents
of it can be accessed: parents might have been freed already by rmdir.

This causes a bug in case of use_hierarchy==1, because res_counter_uncharge
climb up the tree.

Check if the memcg is obsolete, and don't call res_counter_uncharge when obsole.

Signed-off-by: Daisuke Nishimura <nishimura@xxxxxxxxxxxxxxxxx>
---
 mm/memcontrol.c |    9 ++++++---
 1 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index fb62b43..4ee95a8 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1182,7 +1182,8 @@ int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
 		/* avoid double counting */
 		mem = swap_cgroup_record(ent, NULL);
 		if (mem) {
-			res_counter_uncharge(&mem->memsw, PAGE_SIZE);
+			if (!mem_cgroup_is_obsolete(mem))
+				res_counter_uncharge(&mem->memsw, PAGE_SIZE);
 			mem_cgroup_put(mem);
 		}
 	}
@@ -1252,7 +1253,8 @@ void mem_cgroup_commit_charge_swapin(struct page *page, struct mem_cgroup *ptr)
 		struct mem_cgroup *memcg;
 		memcg = swap_cgroup_record(ent, NULL);
 		if (memcg) {
-			res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
+			if (!mem_cgroup_is_obsolete(memcg))
+				res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
 			mem_cgroup_put(memcg);
 		}
 
@@ -1397,7 +1399,8 @@ void mem_cgroup_uncharge_swap(swp_entry_t ent)
 
 	memcg = swap_cgroup_record(ent, NULL);
 	if (memcg) {
-		res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
+		if (!mem_cgroup_is_obsolete(memcg))
+			res_counter_uncharge(&memcg->memsw, PAGE_SIZE);
 		mem_cgroup_put(memcg);
 	}
 }
--
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