[BUGFIX][PATCH mmotm] memcg: fix for hierarchical reclaim

[Daisuke Nishimura <d-nishimura@mtf.biglobe.ne.jp>]

mem_cgroup_from_res_counter should handle both mem->res and mem->memsw.
This bug leads to NULL pointer dereference BUG at mem_cgroup_calc_reclaim.

Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
---
This is fix for memory-cgroup-hierarchical-reclaim-v4.patch.

 mm/memcontrol.c |   23 +++++++++--------------
 1 files changed, 9 insertions(+), 14 deletions(-)

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d177ed7..ac445cf 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -468,11 +468,8 @@ unsigned long mem_cgroup_isolate_pages(unsigned long nr_to_scan,
 	return nr_taken;
 }
 
-static struct mem_cgroup *
-mem_cgroup_from_res_counter(struct res_counter *counter)
-{
-	return container_of(counter, struct mem_cgroup, res);
-}
+#define mem_cgroup_from_res_counter(counter, member)	\
+	container_of(counter, struct mem_cgroup, member)
 
 /*
  * This routine finds the DFS walk successor. This routine should be
@@ -665,18 +662,16 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm,
 			/* mem+swap counter fails */
 			res_counter_uncharge(&mem->res, PAGE_SIZE);
 			noswap = true;
-		}
+			mem_over_limit = mem_cgroup_from_res_counter(fail_res,
+									memsw);
+		} else
+			/* mem counter fails */
+			mem_over_limit = mem_cgroup_from_res_counter(fail_res,
+									res);
+
 		if (!(gfp_mask & __GFP_WAIT))
 			goto nomem;
 
-		/*
-		 * Is one of our ancestors over their limit?
-		 */
-		if (fail_res)
-			mem_over_limit = mem_cgroup_from_res_counter(fail_res);
-		else
-			mem_over_limit = mem;
-
 		ret = mem_cgroup_hierarchical_reclaim(mem_over_limit, gfp_mask,
 							noswap);
 

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