[PATCH] Memory controller use rcu_read_lock() in mem_cgroup_cache_charge()

Hugh Dickins noticed that we were using rcu_dereference() without
rcu_read_lock() in the cache charging routine. The patch below fixes
this problem

Signed-off-by: Balbir Singh <[email protected]>
---

 mm/memcontrol.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff -puN mm/memcontrol.c~memory-controller-use-rcu-lead-lock mm/memcontrol.c
--- linux-2.6.24-rc5/mm/memcontrol.c~memory-controller-use-rcu-lead-lock	2007-12-19 11:52:44.000000000 +0530
+++ linux-2.6.24-rc5-balbir/mm/memcontrol.c	2007-12-20 14:01:45.000000000 +0530
@@ -717,16 +717,20 @@ int mem_cgroup_charge(struct page *page,
 int mem_cgroup_cache_charge(struct page *page, struct mm_struct *mm,
 				gfp_t gfp_mask)
 {
+	int ret = 0;
 	struct mem_cgroup *mem;
 	if (!mm)
 		mm = &init_mm;
 
+	rcu_read_lock();
 	mem = rcu_dereference(mm->mem_cgroup);
+	css_get(&mem->css);
+	rcu_read_unlock();
 	if (mem->control_type == MEM_CGROUP_TYPE_ALL)
-		return mem_cgroup_charge_common(page, mm, gfp_mask,
+		ret = mem_cgroup_charge_common(page, mm, gfp_mask,
 				MEM_CGROUP_CHARGE_TYPE_CACHE);
-	else
-		return 0;
+	css_put(&mem->css);
+	return ret;
 }
 
 /*
_

-- 
	Warm Regards,
	Balbir Singh
	Linux Technology Center
	IBM, ISTL
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