memcg: css_id() must be called under rcu_read_lock()

This patch fixes task_in_mem_cgroup(), mem_cgroup_uncharge_swapcache(),
mem_cgroup_move_swap_account(), and is_target_pte_for_mc() to protect
calls to css_id().  An additional RCU lockdep splat was reported for
memcg_oom_wake_function(), however, this function is not yet in
mainline as of 2.6.34-rc5.

Reported-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Tested-by: Li Zefan <lizf@cn.fujitsu.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Andrew Morton <akpm@linux-foundation.org>

1 files changed, 16 insertions, 5 deletions

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index f4ede99c8b9b..e06490d4ae5e 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -811,10 +811,12 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *mem)
          * enabled in "curr" and "curr" is a child of "mem" in *cgroup*
          * hierarchy(even if use_hierarchy is disabled in "mem").
          */
+        rcu_read_lock();
         if (mem->use_hierarchy)
                 ret = css_is_ancestor(&curr->css, &mem->css);
         else
                 ret = (curr == mem);
+        rcu_read_unlock();
         css_put(&curr->css);
         return ret;
 }
@@ -2312,7 +2314,9 @@ mem_cgroup_uncharge_swapcache(struct page *page, swp_entry_t ent, bool swapout)
 
         /* record memcg information */
         if (do_swap_account && swapout && memcg) {
+                rcu_read_lock();
                 swap_cgroup_record(ent, css_id(&memcg->css));
+                rcu_read_unlock();
                 mem_cgroup_get(memcg);
         }
         if (swapout && memcg)
@@ -2369,8 +2373,10 @@ static int mem_cgroup_move_swap_account(swp_entry_t entry,
 {
         unsigned short old_id, new_id;
 
+        rcu_read_lock();
         old_id = css_id(&from->css);
         new_id = css_id(&to->css);
+        rcu_read_unlock();
 
         if (swap_cgroup_cmpxchg(entry, old_id, new_id) == old_id) {
                 mem_cgroup_swap_statistics(from, false);
@@ -4038,11 +4044,16 @@ static int is_target_pte_for_mc(struct vm_area_struct *vma,
                         put_page(page);
         }
         /* throught */
-        if (ent.val && do_swap_account && !ret &&
-                        css_id(&mc.from->css) == lookup_swap_cgroup(ent)) {
-                ret = MC_TARGET_SWAP;
-                if (target)
-                        target->ent = ent;
+        if (ent.val && do_swap_account && !ret) {
+                unsigned short id;
+                rcu_read_lock();
+                id = css_id(&mc.from->css);
+                rcu_read_unlock();
+                if (id == lookup_swap_cgroup(ent)) {
+                        ret = MC_TARGET_SWAP;
+                        if (target)
+                                target->ent = ent;
+                }
         }
         return ret;
 }