mm, memcg: don't take task_lock in task_in_mem_cgroup

For processes that have detached their mm's, task_in_mem_cgroup()
unnecessarily takes task_lock() when rcu_read_lock() is all that is
necessary to call mem_cgroup_from_task().

While we're here, switch task_in_mem_cgroup() to return bool.

Signed-off-by: David Rientjes <rientjes@google.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 11 insertions, 9 deletions

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index d6183f06d8c1..7b4d9d79570b 100644
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -77,7 +77,8 @@ extern void mem_cgroup_uncharge_cache_page(struct page *page);
 
 bool __mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
                                   struct mem_cgroup *memcg);
-int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *memcg);
+bool task_in_mem_cgroup(struct task_struct *task,
+                        const struct mem_cgroup *memcg);
 
 extern struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page);
 extern struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p);
@@ -273,10 +274,10 @@ static inline bool mm_match_cgroup(struct mm_struct *mm,
         return true;
 }
 
-static inline int task_in_mem_cgroup(struct task_struct *task,
-                                     const struct mem_cgroup *memcg)
+static inline bool task_in_mem_cgroup(struct task_struct *task,
+                                      const struct mem_cgroup *memcg)
 {
-        return 1;
+        return true;
 }
 
 static inline struct cgroup_subsys_state
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 194721839cf5..4748966b1511 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1448,11 +1448,12 @@ static bool mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
         return ret;
 }
 
-int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *memcg)
+bool task_in_mem_cgroup(struct task_struct *task,
+                        const struct mem_cgroup *memcg)
 {
-        int ret;
         struct mem_cgroup *curr = NULL;
         struct task_struct *p;
+        bool ret;
 
         p = find_lock_task_mm(task);
         if (p) {
@@ -1464,14 +1465,14 @@ int task_in_mem_cgroup(struct task_struct *task, const struct mem_cgroup *memcg)
                  * killer still needs to detect if they have already been oom
                  * killed to prevent needlessly killing additional tasks.
                  */
-                task_lock(task);
+                rcu_read_lock();
                 curr = mem_cgroup_from_task(task);
                 if (curr)
                         css_get(&curr->css);
-                task_unlock(task);
+                rcu_read_unlock();
         }
         if (!curr)
-                return 0;
+                return false;
         /*
          * We should check use_hierarchy of "memcg" not "curr". Because checking
          * use_hierarchy of "curr" here make this function true if hierarchy is