mm: memcontrol: pull the NULL check from __mem_cgroup_same_or_subtree()

The NULL in mm_match_cgroup() comes from a possibly exiting mm->owner.  It
makes a lot more sense to check where it's looked up, rather than check
for it in __mem_cgroup_same_or_subtree() where it's unexpected.

No other callsite passes NULL to __mem_cgroup_same_or_subtree().

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Reviewed-by: Vladimir Davydov <vdavydov@parallels.com>
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>

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index ea007615e8f95182cf2097ecc295ae8738105346..e32ab948f5893c31693486444d9a05d6ffce1316 100644 (file)
--- a/include/linux/memcontrol.h
+++ b/include/linux/memcontrol.h
@@ -83,11 +83,12 @@ static inline
 bool mm_match_cgroup(const struct mm_struct *mm, const struct mem_cgroup *memcg)
 {
        struct mem_cgroup *task_memcg;
-       bool match;
+       bool match = false;
 
        rcu_read_lock();
        task_memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
-       match = __mem_cgroup_same_or_subtree(memcg, task_memcg);
+       if (task_memcg)
+               match = __mem_cgroup_same_or_subtree(memcg, task_memcg);
        rcu_read_unlock();
        return match;
 }

diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index 367cc57df3628f6ec63ad203ce30b70d18649cda..e5dcebd71dfb05cf960d79b575d29e39961aed2e 100644 (file)
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1337,7 +1337,7 @@ bool __mem_cgroup_same_or_subtree(const struct mem_cgroup *root_memcg,
 {
        if (root_memcg == memcg)
                return true;
-       if (!root_memcg->use_hierarchy || !memcg)
+       if (!root_memcg->use_hierarchy)
                return false;
        return cgroup_is_descendant(memcg->css.cgroup, root_memcg->css.cgroup);
 }