[patch 2/3] mm: memcontrol: pull the NULL check from __mem_cgroup_same_or_subtree()

Johannes Weiner
2014-10-24T13:49:48Z

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>
---
include/linux/memcontrol.h | 5 +++--
mm/memcontrol.c | 2 +-
2 files changed, 4 insertions(+), 3 deletions(-)

diff --git a/include/linux/memcontrol.h b/include/linux/memcontrol.h
index ea007615e8f9..e32ab948f589 100644
--- 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 bdf8520979cf..15b1c5110a8f 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1316,7 +1316,7 @@ 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);
}
--
2.1.2