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 <[email protected]> Reviewed-by: Vladimir Davydov <[email protected]> Acked-by: Michal Hocko <[email protected]> Signed-off-by: Andrew Morton <[email protected]> Signed-off-by: Linus Torvalds <[email protected]>
vincehsu · Dec 11, 2014 · 413918b · 413918b
1 parent c01f46c
commit 413918b
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Showing 2 changed files with 4 additions and 3 deletions.
diff --git 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
@@ -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);
 }