cpuset: remove unneeded NODEMASK_ALLOC() in cpuset_attach()

oldcs->mems_allowed is not modified during cpuset_attach(), so we don't
have to copy it to a buffer allocated by NODEMASK_ALLOC().  Just pass it
to cpuset_migrate_mm().
Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Paul Menage <menage@google.com>
Acked-by: David Rientjes <rientjes@google.com>
Cc: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/cpuset.c

@@ -1438,10 +1438,9 @@ static void cpuset_attach(struct cgroup_subsys *ss, struct cgroup *cont,
 	struct mm_struct *mm;
 	struct cpuset *cs = cgroup_cs(cont);
 	struct cpuset *oldcs = cgroup_cs(oldcont);
-	NODEMASK_ALLOC(nodemask_t, from, GFP_KERNEL);
 	NODEMASK_ALLOC(nodemask_t, to, GFP_KERNEL);
 
-	if (from == NULL || to == NULL)
+	if (to == NULL)
 		goto alloc_fail;
 
 	if (cs == &top_cpuset) {
@@ -1463,18 +1462,16 @@ static void cpuset_attach(struct cgroup_subsys *ss, struct cgroup *cont,
 	}
 
 	/* change mm; only needs to be done once even if threadgroup */
-	*from = oldcs->mems_allowed;
 	*to = cs->mems_allowed;
 	mm = get_task_mm(tsk);
 	if (mm) {
 		mpol_rebind_mm(mm, to);
 		if (is_memory_migrate(cs))
-			cpuset_migrate_mm(mm, from, to);
+			cpuset_migrate_mm(mm, &oldcs->mems_allowed, to);
 		mmput(mm);
 	}
 
 alloc_fail:
-	NODEMASK_FREE(from);
 	NODEMASK_FREE(to);
 }