1 files changed, 22 insertions, 18 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 312961ef3ccc..0b361a0b58f6 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1487,7 +1487,6 @@ static void cpuset_attach(struct cgroup_subsys_state *css,
 {
         /* static buf protected by cpuset_mutex */
         static nodemask_t cpuset_attach_nodemask_to;
-        struct mm_struct *mm;
         struct task_struct *task;
         struct task_struct *leader = cgroup_taskset_first(tset);
         struct cpuset *cs = css_cs(css);
@@ -1515,26 +1514,31 @@ static void cpuset_attach(struct cgroup_subsys_state *css,
         }
 
         /*
-         * Change mm, possibly for multiple threads in a threadgroup. This is
-         * expensive and may sleep.
+         * Change mm, possibly for multiple threads in a threadgroup. This
+         * is expensive and may sleep and should be moved outside migration
+         * path proper.
          */
         cpuset_attach_nodemask_to = cs->effective_mems;
-        mm = get_task_mm(leader);
-        if (mm) {
-                mpol_rebind_mm(mm, &cpuset_attach_nodemask_to);
-
-                /*
-                 * old_mems_allowed is the same with mems_allowed here, except
-                 * if this task is being moved automatically due to hotplug.
-                 * In that case @mems_allowed has been updated and is empty,
-                 * so @old_mems_allowed is the right nodesets that we migrate
-                 * mm from.
-                 */
-                if (is_memory_migrate(cs)) {
-                        cpuset_migrate_mm(mm, &oldcs->old_mems_allowed,
-                                          &cpuset_attach_nodemask_to);
+        if (thread_group_leader(leader)) {
+                struct mm_struct *mm = get_task_mm(leader);
+
+                if (mm) {
+                        mpol_rebind_mm(mm, &cpuset_attach_nodemask_to);
+
+                        /*
+                         * old_mems_allowed is the same with mems_allowed
+                         * here, except if this task is being moved
+                         * automatically due to hotplug.  In that case
+                         * @mems_allowed has been updated and is empty, so
+                         * @old_mems_allowed is the right nodesets that we
+                         * migrate mm from.
+                         */
+                        if (is_memory_migrate(cs)) {
+                                cpuset_migrate_mm(mm, &oldcs->old_mems_allowed,
+                                                  &cpuset_attach_nodemask_to);
+                        }
+                        mmput(mm);
                 }
-                mmput(mm);
         }
 
         cs->old_mems_allowed = cpuset_attach_nodemask_to;