cgroup, cpuset: replace move_member_tasks_to_cpuset() with cgroup_transfer_tasks()

When a cpuset becomes empty (no CPU or memory), its tasks are
transferred with the nearest ancestor with execution resources.  This
is implemented using cgroup_scan_tasks() with a callback which grabs
cgroup_mutex and invokes cgroup_attach_task() on each task.

Both cgroup_mutex and cgroup_attach_task() are scheduled to be
unexported.  Implement cgroup_transfer_tasks() in cgroup proper which
is essentially the same as move_member_tasks_to_cpuset() except that
it takes cgroups instead of cpusets and @to comes before @from like
normal functions with those arguments, and replace
move_member_tasks_to_cpuset() with it.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>

1 files changed, 6 insertions, 45 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 98d458aad789..866d78ee7930 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -1994,50 +1994,6 @@ int __init cpuset_init(void)
         return 0;
 }
 
-/**
- * cpuset_do_move_task - move a given task to another cpuset
- * @tsk: pointer to task_struct the task to move
- * @scan: struct cgroup_scanner contained in its struct cpuset_hotplug_scanner
- *
- * Called by cgroup_scan_tasks() for each task in a cgroup.
- * Return nonzero to stop the walk through the tasks.
- */
-static void cpuset_do_move_task(struct task_struct *tsk,
-                                struct cgroup_scanner *scan)
-{
-        struct cgroup *new_cgroup = scan->data;
-
-        cgroup_lock();
-        cgroup_attach_task(new_cgroup, tsk, false);
-        cgroup_unlock();
-}
-
-/**
- * move_member_tasks_to_cpuset - move tasks from one cpuset to another
- * @from: cpuset in which the tasks currently reside
- * @to: cpuset to which the tasks will be moved
- *
- * Called with cpuset_mutex held
- * callback_mutex must not be held, as cpuset_attach() will take it.
- *
- * The cgroup_scan_tasks() function will scan all the tasks in a cgroup,
- * calling callback functions for each.
- */
-static void move_member_tasks_to_cpuset(struct cpuset *from, struct cpuset *to)
-{
-        struct cgroup_scanner scan;
-
-        scan.cg = from->css.cgroup;
-        scan.test_task = NULL; /* select all tasks in cgroup */
-        scan.process_task = cpuset_do_move_task;
-        scan.heap = NULL;
-        scan.data = to->css.cgroup;
-
-        if (cgroup_scan_tasks(&scan))
-                printk(KERN_ERR "move_member_tasks_to_cpuset: "
-                                "cgroup_scan_tasks failed\n");
-}
-
 /*
  * If CPU and/or memory hotplug handlers, below, unplug any CPUs
  * or memory nodes, we need to walk over the cpuset hierarchy,
@@ -2058,7 +2014,12 @@ static void remove_tasks_in_empty_cpuset(struct cpuset *cs)
                         nodes_empty(parent->mems_allowed))
                 parent = parent_cs(parent);
 
-        move_member_tasks_to_cpuset(cs, parent);
+        if (cgroup_transfer_tasks(parent->css.cgroup, cs->css.cgroup)) {
+                rcu_read_lock();
+                printk(KERN_ERR "cpuset: failed to transfer tasks out of empty cpuset %s\n",
+                       cgroup_name(cs->css.cgroup));
+                rcu_read_unlock();
+        }
 }
 
 /**