sched: Fix race between task_group and sched_task_group

patch/kernel-sched-core-fix-cgroup-fork-race.patch

@@ -0,0 +1,46 @@
+[PATCH] sched: Fix race between task_group and sched_task_group
+
+From: Pavel Shirshov <pavelsh@microsoft.com>
+
+Patch: http://marc.info/?l=linux-kernel&m=141440511931665
+
+The race may happen when somebody is changing task_group of a forking task.
+Child's cgroup is the same as parent's after dup_task_struct() (there just
+memory copying). Also, cfs_rq and rt_rq are the same as parent's.
+
+But if parent changes its task_group before it's called cgroup_post_fork(),
+we do not reflect this situation on child. Child's cfs_rq and rt_rq remain
+the same, while child's task_group changes in cgroup_post_fork().
+
+To fix this we introduce fork() method, which calls sched_move_task() directly.
+This function changes sched_task_group on appropriate (also its logic has
+no problem with freshly created tasks, so we shouldn't introduce something
+special; we are able just to use it).
+---
+ kernel/sched/core.c |    6 ++++++
+ 1 file changed, 6 insertions(+)
+
+diff --git a/kernel/sched/core.c b/kernel/sched/core.c
+index 8cbf68e..8077b8e 100644
+--- a/kernel/sched/core.c
++++ b/kernel/sched/core.c
+@@ -7793,6 +7793,11 @@ static void cpu_cgroup_css_offline(struct cgroup_subsys_state *css)
+ 	sched_offline_group(tg);
+ }
+
++static void cpu_cgroup_fork(struct task_struct *task)
++{
++	sched_move_task(task);
++}
++
+ static int cpu_cgroup_can_attach(struct cgroup_subsys_state *css,
+ 				 struct cgroup_taskset *tset)
+ {
+@@ -8159,6 +8164,7 @@ struct cgroup_subsys cpu_cgrp_subsys = {
+ 	.css_free	= cpu_cgroup_css_free,
+ 	.css_online	= cpu_cgroup_css_online,
+ 	.css_offline	= cpu_cgroup_css_offline,
++	.fork           = cpu_cgroup_fork,
+ 	.can_attach	= cpu_cgroup_can_attach,
+ 	.attach		= cpu_cgroup_attach,
+ 	.exit		= cpu_cgroup_exit,

patch/series

@@ -1,4 +1,5 @@
 # This series applies on GIT commit 1451b36b2b0d62178e42f648d8a18131af18f7d8
+kernel-sched-core-fix-cgroup-fork-race.patch
 config-dell-s6000.patch
 config-mlnx-sn2700.patch
 driver-at24-fix-odd-length-two-byte-access.patch