Commit eeb61e53 authored Oct 27, 2014 by Kirill Tkhai Committed by Ingo Molnar Oct 28, 2014

sched: Fix race between task_group and sched_task_group

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).

Possibly, this decides the Burke Libbey's problem: https://lkml.org/lkml/2014/10/24/456

Signed-off-by: Kirill Tkhai <ktkhai@parallels.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/1414405105.19914.169.camel@tkhai

Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent cac7f242

kernel/sched/core.c

+6 −0

Original line number	Diff line number	Diff line
		@@ -7833,6 +7833,11 @@ 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)
		{
		@@ -8205,6 +8210,7 @@ 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,

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