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From: Kirill Tkhai <ktkhai@parallels.com>
To: <linux-kernel@vger.kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Oleg Nesterov <oleg@redhat.com>, Ingo Molnar <mingo@redhat.com>,
	Burke Libbey <burke.libbey@shopify.com>,
	Vladimir Davydov <vdavydov@parallels.com>,
	Kirill Tkhai <tkhai@yandex.ru>
Subject: [PATCH] sched: Fix race between task_group and sched_task_group
Date: Mon, 27 Oct 2014 14:18:25 +0400
Message-ID: <1414405105.19914.169.camel@tkhai> (raw)


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>
---
 kernel/sched/core.c |    6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 4499950..dde8adb 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -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,




             reply index

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-10-27 10:18 Kirill Tkhai [this message]
2014-10-27 12:21 ` Peter Zijlstra
2014-10-27 23:04 ` Oleg Nesterov
2014-10-28  5:24   ` Kirill Tkhai
2014-10-28 22:52     ` Oleg Nesterov
2014-10-29  3:20       ` Kirill Tkhai
2014-10-29  9:16         ` Peter Zijlstra
2014-10-29 11:13           ` Kirill Tkhai
2014-10-29 19:21         ` Oleg Nesterov
2014-11-04 16:07     ` [tip:sched/urgent] sched: Remove lockdep check in sched_move_task () tip-bot for Kirill Tkhai
2014-10-28 11:01 ` [tip:sched/core] sched: Fix race between task_group and sched_task_group tip-bot for Kirill Tkhai
2015-01-26 23:46 ` [PATCH] " Sasha Levin
2015-01-27  8:48   ` Peter Zijlstra
2015-01-27  9:31   ` Peter Zijlstra

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