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Patch "sched/cgroup: Fix/cleanup cgroup teardown/init" has been added to the 4.5-stable tree

PATCH [email protected] 1 participant 1 message Apr 28, 2016

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This is a note to let you know that I've just added the patch titled

sched/cgroup: Fix/cleanup cgroup teardown/init

to the 4.5-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
sched-cgroup-fix-cleanup-cgroup-teardown-init.patch
and it can be found in the queue-4.5 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From 2f5177f0fd7e531b26d54633be62d1d4cb94621c Mon Sep 17 00:00:00 2001

From: Peter Zijlstra <[email protected]>
Date: Wed, 16 Mar 2016 16:22:45 +0100
Subject: sched/cgroup: Fix/cleanup cgroup teardown/init

From: Peter Zijlstra <[email protected]>

commit 2f5177f0fd7e531b26d54633be62d1d4cb94621c upstream.

The CPU controller hasn't kept up with the various changes in the whole cgroup initialization / destruction sequence, and commit:

2e91fa7f6d45 ("cgroup: keep zombies associated with their original cgroups")

caused it to explode.

The reason for this is that zombies do not inhibit css_offline() from being called, but do stall css_released(). Now we tear down the cfs_rq structures on css_offline() but zombies can run after that, leading to use-after-free issues.

The solution is to move the tear-down to css_released(), which guarantees nobody (including no zombies) is still using our cgroup.

Furthermore, a few simple cleanups are possible too. There doesn't appear to be any point to us using css_online() (anymore?) so fold that in css_alloc().

And since cgroup code guarantees an RCU grace period between css_released() and css_free() we can forgo using call_rcu() and free the stuff immediately.

Suggested-by Tejun Heo <[email protected]>
Reported-by Kazuki Yamaguchi <[email protected]>
Reported-by Niklas Cassel <[email protected]>
Tested-by Niklas Cassel <[email protected]>
Signed-off-by Peter Zijlstra (Intel) <[email protected]>
Acked-by Tejun Heo <[email protected]>
Cc Linus Torvalds <[email protected]>
Cc Peter Zijlstra <[email protected]>
Cc Thomas Gleixner <[email protected]>
Fixes 2e91fa7f6d45 ("cgroup: keep zombies associated with their original cgroups")
Link http://lkml.kernel.org/r/[email protected] open here
Signed-off-by Ingo Molnar <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 kernel/sched/core.c |   35 ++++++++++++++---------------------
 1 file changed, 14 insertions(+), 21 deletions(-)
kernel/sched/core.c +14 -21
@@ -7802,7 +7802,7 @@ void set_curr_task(int cpu, struct task_
 /* task_group_lock serializes the addition/removal of task groups */
 static DEFINE_SPINLOCK(task_group_lock);
 
-static void free_sched_group(struct task_group *tg)
+static void sched_free_group(struct task_group *tg)
 {
 	free_fair_sched_group(tg);
 	free_rt_sched_group(tg);

@@ -7828,7 +7828,7 @@ struct task_group *sched_create_group(st
 	return tg;
 
 err:
-	free_sched_group(tg);
+	sched_free_group(tg);
 	return ERR_PTR(-ENOMEM);
 }
 

@@ -7848,17 +7848,16 @@ void sched_online_group(struct task_grou
 }
 
 /* rcu callback to free various structures associated with a task group */
-static void free_sched_group_rcu(struct rcu_head *rhp)
+static void sched_free_group_rcu(struct rcu_head *rhp)
 {
 	/* now it should be safe to free those cfs_rqs */
-	free_sched_group(container_of(rhp, struct task_group, rcu));
+	sched_free_group(container_of(rhp, struct task_group, rcu));
 }
 
-/* Destroy runqueue etc associated with a task group */
 void sched_destroy_group(struct task_group *tg)
 {
 	/* wait for possible concurrent references to cfs_rqs complete */
-	call_rcu(&tg->rcu, free_sched_group_rcu);
+	call_rcu(&tg->rcu, sched_free_group_rcu);
 }
 
 void sched_offline_group(struct task_group *tg)

@@ -8319,31 +8318,26 @@ cpu_cgroup_css_alloc(struct cgroup_subsy
 	if (IS_ERR(tg))
 		return ERR_PTR(-ENOMEM);
 
+	sched_online_group(tg, parent);
+
 	return &tg->css;
 }
 
-static int cpu_cgroup_css_online(struct cgroup_subsys_state *css)
+static void cpu_cgroup_css_released(struct cgroup_subsys_state *css)
 {
 	struct task_group *tg = css_tg(css);
-	struct task_group *parent = css_tg(css->parent);
 
-	if (parent)
-		sched_online_group(tg, parent);
-	return 0;
+	sched_offline_group(tg);
 }
 
 static void cpu_cgroup_css_free(struct cgroup_subsys_state *css)
 {
 	struct task_group *tg = css_tg(css);
 
-	sched_destroy_group(tg);
-}
-
-static void cpu_cgroup_css_offline(struct cgroup_subsys_state *css)
-{
-	struct task_group *tg = css_tg(css);
-
-	sched_offline_group(tg);
+	/*
+	 * Relies on the RCU grace period between css_released() and this.
+	 */
+	sched_free_group(tg);
 }
 
 static void cpu_cgroup_fork(struct task_struct *task)

@@ -8703,9 +8697,8 @@ static struct cftype cpu_files[] = {
 
 struct cgroup_subsys cpu_cgrp_subsys = {
 	.css_alloc	= cpu_cgroup_css_alloc,
+	.css_released	= cpu_cgroup_css_released,
 	.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,

Patches currently in stable-queue which might be from [email protected] are

queue-4.5/sched-cgroup-fix-cleanup-cgroup-teardown-init.patch queue-4.5/x86-mce-avoid-using-object-after-free-in-genpool.patch