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sched/cgroup: Fix/cleanup cgroup teardown/init

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

  2e91fa7f6d ("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 <tj@kernel.org>
Reported-by: Kazuki Yamaguchi <k@rhe.jp>
Reported-by: Niklas Cassel <niklas.cassel@axis.com>
Tested-by: Niklas Cassel <niklas.cassel@axis.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Tejun Heo <tj@kernel.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 2e91fa7f6d ("cgroup: keep zombies associated with their original cgroups")
Link: http://lkml.kernel.org/r/20160316152245.GY6344@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Peter Zijlstra 2016-03-16 16:22:45 +01:00 committed by Ingo Molnar
parent 42e405f7b1
commit 2f5177f0fd
1 changed files with 14 additions and 21 deletions
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35
kernel/sched/core.c
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@ -7536,7 +7536,7 @@ void set_curr_task(int cpu, struct task_struct *p)
/* 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);
@ -7562,7 +7562,7 @@ struct task_group *sched_create_group(struct task_group *parent)
return tg;
err:
free_sched_group(tg);
sched_free_group(tg);
return ERR_PTR(-ENOMEM);
}
@ -7582,17 +7582,16 @@ void sched_online_group(struct task_group *tg, struct task_group *parent)
}
/* 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)
@ -8051,31 +8050,26 @@ cpu_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
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)
@ -8435,9 +8429,8 @@ 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,