This commit backports 2f5177f0fd7e531b26d54633be62d1d4cb94621c
from the mainline tree.
We've seen frequent oopses with linux-yocto-4.4 and this commit
helps to get rid of those.
Changes:
Peter Zijlstra (1):
sched/cgroup: Fix/cleanup cgroup teardown/init
kernel/sched/core.c | 35 ++++++++++++++---------------------
1 file changed, 14 insertions(+), 21 deletions(-)
Commit log:
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.
Signed-off-by: Mikko Ylinen <mikko.yli...@intel.com>
---
kernel/sched/core.c | 35 ++++++++++++++---------------------
1 file changed, 14 insertions(+), 21 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index eb70592..bcda4f8 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -7692,7 +7692,7 @@ 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);
@@ -7718,7 +7718,7 @@ 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);
}
@@ -7738,17 +7738,16 @@ 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)
@@ -8209,31 +8208,26 @@ 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, void *private)
@@ -8593,9 +8587,8 @@ 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,
--
2.8.0.rc3
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