The commit is pushed to "branch-rh7-3.10.0-1127.8.2.vz7.151.x-ovz" and will
appear at https://src.openvz.org/scm/ovz/vzkernel.git
after rh7-3.10.0-1127.8.2.vz7.151.1
------>
commit 5734a6a5e6210131d971831341eca7fd2673c660
Author: Tejun Heo <[email protected]>
Date: Mon May 18 22:33:57 2020 +0300
ms/cgroup: make sure a parent css isn't offlined before its children
There are three subsystem callbacks in css shutdown path -
css_offline(), css_released() and css_free(). Except for
css_released(), cgroup core didn't guarantee the order of invocation.
css_offline() or css_free() could be called on a parent css before its
children. This behavior is unexpected and led to bugs in cpu and
memory controller.
This patch updates offline path so that a parent css is never offlined
before its children. Each css keeps online_cnt which reaches zero iff
itself and all its children are offline and offline_css() is invoked
only after online_cnt reaches zero.
This fixes the memory controller bug and allows the fix for cpu
controller.
Signed-off-by: Tejun Heo <[email protected]>
Reported-and-tested-by: Christian Borntraeger <[email protected]>
Reported-by: Brian Christiansen <[email protected]>
Link: http://lkml.kernel.org/g/[email protected]
Link:
http://lkml.kernel.org/g/cakb58ikdkzc8ret31wbkd99+hxnzjk4+fbmhkgs+nvrc9vj...@mail.gmail.com
Cc: Heiko Carstens <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: [email protected]
https://jira.sw.ru/browse/PSBM-104029
(cherry picked from commit aa226ff4a1ce79f229c6b7a4c0a14e17fececd01)
[aryabinin: User refcounts instead of atomics]
Signed-off-by: Andrey Ryabinin <[email protected]>
---
include/linux/cgroup.h | 6 +++++
kernel/cgroup.c | 66 +++++++++++++++++++++++++++++---------------------
2 files changed, 45 insertions(+), 27 deletions(-)
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index bd48216e7ac29..1c1ee0c458e06 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -242,6 +242,12 @@ struct cgroup {
*/
atomic_t count;
+ /*
+ * Incremented by online self and children. Used to guarantee that
+ * parents are not offlined before their children.
+ */
+ refcount_t online_cnt;
+
int id; /* ida allocated in-hierarchy ID */
/*
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 50d4b3df0f0a1..17ba1ab9c7b04 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -1422,6 +1422,7 @@ static void init_cgroup_root(struct cgroupfs_root *root)
INIT_LIST_HEAD(&root->subsys_list);
INIT_LIST_HEAD(&root->root_list);
INIT_LIST_HEAD(&root->allcg_list);
+ refcount_set(&cgrp->online_cnt, 1);
root->number_of_cgroups = 1;
cgrp->root = root;
cgrp->name = &root_cgroup_name;
@@ -4238,8 +4239,13 @@ static int online_css(struct cgroup_subsys *ss, struct
cgroup *cgrp)
if (ss->css_online)
ret = ss->css_online(cgrp);
- if (!ret)
+ if (!ret) {
cgrp->subsys[ss->subsys_id]->flags |= CSS_ONLINE;
+
+ refcount_inc(&cgrp->online_cnt);
+ if (cgrp->parent)
+ refcount_inc(&cgrp->parent->online_cnt);
+ }
return ret;
}
@@ -4509,9 +4515,11 @@ static void cgroup_css_killed(struct cgroup *cgrp)
if (!atomic_dec_and_test(&cgrp->css_kill_cnt))
return;
- /* percpu ref's of all css's are killed, kick off the next step */
- INIT_WORK(&cgrp->destroy_work, cgroup_offline_fn);
- queue_work(cgroup_destroy_wq, &cgrp->destroy_work);
+ if (refcount_dec_and_test(&cgrp->online_cnt)) {
+ /* percpu ref's of all css's are killed, kick off the next step
*/
+ INIT_WORK(&cgrp->destroy_work, cgroup_offline_fn);
+ queue_work(cgroup_destroy_wq, &cgrp->destroy_work);
+ }
}
static void css_ref_killed_fn(struct percpu_ref *ref)
@@ -4649,37 +4657,41 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
static void cgroup_offline_fn(struct work_struct *work)
{
struct cgroup *cgrp = container_of(work, struct cgroup, destroy_work);
- struct cgroup *parent = cgrp->parent;
- struct dentry *d = cgrp->dentry;
struct cgroup_subsys *ss;
mutex_lock(&cgroup_mutex);
- /*
- * css_tryget() is guaranteed to fail now. Tell subsystems to
- * initate destruction.
- */
- for_each_subsys(cgrp->root, ss)
- offline_css(ss, cgrp);
+ do {
+ struct cgroup *parent = cgrp->parent;
+ struct dentry *d = cgrp->dentry;
- /*
- * Put the css refs from cgroup_destroy_locked(). Each css holds
- * an extra reference to the cgroup's dentry and cgroup removal
- * proceeds regardless of css refs. On the last put of each css,
- * whenever that may be, the extra dentry ref is put so that dentry
- * destruction happens only after all css's are released.
- */
- for_each_subsys(cgrp->root, ss)
- css_put(cgrp->subsys[ss->subsys_id]);
+ /*
+ * css_tryget() is guaranteed to fail now. Tell subsystems to
+ * initate destruction.
+ */
+ for_each_subsys(cgrp->root, ss)
+ offline_css(ss, cgrp);
- /* delete this cgroup from parent->children */
- list_del_rcu(&cgrp->sibling);
- list_del_init(&cgrp->allcg_node);
+ /*
+ * Put the css refs from cgroup_destroy_locked(). Each css
holds
+ * an extra reference to the cgroup's dentry and cgroup removal
+ * proceeds regardless of css refs. On the last put of each
css,
+ * whenever that may be, the extra dentry ref is put so that
dentry
+ * destruction happens only after all css's are released.
+ */
+ for_each_subsys(cgrp->root, ss)
+ css_put(cgrp->subsys[ss->subsys_id]);
- dput(d);
+ /* delete this cgroup from parent->children */
+ list_del_rcu(&cgrp->sibling);
+ list_del_init(&cgrp->allcg_node);
+
+ dput(d);
- set_bit(CGRP_RELEASABLE, &parent->flags);
- check_for_release(parent);
+ set_bit(CGRP_RELEASABLE, &parent->flags);
+ check_for_release(parent);
+ cgrp = parent;
+ } while (cgrp && refcount_dec_and_test(&cgrp->online_cnt));
mutex_unlock(&cgroup_mutex);
}
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