@@ -127,6 +127,12 @@ struct cgroup_subsys_state {
*/
u64 serial_nr;
+ /*
+ * Incremented by online self and children. Used to guarantee that
+ * parents are not offlined before their children.
+ */
+ atomic_t online_cnt;
+
/* percpu_ref killing and RCU release */
struct rcu_head rcu_head;
struct work_struct destroy_work;
@@ -4761,6 +4761,7 @@ static void init_and_link_css(struct cgr
INIT_LIST_HEAD(&css->sibling);
INIT_LIST_HEAD(&css->children);
css->serial_nr = css_serial_nr_next++;
+ atomic_set(&css->online_cnt, 0);
if (cgroup_parent(cgrp)) {
css->parent = cgroup_css(cgroup_parent(cgrp), ss);
@@ -4783,6 +4784,10 @@ static int online_css(struct cgroup_subs
if (!ret) {
css->flags |= CSS_ONLINE;
rcu_assign_pointer(css->cgroup->subsys[ss->id], css);
+
+ atomic_inc(&css->online_cnt);
+ if (css->parent)
+ atomic_inc(&css->parent->online_cnt);
}
return ret;
}
@@ -5020,10 +5025,15 @@ static void css_killed_work_fn(struct wo
container_of(work, struct cgroup_subsys_state, destroy_work);
mutex_lock(&cgroup_mutex);
- offline_css(css);
- mutex_unlock(&cgroup_mutex);
- css_put(css);
+ do {
+ offline_css(css);
+ css_put(css);
+ /* @css can't go away while we're holding cgroup_mutex */
+ css = css->parent;
+ } while (css && atomic_dec_and_test(&css->online_cnt));
+
+ mutex_unlock(&cgroup_mutex);
}
/* css kill confirmation processing requires process context, bounce */
@@ -5032,8 +5042,10 @@ static void css_killed_ref_fn(struct per
struct cgroup_subsys_state *css =
container_of(ref, struct cgroup_subsys_state, refcnt);
- INIT_WORK(&css->destroy_work, css_killed_work_fn);
- queue_work(cgroup_destroy_wq, &css->destroy_work);
+ if (atomic_dec_and_test(&css->online_cnt)) {
+ INIT_WORK(&css->destroy_work, css_killed_work_fn);
+ queue_work(cgroup_destroy_wq, &css->destroy_work);
+ }
}
/**
There are three subsystem callbacks in css shutdown path - css_offline(), css_released() and css_free(). Except for css_released(), cgroup core didn't use to 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 use-after-free in cpu 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 reported cpu controller malfunction. The next patch will update css_free() handling. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-by: Christian Borntraeger <borntraeger@de.ibm.com> Link: http://lkml.kernel.org/g/5698A023.9070703@de.ibm.com Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: stable@vger.kernel.org --- Hello, Christian. Can you please verify whether this patch fixes the issue? Thanks. include/linux/cgroup-defs.h | 6 ++++++ kernel/cgroup.c | 22 +++++++++++++++++----- 2 files changed, 23 insertions(+), 5 deletions(-) -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html