cgroup: introduce CSS_ONLINE flag and on/offline_css() helpers
New helpers on/offline_css() respectively wrap ->post_create() and
->pre_destroy() invocations. online_css() sets CSS_ONLINE after
->post_create() is complete and offline_css() invokes ->pre_destroy()
iff CSS_ONLINE is set and clears it while also handling the temporary
dropping of cgroup_mutex.
This patch doesn't introduce any behavior change at the moment but
will be used to improve cgroup_create() failure path and allow
->post_create() to fail.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 4412d96..78a3d5c 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -4035,6 +4035,42 @@
INIT_WORK(&css->dput_work, css_dput_fn);
}
+/* invoke ->post_create() on a new CSS and mark it online */
+static void online_css(struct cgroup_subsys *ss, struct cgroup *cgrp)
+{
+ lockdep_assert_held(&cgroup_mutex);
+
+ if (ss->post_create)
+ ss->post_create(cgrp);
+ cgrp->subsys[ss->subsys_id]->flags |= CSS_ONLINE;
+}
+
+/* if the CSS is online, invoke ->pre_destory() on it and mark it offline */
+static void offline_css(struct cgroup_subsys *ss, struct cgroup *cgrp)
+ __releases(&cgroup_mutex) __acquires(&cgroup_mutex)
+{
+ struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
+
+ lockdep_assert_held(&cgroup_mutex);
+
+ if (!(css->flags & CSS_ONLINE))
+ return;
+
+ /*
+ * pre_destroy() should be called with cgroup_mutex unlocked. See
+ * 3fa59dfbc3 ("cgroup: fix potential deadlock in pre_destroy") for
+ * details. This temporary unlocking should go away once
+ * cgroup_mutex is unexported from controllers.
+ */
+ if (ss->pre_destroy) {
+ mutex_unlock(&cgroup_mutex);
+ ss->pre_destroy(cgrp);
+ mutex_lock(&cgroup_mutex);
+ }
+
+ cgrp->subsys[ss->subsys_id]->flags &= ~CSS_ONLINE;
+}
+
/*
* cgroup_create - create a cgroup
* @parent: cgroup that will be parent of the new cgroup
@@ -4137,8 +4173,7 @@
dget(dentry);
/* creation succeeded, notify subsystems */
- if (ss->post_create)
- ss->post_create(cgrp);
+ online_css(ss, cgrp);
}
err = cgroup_populate_dir(cgrp, true, root->subsys_mask);
@@ -4240,18 +4275,9 @@
}
set_bit(CGRP_REMOVED, &cgrp->flags);
- /*
- * Tell subsystems to initate destruction. pre_destroy() should be
- * called with cgroup_mutex unlocked. See 3fa59dfbc3 ("cgroup: fix
- * potential deadlock in pre_destroy") for details. This temporary
- * unlocking should go away once cgroup_mutex is unexported from
- * controllers.
- */
- mutex_unlock(&cgroup_mutex);
+ /* tell subsystems to initate destruction */
for_each_subsys(cgrp->root, ss)
- if (ss->pre_destroy)
- ss->pre_destroy(cgrp);
- mutex_lock(&cgroup_mutex);
+ offline_css(ss, cgrp);
/*
* Put all the base refs. Each css holds an extra reference to the
@@ -4354,9 +4380,7 @@
BUG_ON(!list_empty(&init_task.tasks));
ss->active = 1;
-
- if (ss->post_create)
- ss->post_create(dummytop);
+ online_css(ss, dummytop);
mutex_unlock(&cgroup_mutex);
@@ -4469,9 +4493,7 @@
write_unlock(&css_set_lock);
ss->active = 1;
-
- if (ss->post_create)
- ss->post_create(dummytop);
+ online_css(ss, dummytop);
/* success! */
mutex_unlock(&cgroup_mutex);
@@ -4501,12 +4523,9 @@
*/
BUG_ON(ss->root != &rootnode);
- /* ->pre_destroy() should be called outside cgroup_mutex for now */
- if (ss->pre_destroy)
- ss->pre_destroy(dummytop);
-
mutex_lock(&cgroup_mutex);
+ offline_css(ss, dummytop);
ss->active = 0;
if (ss->use_id) {