[PATCH v2 5/6] cgroups: Triger BUG if a bindable subsystem calls css_get()

[Li Zefan <lizf@cn.fujitsu.com>]

For now unbindable subsystems should not use css_get/put(), so check
this misuse.

Signed-off-by: Li Zefan <lizf@cn.fujitsu.com>
---
 include/linux/cgroup.h |    7 +++++--
 kernel/cgroup.c        |    5 +++++
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 17579b2..e8ad9f1 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -80,13 +80,15 @@ struct cgroup_subsys_state {
 
 /* bits in struct cgroup_subsys_state flags field */
 enum {
-	CSS_ROOT, /* This CSS is the root of the subsystem */
-	CSS_REMOVED, /* This CSS is dead */
+	CSS_ROOT,	/* This CSS is the root of the subsystem */
+	CSS_REMOVED,	/* This CSS is dead */
+	CSS_NO_GET,	/* Forbid calling css_get/put() */
 };
 
 /* Caller must verify that the css is not for root cgroup */
 static inline void __css_get(struct cgroup_subsys_state *css, int count)
 {
+	BUG_ON(test_bit(CSS_NO_GET, &css->flags));
 	atomic_add(count, &css->refcnt);
 }
 
@@ -131,6 +133,7 @@ static inline bool css_tryget(struct cgroup_subsys_state *css)
 {
 	if (test_bit(CSS_ROOT, &css->flags))
 		return true;
+	BUG_ON(test_bit(CSS_NO_GET, &css->flags));
 	while (!atomic_inc_not_zero(&css->refcnt)) {
 		if (test_bit(CSS_REMOVED, &css->flags))
 			return false;
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index fa2c5de..d49a459 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -938,6 +938,11 @@ static void init_cgroup_css(struct cgroup_subsys_state *css,
 	atomic_set(&css->refcnt, 1);
 	css->flags = 0;
 	css->id = NULL;
+
+	/* For now, unbindable subsystems should not call css_get/put(). */
+	if (ss->unbindable)
+		set_bit(CSS_NO_GET, &css->flags);
+
 	if (cgrp == dummytop)
 		set_bit(CSS_ROOT, &css->flags);
 	BUG_ON(cgrp->subsys[ss->subsys_id]);
-- 
1.6.3