[PATCH 6/7] cgroups: Warn if a bindable subsystem calls css_get()

[Li Zefan]

For now bindable subsystems should not use css_get/put(), so warn
on this misuse.

Signed-off-by: Li Zefan <lizf@xxxxxxxxxxxxxx>
---
 include/linux/cgroup.h |    7 +++++--
 kernel/cgroup.c        |    3 +++
 2 files changed, 8 insertions(+), 2 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 1e4e1df..10e4e02 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);
 }
 
@@ -119,6 +121,7 @@ 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 12c1f7c..88e265d 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -936,6 +936,9 @@ static void init_cgroup_css(struct cgroup_subsys_state *css,
 	css->cgroup = cgrp;
 	atomic_set(&css->refcnt, 1);
 	css->flags = 0;
+	/* For now, a bindable subsystem should not call css_get/put(). */
+	if (ss->can_bind)
+		set_bit(CSS_NO_GET, &css->flags);
 	css->id = NULL;
 	if (cgrp == dummytop)
 		set_bit(CSS_ROOT, &css->flags);
-- 
1.7.0.1

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