cgroup: cgroup refcnt functions should be exported when CONFIG_DEBUG_CGROUP_REF

6ab4286 ("cgroup: Implement DEBUG_CGROUP_REF") added a config option
which forces cgroup refcnt functions to be not inlined so that they can be
kprobed for debugging. However, it forgot export them when the config is
enabled breaking modules which make use of css reference counting.

Fix it by adding CGROUP_REF_EXPORT() macro to cgroup_refcnt.h which is
defined to EXPORT_SYMBOL_GPL when CONFIG_DEBUG_CGROUP_REF is set.

Signed-off-by: Tejun Heo <tj@kernel.org>
Fixes: 6ab4286 ("cgroup: Implement DEBUG_CGROUP_REF")

Author: htejun

include/linux/cgroup.h

@@ -318,6 +318,7 @@ void css_put(struct cgroup_subsys_state *css);
 void css_put_many(struct cgroup_subsys_state *css, unsigned int n);
 #else
 #define CGROUP_REF_FN_ATTRS	static inline
+#define CGROUP_REF_EXPORT(fn)
 #include <linux/cgroup_refcnt.h>
 #endif
 

include/linux/cgroup_refcnt.h

@@ -10,6 +10,7 @@ void css_get(struct cgroup_subsys_state *css)
 	if (!(css->flags & CSS_NO_REF))
 		percpu_ref_get(&css->refcnt);
 }
+CGROUP_REF_EXPORT(css_get)
 
 /**
  * css_get_many - obtain references on the specified css
@@ -24,6 +25,7 @@ void css_get_many(struct cgroup_subsys_state *css, unsigned int n)
 	if (!(css->flags & CSS_NO_REF))
 		percpu_ref_get_many(&css->refcnt, n);
 }
+CGROUP_REF_EXPORT(css_get_many)
 
 /**
  * css_tryget - try to obtain a reference on the specified css
@@ -43,6 +45,7 @@ bool css_tryget(struct cgroup_subsys_state *css)
 		return percpu_ref_tryget(&css->refcnt);
 	return true;
 }
+CGROUP_REF_EXPORT(css_tryget)
 
 /**
  * css_tryget_online - try to obtain a reference on the specified css if online
@@ -61,6 +64,7 @@ bool css_tryget_online(struct cgroup_subsys_state *css)
 		return percpu_ref_tryget_live(&css->refcnt);
 	return true;
 }
+CGROUP_REF_EXPORT(css_tryget_online)
 
 /**
  * css_put - put a css reference
@@ -74,6 +78,7 @@ void css_put(struct cgroup_subsys_state *css)
 	if (!(css->flags & CSS_NO_REF))
 		percpu_ref_put(&css->refcnt);
 }
+CGROUP_REF_EXPORT(css_put)
 
 /**
  * css_put_many - put css references
@@ -88,3 +93,4 @@ void css_put_many(struct cgroup_subsys_state *css, unsigned int n)
 	if (!(css->flags & CSS_NO_REF))
 		percpu_ref_put_many(&css->refcnt, n);
 }
+CGROUP_REF_EXPORT(css_put_many)

kernel/cgroup/cgroup.c

@@ -250,6 +250,7 @@ static int cgroup_addrm_files(struct cgroup_subsys_state *css,
 
 #ifdef CONFIG_DEBUG_CGROUP_REF
 #define CGROUP_REF_FN_ATTRS	noinline
+#define CGROUP_REF_EXPORT(fn)	EXPORT_SYMBOL_GPL(fn);
 #include <linux/cgroup_refcnt.h>
 #endif