[PATCH 2/4] cgroup:add css_is_populated

[KAMEZAWA Hiroyuki]

From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>

cgroup creation is done in several stages.
After allocated and linked to cgroup's hierarchy tree, all necessary
control files are created.

When using CSS_ID, scanning cgroups without cgrouo_lock(), status
of cgroup is important. At removal of cgroup/css, css_tryget() works fine
and we can write a safe code. At creation, we need some flag to show 
"This cgroup is not ready yet"

This patch adds CSS_POPULATED flag.

Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>

---
Index: mmotm-2.6.29-Jan14/include/linux/cgroup.h
===================================================================
--- mmotm-2.6.29-Jan14.orig/include/linux/cgroup.h
+++ mmotm-2.6.29-Jan14/include/linux/cgroup.h
@@ -69,6 +69,7 @@ struct cgroup_subsys_state {
 enum {
 	CSS_ROOT, /* This CSS is the root of the subsystem */
 	CSS_REMOVED, /* This CSS is dead */
+	CSS_POPULATED, /* This CSS finished all initialization */
 };
 
 /*
@@ -90,6 +91,11 @@ static inline bool css_is_removed(struct
 	return test_bit(CSS_REMOVED, &css->flags);
 }
 
+static inline bool css_is_populated(struct cgroup_subsys_state *css)
+{
+	return test_bit(CSS_POPULATED, &css->flags);
+}
+
 /*
  * Call css_tryget() to take a reference on a css if your existing
  * (known-valid) reference isn't already ref-counted. Returns false if
Index: mmotm-2.6.29-Jan14/kernel/cgroup.c
===================================================================
--- mmotm-2.6.29-Jan14.orig/kernel/cgroup.c
+++ mmotm-2.6.29-Jan14/kernel/cgroup.c
@@ -2326,8 +2326,10 @@ static int cgroup_populate_dir(struct cg
 	}
 
 	for_each_subsys(cgrp->root, ss) {
+		struct cgroup_subsys_state *css = cgrp->subsys[ss->subsys_id];
 		if (ss->populate && (err = ss->populate(ss, cgrp)) < 0)
 			return err;
+		set_bit(CSS_POPULATED, &css->flags);
 	}
 
 	return 0;

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