[PATCH 1/2] cgroup: Set CGRP_RELEASABLE when adding to a cgroup

[Colin Cross <ccross@android.com>]

Changes the meaning of CGRP_RELEASABLE to be set on any cgroup
that has ever had a task or cgroup in it, or had css_get called
on it.  The bit is set in cgroup_attach_task, cgroup_create,
and __css_get.  It is not necessary to set the bit in
cgroup_fork, as the task is either in the root cgroup, in
which can never be released, or the task it was forked from
already set the bit in croup_attach_task.

Signed-off-by: Colin Cross <ccross@android.com>
---
 include/linux/cgroup.h |   12 +--------
 kernel/cgroup.c        |   54 ++++++++++++++++++++---------------------------
 2 files changed, 25 insertions(+), 41 deletions(-)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index ed4ba11..9e13078 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -84,12 +84,6 @@ enum {
 	CSS_REMOVED, /* This CSS is dead */
 };
 
-/* Caller must verify that the css is not for root cgroup */
-static inline void __css_get(struct cgroup_subsys_state *css, int count)
-{
-	atomic_add(count, &css->refcnt);
-}
-
 /*
  * Call css_get() to hold a reference on the css; it can be used
  * for a reference obtained via:
@@ -97,6 +91,7 @@ static inline void __css_get(struct cgroup_subsys_state *css, int count)
  * - task->cgroups for a locked task
  */
 
+extern void __css_get(struct cgroup_subsys_state *css, int count);
 static inline void css_get(struct cgroup_subsys_state *css)
 {
 	/* We don't need to reference count the root state */
@@ -143,10 +138,7 @@ static inline void css_put(struct cgroup_subsys_state *css)
 enum {
 	/* Control Group is dead */
 	CGRP_REMOVED,
-	/*
-	 * Control Group has previously had a child cgroup or a task,
-	 * but no longer (only if CGRP_NOTIFY_ON_RELEASE is set)
-	 */
+	/* Control Group has ever had a child cgroup or a task */
 	CGRP_RELEASABLE,
 	/* Control Group requires release notifications to userspace */
 	CGRP_NOTIFY_ON_RELEASE,
diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 66a416b..34e855e 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -338,7 +338,15 @@ static void free_css_set_rcu(struct rcu_head *obj)
  * compiled into their kernel but not actually in use */
 static int use_task_css_set_links __read_mostly;
 
-static void __put_css_set(struct css_set *cg, int taskexit)
+/*
+ * refcounted get/put for css_set objects
+ */
+static inline void get_css_set(struct css_set *cg)
+{
+	atomic_inc(&cg->refcount);
+}
+
+static void put_css_set(struct css_set *cg)
 {
 	struct cg_cgroup_link *link;
 	struct cg_cgroup_link *saved_link;
@@ -364,12 +372,8 @@ static void __put_css_set(struct css_set *cg, int taskexit)
 		struct cgroup *cgrp = link->cgrp;
 		list_del(&link->cg_link_list);
 		list_del(&link->cgrp_link_list);
-		if (atomic_dec_and_test(&cgrp->count) &&
-		    notify_on_release(cgrp)) {
-			if (taskexit)
-				set_bit(CGRP_RELEASABLE, &cgrp->flags);
+		if (atomic_dec_and_test(&cgrp->count))
 			check_for_release(cgrp);
-		}
 
 		kfree(link);
 	}
@@ -379,24 +383,6 @@ static void __put_css_set(struct css_set *cg, int taskexit)
 }
 
 /*
- * refcounted get/put for css_set objects
- */
-static inline void get_css_set(struct css_set *cg)
-{
-	atomic_inc(&cg->refcount);
-}
-
-static inline void put_css_set(struct css_set *cg)
-{
-	__put_css_set(cg, 0);
-}
-
-static inline void put_css_set_taskexit(struct css_set *cg)
-{
-	__put_css_set(cg, 1);
-}
-
-/*
  * compare_css_sets - helper function for find_existing_css_set().
  * @cg: candidate css_set being tested
  * @old_cg: existing css_set for a task
@@ -1801,7 +1787,7 @@ int cgroup_attach_task(struct cgroup *cgrp, struct task_struct *tsk)
 		if (ss->attach)
 			ss->attach(ss, cgrp, oldcgrp, tsk, false);
 	}
-	set_bit(CGRP_RELEASABLE, &oldcgrp->flags);
+	set_bit(CGRP_RELEASABLE, &cgrp->flags);
 	synchronize_rcu();
 	put_css_set(cg);
 
@@ -3427,6 +3413,8 @@ static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
 	if (err < 0)
 		goto err_remove;
 
+	set_bit(CGRP_RELEASABLE, &parent->flags);
+
 	/* The cgroup directory was pre-locked for us */
 	BUG_ON(!mutex_is_locked(&cgrp->dentry->d_inode->i_mutex));
 
@@ -3645,7 +3633,6 @@ again:
 	cgroup_d_remove_dir(d);
 	dput(d);
 
-	set_bit(CGRP_RELEASABLE, &parent->flags);
 	check_for_release(parent);
 
 	/*
@@ -4240,7 +4227,7 @@ void cgroup_exit(struct task_struct *tsk, int run_callbacks)
 	tsk->cgroups = &init_css_set;
 	task_unlock(tsk);
 	if (cg)
-		put_css_set_taskexit(cg);
+		put_css_set(cg);
 }
 
 /**
@@ -4410,6 +4397,14 @@ static void check_for_release(struct cgroup *cgrp)
 }
 
 /* Caller must verify that the css is not for root cgroup */
+void __css_get(struct cgroup_subsys_state *css, int count)
+{
+	atomic_add(count, &css->refcnt);
+	set_bit(CGRP_RELEASABLE, &css->cgroup->flags);
+}
+EXPORT_SYMBOL_GPL(__css_get);
+
+/* Caller must verify that the css is not for root cgroup */
 void __css_put(struct cgroup_subsys_state *css, int count)
 {
 	struct cgroup *cgrp = css->cgroup;
@@ -4417,10 +4412,7 @@ void __css_put(struct cgroup_subsys_state *css, int count)
 	rcu_read_lock();
 	val = atomic_sub_return(count, &css->refcnt);
 	if (val == 1) {
-		if (notify_on_release(cgrp)) {
-			set_bit(CGRP_RELEASABLE, &cgrp->flags);
-			check_for_release(cgrp);
-		}
+		check_for_release(cgrp);
 		cgroup_wakeup_rmdir_waiter(cgrp);
 	}
 	rcu_read_unlock();
-- 
1.7.3.1