cgroup: rename css_tryget*() to css_tryget_online*()

Unlike the more usual refcnting, what css_tryget() provides is the
distinction between online and offline csses instead of protection
against upping a refcnt which already reached zero.  cgroup is
planning to provide actual tryget which fails if the refcnt already
reached zero.  Let's rename the existing trygets so that they clearly
indicate that they're onliness.

I thought about keeping the existing names as-are and introducing new
names for the planned actual tryget; however, given that each
controller participates in the synchronization of the online state, it
seems worthwhile to make it explicit that these functions are about
on/offline state.

Rename css_tryget() to css_tryget_online() and css_tryget_from_dir()
to css_tryget_online_from_dir().  This is pure rename.

v2: cgroup_freezer grew new usages of css_tryget().  Update
    accordingly.

Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Michal Hocko <mhocko@suse.cz>
Acked-by: Li Zefan <lizefan@huawei.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>

4 files changed, 27 insertions, 26 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 7633703e9baf..671d8a6dae37 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -3771,7 +3771,7 @@ int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
 
 	/*
 	 * We aren't being called from kernfs and there's no guarantee on
-	 * @kn->priv's validity.  For this and css_tryget_from_dir(),
+	 * @kn->priv's validity.  For this and css_tryget_online_from_dir(),
 	 * @kn->priv is RCU safe.  Let's do the RCU dancing.
 	 */
 	rcu_read_lock();
@@ -4060,9 +4060,9 @@ err:
  *    Implemented in kill_css().
  *
  * 2. When the percpu_ref is confirmed to be visible as killed on all CPUs
- *    and thus css_tryget() is guaranteed to fail, the css can be offlined
- *    by invoking offline_css().  After offlining, the base ref is put.
- *    Implemented in css_killed_work_fn().
+ *    and thus css_tryget_online() is guaranteed to fail, the css can be
+ *    offlined by invoking offline_css().  After offlining, the base ref is
+ *    put.  Implemented in css_killed_work_fn().
  *
  * 3. When the percpu_ref reaches zero, the only possible remaining
  *    accessors are inside RCU read sections.  css_release() schedules the
@@ -4386,7 +4386,7 @@ static int cgroup_mkdir(struct kernfs_node *parent_kn, const char *name,
 
 /*
  * This is called when the refcnt of a css is confirmed to be killed.
- * css_tryget() is now guaranteed to fail.
+ * css_tryget_online() is now guaranteed to fail.
  */
 static void css_killed_work_fn(struct work_struct *work)
 {
@@ -4398,8 +4398,8 @@ static void css_killed_work_fn(struct work_struct *work)
 	mutex_lock(&cgroup_mutex);
 
 	/*
-	 * css_tryget() is guaranteed to fail now.  Tell subsystems to
-	 * initate destruction.
+	 * css_tryget_online() is guaranteed to fail now.  Tell subsystems
+	 * to initate destruction.
 	 */
 	offline_css(css);
 
@@ -4440,8 +4440,8 @@ static void css_killed_ref_fn(struct percpu_ref *ref)
  *
  * This function initiates destruction of @css by removing cgroup interface
  * files and putting its base reference.  ->css_offline() will be invoked
- * asynchronously once css_tryget() is guaranteed to fail and when the
- * reference count reaches zero, @css will be released.
+ * asynchronously once css_tryget_online() is guaranteed to fail and when
+ * the reference count reaches zero, @css will be released.
  */
 static void kill_css(struct cgroup_subsys_state *css)
 {
@@ -4462,7 +4462,7 @@ static void kill_css(struct cgroup_subsys_state *css)
 	/*
 	 * cgroup core guarantees that, by the time ->css_offline() is
 	 * invoked, no new css reference will be given out via
-	 * css_tryget().  We can't simply call percpu_ref_kill() and
+	 * css_tryget_online().  We can't simply call percpu_ref_kill() and
 	 * proceed to offlining css's because percpu_ref_kill() doesn't
 	 * guarantee that the ref is seen as killed on all CPUs on return.
 	 *
@@ -4478,9 +4478,9 @@ static void kill_css(struct cgroup_subsys_state *css)
  *
  * css's make use of percpu refcnts whose killing latency shouldn't be
  * exposed to userland and are RCU protected.  Also, cgroup core needs to
- * guarantee that css_tryget() won't succeed by the time ->css_offline() is
- * invoked.  To satisfy all the requirements, destruction is implemented in
- * the following two steps.
+ * guarantee that css_tryget_online() won't succeed by the time
+ * ->css_offline() is invoked.  To satisfy all the requirements,
+ * destruction is implemented in the following two steps.
  *
  * s1. Verify @cgrp can be destroyed and mark it dying.  Remove all
  *     userland visible parts and start killing the percpu refcnts of
@@ -4574,9 +4574,9 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
 	/*
 	 * There are two control paths which try to determine cgroup from
 	 * dentry without going through kernfs - cgroupstats_build() and
-	 * css_tryget_from_dir().  Those are supported by RCU protecting
-	 * clearing of cgrp->kn->priv backpointer, which should happen
-	 * after all files under it have been removed.
+	 * css_tryget_online_from_dir().  Those are supported by RCU
+	 * protecting clearing of cgrp->kn->priv backpointer, which should
+	 * happen after all files under it have been removed.
 	 */
 	kernfs_remove(cgrp->kn);	/* @cgrp has an extra ref on its kn */
 	RCU_INIT_POINTER(*(void __rcu __force **)&cgrp->kn->priv, NULL);
@@ -5173,7 +5173,7 @@ static int __init cgroup_disable(char *str)
 __setup("cgroup_disable=", cgroup_disable);
 
 /**
- * css_tryget_from_dir - get corresponding css from the dentry of a cgroup dir
+ * css_tryget_online_from_dir - get corresponding css from a cgroup dentry
  * @dentry: directory dentry of interest
  * @ss: subsystem of interest
  *
@@ -5181,8 +5181,8 @@ __setup("cgroup_disable=", cgroup_disable);
  * to get the corresponding css and return it.  If such css doesn't exist
  * or can't be pinned, an ERR_PTR value is returned.
  */
-struct cgroup_subsys_state *css_tryget_from_dir(struct dentry *dentry,
-						struct cgroup_subsys *ss)
+struct cgroup_subsys_state *css_tryget_online_from_dir(struct dentry *dentry,
+						       struct cgroup_subsys *ss)
 {
 	struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
 	struct cgroup_subsys_state *css = NULL;
@@ -5204,7 +5204,7 @@ struct cgroup_subsys_state *css_tryget_from_dir(struct dentry *dentry,
 	if (cgrp)
 		css = cgroup_css(cgrp, ss);
 
-	if (!css || !css_tryget(css))
+	if (!css || !css_tryget_online(css))
 		css = ERR_PTR(-ENOENT);
 
 	rcu_read_unlock();
diff --git a/kernel/cgroup_freezer.c b/kernel/cgroup_freezer.c
index 345628c78b5b..0398f7e9ac81 100644
--- a/kernel/cgroup_freezer.c
+++ b/kernel/cgroup_freezer.c
@@ -304,7 +304,7 @@ static int freezer_read(struct seq_file *m, void *v)
 
 	/* update states bottom-up */
 	css_for_each_descendant_post(pos, css) {
-		if (!css_tryget(pos))
+		if (!css_tryget_online(pos))
 			continue;
 		rcu_read_unlock();
 
@@ -404,7 +404,7 @@ static void freezer_change_state(struct freezer *freezer, bool freeze)
 		struct freezer *pos_f = css_freezer(pos);
 		struct freezer *parent = parent_freezer(pos_f);
 
-		if (!css_tryget(pos))
+		if (!css_tryget_online(pos))
 			continue;
 		rcu_read_unlock();
 
diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index 7c0e8da59e26..37ca0a5c226d 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -872,7 +872,7 @@ static void update_tasks_cpumask_hier(struct cpuset *root_cs, bool update_root)
 				continue;
 			}
 		}
-		if (!css_tryget(&cp->css))
+		if (!css_tryget_online(&cp->css))
 			continue;
 		rcu_read_unlock();
 
@@ -1108,7 +1108,7 @@ static void update_tasks_nodemask_hier(struct cpuset *root_cs, bool update_root)
 				continue;
 			}
 		}
-		if (!css_tryget(&cp->css))
+		if (!css_tryget_online(&cp->css))
 			continue;
 		rcu_read_unlock();
 
@@ -2153,7 +2153,7 @@ static void cpuset_hotplug_workfn(struct work_struct *work)
 
 		rcu_read_lock();
 		cpuset_for_each_descendant_pre(cs, pos_css, &top_cpuset) {
-			if (cs == &top_cpuset || !css_tryget(&cs->css))
+			if (cs == &top_cpuset || !css_tryget_online(&cs->css))
 				continue;
 			rcu_read_unlock();
 
diff --git a/kernel/events/core.c b/kernel/events/core.c
index f83a71a3e46d..077968d19b8a 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -607,7 +607,8 @@ static inline int perf_cgroup_connect(int fd, struct perf_event *event,
 	if (!f.file)
 		return -EBADF;
 
-	css = css_tryget_from_dir(f.file->f_dentry, &perf_event_cgrp_subsys);
+	css = css_tryget_online_from_dir(f.file->f_dentry,
+					 &perf_event_cgrp_subsys);
 	if (IS_ERR(css)) {
 		ret = PTR_ERR(css);
 		goto out;