[tip: sched/psi] cgroup: Implement cgroup_file_show()

[tip-bot2 for Tejun Heo]

The following commit has been merged into the sched/psi branch of tip:

Commit-ID:     e2691f6b44ed2135bfd005ad5fbabac4f433a7a1
Gitweb:        https://git.kernel.org/tip/e2691f6b44ed2135bfd005ad5fbabac4f433a7a1
Author:        Tejun Heo <tj@xxxxxxxxxx>
AuthorDate:    Sat, 27 Aug 2022 19:04:40 -10:00
Committer:     Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
CommitterDate: Thu, 01 Sep 2022 18:08:44 +02:00

cgroup: Implement cgroup_file_show()

Add cgroup_file_show() which allows toggling visibility of a cgroup file
using the new kernfs_show(). This will be used to hide psi interface files
on cgroups where it's disabled.

Cc: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Tested-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
Reviewed-by: Chengming Zhou <zhouchengming@xxxxxxxxxxxxx>
Signed-off-by: Tejun Heo <tj@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20220828050440.734579-10-tj@xxxxxxxxxx
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 include/linux/cgroup.h |  1 +
 kernel/cgroup/cgroup.c | 20 ++++++++++++++++++++
 2 files changed, 21 insertions(+)

diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index ed53bfe..f61dd13 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -114,6 +114,7 @@ int cgroup_add_dfl_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
 int cgroup_add_legacy_cftypes(struct cgroup_subsys *ss, struct cftype *cfts);
 int cgroup_rm_cftypes(struct cftype *cfts);
 void cgroup_file_notify(struct cgroup_file *cfile);
+void cgroup_file_show(struct cgroup_file *cfile, bool show);
 
 int task_cgroup_path(struct task_struct *task, char *buf, size_t buflen);
 int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry);
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index ffaccd6..217469a 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -4340,6 +4340,26 @@ void cgroup_file_notify(struct cgroup_file *cfile)
 }
 
 /**
+ * cgroup_file_show - show or hide a hidden cgroup file
+ * @cfile: target cgroup_file obtained by setting cftype->file_offset
+ * @show: whether to show or hide
+ */
+void cgroup_file_show(struct cgroup_file *cfile, bool show)
+{
+	struct kernfs_node *kn;
+
+	spin_lock_irq(&cgroup_file_kn_lock);
+	kn = cfile->kn;
+	kernfs_get(kn);
+	spin_unlock_irq(&cgroup_file_kn_lock);
+
+	if (kn)
+		kernfs_show(kn, show);
+
+	kernfs_put(kn);
+}
+
+/**
  * css_next_child - find the next child of a given css
  * @pos: the current position (%NULL to initiate traversal)
  * @parent: css whose children to walk