cgroup: minor updates around cgroup_clear_directory()

* Rename it to cgroup_clear_dir() and make it take the pointer to the
  target cgroup instead of the the dentry.  This makes the function
  consistent with its counterpart - cgroup_populate_dir().

* Move cgroup_clear_directory() invocation from cgroup_d_remove_dir()
  to cgroup_remount() so that the function doesn't have to determine
  the cgroup pointer back from the dentry.  cgroup_d_remove_dir() now
  only deals with vfs, which is slightly cleaner.

This patch doesn't introduce any functional differences.
Signed-off-by: Tejun Heo <tj@kernel.org>
Acked-by: Li Zefan <lizefan@huawei.com>

kernel/cgroup.c

@@ -957,15 +957,14 @@ static void cgroup_rm_file(struct cgroup *cgrp, const struct cftype *cft)
 }
 
 /**
- * cgroup_clear_directory - selective removal of base and subsystem files
- * @dir: directory containing the files
+ * cgroup_clear_dir - selective removal of base and subsystem files
+ * @cgrp: target cgroup
  * @base_files: true if the base files should be removed
  * @subsys_mask: mask of the subsystem ids whose files should be removed
  */
-static void cgroup_clear_directory(struct dentry *dir, bool base_files,
+static void cgroup_clear_dir(struct cgroup *cgrp, bool base_files,
 			     unsigned long subsys_mask)
 {
-	struct cgroup *cgrp = __d_cgrp(dir);
 	struct cgroup_subsys *ss;
 
 	for_each_root_subsys(cgrp->root, ss) {
@@ -987,9 +986,6 @@ static void cgroup_clear_directory(struct dentry *dir, bool base_files,
 static void cgroup_d_remove_dir(struct dentry *dentry)
 {
 	struct dentry *parent;
-	struct cgroupfs_root *root = dentry->d_sb->s_fs_info;
-
-	cgroup_clear_directory(dentry, true, root->subsys_mask);
 
 	parent = dentry->d_parent;
 	spin_lock(&parent->d_lock);
@@ -1376,7 +1372,7 @@ static int cgroup_remount(struct super_block *sb, int *flags, char *data)
 	 * this before rebind_subsystems, since rebind_subsystems may
 	 * change this hierarchy's subsys_list.
 	 */
-	cgroup_clear_directory(cgrp->dentry, false, removed_mask);
+	cgroup_clear_dir(cgrp, false, removed_mask);
 
 	ret = rebind_subsystems(root, added_mask, removed_mask);
 	if (ret) {
@@ -4541,9 +4537,10 @@ static int cgroup_destroy_locked(struct cgroup *cgrp)
 	raw_spin_unlock(&release_list_lock);
 
 	/*
-	 * Remove @cgrp directory.  The removal puts the base ref but we
-	 * aren't quite done with @cgrp yet, so hold onto it.
+	 * Clear and remove @cgrp directory.  The removal puts the base ref
+	 * but we aren't quite done with @cgrp yet, so hold onto it.
 	 */
+	cgroup_clear_dir(cgrp, true, cgrp->root->subsys_mask);
 	dget(d);
 	cgroup_d_remove_dir(d);