[PATCH] taskstats: fix CGROUPSTATS_CMD_GET for cgroup v2

[Chengming Zhou]

We found cgroupstats_build would return -EINVAL when using netlink
CGROUPSTATS_CMD_GET interface to get stats on cgroup v2. Fix it by
supporting cgroup v2 kernfs directory in cgroupstats_build, and export
cgroup2_fs_type like we did for cgroup_fs_type.

Reported-by: Daowen Luo <luodaowen.back...@bytedance.com>
Tested-by: Chengming Zhou <zhouchengm...@bytedance.com>
Signed-off-by: Chengming Zhou <zhouchengm...@bytedance.com>
---
 kernel/cgroup/cgroup-internal.h | 1 +
 kernel/cgroup/cgroup-v1.c       | 5 +++--
 kernel/cgroup/cgroup.c          | 3 +--
 3 files changed, 5 insertions(+), 4 deletions(-)

diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
index bfbeabc17a9d..9ca05fb513c2 100644
--- a/kernel/cgroup/cgroup-internal.h
+++ b/kernel/cgroup/cgroup-internal.h
@@ -151,6 +151,7 @@ extern spinlock_t css_set_lock;
 extern struct cgroup_subsys *cgroup_subsys[];
 extern struct list_head cgroup_roots;
 extern struct file_system_type cgroup_fs_type;
+extern struct file_system_type cgroup2_fs_type;
 
 /* iterate across the hierarchies */
 #define for_each_root(root)                                            \
diff --git a/kernel/cgroup/cgroup-v1.c b/kernel/cgroup/cgroup-v1.c
index 191c329e482a..6d9e9b553276 100644
--- a/kernel/cgroup/cgroup-v1.c
+++ b/kernel/cgroup/cgroup-v1.c
@@ -686,13 +686,14 @@ int proc_cgroupstats_show(struct seq_file *m, void *v)
 int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
 {
        struct kernfs_node *kn = kernfs_node_from_dentry(dentry);
+       struct file_system_type *s_type = dentry->d_sb->s_type;
        struct cgroup *cgrp;
        struct css_task_iter it;
        struct task_struct *tsk;
 
        /* it should be kernfs_node belonging to cgroupfs and is a directory */
-       if (dentry->d_sb->s_type != &cgroup_fs_type || !kn ||
-           kernfs_type(kn) != KERNFS_DIR)
+       if ((s_type != &cgroup_fs_type && s_type != &cgroup2_fs_type) ||
+           !kn || kernfs_type(kn) != KERNFS_DIR)
                return -EINVAL;
 
        mutex_lock(&cgroup_mutex);
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index dd247747ec14..0e23ae3b1e56 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -206,7 +206,6 @@ struct cgroup_namespace init_cgroup_ns = {
        .root_cset      = &init_css_set,
 };
 
-static struct file_system_type cgroup2_fs_type;
 static struct cftype cgroup_base_files[];
 
 static int cgroup_apply_control(struct cgroup *cgrp);
@@ -2162,7 +2161,7 @@ struct file_system_type cgroup_fs_type = {
        .fs_flags               = FS_USERNS_MOUNT,
 };
 
-static struct file_system_type cgroup2_fs_type = {
+struct file_system_type cgroup2_fs_type = {
        .name                   = "cgroup2",
        .init_fs_context        = cgroup_init_fs_context,
        .parameters             = cgroup2_fs_parameters,
-- 
2.11.0