7 files changed, 75 insertions, 28 deletions

diff --git a/Documentation/cgroup-v2.txt b/Documentation/cgroup-v2.txt
index 0bbdc720dd7c..779211fbb69f 100644
--- a/Documentation/cgroup-v2.txt
+++ b/Documentation/cgroup-v2.txt
@@ -886,15 +886,6 @@ All cgroup core files are prefixed with "cgroup."
                 A dying cgroup can consume system resources not exceeding
                 limits, which were active at the moment of cgroup deletion.
 
-          cpu.usage_usec
-                CPU time consumed in the subtree.
-
-          cpu.user_usec
-                User CPU time consumed in the subtree.
-
-          cpu.system_usec
-                System CPU time consumed in the subtree.
-
 
 Controllers
 ===========
@@ -915,12 +906,16 @@ All time durations are in microseconds.
 
   cpu.stat
         A read-only flat-keyed file which exists on non-root cgroups.
+        This file exists whether the controller is enabled or not.
 
-        It reports the following six stats:
+        It always reports the following three stats:
 
         - usage_usec
         - user_usec
         - system_usec
+
+        and the following three when the controller is enabled:
+
         - nr_periods
         - nr_throttled
         - throttled_usec
diff --git a/include/linux/cgroup-defs.h b/include/linux/cgroup-defs.h
index 3e55bbd31ad1..ada6df7b1f55 100644
--- a/include/linux/cgroup-defs.h
+++ b/include/linux/cgroup-defs.h
@@ -569,6 +569,8 @@ struct cgroup_subsys {
         void (*css_released)(struct cgroup_subsys_state *css);
         void (*css_free)(struct cgroup_subsys_state *css);
         void (*css_reset)(struct cgroup_subsys_state *css);
+        int (*css_extra_stat_show)(struct seq_file *seq,
+                                   struct cgroup_subsys_state *css);
 
         int (*can_attach)(struct cgroup_taskset *tset);
         void (*cancel_attach)(struct cgroup_taskset *tset);
diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h
index 328a70ce0e23..03cad08b09d1 100644
--- a/include/linux/cgroup.h
+++ b/include/linux/cgroup.h
@@ -703,8 +703,6 @@ static inline void cpuacct_account_field(struct task_struct *tsk, int index,
                                          u64 val) {}
 #endif
 
-void cgroup_stat_show_cputime(struct seq_file *seq, const char *prefix);
-
 void __cgroup_account_cputime(struct cgroup *cgrp, u64 delta_exec);
 void __cgroup_account_cputime_field(struct cgroup *cgrp,
                                     enum cpu_usage_stat index, u64 delta_exec);
diff --git a/kernel/cgroup/cgroup-internal.h b/kernel/cgroup/cgroup-internal.h
index fa642c99586a..4dc317090920 100644
--- a/kernel/cgroup/cgroup-internal.h
+++ b/kernel/cgroup/cgroup-internal.h
@@ -205,6 +205,7 @@ int cgroup_task_count(const struct cgroup *cgrp);
 void cgroup_stat_flush(struct cgroup *cgrp);
 int cgroup_stat_init(struct cgroup *cgrp);
 void cgroup_stat_exit(struct cgroup *cgrp);
+void cgroup_stat_show_cputime(struct seq_file *seq);
 void cgroup_stat_boot(void);
 
 /*
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 7975b20f1fd1..d9773e49a1b4 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -464,6 +464,28 @@ static struct cgroup_subsys_state *cgroup_css(struct cgroup *cgrp,
 }
 
 /**
+ * cgroup_tryget_css - try to get a cgroup's css for the specified subsystem
+ * @cgrp: the cgroup of interest
+ * @ss: the subsystem of interest
+ *
+ * Find and get @cgrp's css assocaited with @ss.  If the css doesn't exist
+ * or is offline, %NULL is returned.
+ */
+static struct cgroup_subsys_state *cgroup_tryget_css(struct cgroup *cgrp,
+                                                     struct cgroup_subsys *ss)
+{
+        struct cgroup_subsys_state *css;
+
+        rcu_read_lock();
+        css = cgroup_css(cgrp, ss);
+        if (!css || !css_tryget_online(css))
+                css = NULL;
+        rcu_read_unlock();
+
+        return css;
+}
+
+/**
  * cgroup_e_css - obtain a cgroup's effective css for the specified subsystem
  * @cgrp: the cgroup of interest
  * @ss: the subsystem of interest (%NULL returns @cgrp->self)
@@ -3311,11 +3333,40 @@ static int cgroup_stat_show(struct seq_file *seq, void *v)
         seq_printf(seq, "nr_dying_descendants %d\n",
                    cgroup->nr_dying_descendants);
 
-        cgroup_stat_show_cputime(seq, "cpu.");
-
         return 0;
 }
 
+static int __maybe_unused cgroup_extra_stat_show(struct seq_file *seq,
+                                                 struct cgroup *cgrp, int ssid)
+{
+        struct cgroup_subsys *ss = cgroup_subsys[ssid];
+        struct cgroup_subsys_state *css;
+        int ret;
+
+        if (!ss->css_extra_stat_show)
+                return 0;
+
+        css = cgroup_tryget_css(cgrp, ss);
+        if (!css)
+                return 0;
+
+        ret = ss->css_extra_stat_show(seq, css);
+        css_put(css);
+        return ret;
+}
+
+static int cpu_stat_show(struct seq_file *seq, void *v)
+{
+        struct cgroup *cgrp = seq_css(seq)->cgroup;
+        int ret = 0;
+
+        cgroup_stat_show_cputime(seq);
+#ifdef CONFIG_CGROUP_SCHED
+        ret = cgroup_extra_stat_show(seq, cgrp, cpu_cgrp_id);
+#endif
+        return ret;
+}
+
 static int cgroup_file_open(struct kernfs_open_file *of)
 {
         struct cftype *cft = of->kn->priv;
@@ -4423,6 +4474,11 @@ static struct cftype cgroup_base_files[] = {
                 .name = "cgroup.stat",
                 .seq_show = cgroup_stat_show,
         },
+        {
+                .name = "cpu.stat",
+                .flags = CFTYPE_NOT_ON_ROOT,
+                .seq_show = cpu_stat_show,
+        },
         { }     /* terminate */
 };
 
diff --git a/kernel/cgroup/stat.c b/kernel/cgroup/stat.c
index 9cce79e89320..133b465691d6 100644
--- a/kernel/cgroup/stat.c
+++ b/kernel/cgroup/stat.c
@@ -256,7 +256,7 @@ void __cgroup_account_cputime_field(struct cgroup *cgrp,
         cgroup_cpu_stat_account_end(cgrp, cstat);
 }
 
-void cgroup_stat_show_cputime(struct seq_file *seq, const char *prefix)
+void cgroup_stat_show_cputime(struct seq_file *seq)
 {
         struct cgroup *cgrp = seq_css(seq)->cgroup;
         u64 usage, utime, stime;
@@ -278,10 +278,10 @@ void cgroup_stat_show_cputime(struct seq_file *seq, const char *prefix)
         do_div(utime, NSEC_PER_USEC);
         do_div(stime, NSEC_PER_USEC);
 
-        seq_printf(seq, "%susage_usec %llu\n"
-                   "%suser_usec %llu\n"
-                   "%ssystem_usec %llu\n",
-                   prefix, usage, prefix, utime, prefix, stime);
+        seq_printf(seq, "usage_usec %llu\n"
+                   "user_usec %llu\n"
+                   "system_usec %llu\n",
+                   usage, utime, stime);
 }
 
 int cgroup_stat_init(struct cgroup *cgrp)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index ad255162a830..0b3eec389552 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6678,13 +6678,12 @@ static struct cftype cpu_legacy_files[] = {
         { }     /* Terminate */
 };
 
-static int cpu_stat_show(struct seq_file *sf, void *v)
+static int cpu_extra_stat_show(struct seq_file *sf,
+                               struct cgroup_subsys_state *css)
 {
-        cgroup_stat_show_cputime(sf, "");
-
 #ifdef CONFIG_CFS_BANDWIDTH
         {
-                struct task_group *tg = css_tg(seq_css(sf));
+                struct task_group *tg = css_tg(css);
                 struct cfs_bandwidth *cfs_b = &tg->cfs_bandwidth;
                 u64 throttled_usec;
 
@@ -6817,11 +6816,6 @@ static ssize_t cpu_max_write(struct kernfs_open_file *of,
 #endif
 
 static struct cftype cpu_files[] = {
-        {
-                .name = "stat",
-                .flags = CFTYPE_NOT_ON_ROOT,
-                .seq_show = cpu_stat_show,
-        },
 #ifdef CONFIG_FAIR_GROUP_SCHED
         {
                 .name = "weight",
@@ -6852,6 +6846,7 @@ struct cgroup_subsys cpu_cgrp_subsys = {
         .css_online     = cpu_cgroup_css_online,
         .css_released   = cpu_cgroup_css_released,
         .css_free       = cpu_cgroup_css_free,
+        .css_extra_stat_show = cpu_extra_stat_show,
         .fork           = cpu_cgroup_fork,
         .can_attach     = cpu_cgroup_can_attach,
         .attach         = cpu_cgroup_attach,