[PATCH 5/6] psi: add psi group for the root cgroup

[Luka Bai <lukafocus@icloud.com>]

From: Luka Bai <lukabai@tencent.com>

Cgroup_psi() now includes a condition, and checks against whether
the cgroup is the root cgroup to decide whether to use psi_system
instead of cgrp->psi. This is mostly because the default hierarchy
does not have any psi group attached. So we make psi_system as
its psi group, and remove the if condition in cgroup_psi().

Signed-off-by: Luka Bai <lukabai@tencent.com>
---
 include/linux/psi.h    | 2 +-
 kernel/cgroup/cgroup.c | 3 +++
 2 files changed, 4 insertions(+), 1 deletion(-)

diff --git a/include/linux/psi.h b/include/linux/psi.h
index e0745873e3f2..8f2db511d051 100644
--- a/include/linux/psi.h
+++ b/include/linux/psi.h
@@ -34,7 +34,7 @@ __poll_t psi_trigger_poll(void **trigger_ptr, struct file *file,
 #ifdef CONFIG_CGROUPS
 static inline struct psi_group *cgroup_psi(struct cgroup *cgrp)
 {
-	return cgroup_ino(cgrp) == 1 ? &psi_system : cgrp->psi;
+	return cgrp->psi;
 }
 
 int psi_cgroup_alloc(struct cgroup *cgrp);
diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index 43adc96c7f1a..357c68662d18 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -178,6 +178,9 @@ static DEFINE_PER_CPU(struct cgroup_rstat_base_cpu, root_rstat_base_cpu);
 /* the default hierarchy */
 struct cgroup_root cgrp_dfl_root = {
 	.cgrp.self.rstat_cpu = &root_rstat_cpu,
+#ifdef CONFIG_PSI
+	.cgrp.psi = &psi_system,
+#endif
 	.cgrp.rstat_base_cpu = &root_rstat_base_cpu,
 };
 EXPORT_SYMBOL_GPL(cgrp_dfl_root);

-- 
2.52.0