[PATCH] psi: Inherit parent cgroup psi enable state

[Chuyi Zhou]

Currently when a parent cgroup disables psi through cgroup.pressure, newly
created child cgroups do not inherit the psi state of the parent cgroup.

This patch tries to solve this issue. When a child cgroup is created, it
would inherit the psi enabled state of the parent in group_init().
Once the enable state is found to be false in the css_populate_dir(), the
{cpu, io, memory}.pressure files will be hidden using cgroup_file_show().

Signed-off-by: Chuyi Zhou <zhouchuyi@xxxxxxxxxxxxx>
---
 kernel/cgroup/cgroup.c | 21 +++++++++++++++++++--
 kernel/sched/psi.c     |  4 ++--
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/kernel/cgroup/cgroup.c b/kernel/cgroup/cgroup.c
index c8e4b62b436a4..775fe528efcad 100644
--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -1719,6 +1719,24 @@ static void css_clear_dir(struct cgroup_subsys_state *css)
 	}
 }
 
+static int populate_psi_files(struct cgroup_subsys_state *css)
+{
+	struct cgroup *cgrp = css->cgroup;
+	int ret, i;
+
+	ret = cgroup_addrm_files(css, cgrp, cgroup_psi_files, true);
+	if (ret < 0)
+		return ret;
+
+	if (cgrp->psi && !cgrp->psi->enabled) {
+		for (i = 0; i < NR_PSI_RESOURCES; i++)
+			cgroup_file_show(&cgrp->psi_files[i], 0);
+	}
+
+	return ret;
+}
+
+
 /**
  * css_populate_dir - create subsys files in a cgroup directory
  * @css: target css
@@ -1742,8 +1760,7 @@ static int css_populate_dir(struct cgroup_subsys_state *css)
 				return ret;
 
 			if (cgroup_psi_enabled()) {
-				ret = cgroup_addrm_files(css, cgrp,
-							 cgroup_psi_files, true);
+				ret = populate_psi_files(css);
 				if (ret < 0) {
 					cgroup_addrm_files(css, cgrp,
 							   cgroup_base_files, false);
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index 020d58967d4e8..d0aa17b368819 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -180,7 +180,7 @@ static void group_init(struct psi_group *group)
 {
 	int cpu;
 
-	group->enabled = true;
+	group->enabled = group->parent ? group->parent->enabled : true;
 	for_each_possible_cpu(cpu)
 		seqcount_init(&per_cpu_ptr(group->pcpu, cpu)->seq);
 	group->avg_last_update = sched_clock();
@@ -1114,8 +1114,8 @@ int psi_cgroup_alloc(struct cgroup *cgroup)
 		kfree(cgroup->psi);
 		return -ENOMEM;
 	}
-	group_init(cgroup->psi);
 	cgroup->psi->parent = cgroup_psi(cgroup_parent(cgroup));
+	group_init(cgroup->psi);
 	return 0;
 }
 
-- 
2.20.1