From 66b3e537b50cd2b46b71edb6ffeef633d1224d10 Mon Sep 17 00:00:00 2001
From: Phil Elwell <phil@raspberrypi.org>
Date: Mon, 27 Nov 2017 17:14:54 +0000
Subject: [PATCH] cgroup: Disable cgroup "memory" by default

Some Raspberry Pis have limited RAM and most users won't use the
cgroup memory support so it is disabled by default. Enable with:

    cgroup_enable=memory

See: https://github.com/raspberrypi/linux/issues/1950

Signed-off-by: Phil Elwell <phil@raspberrypi.org>
---
 kernel/cgroup/cgroup.c | 38 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

--- a/kernel/cgroup/cgroup.c
+++ b/kernel/cgroup/cgroup.c
@@ -5219,6 +5219,9 @@ int __init cgroup_init_early(void)
 	return 0;
 }
 
+static u16 cgroup_enable_mask __initdata;
+static int __init cgroup_disable(char *str);
+
 /**
  * cgroup_init - cgroup initialization
  *
@@ -5256,6 +5259,12 @@ int __init cgroup_init(void)
 
 	mutex_unlock(&cgroup_mutex);
 
+	/*
+	 * Apply an implicit disable, knowing that an explicit enable will
+	 * prevent if from doing anything.
+	 */
+	cgroup_disable("memory");
+
 	for_each_subsys(ss, ssid) {
 		if (ss->early_init) {
 			struct cgroup_subsys_state *css =
@@ -5637,6 +5646,10 @@ static int __init cgroup_disable(char *s
 			    strcmp(token, ss->legacy_name))
 				continue;
 
+			/* An explicit cgroup_enable overrides a disable */
+			if (cgroup_enable_mask & (1 << i))
+				continue;
+
 			static_branch_disable(cgroup_subsys_enabled_key[i]);
 			pr_info("Disabling %s control group subsystem\n",
 				ss->name);
@@ -5646,6 +5659,31 @@ static int __init cgroup_disable(char *s
 }
 __setup("cgroup_disable=", cgroup_disable);
 
+static int __init cgroup_enable(char *str)
+{
+	struct cgroup_subsys *ss;
+	char *token;
+	int i;
+
+	while ((token = strsep(&str, ",")) != NULL) {
+		if (!*token)
+			continue;
+
+		for_each_subsys(ss, i) {
+			if (strcmp(token, ss->name) &&
+			    strcmp(token, ss->legacy_name))
+				continue;
+
+			cgroup_enable_mask |= 1 << i;
+			static_branch_enable(cgroup_subsys_enabled_key[i]);
+			pr_info("Enabling %s control group subsystem\n",
+				ss->name);
+		}
+	}
+	return 1;
+}
+__setup("cgroup_enable=", cgroup_enable);
+
 /**
  * css_tryget_online_from_dir - get corresponding css from a cgroup dentry
  * @dentry: directory dentry of interest