net: make default_rps_mask a per netns attribute

That really was meant to be a per netns attribute from the beginning.

The idea is that once proper isolation is in place in the main
namespace, additional demux in the child namespaces will be redundant.
Let's make child netns default rps mask empty by default.

To avoid bloating the netns with a possibly large cpumask, allocate
it on-demand during the first write operation.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 38 insertions, 13 deletions

diff --git a/net/core/sysctl_net_core.c b/net/core/sysctl_net_core.c
index 7130e6d9e263..74842b453407 100644
--- a/net/core/sysctl_net_core.c
+++ b/net/core/sysctl_net_core.c
@@ -74,24 +74,47 @@ static void dump_cpumask(void *buffer, size_t *lenp, loff_t *ppos,
 #endif
 
 #ifdef CONFIG_RPS
-struct cpumask rps_default_mask;
+
+static struct cpumask *rps_default_mask_cow_alloc(struct net *net)
+{
+	struct cpumask *rps_default_mask;
+
+	if (net->core.rps_default_mask)
+		return net->core.rps_default_mask;
+
+	rps_default_mask = kzalloc(cpumask_size(), GFP_KERNEL);
+	if (!rps_default_mask)
+		return NULL;
+
+	/* pairs with READ_ONCE in rx_queue_default_mask() */
+	WRITE_ONCE(net->core.rps_default_mask, rps_default_mask);
+	return rps_default_mask;
+}
 
 static int rps_default_mask_sysctl(struct ctl_table *table, int write,
 				   void *buffer, size_t *lenp, loff_t *ppos)
 {
+	struct net *net = (struct net *)table->data;
 	int err = 0;
 
 	rtnl_lock();
 	if (write) {
-		err = cpumask_parse(buffer, &rps_default_mask);
+		struct cpumask *rps_default_mask = rps_default_mask_cow_alloc(net);
+
+		err = -ENOMEM;
+		if (!rps_default_mask)
+			goto done;
+
+		err = cpumask_parse(buffer, rps_default_mask);
 		if (err)
 			goto done;
 
-		err = rps_cpumask_housekeeping(&rps_default_mask);
+		err = rps_cpumask_housekeeping(rps_default_mask);
 		if (err)
 			goto done;
 	} else {
-		dump_cpumask(buffer, lenp, ppos, &rps_default_mask);
+		dump_cpumask(buffer, lenp, ppos,
+			     net->core.rps_default_mask ? : cpu_none_mask);
 	}
 
 done:
@@ -508,11 +531,6 @@ static struct ctl_table net_core_table[] = {
 		.mode		= 0644,
 		.proc_handler	= rps_sock_flow_sysctl
 	},
-	{
-		.procname	= "rps_default_mask",
-		.mode		= 0644,
-		.proc_handler	= rps_default_mask_sysctl
-	},
 #endif
 #ifdef CONFIG_NET_FLOW_LIMIT
 	{
@@ -639,6 +657,14 @@ static struct ctl_table net_core_table[] = {
 };
 
 static struct ctl_table netns_core_table[] = {
+#if IS_ENABLED(CONFIG_RPS)
+	{
+		.procname	= "rps_default_mask",
+		.data		= &init_net,
+		.mode		= 0644,
+		.proc_handler	= rps_default_mask_sysctl
+	},
+#endif
 	{
 		.procname	= "somaxconn",
 		.data		= &init_net.core.sysctl_somaxconn,
@@ -706,6 +732,9 @@ static __net_exit void sysctl_core_net_exit(struct net *net)
 	tbl = net->core.sysctl_hdr->ctl_table_arg;
 	unregister_net_sysctl_table(net->core.sysctl_hdr);
 	BUG_ON(tbl == netns_core_table);
+#if IS_ENABLED(CONFIG_RPS)
+	kfree(net->core.rps_default_mask);
+#endif
 	kfree(tbl);
 }
 
@@ -716,10 +745,6 @@ static __net_initdata struct pernet_operations sysctl_core_ops = {
 
 static __init int sysctl_core_init(void)
 {
-#if IS_ENABLED(CONFIG_RPS)
-	cpumask_copy(&rps_default_mask, cpu_none_mask);
-#endif
-
 	register_net_sysctl(&init_net, "net/core", net_core_table);
 	return register_pernet_subsys(&sysctl_core_ops);
 }