tcp_metrics: hash table allocation cleanup

After commit 098a697 ("tcp_metrics: Use a single hash table
for all network namespaces.") we can avoid calling tcp_net_metrics_init()
for each new netns.

Instead, rename tcp_net_metrics_init() to tcp_metrics_hash_alloc(),
and move it to __init section.

Also move tcpmhash_entries to __initdata section.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Link: https://lore.kernel.org/r/20230803135417.2716879-1-edumazet@google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

net/ipv4/tcp_metrics.c

@@ -990,7 +990,7 @@ static struct genl_family tcp_metrics_nl_family __ro_after_init = {
 	.resv_start_op	= TCP_METRICS_CMD_DEL + 1,
 };
 
-static unsigned int tcpmhash_entries;
+static unsigned int tcpmhash_entries __initdata;
 static int __init set_tcpmhash_entries(char *str)
 {
 	ssize_t ret;
@@ -1006,15 +1006,11 @@ static int __init set_tcpmhash_entries(char *str)
 }
 __setup("tcpmhash_entries=", set_tcpmhash_entries);
 
-static int __net_init tcp_net_metrics_init(struct net *net)
+static void __init tcp_metrics_hash_alloc(void)
 {
+	unsigned int slots = tcpmhash_entries;
 	size_t size;
-	unsigned int slots;
 
-	if (!net_eq(net, &init_net))
-		return 0;
-
-	slots = tcpmhash_entries;
 	if (!slots) {
 		if (totalram_pages() >= 128 * 1024)
 			slots = 16 * 1024;
@@ -1027,9 +1023,7 @@ static int __net_init tcp_net_metrics_init(struct net *net)
 
 	tcp_metrics_hash = kvzalloc(size, GFP_KERNEL);
 	if (!tcp_metrics_hash)
-		return -ENOMEM;
-
-	return 0;
+		panic("Could not allocate the tcp_metrics hash table\n");
 }
 
 static void __net_exit tcp_net_metrics_exit_batch(struct list_head *net_exit_list)
@@ -1038,17 +1032,18 @@ static void __net_exit tcp_net_metrics_exit_batch(struct list_head *net_exit_lis
 }
 
 static __net_initdata struct pernet_operations tcp_net_metrics_ops = {
-	.init		=	tcp_net_metrics_init,
 	.exit_batch	=	tcp_net_metrics_exit_batch,
 };
 
 void __init tcp_metrics_init(void)
 {
 	int ret;
 
+	tcp_metrics_hash_alloc();
+
 	ret = register_pernet_subsys(&tcp_net_metrics_ops);
 	if (ret < 0)
-		panic("Could not allocate the tcp_metrics hash table\n");
+		panic("Could not register tcp_net_metrics_ops\n");
 
 	ret = genl_register_family(&tcp_metrics_nl_family);
 	if (ret < 0)