net/smc: Fix possible leaked pernet namespace in smc_init()

In smc_init(), register_pernet_subsys(&smc_net_stat_ops) is called
without any error handling.
If it fails, registering of &smc_net_ops won't be reverted.
And if smc_nl_init() fails, &smc_net_stat_ops itself won't be reverted.

This leaves wild ops in subsystem linkedlist and when another module
tries to call register_pernet_operations() it triggers page fault:

BUG: unable to handle page fault for address: fffffbfff81b964c
RIP: 0010:register_pernet_operations+0x1b9/0x5f0
Call Trace:
  <TASK>
  register_pernet_subsys+0x29/0x40
  ebtables_init+0x58/0x1000 [ebtables]
  ...

Fixes: 194730a ("net/smc: Make SMC statistics network namespace aware")
Signed-off-by: Chen Zhongjin <[email protected]>
Reviewed-by: Tony Lu <[email protected]>
Reviewed-by: Wenjia Zhang <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jakub Kicinski <[email protected]>

net/smc/af_smc.c

@@ -3380,14 +3380,14 @@ static int __init smc_init(void)
 
 	rc = register_pernet_subsys(&smc_net_stat_ops);
 	if (rc)
-		return rc;
+		goto out_pernet_subsys;
 
 	smc_ism_init();
 	smc_clc_init();
 
 	rc = smc_nl_init();
 	if (rc)
-		goto out_pernet_subsys;
+		goto out_pernet_subsys_stat;
 
 	rc = smc_pnet_init();
 	if (rc)
@@ -3480,6 +3480,8 @@ static int __init smc_init(void)
 	smc_pnet_exit();
 out_nl:
 	smc_nl_exit();
+out_pernet_subsys_stat:
+	unregister_pernet_subsys(&smc_net_stat_ops);
 out_pernet_subsys:
 	unregister_pernet_subsys(&smc_net_ops);