inet_diag: annotate data-races around inet_diag_table[]

inet_diag_lock_handler() reads inet_diag_table[proto] locklessly.

Use READ_ONCE()/WRITE_ONCE() annotations to avoid potential issues.

Fixes: d523a328 ("[INET]: Fix inet_diag dead-lock regression")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Guillaume Nault <gnault@redhat.com>
Reviewed-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

net/ipv4/inet_diag.c

@@ -57,7 +57,7 @@ static const struct inet_diag_handler *inet_diag_lock_handler(int proto)
 		return ERR_PTR(-ENOENT);
 	}
 
-	if (!inet_diag_table[proto])
+	if (!READ_ONCE(inet_diag_table[proto]))
 		sock_load_diag_module(AF_INET, proto);
 
 	mutex_lock(&inet_diag_table_mutex);
@@ -1503,7 +1503,7 @@ int inet_diag_register(const struct inet_diag_handler *h)
 	mutex_lock(&inet_diag_table_mutex);
 	err = -EEXIST;
 	if (!inet_diag_table[type]) {
-		inet_diag_table[type] = h;
+		WRITE_ONCE(inet_diag_table[type], h);
 		err = 0;
 	}
 	mutex_unlock(&inet_diag_table_mutex);
@@ -1520,7 +1520,7 @@ void inet_diag_unregister(const struct inet_diag_handler *h)
 		return;
 
 	mutex_lock(&inet_diag_table_mutex);
-	inet_diag_table[type] = NULL;
+	WRITE_ONCE(inet_diag_table[type], NULL);
 	mutex_unlock(&inet_diag_table_mutex);
 }
 EXPORT_SYMBOL_GPL(inet_diag_unregister);