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: d523a328fb02 ("[INET]: Fix inet_diag dead-lock regression")
Signed-off-by: Eric Dumazet <[e-mail]>
Reviewed-by: Guillaume Nault <[e-mail]>
Reviewed-by: Kuniyuki Iwashima <[e-mail]>
Reviewed-by: Willem de Bruijn <[e-mail]>
Signed-off-by: Paolo Abeni <[e-mail]>

net/ipv4/inet_diag.c

···
 		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);
···
 	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);
···
 		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);