Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755488AbaKPPoK (ORCPT ); Sun, 16 Nov 2014 10:44:10 -0500 Received: from mail3-relais-sop.national.inria.fr ([192.134.164.104]:32481 "EHLO mail3-relais-sop.national.inria.fr" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755198AbaKPPoJ (ORCPT ); Sun, 16 Nov 2014 10:44:09 -0500 X-IronPort-AV: E=Sophos;i="5.07,397,1413237600"; d="scan'208";a="88608604" Date: Sun, 16 Nov 2014 16:43:51 +0100 (CET) From: Julia Lawall X-X-Sender: jll@hadrien To: SF Markus Elfring cc: Julia Lawall , Ananth N Mavinakayanahalli , Anil S Keshavamurthy , "David S. Miller" , Masami Hiramatsu , kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org, Coccinelle Subject: Re: [Cocci] [PATCH 1/1] kprobes: Deletion of an unnecessary check before the function call "module_put" In-Reply-To: <5468B3FD.20409@users.sourceforge.net> Message-ID: References: <5307CAA2.8060406@users.sourceforge.net> <530A086E.8010901@users.sourceforge.net> <530A72AA.3000601@users.sourceforge.net> <530B5FB6.6010207@users.sourceforge.net> <530C5E18.1020800@users.sourceforge.net> <530CD2C4.4050903@users.sourceforge.net> <530CF8FF.8080600@users.sourceforge.net> <530DD06F.4090703@users.sourceforge.net> <5317A59D.4@users.sourceforge.net> <546899CF.8020808@users.sourceforge.net> <5468B3FD.20409@users.sourceforge.net> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, 16 Nov 2014, SF Markus Elfring wrote: > >> diff --git a/kernel/kprobes.c b/kernel/kprobes.c > >> index 3995f54..f1e7d45 100644 > >> --- a/kernel/kprobes.c > >> +++ b/kernel/kprobes.c > >> @@ -1527,8 +1527,7 @@ int register_kprobe(struct kprobe *p) > >> out: > >> mutex_unlock(&kprobe_mutex); > >> > >> - if (probed_mod) > >> - module_put(probed_mod); > >> + module_put(probed_mod); > > > > There is an out label, so please check whether the labels could not be > > better positioned to avoid calling module_put when it is not needed. > > I do not see refactoring opportunities around jump labels in this use case > for the implementation of the register_kprobe() function so far because > the mutex_unlock() function must be called. > Would you like to suggest any other source code fine-tuning? OK. I don't think that removing the if is a good choice in this case. The code ret = check_kprobe_address_safe(p, &probed_mod); is unusual, in that it can fail to do anything in two ways. One is by setting ret, on detecting an error, and the other is by returning 0 but still putting a NULL value in probed_mod when there is nothing to do. Thus, in the successful execution of the rest of the function, a probed module might or might not exist. The if around the module_put is helpful to the reader to understand that this possibility exists. julia -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/