From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753006Ab2KLPxI (ORCPT ); Mon, 12 Nov 2012 10:53:08 -0500 Received: from userp1040.oracle.com ([156.151.31.81]:30571 "EHLO userp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751283Ab2KLPxG (ORCPT ); Mon, 12 Nov 2012 10:53:06 -0500 Message-ID: <50A11B3B.1080600@oracle.com> Date: Mon, 12 Nov 2012 10:52:27 -0500 From: Sasha Levin User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:16.0) Gecko/20121024 Thunderbird/16.0.1 MIME-Version: 1.0 To: Russell King - ARM Linux CC: Maarten Lankhorst , linux-kernel@vger.kernel.org, Kukjin Kim , linux-arm-kernel@lists.infradead.org, linux-samsung-soc@vger.kernel.org Subject: Re: [PATCH] ARM: EXYNOS: use BUG_ON where possible References: <1352406191-14303-1-git-send-email-sasha.levin@oracle.com> <1352406191-14303-5-git-send-email-sasha.levin@oracle.com> <50A111DD.6080504@gmail.com> <20121112152349.GH28327@n2100.arm.linux.org.uk> In-Reply-To: <20121112152349.GH28327@n2100.arm.linux.org.uk> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit X-Source-IP: ucsinet22.oracle.com [156.151.31.94] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/12/2012 10:23 AM, Russell King - ARM Linux wrote: > On Mon, Nov 12, 2012 at 04:12:29PM +0100, Maarten Lankhorst wrote: >> Op 08-11-12 21:23, Sasha Levin schreef: >>> @@ -465,10 +465,8 @@ static void __init combiner_cascade_irq(unsigned int combiner_nr, unsigned int i >>> else >>> max_nr = EXYNOS4_MAX_COMBINER_NR; >>> >>> - if (combiner_nr >= max_nr) >>> - BUG(); >>> - if (irq_set_handler_data(irq, &combiner_data[combiner_nr]) != 0) >>> - BUG(); >>> + BUG_ON(combiner_nr >= max_nr); >>> + BUG_ON(irq_set_handler_data(irq, &combiner_data[combiner_nr]) != 0); >> >> Is it really a good idea to put functions that perform work in a BUG_ON? >> I don't know, but for some reason it just feels wrong. I'd expect code to >> compile fine if BUG_ON was a noop, so doing verification calls only, not >> actual work.. > > Well, it is currently defined as: > > include/asm-generic/bug.h:#define BUG_ON(condition) do { if (unlikely(condition)) BUG(); } while(0) > include/asm-generic/bug.h:#define BUG_ON(condition) do { if (condition) ; } while(0) > > but as these can be overridden, I don't think relying on those > implementations is a good idea; to do so would be fragile. Eg, what if > the BUG_ON() implementation becomes just: > > #define BUG_ON(x) > > then the function call itself vanishes. So, only put the actual bug test > inside a BUG_ON(), not the functional part which must always be executed. Even if we ignore that modifying the side-effects is wrong, there's already more than enough code in the kernel (both in kernel/ / mm/, and in arch/) to cause breakage if for some reason the expression is not evaluated. If some arch decides to not evaluate the expression there it's going to be inherently broken. Thanks, Sasha