From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757024AbYLaXlS (ORCPT ); Wed, 31 Dec 2008 18:41:18 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752275AbYLaXlE (ORCPT ); Wed, 31 Dec 2008 18:41:04 -0500 Received: from waste.org ([66.93.16.53]:60590 "EHLO waste.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752164AbYLaXlD (ORCPT ); Wed, 31 Dec 2008 18:41:03 -0500 Subject: Re: random.c changes for sparse irq_desc are crap From: Matt Mackall To: Yinghai Lu Cc: Linux Kernel Mailing List , Linus Torvalds , Ingo Molnar In-Reply-To: <495BFB48.8080506@kernel.org> References: <1230748169.19620.132.camel@calx> <495BFB48.8080506@kernel.org> Content-Type: text/plain Date: Wed, 31 Dec 2008 17:40:26 -0600 Message-Id: <1230766826.19620.150.camel@calx> Mime-Version: 1.0 X-Mailer: Evolution 2.22.3.1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, 2008-12-31 at 15:07 -0800, Yinghai Lu wrote: > Matt Mackall wrote: > > I just noticed you merged a change that pointlessly converts two > > random.c functions into ugly random.h inlines without going through the > > maintainer. > > > > I also don't like the look of the newly-introduced sparse variants of > > these functions. Failure to find an irq descriptor in > > get_timer_rand_state is a BUG_ON should-never-happen sort of condition, > > not something to silently ignore. Letting the code try to dereference > > NULL is preferred here: we'll actually be able to find and fix the > > broken driver that's throwing around meaningless irq vectors. > > > > Throwing away the timer_state pointer in the set_timer_rand_state > > function is similarly bogus in addition to being a memory leak. > > > > Please fix this up. > > > > want something like this? Not quite. First, please turn these back into normal functions in random.c. Inlining functions is generally discouraged these days unless you have a good reason and numbers to back it up. Second, as I tried to explain above, BUG_ON(!desc) is doing very little that the subsequent desc->timer_rand_state wouldn't already do (generating a traceback). In cases where dereferencing NULL should never happen, it's preferable to not add the extra check and just let the oops happen. We'll still get a backtrace if anything ever goes wrong, but we won't have wasted any code space or CPU cycles when it doesn't. -- Mathematics is the supreme nostalgia of our time.