From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751966AbcISPWk (ORCPT ); Mon, 19 Sep 2016 11:22:40 -0400 Received: from mail-pa0-f48.google.com ([209.85.220.48]:35190 "EHLO mail-pa0-f48.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751639AbcISPWh (ORCPT ); Mon, 19 Sep 2016 11:22:37 -0400 Subject: Re: [PATCH] sbitmap: avoid maybe-uninitialized warning To: Arnd Bergmann References: <20160919123359.1225305-1-arnd@arndb.de> <6efcc3e0-b85f-9612-2562-d37922a1dc92@kernel.dk> <2163656.5SLNssdXj1@wuerfel> Cc: Omar Sandoval , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org From: Jens Axboe Message-ID: <940657ab-4092-cebd-127e-6628adcf96b5@kernel.dk> Date: Mon, 19 Sep 2016 09:22:34 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0 MIME-Version: 1.0 In-Reply-To: <2163656.5SLNssdXj1@wuerfel> Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 09/19/2016 09:14 AM, Arnd Bergmann wrote: > On Monday, September 19, 2016 8:43:12 AM CEST Jens Axboe wrote: >> On 09/19/2016 06:33 AM, Arnd Bergmann wrote: >>> The sbitmap code that has just been turned into a library module >>> returns uninitialized data for sbitmap_weight(), as pointed out by >>> gcc when building with -Wmaybe-uninitialized: >>> >>> lib/sbitmap.c: In function 'sbitmap_weight': >>> lib/sbitmap.c:179:9: error: 'weight' may be used uninitialized in this function [-Werror=maybe-uninitialized] >>> >>> Note that the value is never initialized, we just add data on >>> top, so it is wrong regardless of sb->map_nr. >>> >>> This adds the missing initialization. >> >> Thanks Arnd, Colin sent the same patch and I applied it. Note that: > > Ok, thanks! > >>> Fixes: 88459642cba4 ("blk-mq: abstract tag allocation out into sbitmap library") >> >> that isn't truly correct, that patch is just what moved the code. The >> bug predates that commit. > > It's not important as long as the bug is fixed now, but I think it was > correct before that move, we just lost the 'used=0' initialization, > which also triggered the warning: > > -static unsigned int bt_unused_tags(struct blk_mq_bitmap_tags *bt) > -{ > - unsigned int i, used; > - > - for (i = 0, used = 0; i < bt->map_nr; i++) { > - struct blk_align_bitmap *bm = &bt->map[i]; > - > - used += bitmap_weight(&bm->word, bm->depth); > } > > - return bt->depth - used; > } I missed that, as I generally never use double inits in for loops, but I guess I did for this one. But you are right, the bug was introduced with the recent move, so your Fixes was completely correct. Omar loses a cookie. -- Jens Axboe