From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id E1825C43218 for ; Fri, 26 Apr 2019 14:27:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BCEB5206E0 for ; Fri, 26 Apr 2019 14:27:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726549AbfDZO1b (ORCPT ); Fri, 26 Apr 2019 10:27:31 -0400 Received: from mx2.suse.de ([195.135.220.15]:56348 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1726189AbfDZO1b (ORCPT ); Fri, 26 Apr 2019 10:27:31 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 5D84FAF50; Fri, 26 Apr 2019 14:27:29 +0000 (UTC) Subject: Re: [PATCH] bcache: avoid clang -Wunintialized warning To: Nathan Chancellor Cc: Arnd Bergmann , Kent Overstreet , clang-built-linux@googlegroups.com, Nick Desaulniers , Jens Axboe , Shenghui Wang , Hannes Reinecke , linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org References: <20190322143507.1256436-1-arnd@arndb.de> <20190425180853.GA4507@archlinux-i9> <44474338-8031-13eb-1e95-376c1036b611@suse.de> <20190426130134.GB12483@archlinux-i9> From: Coly Li Openpgp: preference=signencrypt Organization: SUSE Labs Message-ID: Date: Fri, 26 Apr 2019 22:27:17 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.14; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190426130134.GB12483@archlinux-i9> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2019/4/26 9:01 下午, Nathan Chancellor wrote: > On Fri, Apr 26, 2019 at 10:43:01AM +0800, Coly Li wrote: >> On 2019/4/26 2:08 上午, Nathan Chancellor wrote: >>> On Fri, Mar 22, 2019 at 03:35:00PM +0100, Arnd Bergmann wrote: >>>> clang has identified a code path in which it thinks a >>>> variable may be unused: >>>> >>>> drivers/md/bcache/alloc.c:333:4: error: variable 'bucket' is used uninitialized whenever 'if' condition is false >>>> [-Werror,-Wsometimes-uninitialized] >>>> fifo_pop(&ca->free_inc, bucket); >>>> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ >>>> drivers/md/bcache/util.h:219:27: note: expanded from macro 'fifo_pop' >>>> #define fifo_pop(fifo, i) fifo_pop_front(fifo, (i)) >>>> ^~~~~~~~~~~~~~~~~~~~~~~~~ >>>> drivers/md/bcache/util.h:189:6: note: expanded from macro 'fifo_pop_front' >>>> if (_r) { \ >>>> ^~ >>>> drivers/md/bcache/alloc.c:343:46: note: uninitialized use occurs here >>>> allocator_wait(ca, bch_allocator_push(ca, bucket)); >>>> ^~~~~~ >>>> drivers/md/bcache/alloc.c:287:7: note: expanded from macro 'allocator_wait' >>>> if (cond) \ >>>> ^~~~ >>>> drivers/md/bcache/alloc.c:333:4: note: remove the 'if' if its condition is always true >>>> fifo_pop(&ca->free_inc, bucket); >>>> ^ >>>> drivers/md/bcache/util.h:219:27: note: expanded from macro 'fifo_pop' >>>> #define fifo_pop(fifo, i) fifo_pop_front(fifo, (i)) >>>> ^ >>>> drivers/md/bcache/util.h:189:2: note: expanded from macro 'fifo_pop_front' >>>> if (_r) { \ >>>> ^ >>>> drivers/md/bcache/alloc.c:331:15: note: initialize the variable 'bucket' to silence this warning >>>> long bucket; >>>> ^ >>>> >>>> This cannot happen in practice because we only enter the loop >>>> if there is at least one element in the list. >>>> >>>> Slightly rearranging the code makes this clearer to both the >>>> reader and the compiler, which avoids the warning. >>>> >>>> Signed-off-by: Arnd Bergmann >>>> --- >>>> drivers/md/bcache/alloc.c | 5 +++-- >>>> 1 file changed, 3 insertions(+), 2 deletions(-) >>>> >>>> diff --git a/drivers/md/bcache/alloc.c b/drivers/md/bcache/alloc.c >>>> index 5002838ea476..f8986effcb50 100644 >>>> --- a/drivers/md/bcache/alloc.c >>>> +++ b/drivers/md/bcache/alloc.c >>>> @@ -327,10 +327,11 @@ static int bch_allocator_thread(void *arg) >>>> * possibly issue discards to them, then we add the bucket to >>>> * the free list: >>>> */ >>>> - while (!fifo_empty(&ca->free_inc)) { >>>> + while (1) { >>>> long bucket; >>>> >>>> - fifo_pop(&ca->free_inc, bucket); >>>> + if (!fifo_pop(&ca->free_inc, bucket)) >>>> + break; >>>> >>>> if (ca->discard) { >>>> mutex_unlock(&ca->set->bucket_lock); >>>> -- >>>> 2.20.0 >>>> >>> >>> Hi all, >>> >>> Could someone please review/pick this up? This is one of two remaining >>> -Wsometimes-uninitialized warnings among arm, arm64, and x86_64 >>> all{yes,mod}config and I'd like to get it turned on as soon as possible >>> to catch more bugs. >> >> Hi Nathan, >> >> It is in Jens' block tree for-next branch already, for Linux v5.2 merge >> window. >> >> Thanks. >> >> -- >> >> Coly Li > > Hi Coly, > > Thank you for the reply and heads up, it hadn't hit -next when I sent > that message and I didn't check Jens' tree. > > I appreciate you picking it up! Hi Nathan, You are welcome, and thanks for the contribution to make bcache better :-) -- Coly Li