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,URIBL_BLOCKED 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 E8AE0C43219 for ; Fri, 26 Apr 2019 02:43:17 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D29492084F for ; Fri, 26 Apr 2019 02:43:17 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729561AbfDZCnQ (ORCPT ); Thu, 25 Apr 2019 22:43:16 -0400 Received: from mx2.suse.de ([195.135.220.15]:49630 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1728700AbfDZCnQ (ORCPT ); Thu, 25 Apr 2019 22:43:16 -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 BEEFCAFEA; Fri, 26 Apr 2019 02:43:13 +0000 (UTC) Subject: Re: [PATCH] bcache: avoid clang -Wunintialized warning To: Nathan Chancellor , Arnd Bergmann Cc: 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> From: Coly Li Openpgp: preference=signencrypt Organization: SUSE Labs Message-ID: <44474338-8031-13eb-1e95-376c1036b611@suse.de> Date: Fri, 26 Apr 2019 10:43:01 +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: <20190425180853.GA4507@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 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