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=-14.0 required=3.0 tests=BAYES_00,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 BA637C43603 for ; Mon, 17 May 2021 14:48:48 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9E6F560C41 for ; Mon, 17 May 2021 14:48:48 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241992AbhEQOt1 (ORCPT ); Mon, 17 May 2021 10:49:27 -0400 Received: from mail-il1-f178.google.com ([209.85.166.178]:34759 "EHLO mail-il1-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239534AbhEQOkk (ORCPT ); Mon, 17 May 2021 10:40:40 -0400 Received: by mail-il1-f178.google.com with SMTP id c16so6311491ilo.1 for ; Mon, 17 May 2021 07:39:23 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=jH0fCm6/ssgqTQFTtYAxRzZAnMgRul40cu4aOLtnS2s=; b=UKZLohwHmqWAw1tZjA+KYAX6m9EBndA62UT92/8NM5MD0isXR2WVpmTIgezqxrNtar tiTVZGiRP+8rF681iakwJ5jq10DeFMVSKhcvpXqeQNeKQ8lGJH4DVvzVvPuvHF28vn1h aDgj8JWe8IHJZ1reAFAnNbub6VDiB9AbCRZBe6VlE37Bi/Q+XVSyuORX9ba2vNtuuq0r EVgdu1qn6dl5z/ld0FJF38O43p3cWECIRHGaAnpz6FAjlW2+Skb1MKQCANiXdnlYySfU 8s0i6S3JEuZsTBT2tq8FWutUPvASWOvLm+SygMplE4vX7WAdPXokR3qZuXxwH2PMOkZH P8dg== X-Gm-Message-State: AOAM5308kL5nZg1lchbomuYhRShYktVaqlCLi6gR2U1jNlzNKqPViPMw E3xaeuAu+84yE2VQziZberU= X-Google-Smtp-Source: ABdhPJycdz0JtI1u2VVpJ/hbQoX+Bdowg/jnuMQPSv/KFHO5P0NxYLYnt+QC2OC5JOsMPJu3bdR/ZQ== X-Received: by 2002:a05:6e02:1a0c:: with SMTP id s12mr6006ild.201.1621262363435; Mon, 17 May 2021 07:39:23 -0700 (PDT) Received: from google.com (243.199.238.35.bc.googleusercontent.com. [35.238.199.243]) by smtp.gmail.com with ESMTPSA id u18sm1112124ilj.20.2021.05.17.07.39.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 May 2021 07:39:22 -0700 (PDT) Date: Mon, 17 May 2021 14:39:21 +0000 From: Dennis Zhou To: Tom Rix Cc: tj@kernel.org, cl@linux.com, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] percpu: initialize best_upa variable Message-ID: References: <20210515180817.1751084-1-trix@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 17, 2021 at 06:17:47AM -0700, Tom Rix wrote: > > On 5/16/21 7:05 PM, Dennis Zhou wrote: > > Hello, > > > > On Sat, May 15, 2021 at 11:08:17AM -0700, trix@redhat.com wrote: > > > From: Tom Rix > > > > > > Static analysis reports this problem > > > percpu.c:2945:6: warning: Assigned value is garbage or undefined > > > upa = best_upa; > > > ^ ~~~~~~~~ > > > best_upa may not be set, so initialize it. > > > > > > Signed-off-by: Tom Rix > > > --- > > > mm/percpu.c | 1 + > > > 1 file changed, 1 insertion(+) > > > > > > diff --git a/mm/percpu.c b/mm/percpu.c > > > index a257c3efdf18b..6578b706fae81 100644 > > > --- a/mm/percpu.c > > > +++ b/mm/percpu.c > > > @@ -2916,6 +2916,7 @@ static struct pcpu_alloc_info * __init __flatten pcpu_build_alloc_info( > > > * Related to atom_size, which could be much larger than the unit_size. > > > */ > > > last_allocs = INT_MAX; > > > + best_upa = max_upa; > > > for (upa = max_upa; upa; upa--) { > > > int allocs = 0, wasted = 0; > > > -- > > > 2.26.3 > > > > > I think the proper fix would be: > > > > best_upa = 0; > > I was looking for initializing with something that would work. > I think I prefer setting it to 0 because it forces the loop to have succeeded vs being able to bypass it if the for loop logic was changed. > > for (...) { } > > BUG_ON(!best_upa); > WARN_ON instead? This is initialization code. So if upa == 0, it really is a problem. Having 0 units per allocation is bogus. > > upa = best_upa; > > > > If you're fine with this I'll make the changes and apply it to > > for-5.13-fixes. > > > > Can you also tell me what static analysis tool produced this? I'm just a > > little curious because this code hasn't changed in several years so I'd > > have expected some static analyzer to have caught this by now. > > Clang 10 > > Tom > Thanks, Dennis