From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-ej1-f67.google.com (mail-ej1-f67.google.com [209.85.218.67]) by mx.groups.io with SMTP id smtpd.web12.16252.1601368939977650648 for ; Tue, 29 Sep 2020 01:42:20 -0700 Authentication-Results: mx.groups.io; dkim=pass header.i=@gmail.com header.s=20161025 header.b=C9E4mLgN; spf=pass (domain: gmail.com, ip: 209.85.218.67, mailfrom: lukas.bulwahn@gmail.com) Received: by mail-ej1-f67.google.com with SMTP id j11so13874489ejk.0 for ; Tue, 29 Sep 2020 01:42:19 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:date:to:cc:subject:in-reply-to:message-id:references :user-agent:mime-version; bh=lMOqo3ypO/SZ3oHUy6euRnuasGkm67DC6ZbiwUFwB8M=; b=C9E4mLgNTPQm8NqaAoz6itH7ufzLLW2Afp390W5SRJ4Rdbl7etn2wAbpam4yITVwLD F6FwrUs08Nvzo3Mfl42l34qKUnxrHpNoeI4tuU4Rh5fdZSfPxUztwLF3B8mRIf+EFyTV Bw1kXUFQm0WiVqzUhAXpob85WyYHYrBekAyw4cYZeVFKbNMVv3Lb2xSuVqe13M3RxfjP KdrELuR5PtKXB6MbMdbyIvZpTiEB14c8DNlnX3V1U7sPu/om8bscAIW+QwD0756G5JJb 3SL0nmILrDsE4MXwsMmLjKYUtJWrj6PUmyZB5LLwrM1DZ4kB+fPrk7jWxb/T3ePyRn8t njcQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:date:to:cc:subject:in-reply-to:message-id :references:user-agent:mime-version; bh=lMOqo3ypO/SZ3oHUy6euRnuasGkm67DC6ZbiwUFwB8M=; b=d0L8AmJSoz2WnWoSR3AcL23LbRCxEX7IA+CWHvaf1uO/tik2RSOi7DcFzrrqV9nz/D pwD9PW582jWSLdo4yYKbUV95D/LAVo6w7t3iuBnWPe4A6R+LPoN3vkEpkORQur9TxtZv Vc37HSNFVFwgeMcAgv0h9X0Hx0CrvV8wE/7h/6ZUS6lpO+LsuHpygkoob5rbizEqTtOR kLjUspDcoOu0D+GbP6sh2CK1+FFb5IHlNu0Ank7u7DPS+qU4BSBsAw3PM1qWQoU+KiSF 6YUosTkozKROxJq8IWjr2qKr+aXbxD1d8h2KKOYVSSvWlxF9SgKnnZwzXbVGyp7guEkU 1Lyw== X-Gm-Message-State: AOAM530sJ1iutelOI5ppkXF+eNTo+v5A5oX5+mhasfFt/ROrhIFLoSuu 1UqYD4V+Zg2520g26kRsYSk= X-Google-Smtp-Source: ABdhPJzGWfoP9r1EYK/PGbfUWz5nDplWzfMQE+vmcmMJK3RNsVSeyNcSHA23E0BLUDmcdQqqkuVHYg== X-Received: by 2002:a17:906:f755:: with SMTP id jp21mr326002ejb.97.1601368938287; Tue, 29 Sep 2020 01:42:18 -0700 (PDT) Return-Path: Received: from felia ([2001:16b8:2d89:9100:6c4a:28e4:c658:86f9]) by smtp.gmail.com with ESMTPSA id u9sm4528036eje.119.2020.09.29.01.42.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 29 Sep 2020 01:42:17 -0700 (PDT) From: "Lukas Bulwahn" X-Google-Original-From: Lukas Bulwahn Date: Tue, 29 Sep 2020 10:42:15 +0200 (CEST) X-X-Sender: lukas@felia To: Dave Hansen cc: Lukas Bulwahn , Dave Hansen , Andy Lutomirski , Peter Zijlstra , Thomas Gleixner , Ingo Molnar , Borislav Petkov , x86@kernel.org, "H. Peter Anvin" , Nathan Chancellor , Nick Desaulniers , linux-kernel@vger.kernel.org, clang-built-linux@googlegroups.com, kernel-janitors@vger.kernel.org, linux-safety@lists.elisa.tech Subject: Re: [PATCH] x86/mm: drop superfluous initialization In-Reply-To: <1d376c1f-2f14-5c29-671e-ca59853fa4a4@intel.com> Message-ID: References: <20200928100004.25674-1-lukas.bulwahn@gmail.com> <1d376c1f-2f14-5c29-671e-ca59853fa4a4@intel.com> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII On Mon, 28 Sep 2020, Dave Hansen wrote: > On 9/28/20 3:00 AM, Lukas Bulwahn wrote: > > diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c > > index c7a47603537f..5632f02146ca 100644 > > --- a/arch/x86/mm/init.c > > +++ b/arch/x86/mm/init.c > > @@ -609,7 +609,7 @@ static void __init memory_map_top_down(unsigned long map_start, > > step_size = PMD_SIZE; > > max_pfn_mapped = 0; /* will get exact value next */ > > min_pfn_mapped = real_end >> PAGE_SHIFT; > > - last_start = start = real_end; > > + last_start = real_end; > > Thanks for finding this. > > This becomes even more obviously correct if we just move the 'start' > declaration into the while() loop. If we do that, it puts the three > assignment locations right next to the definition, and its trivial to > spot that the initialization was not missed: > > while (last_start > map_start) { > unsigned long start; > > if (last_start > step_size) { > start = round_down(last_start - 1, step_size); > if (start < map_start) > start = map_start; > } else > start = map_start; > ... > Agree, this point is simply a question of style: Shall local variables be defined as "local" as possible or simply consistently at the beginning of each function? If there are no strong opinions of style, I would just keep this patch as-is. > Either way, your patch looks correct to me: > > Acked-by: Dave Hansen > Thanks for the Ack. Lukas