From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755350AbcI2L3p (ORCPT ); Thu, 29 Sep 2016 07:29:45 -0400 Received: from sender153-mail.zoho.com ([74.201.84.153]:25320 "EHLO sender153-mail.zoho.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754986AbcI2L32 (ORCPT ); Thu, 29 Sep 2016 07:29:28 -0400 DomainKey-Signature: a=rsa-sha1; q=dns; c=nofws; s=zapps768; d=zoho.com; h=subject:to:references:cc:from:message-id:date:user-agent:mime-version:in-reply-to:content-type; b=F973Qq1o1wDgc5exSwozu/0l//5QY5rjmYNjjcLAkf3UP1MjzKr/uOCECK1YdRdMN39XtguSjdYN 4byZ9nw5nqvUS2Z4DRYMt8v0eAh9o1Fh5tM+c1/tpkPXgy/ZiHev Subject: Re: [RESEND PATCH 1/1] mm/percpu.c: correct max_distance calculation for pcpu_embed_first_chunk() To: Tejun Heo References: <7180d3c9-45d3-ffd2-cf8c-0d925f888a4d@zoho.com> <0310bf92-c8da-459f-58e3-40b8bfbb7223@zoho.com> <20160929103507.GA25170@mtj.duckdns.org> Cc: zijun_hu@htc.com, Andrew Morton , "linux-kernel@vger.kernel.org" , linux-mm@kvack.org, cl@linux.com From: zijun_hu Message-ID: Date: Thu, 29 Sep 2016 19:29:12 +0800 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.3.0 MIME-Version: 1.0 In-Reply-To: <20160929103507.GA25170@mtj.duckdns.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2016/9/29 18:35, Tejun Heo wrote: > Hello, > > On Sat, Sep 24, 2016 at 07:20:49AM +0800, zijun_hu wrote: >> it is error to represent the max range max_distance spanned by all the >> group areas as the offset of the highest group area plus unit size in >> pcpu_embed_first_chunk(), it should equal to the offset plus the size >> of the highest group area >> >> in order to fix this issue,let us find the highest group area who has the >> biggest base address among all the ones, then max_distance is formed by >> add it's offset and size value > > [PATCH] percpu: fix max_distance calculation in pcpu_embed_first_chunk() > > pcpu_embed_first_chunk() calculates the range a percpu chunk spans > into max_distance and uses it to ensure that a chunk is not too big > compared to the total vmalloc area. However, during calculation, it > used incorrect top address by adding a unit size to the higest > group's base address. > > This can make the calculated max_distance slightly smaller than the > actual distance although given the scale of values involved the error > is very unlikely to have an actual impact. > > Fix this issue by adding the group's size instead of a unit size. > >> the type of variant max_distance is changed from size_t to unsigned long >> to prevent potential overflow > > This doesn't make any sense. All the values involved are valid > addresses (or +1 of it), they can't overflow and size_t is the same > size as ulong. > >> @@ -2025,17 +2026,18 @@ int __init pcpu_embed_first_chunk(size_t reserved_size, size_t dyn_size, >> } >> >> /* base address is now known, determine group base offsets */ >> - max_distance = 0; >> + i = 0; >> for (group = 0; group < ai->nr_groups; group++) { >> ai->groups[group].base_offset = areas[group] - base; >> - max_distance = max_t(size_t, max_distance, >> - ai->groups[group].base_offset); >> + if (areas[group] > areas[i]) >> + i = group; >> } >> - max_distance += ai->unit_size; >> + max_distance = ai->groups[i].base_offset + >> + (unsigned long)ai->unit_size * ai->groups[i].nr_units; > > I don't think you need ulong cast here. > > Thanks. > okay, thanks for your reply i will correct this in another patch