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=-5.5 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 7883EC4346E for ; Fri, 25 Sep 2020 02:34:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3E24320BED for ; Fri, 25 Sep 2020 02:34:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726818AbgIYCeM (ORCPT ); Thu, 24 Sep 2020 22:34:12 -0400 Received: from mail-pf1-f194.google.com ([209.85.210.194]:42480 "EHLO mail-pf1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726448AbgIYCeM (ORCPT ); Thu, 24 Sep 2020 22:34:12 -0400 Received: by mail-pf1-f194.google.com with SMTP id d6so1727205pfn.9; Thu, 24 Sep 2020 19:34:11 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:cc:references:from:autocrypt :message-id:date:user-agent:mime-version:in-reply-to :content-language:content-transfer-encoding; bh=LrhMniYN89vNM15l1Ybxlbhe9ls/Xhv7pWfUsWlH+P0=; b=AMlILOoWaY2KNI2wnHubTHT1vu6EqE6weSL8TZr9cEV8kr2kgKn8C3hO48aKaEtIpF UH949xC8JSuoJggPbJ5tG50zDRJFoJGQa6ZC5HUA6u29MYc8cZSoteNH9XDUbTwrMyJn b93gR15zJMSO+YL4o4USvangiOEU+B7ghtTr28RTyfZ54k2hlNvJH+CREj2HYOaRE+i2 Sd66KBzjg0HBldi0tS4HsPTc7oOi9rlHsn2Fnt13uHWEMRWEdLsr2xn/HKkpavEy9Fkn 89yOirUecWy5eqTSVWwTG8bkkIKvjPhC5SGRB6w2d5omFMF/k5wTq3DH2Iw0Q0mqMF47 6tNg== X-Gm-Message-State: AOAM530HVAum7z+UzqtBlJihszj0KgY7Y3icP9Z7SVjbaVJkIlxHq0pQ jXKcBXim4r85+SOmfjhePUEmLyqnTuM= X-Google-Smtp-Source: ABdhPJyoaIVJxw4gUpuZ8c8/aQO3LSBwKYrA4yPBV99yUCk19XBovEnWGmhyLNc8feEit7hjh+hljw== X-Received: by 2002:a17:902:7484:b029:d1:dea3:a490 with SMTP id h4-20020a1709027484b02900d1dea3a490mr2115132pll.30.1601001250960; Thu, 24 Sep 2020 19:34:10 -0700 (PDT) Received: from ?IPv6:2601:647:4000:d7:755a:78b:43e0:7557? ([2601:647:4000:d7:755a:78b:43e0:7557]) by smtp.gmail.com with ESMTPSA id 1sm590573pgm.4.2020.09.24.19.34.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Thu, 24 Sep 2020 19:34:10 -0700 (PDT) Subject: Re: lib/scatterlist.c : sgl_alloc_order promises more than it delivers To: dgilbert@interlog.com, SCSI development list , "linux-block@vger.kernel.org" Cc: "Martin K. Petersen" , USB list References: From: Bart Van Assche Autocrypt: addr=bvanassche@acm.org; prefer-encrypt=mutual; keydata= mQENBFSOu4oBCADcRWxVUvkkvRmmwTwIjIJvZOu6wNm+dz5AF4z0FHW2KNZL3oheO3P8UZWr LQOrCfRcK8e/sIs2Y2D3Lg/SL7qqbMehGEYcJptu6mKkywBfoYbtBkVoJ/jQsi2H0vBiiCOy fmxMHIPcYxaJdXxrOG2UO4B60Y/BzE6OrPDT44w4cZA9DH5xialliWU447Bts8TJNa3lZKS1 AvW1ZklbvJfAJJAwzDih35LxU2fcWbmhPa7EO2DCv/LM1B10GBB/oQB5kvlq4aA2PSIWkqz4 3SI5kCPSsygD6wKnbRsvNn2mIACva6VHdm62A7xel5dJRfpQjXj2snd1F/YNoNc66UUTABEB AAG0JEJhcnQgVmFuIEFzc2NoZSA8YnZhbmFzc2NoZUBhY20ub3JnPokBOQQTAQIAIwUCVI67 igIbAwcLCQgHAwIBBhUIAgkKCwQWAgMBAh4BAheAAAoJEHFcPTXFzhAJ8QkH/1AdXblKL65M Y1Zk1bYKnkAb4a98LxCPm/pJBilvci6boefwlBDZ2NZuuYWYgyrehMB5H+q+Kq4P0IBbTqTa jTPAANn62A6jwJ0FnCn6YaM9TZQjM1F7LoDX3v+oAkaoXuq0dQ4hnxQNu792bi6QyVdZUvKc macVFVgfK9n04mL7RzjO3f+X4midKt/s+G+IPr4DGlrq+WH27eDbpUR3aYRk8EgbgGKvQFdD CEBFJi+5ZKOArmJVBSk21RHDpqyz6Vit3rjep7c1SN8s7NhVi9cjkKmMDM7KYhXkWc10lKx2 RTkFI30rkDm4U+JpdAd2+tP3tjGf9AyGGinpzE2XY1K5AQ0EVI67igEIAKiSyd0nECrgz+H5 PcFDGYQpGDMTl8MOPCKw/F3diXPuj2eql4xSbAdbUCJzk2ETif5s3twT2ER8cUTEVOaCEUY3 eOiaFgQ+nGLx4BXqqGewikPJCe+UBjFnH1m2/IFn4T9jPZkV8xlkKmDUqMK5EV9n3eQLkn5g lco+FepTtmbkSCCjd91EfThVbNYpVQ5ZjdBCXN66CKyJDMJ85HVr5rmXG/nqriTh6cv1l1Js T7AFvvPjUPknS6d+BETMhTkbGzoyS+sywEsQAgA+BMCxBH4LvUmHYhpS+W6CiZ3ZMxjO8Hgc ++w1mLeRUvda3i4/U8wDT3SWuHcB3DWlcppECLkAEQEAAYkBHwQYAQIACQUCVI67igIbDAAK CRBxXD01xc4QCZ4dB/0QrnEasxjM0PGeXK5hcZMT9Eo998alUfn5XU0RQDYdwp6/kMEXMdmT oH0F0xB3SQ8WVSXA9rrc4EBvZruWQ+5/zjVrhhfUAx12CzL4oQ9Ro2k45daYaonKTANYG22y //x8dLe2Fv1By4SKGhmzwH87uXxbTJAUxiWIi1np0z3/RDnoVyfmfbbL1DY7zf2hYXLLzsJR mSsED/1nlJ9Oq5fALdNEPgDyPUerqHxcmIub+pF0AzJoYHK5punqpqfGmqPbjxrJLPJfHVKy goMj5DlBMoYqEgpbwdUYkH6QdizJJCur4icy8GUNbisFYABeoJ91pnD4IGei3MTdvINSZI5e Message-ID: Date: Thu, 24 Sep 2020 19:34:08 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 2020-09-24 18:46, Douglas Gilbert wrote: >         /* Check for integer overflow */ >         if (length > (nent << (PAGE_SHIFT + order))) >                 return NULL; > > Well _integers_ don't wrap, but that pedantic point aside, 'nent' is an > unsigned int which means the rhs expression cannot represent 2^32 or > higher. So if length >= 2^32 the function fails (i.e. returns NULL). > > On 8 GiB and 16 GiB machines I can easily build 6 or 12 GiB sgl_s (with > scsi_debug) but only if no single allocation is >= 4 GiB due to the > above check. > > So is the above check intended to do that or is it a bug? The above check verifies that nent << (PAGE_SHIFT + order) == (uint64_t)nent << (PAGE_SHIFT + order). So I think it does what the comment says it does. Bart.