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=-2.2 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,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 CEA07C432C0 for ; Tue, 3 Dec 2019 21:03:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 9712320640 for ; Tue, 3 Dec 2019 21:03:50 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=kernel-dk.20150623.gappssmtp.com header.i=@kernel-dk.20150623.gappssmtp.com header.b="bjMRZrmx" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727508AbfLCVDu (ORCPT ); Tue, 3 Dec 2019 16:03:50 -0500 Received: from mail-il1-f196.google.com ([209.85.166.196]:32796 "EHLO mail-il1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727614AbfLCVDt (ORCPT ); Tue, 3 Dec 2019 16:03:49 -0500 Received: by mail-il1-f196.google.com with SMTP id r81so4571144ilk.0 for ; Tue, 03 Dec 2019 13:03:49 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel-dk.20150623.gappssmtp.com; s=20150623; h=subject:to:cc:references:from:message-id:date:user-agent :mime-version:in-reply-to:content-language:content-transfer-encoding; bh=sFn+q5M4OQGy2hAfzIasEpnp/G/IQ19ZE4PBt4z+hKs=; b=bjMRZrmxdnENLVxHQwgxiuGhs/pIOOCI7RPVi2IMk3lwgTI7aNB9AryFTQFJ6N34Zz znaAPt4pAIhJrr9eVmUHVToYCNxheTmgPByX99LYCSyVMAjJEY/6aWBIurQG20+1KE2p B7Xx7tBoXqf5elHivpFxXrpx4F+ZdXzRwgJntZCgFBhUIp+3zU9jA7Kkfwf5ndxxUYIF vegXLjcgvhs/y083uQx2obugP2D9bv+dEvcAIvjPPJkew84MoNsU4x0d1yfbOK0T00eX t7g3EDZUcj29+n0c7bK3y+ZSqCCnnlF8cPzoVC2tHqeAUYF8OaAC3w0H9ET1FuwRzPg/ /qqg== 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:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=sFn+q5M4OQGy2hAfzIasEpnp/G/IQ19ZE4PBt4z+hKs=; b=HpwfF8TwssDrea/PTWxwbhQzQXhiD8CWJiwqoeBgywinXML3h8ajaRpiVhQIG3w1md V4G5w41vWIqdhBq2xjZcp65P3CB0nu/wbFq+8xlBwAU5e34pqPRKGmKqJMz0YhKAUd2K HqcwiD394qbYGPYFMGc39dxM9jaWvpx/6AQDIRew6qY4bptbUfrl2RtokbG7ZInS5Gmc ghtaWVUMLNTndvF7DPxY/LSgzoHDNzAc/WKiWsc0WJWQW8SnDJ7kn5QsROvjGd4yQ+1X GkDw1CrXSy5kTbMWmthxnv+7CchhcSrsb+kFHOAREpLT1sZ2NkNOREJILiLC4gsylYzf wv/A== X-Gm-Message-State: APjAAAVdTz5c/CMMbDg3vlaJ+dZDYyXTLVL2l7Lc3MOMpcaBDwMXr/kk Tljh31S0oVAZS9tipBrEnNqtpg== X-Google-Smtp-Source: APXvYqynb9y1GtIc2v9Jt2I8gQfLy2oB0u+TVZ+0gIHqiiCdzgQ3Kw9UoB/KAiRWf5JLsPyTkN/pBA== X-Received: by 2002:a92:d282:: with SMTP id p2mr134806ilp.73.1575407028959; Tue, 03 Dec 2019 13:03:48 -0800 (PST) Received: from [192.168.1.159] ([65.144.74.34]) by smtp.gmail.com with ESMTPSA id a81sm1136094ill.31.2019.12.03.13.03.47 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 03 Dec 2019 13:03:48 -0800 (PST) Subject: Re: [PATCH] xen/blkback: Avoid unmapping unmapped grant pages To: SeongJae Park , konrad.wilk@oracle.com, roger.pau@citrix.com Cc: xen-devel@lists.xenproject.org, linux-block@vger.kernel.org, linux-kernel@vger.kernel.org, SeongJae Park References: <20191126153605.27564-1-sjpark@amazon.com> From: Jens Axboe Message-ID: <43f9881b-4a88-47e9-c321-19033a2bc872@kernel.dk> Date: Tue, 3 Dec 2019 14:03:46 -0700 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.2.1 MIME-Version: 1.0 In-Reply-To: <20191126153605.27564-1-sjpark@amazon.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 11/26/19 8:36 AM, SeongJae Park wrote: > From: SeongJae Park > > For each I/O request, blkback first maps the foreign pages for the > request to its local pages. If an allocation of a local page for the > mapping fails, it should unmap every mapping already made for the > request. > > However, blkback's handling mechanism for the allocation failure does > not mark the remaining foreign pages as unmapped. Therefore, the unmap > function merely tries to unmap every valid grant page for the request, > including the pages not mapped due to the allocation failure. On a > system that fails the allocation frequently, this problem leads to > following kernel crash. > > [ 372.012538] BUG: unable to handle kernel NULL pointer dereference at 0000000000000001 > [ 372.012546] IP: [] gnttab_unmap_refs.part.7+0x1c/0x40 > [ 372.012557] PGD 16f3e9067 PUD 16426e067 PMD 0 > [ 372.012562] Oops: 0002 [#1] SMP > [ 372.012566] Modules linked in: act_police sch_ingress cls_u32 > ... > [ 372.012746] Call Trace: > [ 372.012752] [] gnttab_unmap_refs+0x34/0x40 > [ 372.012759] [] xen_blkbk_unmap+0x83/0x150 [xen_blkback] > ... > [ 372.012802] [] dispatch_rw_block_io+0x970/0x980 [xen_blkback] > ... > Decompressing Linux... Parsing ELF... done. > Booting the kernel. > [ 0.000000] Initializing cgroup subsys cpuset > > This commit fixes this problem by marking the grant pages of the given > request that didn't mapped due to the allocation failure as invalid. > > Fixes: c6cc142dac52 ("xen-blkback: use balloon pages for all mappings") Queued up with Roger's reviewed-by. -- Jens Axboe