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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 59622C10F03 for ; Fri, 22 Mar 2019 16:10:37 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 172F8218A2 for ; Fri, 22 Mar 2019 16:10:36 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 172F8218A2 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id CE3406B0003; Fri, 22 Mar 2019 12:10:35 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id CB9416B0006; Fri, 22 Mar 2019 12:10:35 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B5B886B0007; Fri, 22 Mar 2019 12:10:35 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from mail-qt1-f197.google.com (mail-qt1-f197.google.com [209.85.160.197]) by kanga.kvack.org (Postfix) with ESMTP id 93F776B0003 for ; Fri, 22 Mar 2019 12:10:35 -0400 (EDT) Received: by mail-qt1-f197.google.com with SMTP id q21so2748307qtf.10 for ; Fri, 22 Mar 2019 09:10:35 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-original-authentication-results:x-gm-message-state:subject:to:cc :references:from:openpgp:autocrypt:organization:message-id:date :user-agent:mime-version:in-reply-to:content-transfer-encoding :content-language; bh=DYZRW1HbMw0mjSRErQnXpeaeAikC5qL3028WMKtAUaQ=; b=A59TmUAlzduTqvQgcHsxqTGLYYugBH3xPkoxs1BgYCxceBfKYC9kJoj0JMQtVz3PoE ZozoIFWeuz1ApSrD7dvJryvbjF8s3GaA+FGuI6OW4nDnn05z0AN+fhnqpPULiJ0ZZozD 8KUQCjKEmdyqR7maBv7vvRkp0RS4/INFLQ1GcIhcIc+ZBuafHeH1k7fDap6UJ0r6BZa8 QrTz/R/HVOgjPVwbK+qzjj1a76TZFzILJccY9mqp8eMXlOeWIN7HhBEWyZ2C7HdQvGSf XSBVwLdrIxRXqTGbsD3+sgrOWplLfbwF13/EIzO+n1QDMRNaJS7DC3T3O3rrLwbhHu7h yXkw== X-Original-Authentication-Results: mx.google.com; spf=pass (google.com: domain of longman@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=longman@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com X-Gm-Message-State: APjAAAWnVH4dOYuXUfWZU2CpKiYLH3O6s8x4n9znEoj7QhsYcOrd9MuG LCB7av0L48BfuJLbbwDG4ut8QZc1jUVvxSQN8yo6+0r+fvE5HNwUM+KQoQPxrkvMbg2tsZ83R49 1f9ITNyUDcoujELluf0LUNkDcNCJXMy9gPagRsacqi1tZuUfPrh+xU/ALKDxczUGQJQ== X-Received: by 2002:ac8:27a6:: with SMTP id w35mr8691078qtw.157.1553271035305; Fri, 22 Mar 2019 09:10:35 -0700 (PDT) X-Google-Smtp-Source: APXvYqySHloNa1oS+Lr3U/k3rAMzCoosS5D2uEGymiZ9al5Hj4kgrWbf9d2lSrOIu1zbeLjG7LYR X-Received: by 2002:ac8:27a6:: with SMTP id w35mr8691002qtw.157.1553271034506; Fri, 22 Mar 2019 09:10:34 -0700 (PDT) ARC-Seal: i=1; a=rsa-sha256; t=1553271034; cv=none; d=google.com; s=arc-20160816; b=X0dvmsxWzEcd7G8WdjSXdh0h6DMsummJ1cFegmJeN5Z0rTlHMSe4Yre5ekfuEUzean VK2D9tvRrEqIC4poeEustJ+/PETxG8xY5XflCo2HTTtxec1SLtLwcjYqCl8RMsfwVViv ZPrE88EKUVxWwdfzdXQNND2j/KwnP5kYEhowSxZxSyZ6/XX5aiPVGtewY8VmSN0XQbhL Hrb8sgmZb8CigM/5C+D4v962upAvil3Aqo50AO/yDz/DAKheR14LW4foZYRc7tbbzNoy 08kjFy8sLNy4EmVvn8FqiBr7F0HubtUu24WHvQBaMFHCPES1Ve+uADrbNC9ewW/UjO2x /1Cg== ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=arc-20160816; h=content-language:content-transfer-encoding:in-reply-to:mime-version :user-agent:date:message-id:organization:autocrypt:openpgp:from :references:cc:to:subject; bh=DYZRW1HbMw0mjSRErQnXpeaeAikC5qL3028WMKtAUaQ=; b=ZnLVq6RnebxLZHGtAuu89/XkoAt4OSZQwzXauAvoeRpZfy5iNqT40ldim+7Phdz9GQ o3IFd3V+i2/GsRk3t0Z68M32cITUKUJZU87679BpxF3QHWzmI7ZaEseA4kdDicRBmdx0 xKAVw7eIMvS10ljEqbiDXZus8TI4ax4gxp9AihmTgFuKcO2m3UECKxJaPe5KtB0eyao/ 4RLO1aQ3GqKHS5+XnjOAWHuKaTuLwSjfYIbRVFsPeZuKM9o6AhKa7CWdCaTFElFoq5pR aVDWfUXsjaKJvMfr4pFv99PIpg0GwZwA27jAKp68PRfUB+NIot5DBWRwH9+yb/UusbdK m0Dw== ARC-Authentication-Results: i=1; mx.google.com; spf=pass (google.com: domain of longman@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=longman@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from mx1.redhat.com (mx1.redhat.com. [209.132.183.28]) by mx.google.com with ESMTPS id u17si1983252qvm.77.2019.03.22.09.10.34 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 22 Mar 2019 09:10:34 -0700 (PDT) Received-SPF: pass (google.com: domain of longman@redhat.com designates 209.132.183.28 as permitted sender) client-ip=209.132.183.28; Authentication-Results: mx.google.com; spf=pass (google.com: domain of longman@redhat.com designates 209.132.183.28 as permitted sender) smtp.mailfrom=longman@redhat.com; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=redhat.com Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id E82F38666D; Fri, 22 Mar 2019 16:10:32 +0000 (UTC) Received: from llong.remote.csb (dhcp-17-47.bos.redhat.com [10.18.17.47]) by smtp.corp.redhat.com (Postfix) with ESMTP id 472915C579; Fri, 22 Mar 2019 16:10:28 +0000 (UTC) Subject: Re: [PATCH 2/4] signal: Make flush_sigqueue() use free_q to release memory To: Oleg Nesterov , Matthew Wilcox Cc: Andrew Morton , Christoph Lameter , Pekka Enberg , David Rientjes , Joonsoo Kim , linux-kernel@vger.kernel.org, linux-mm@kvack.org, selinux@vger.kernel.org, Paul Moore , Stephen Smalley , Eric Paris , "Peter Zijlstra (Intel)" References: <20190321214512.11524-1-longman@redhat.com> <20190321214512.11524-3-longman@redhat.com> <20190322015208.GD19508@bombadil.infradead.org> <20190322111642.GA28876@redhat.com> From: Waiman Long Openpgp: preference=signencrypt Autocrypt: addr=longman@redhat.com; prefer-encrypt=mutual; keydata= xsFNBFgsZGsBEAC3l/RVYISY3M0SznCZOv8aWc/bsAgif1H8h0WPDrHnwt1jfFTB26EzhRea XQKAJiZbjnTotxXq1JVaWxJcNJL7crruYeFdv7WUJqJzFgHnNM/upZuGsDIJHyqBHWK5X9ZO jRyfqV/i3Ll7VIZobcRLbTfEJgyLTAHn2Ipcpt8mRg2cck2sC9+RMi45Epweu7pKjfrF8JUY r71uif2ThpN8vGpn+FKbERFt4hW2dV/3awVckxxHXNrQYIB3I/G6mUdEZ9yrVrAfLw5M3fVU CRnC6fbroC6/ztD40lyTQWbCqGERVEwHFYYoxrcGa8AzMXN9CN7bleHmKZrGxDFWbg4877zX 0YaLRypme4K0ULbnNVRQcSZ9UalTvAzjpyWnlnXCLnFjzhV7qsjozloLTkZjyHimSc3yllH7 VvP/lGHnqUk7xDymgRHNNn0wWPuOpR97J/r7V1mSMZlni/FVTQTRu87aQRYu3nKhcNJ47TGY evz/U0ltaZEU41t7WGBnC7RlxYtdXziEn5fC8b1JfqiP0OJVQfdIMVIbEw1turVouTovUA39 Qqa6Pd1oYTw+Bdm1tkx7di73qB3x4pJoC8ZRfEmPqSpmu42sijWSBUgYJwsziTW2SBi4hRjU h/Tm0NuU1/R1bgv/EzoXjgOM4ZlSu6Pv7ICpELdWSrvkXJIuIwARAQABzR9Mb25nbWFuIExv bmcgPGxsb25nQHJlZGhhdC5jb20+wsF/BBMBAgApBQJYLGRrAhsjBQkJZgGABwsJCAcDAgEG FQgCCQoLBBYCAwECHgECF4AACgkQbjBXZE7vHeYwBA//ZYxi4I/4KVrqc6oodVfwPnOVxvyY oKZGPXZXAa3swtPGmRFc8kGyIMZpVTqGJYGD9ZDezxpWIkVQDnKM9zw/qGarUVKzElGHcuFN ddtwX64yxDhA+3Og8MTy8+8ZucM4oNsbM9Dx171bFnHjWSka8o6qhK5siBAf9WXcPNogUk4S fMNYKxexcUayv750GK5E8RouG0DrjtIMYVJwu+p3X1bRHHDoieVfE1i380YydPd7mXa7FrRl 7unTlrxUyJSiBc83HgKCdFC8+ggmRVisbs+1clMsK++ehz08dmGlbQD8Fv2VK5KR2+QXYLU0 rRQjXk/gJ8wcMasuUcywnj8dqqO3kIS1EfshrfR/xCNSREcv2fwHvfJjprpoE9tiL1qP7Jrq 4tUYazErOEQJcE8Qm3fioh40w8YrGGYEGNA4do/jaHXm1iB9rShXE2jnmy3ttdAh3M8W2OMK 4B/Rlr+Awr2NlVdvEF7iL70kO+aZeOu20Lq6mx4Kvq/WyjZg8g+vYGCExZ7sd8xpncBSl7b3 99AIyT55HaJjrs5F3Rl8dAklaDyzXviwcxs+gSYvRCr6AMzevmfWbAILN9i1ZkfbnqVdpaag QmWlmPuKzqKhJP+OMYSgYnpd/vu5FBbc+eXpuhydKqtUVOWjtp5hAERNnSpD87i1TilshFQm TFxHDzbOwU0EWCxkawEQALAcdzzKsZbcdSi1kgjfce9AMjyxkkZxcGc6Rhwvt78d66qIFK9D Y9wfcZBpuFY/AcKEqjTo4FZ5LCa7/dXNwOXOdB1Jfp54OFUqiYUJFymFKInHQYlmoES9EJEU yy+2ipzy5yGbLh3ZqAXyZCTmUKBU7oz/waN7ynEP0S0DqdWgJnpEiFjFN4/ovf9uveUnjzB6 lzd0BDckLU4dL7aqe2ROIHyG3zaBMuPo66pN3njEr7IcyAL6aK/IyRrwLXoxLMQW7YQmFPSw drATP3WO0x8UGaXlGMVcaeUBMJlqTyN4Swr2BbqBcEGAMPjFCm6MjAPv68h5hEoB9zvIg+fq M1/Gs4D8H8kUjOEOYtmVQ5RZQschPJle95BzNwE3Y48ZH5zewgU7ByVJKSgJ9HDhwX8Ryuia 79r86qZeFjXOUXZjjWdFDKl5vaiRbNWCpuSG1R1Tm8o/rd2NZ6l8LgcK9UcpWorrPknbE/pm MUeZ2d3ss5G5Vbb0bYVFRtYQiCCfHAQHO6uNtA9IztkuMpMRQDUiDoApHwYUY5Dqasu4ZDJk bZ8lC6qc2NXauOWMDw43z9He7k6LnYm/evcD+0+YebxNsorEiWDgIW8Q/E+h6RMS9kW3Rv1N qd2nFfiC8+p9I/KLcbV33tMhF1+dOgyiL4bcYeR351pnyXBPA66ldNWvABEBAAHCwWUEGAEC AA8FAlgsZGsCGwwFCQlmAYAACgkQbjBXZE7vHeYxSQ/+PnnPrOkKHDHQew8Pq9w2RAOO8gMg 9Ty4L54CsTf21Mqc6GXj6LN3WbQta7CVA0bKeq0+WnmsZ9jkTNh8lJp0/RnZkSUsDT9Tza9r GB0svZnBJMFJgSMfmwa3cBttCh+vqDV3ZIVSG54nPmGfUQMFPlDHccjWIvTvyY3a9SLeamaR jOGye8MQAlAD40fTWK2no6L1b8abGtziTkNh68zfu3wjQkXk4kA4zHroE61PpS3oMD4AyI9L 7A4Zv0Cvs2MhYQ4Qbbmafr+NOhzuunm5CoaRi+762+c508TqgRqH8W1htZCzab0pXHRfywtv 0P+BMT7vN2uMBdhr8c0b/hoGqBTenOmFt71tAyyGcPgI3f7DUxy+cv3GzenWjrvf3uFpxYx4 yFQkUcu06wa61nCdxXU/BWFItryAGGdh2fFXnIYP8NZfdA+zmpymJXDQeMsAEHS0BLTVQ3+M 7W5Ak8p9V+bFMtteBgoM23bskH6mgOAw6Cj/USW4cAJ8b++9zE0/4Bv4iaY5bcsL+h7TqQBH Lk1eByJeVooUa/mqa2UdVJalc8B9NrAnLiyRsg72Nurwzvknv7anSgIkL+doXDaG21DgCYTD wGA5uquIgb8p3/ENgYpDPrsZ72CxVC2NEJjJwwnRBStjJOGQX4lV1uhN1XsZjBbRHdKF2W9g weim8xU= Organization: Red Hat Message-ID: Date: Fri, 22 Mar 2019 12:10:27 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20190322111642.GA28876@redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.16 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Fri, 22 Mar 2019 16:10:33 +0000 (UTC) X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 03/22/2019 07:16 AM, Oleg Nesterov wrote: > On 03/21, Matthew Wilcox wrote: >> On Thu, Mar 21, 2019 at 05:45:10PM -0400, Waiman Long wrote: >> >>> To avoid this dire condition and reduce lock hold time of tasklist_lo= ck, >>> flush_sigqueue() is modified to pass in a freeing queue pointer so th= at >>> the actual freeing of memory objects can be deferred until after the >>> tasklist_lock is released and irq re-enabled. >> I think this is a really bad solution. It looks kind of generic, >> but isn't. It's terribly inefficient, and all it's really doing is >> deferring the debugging code until we've re-enabled interrupts. > Agreed. Thanks for looking into that. As I am not knowledgeable enough about the signal handling code path, I choose the lowest risk approach of not trying to change the code flow while deferring memory deallocation after releasing the tasklist_lock. >> We'd be much better off just having a list_head in the caller >> and list_splice() the queue->list onto that caller. Then call >> __sigqueue_free() for each signal on the queue. > This won't work, note the comment which explains the race with sigqueue= _free(). > > Let me think about it... at least we can do something like > > close_the_race_with_sigqueue_free(struct sigpending *queue) > { > struct sigqueue *q, *t; > > list_for_each_entry_safe(q, t, ...) { > if (q->flags & SIGQUEUE_PREALLOC) > list_del_init(&q->list); > } > > called with ->siglock held, tasklist_lock is not needed. > > After that flush_sigqueue() can be called lockless in release_task() re= lease_task. > > I'll try to make the patch tomorrow. > > Oleg. > I am looking forward to it. Thanks, Longman