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 Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id C93B5C63705 for ; Wed, 7 Dec 2022 22:43:14 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id 64B218E0005; Wed, 7 Dec 2022 17:43:14 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 5FAEF8E0001; Wed, 7 Dec 2022 17:43:14 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4760E8E0005; Wed, 7 Dec 2022 17:43:14 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from relay.hostedemail.com (smtprelay0016.hostedemail.com [216.40.44.16]) by kanga.kvack.org (Postfix) with ESMTP id 39E498E0001 for ; Wed, 7 Dec 2022 17:43:14 -0500 (EST) Received: from smtpin23.hostedemail.com (a10.router.float.18 [10.200.18.1]) by unirelay08.hostedemail.com (Postfix) with ESMTP id 1639E140381 for ; Wed, 7 Dec 2022 22:43:14 +0000 (UTC) X-FDA: 80216987508.23.F05240A Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf17.hostedemail.com (Postfix) with ESMTP id 5CD8E40007 for ; Wed, 7 Dec 2022 22:43:09 +0000 (UTC) Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=VU9nXVsh; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf17.hostedemail.com: domain of peterx@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=peterx@redhat.com ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=hostedemail.com; s=arc-20220608; t=1670452992; h=from:from:sender:reply-to:subject:subject:date:date: message-id:message-id:to:to:cc:cc:mime-version:mime-version: content-type:content-type:content-transfer-encoding: in-reply-to:in-reply-to:references:references:dkim-signature; bh=CWjwloNvUEkkIL4IH5jVpeAOiD4Eko/MVERp2bOyZdg=; b=I4UPseSPFe4XHxoeWCa6/xg8zyyKLWyMPCvQ6FFV58hE8N1EySGEy39V/VCZw+1bc4QuRL /Y4zXlgYbkZZhrmaF4TE3E3Ve7qV0ea53fWVgn9aS6SBJA0JaL8tqVmaq4tRYRueMkAPr+ jJntd53OQxHOijk3AOjIcIgn3cwDXQ0= ARC-Authentication-Results: i=1; imf17.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=VU9nXVsh; dmarc=pass (policy=none) header.from=redhat.com; spf=pass (imf17.hostedemail.com: domain of peterx@redhat.com designates 170.10.129.124 as permitted sender) smtp.mailfrom=peterx@redhat.com ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1670452992; a=rsa-sha256; cv=none; b=lBMfKGx2lG2kwcdzVxVhJFOO4iBJsOJQvZJ6cZarwvM8UYjTeE3r9+i4dyYuSDpcw/5PYl l7OEQ5Yjw5fetE23y2+T7WC7NgmVuCEuGRIz+ULn50jH00CFYSsMfRg02NbIRbcw9uZB/N k5M33l/7RPyPqV/RbXNkCnpWb4IspoY= DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1670452989; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=CWjwloNvUEkkIL4IH5jVpeAOiD4Eko/MVERp2bOyZdg=; b=VU9nXVshkihD69icg6t4I579efh3XhiMmCs5E0rWnicRDGWrFYCBKya4bvaDpDvdI3rq9D QMVDlRfRNhPrcNzqBlYiHq+xgAoZQW+LdGPW564pj8/2f2XuMcWedwH7IJlCd3zdVLvSON It49mLuJlJW2JyHq2o/5gD9AzNtdFuY= Received: from mail-qk1-f197.google.com (mail-qk1-f197.google.com [209.85.222.197]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_128_GCM_SHA256) id us-mta-411-z9w6kRc9N22DA4dgalsh8w-1; Wed, 07 Dec 2022 17:43:08 -0500 X-MC-Unique: z9w6kRc9N22DA4dgalsh8w-1 Received: by mail-qk1-f197.google.com with SMTP id j13-20020a05620a410d00b006e08208eb31so26453062qko.3 for ; Wed, 07 Dec 2022 14:43:08 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=CWjwloNvUEkkIL4IH5jVpeAOiD4Eko/MVERp2bOyZdg=; b=1i9WbNDj9Kwqmt/S7uHWPNm/3EsCbN5autejUUjG/uJlf9m5Jq8pWT7dofORdGWH2v xFpl6/IVUkSOuTflmrQ5EbzuTGzMfMDIiUUpQWs17YbUxMVsUNomAAFVTi7+lkMQRegC NlOoBOJpXQtUfXtUU2l1UY+Of7k5iXEbFa3owfwkraW5MhaaZ+bolPZiENRIYEHLiizh yOsHlKAaVntBz4zL9i96k88ZmVB39DQRKs15mdpT6nhf/fwPb8Omg+j/iciXqy3JaG9W oya9AXp5CJAp+IWQVP71i2xSCoizC9qCceWPemsypj1vfmdKyaWLM2RnHkPIOSMrTyfZ Rzaw== X-Gm-Message-State: ANoB5plpqCvjwwvQU08bwqlRTRebldzcnMRbrhH50GD+7BpYI9f7VudS g4Yq/5QhQlzQQo/MvRVgHQNoNQCfy+JcxDbGGGR48AIeM2R4DZ8fzr5uYinrgFqWgsDrtMPiA+J 4BLV7k0POt9Y= X-Received: by 2002:ac8:6b16:0:b0:3a5:c7d9:15f9 with SMTP id w22-20020ac86b16000000b003a5c7d915f9mr1480106qts.49.1670452987687; Wed, 07 Dec 2022 14:43:07 -0800 (PST) X-Google-Smtp-Source: AA0mqf5+IvWHCzpkzEmIQzaT31AjgoZDyI4bcsd2RFr41CcZw0um/Oq2E2tah8eU0le0YiwGZcXHbg== X-Received: by 2002:ac8:6b16:0:b0:3a5:c7d9:15f9 with SMTP id w22-20020ac86b16000000b003a5c7d915f9mr1480084qts.49.1670452987444; Wed, 07 Dec 2022 14:43:07 -0800 (PST) Received: from x1n (bras-base-aurron9127w-grc-46-70-31-27-79.dsl.bell.ca. [70.31.27.79]) by smtp.gmail.com with ESMTPSA id l27-20020ac84cdb000000b00399fe4aac3esm13722291qtv.50.2022.12.07.14.43.06 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 07 Dec 2022 14:43:06 -0800 (PST) Date: Wed, 7 Dec 2022 17:43:05 -0500 From: Peter Xu To: John Hubbard Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Muchun Song , Andrea Arcangeli , James Houghton , Jann Horn , Rik van Riel , Miaohe Lin , Andrew Morton , Mike Kravetz , David Hildenbrand , Nadav Amit Subject: Re: [PATCH v2 04/10] mm/hugetlb: Move swap entry handling into vma lock when faulted Message-ID: References: <20221207203034.650899-1-peterx@redhat.com> <20221207203034.650899-5-peterx@redhat.com> <326789a5-85ba-f13c-389e-fd21d673e3ae@nvidia.com> MIME-Version: 1.0 In-Reply-To: <326789a5-85ba-f13c-389e-fd21d673e3ae@nvidia.com> X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline X-Rspamd-Queue-Id: 5CD8E40007 X-Rspamd-Server: rspam09 X-Rspam-User: X-Stat-Signature: uia1zhc9rjur7cf6xo4kx3a74uszao65 X-HE-Tag: 1670452989-155061 X-HE-Meta: U2FsdGVkX1+CtJzKoSOrrUOwQYBSiPZjKCp/UQuajynJ7B7Iel3+O02t3F8s7FlHirVhQ8F3M299b/wwhcFzR08EsaLlQ9orwpHxoONUPjymy1m8CEU3ZfWZE+6sbWzRIyZTMZv5vTPxm+fUtAIw/X/6o5mDxJ7VwDWapE8JNhmLTlVkfujJB4gpJIg+rLX4G0y3yfb6Qywuz319Z4f5/zn+s9jehz56c/BTeDYw2OxQF806bMuBNG6Q7Py2KgxEkMpsadWnF7US8NSJPE01XMBIhqiNoYWS+NhmPpH6iu3+VPNmos1bcaog5i6OWzCHU7ZrLuReiWB2zObljYnR7XgaOC3rScXnlK5TDltLo8VBqW+Wdr4lpMko4Wm+r/h/sbosDwU93cwVwFWSez/UFGY/5wNaa+ePMcX1IWnaEbSFu3otnBlc3Bt1CiZx4IjD1Vrf1BVQwi3BqrNa7gahixWbHgrHGcFUIWEWHwUmhnj+32Te5fJ/tgLFmvXGg6n3n3TwXtRX+g12y+wkw6l4eq3j8CbqcoNpWbVIChAH1aqFkItqqpTzS5qv6TCSFQrD7vWs3oOK7kDUr8YsV/TNl25OAfOz/6FY9tVKc1QO0LGmGtAlhU2wozbhtXWSiWY0lcFdpSCy86N2Ji/9BR1mV1GFSKTsHUpKBmlrHrroC4YpoXXh6hIM0vguzyCPUqXLX9/cxt+yTW3Zz8TOvYf152e7Q7O/zy+t99ynLujRY92iyf2Aza1wWIY3isP4Io+ZvpIs3iWNk+rRUhEL059nx0pUTMAWQBOnAL3DrW8o5s9LAx0UKLyvNatHuUL/7akmreVw9QdsTV3V9022zJChJO8bhPIQGpijBmEmnvyIAubNcs70oPF2DE/PvzLwylM01agD984vSdStt61Oth7fM46fYvRSkdVlFYPDLOTanF2H9bNJPCkeq2LRM3VEJxiKVqM6PPFgLiBdHJcMIh4 oKSS6mvQ 2jkq1+QQMcmbsTcEhAjDGVbgPSNNQRsOEi9xiuQaa4zbMK64MMVlwNdj0/0Ji06rCJDMQRVJAswEC95Z6q14wWfqckGdIdUITQuvHInt/6JzEIM5kQOsn47B63WkFcB408XVXbppDdVmDrI8agG7l5690SvRX9YKo88dUvv1ZjZDx8pxTPt1euxlmuA== 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: Hi, John, Firstly, thanks for taking a look at the whole set. On Wed, Dec 07, 2022 at 02:36:21PM -0800, John Hubbard wrote: > > @@ -5886,8 +5866,22 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, > > * fault, and is_hugetlb_entry_(migration|hwpoisoned) check will > > * properly handle it. > > */ > > - if (!pte_present(entry)) > > + if (!pte_present(entry)) { > > + if (unlikely(is_hugetlb_entry_migration(entry))) { > > + /* > > + * Release fault lock first because the vma lock is > > + * needed to guard the huge_pte_lockptr() later in > > + * migration_entry_wait_huge(). The vma lock will > > + * be released there. > > + */ > > + mutex_unlock(&hugetlb_fault_mutex_table[hash]); > > + migration_entry_wait_huge(vma, ptep); > > + return 0; > > Oh, but now (and also one other, pre-existing case, above) > hugetlb_fault() is returning with the vma lock held. Note that here migration_entry_wait_huge() will release it. Sorry it's definitely not as straightforward, but this is also something I didn't come up with a better solution, because we need the vma lock to protect the spinlock, which is used in deep code path of the migration code. That's also why I added a rich comment above, and there's "The vma lock will be released there" which is just for that. > This is in contrast > with most of the rest of the function, which takes great care to release > locks before returning. > > Which makes this new case really quite irregular and makes the overall > locking harder to follow. It would be ideal to avoid doing this! But at > the very least, there should be a little note above hugetlb_fault(), > explaining this deviation and how it fits in with the locking rules. > > Do we really have to structure it this way, though? -- Peter Xu