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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5997CC7EE2F for ; Mon, 12 Jun 2023 21:36:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237224AbjFLVgh (ORCPT ); Mon, 12 Jun 2023 17:36:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49850 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233463AbjFLVgf (ORCPT ); Mon, 12 Jun 2023 17:36:35 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 5CC3790 for ; Mon, 12 Jun 2023 14:35:51 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1686605750; 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=NkQV10oF5ZntpZuW0m7Oa1esdGwRfz9LHsmhKjiKPeQ=; b=INXhRbSzs5T/AHBkAwHqLyVppT/dfkCo6u1SOW5ONuQObQhUXe4+6SNjJy/nCZSdnWhURb ApzWg03lj3rfQsUDcPKCs3W8Wpnk5J9t7EValJQNOVzG58zLhLoqlyeiR7f2Rkr4oKoSPY wNEKoKXOuZbqZOIQvKoMMyIduBFddQs= Received: from mail-qv1-f72.google.com (mail-qv1-f72.google.com [209.85.219.72]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-341-VdxBLHlvNsqu4D4i2b8STQ-1; Mon, 12 Jun 2023 17:35:49 -0400 X-MC-Unique: VdxBLHlvNsqu4D4i2b8STQ-1 Received: by mail-qv1-f72.google.com with SMTP id 6a1803df08f44-62dd79f63e0so2256356d6.0 for ; Mon, 12 Jun 2023 14:35:49 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1686605748; x=1689197748; 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=NkQV10oF5ZntpZuW0m7Oa1esdGwRfz9LHsmhKjiKPeQ=; b=ZJTIGW0TnoXXshyq4ELgXTNUgkEh80IduVO7vMYw5QwgezUYLuxGp78PNXf6h4j1Oj FLeIqUBxBifXKL91As3XEryNqeBEZDH1HZpU4p6Kssdmk807156I4rkKWhR7d6cnnzER 2gbDb+2m0tgMrHi7dl1f9xIbV/OVpS+coR3f2S0FXEx7+AtimL08qn3jzYMj9TC+/Si/ RAnsCqWmm54zzuRb3yQTSt0I9zK/37RxMZVGUD382rZMKKn8gRSUWNtdrB0kOpt0yORA N5OmKk8OSMNuJS8HurlV4wC5WdAR98OZIOZmvebyRkk3a9xzbZ8e+ZXmfOTjgI/S53oI Sw5A== X-Gm-Message-State: AC+VfDxXV00t/awtIYYinCgaOjJ1GjoCrA/OEMHqa+TEIJfd3uudlju5 p2i0czjTBCXLx24HLMkQWLHfPB/3V40jBLCIX20a9S7SU+YRy+kRswaN0TniEhl8Wx1sdgzfZwy 0EF8T41TtfbiMD9pEBm1ev/6/Lc44tUJm X-Received: by 2002:ad4:5aea:0:b0:62b:5410:322d with SMTP id c10-20020ad45aea000000b0062b5410322dmr13260516qvh.6.1686605748591; Mon, 12 Jun 2023 14:35:48 -0700 (PDT) X-Google-Smtp-Source: ACHHUZ4hVxn8A37sq0YOY66NVF97sTSXxB2Qm4jGFSmtl+98Zfmt7cWhpbXFa6YFA2pqBxvxrtSgaA== X-Received: by 2002:ad4:5aea:0:b0:62b:5410:322d with SMTP id c10-20020ad45aea000000b0062b5410322dmr13260505qvh.6.1686605748392; Mon, 12 Jun 2023 14:35:48 -0700 (PDT) Received: from x1n (cpe5c7695f3aee0-cm5c7695f3aede.cpe.net.cable.rogers.com. [99.254.144.39]) by smtp.gmail.com with ESMTPSA id x4-20020a0cda04000000b0062df4144a4bsm246507qvj.56.2023.06.12.14.35.47 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 12 Jun 2023 14:35:47 -0700 (PDT) Date: Mon, 12 Jun 2023 17:35:46 -0400 From: Peter Xu To: Mike Kravetz Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrew Morton , Muchun Song , Naoya Horiguchi Subject: Re: [PATCH] mm/hugetlb: Fix pgtable lock on pmd sharing Message-ID: References: <20230612160420.809818-1-peterx@redhat.com> <20230612204418.GD3704@monkey> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20230612204418.GD3704@monkey> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi, Mike! On Mon, Jun 12, 2023 at 01:44:18PM -0700, Mike Kravetz wrote: > Agree with this change. But, it does make one wonder if the pud_clear() > in huge_pmd_unshare is safe. Like here, we really should be holding the > higher level lock but are holding the PMD lock. The vma write lock? My memory tells me that you worked on the vma lock and one major reason was for that, but maybe I missed something? I did check again and all call sites should have that lock held, which looks fine here. One thing worth mention is pmd unshare should also always be gup-fast-safe because it never really releases the pgtable, unlike thp collapse. -- Peter Xu