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 32302C433EF for ; Thu, 3 Feb 2022 22:19:14 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id BCCE86B0074; Thu, 3 Feb 2022 17:19:13 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id B7BC46B0075; Thu, 3 Feb 2022 17:19:13 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id A6B246B0078; Thu, 3 Feb 2022 17:19:13 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0111.hostedemail.com [216.40.44.111]) by kanga.kvack.org (Postfix) with ESMTP id 991296B0074 for ; Thu, 3 Feb 2022 17:19:13 -0500 (EST) Received: from smtpin13.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 5930E9A274 for ; Thu, 3 Feb 2022 22:19:13 +0000 (UTC) X-FDA: 79102885386.13.1AF5CC7 Received: from mail-ej1-f47.google.com (mail-ej1-f47.google.com [209.85.218.47]) by imf12.hostedemail.com (Postfix) with ESMTP id 00C2F40003 for ; Thu, 3 Feb 2022 22:19:12 +0000 (UTC) Received: by mail-ej1-f47.google.com with SMTP id m4so13098103ejb.9 for ; Thu, 03 Feb 2022 14:19:12 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=GOu/1THglDVeJl3U7MMSrfyxTvyCi8aFtyQJKOPt1yo=; b=Bkxytx1rYCwS7T3hdaz6quufzPxCnjE+wsE5ldbaUW5t8fCGwpg505DKUwCU7oEcWu 6Apaly4e9E/MpN0+MVpfHbPNW4lCkJUnWXeIkflNFURTUP5FGMGs+B/8rb5G8hK748L+ 7x9qH2FoOoewr/gQQoNh+LNcw+eZv21u3BKkhYK6YQwGSu5TulCA7ZLace6IcmTfnI/L tnJlip18l6nXRLWAnzbn+iDSG63aeQH0NPEn/XSoVbSb2PkhE5MGs8exnVYgn5Uxb1k/ gbHmrmSLGke6jdHWI8B0KagLzMm+Ytgpi1QW+JJJKbEzT/lEnCL35tiQJaWea8VmWcOm 7xNQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=GOu/1THglDVeJl3U7MMSrfyxTvyCi8aFtyQJKOPt1yo=; b=EuBvXCP/9ddeLYkd8rvan6RgoMUJSaAw83ZPl03/jC+z/wR4oKU15BMY6Nnm8Qx172 WI55bQE5DnrqENVAM50YKyHdPGGemr39Fx60FiL+CY7fViXOv5TZ8TbOcsWoDMgFHQLg qpBqEDufnhUwlA6dTr7mKde6AlCMKYuqbFi3XDIp4BFXg4QjGwyc5UP8hEmFQzoddgcd UFort5svdEvOYg3TIff+s84ebyyvjAXxTGyKLvY6d193Jb9DXqfRWdINjDCTuE6izztP qQR0TGWN507mq1+9ik6dIovON5BWyHR9IwaIUXKrN7zClg4BM+842MFGJp1MiL9BKxui 8lRw== X-Gm-Message-State: AOAM533PFIKIV6Kv9o8QKBc4yzHFMAu/ZGxWdEgaybS+ciJzISMpQpkJ 46NCKuP3EPPdimnM5irPVl0T3uU66sSBvVMK2EE= X-Google-Smtp-Source: ABdhPJxI8SMxBz0kZoZ/OkQC6HVudR43k5HUeEvEqSyhCy3Q02/zu7na+zZTa14XBq/mhwevczEjO49BPLpith+IgMs= X-Received: by 2002:a17:907:6e1a:: with SMTP id sd26mr22848ejc.270.1643926751588; Thu, 03 Feb 2022 14:19:11 -0800 (PST) MIME-Version: 1.0 References: <20220203182641.824731-1-shy828301@gmail.com> <20220203141226.d510a9fe3fb1f55fc75926e5@linux-foundation.org> In-Reply-To: <20220203141226.d510a9fe3fb1f55fc75926e5@linux-foundation.org> From: Yang Shi Date: Thu, 3 Feb 2022 14:18:56 -0800 Message-ID: Subject: Re: [v4 PATCH] fs/proc: task_mmu.c: don't read mapcount for migration entry To: Andrew Morton Cc: "Kirill A. Shutemov" , Jann Horn , Matthew Wilcox , David Hildenbrand , Linux MM , Linux Kernel Mailing List , stable Content-Type: text/plain; charset="UTF-8" X-Rspamd-Queue-Id: 00C2F40003 X-Rspam-User: nil Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=gmail.com header.s=20210112 header.b=Bkxytx1r; dmarc=pass (policy=none) header.from=gmail.com; spf=pass (imf12.hostedemail.com: domain of shy828301@gmail.com designates 209.85.218.47 as permitted sender) smtp.mailfrom=shy828301@gmail.com X-Stat-Signature: eq5tmui56khaui6ukhz9tceadqzpf8mh X-Rspamd-Server: rspam08 X-HE-Tag: 1643926752-155727 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 Thu, Feb 3, 2022 at 2:12 PM Andrew Morton wrote: > > On Thu, 3 Feb 2022 10:26:41 -0800 Yang Shi wrote: > > > v4: * s/Treated/Treat per David > > * Collected acked-by tag from David > > v3: * Fixed the fix tag, the one used by v2 was not accurate > > * Added comment about the risk calling page_mapcount() per David > > * Fix pagemap > > v2: * Added proper fix tag per Jann Horn > > * Rebased to the latest linus's tree > > The v2->v4 delta shows changes which aren't described above? They are. v4: * s/Treated/Treat per David * Collected acked-by tag from David v3: * Fixed the fix tag, the one used by v2 was not accurate * Added comment about the risk calling page_mapcount() per David * Fix pagemap > > --- a/fs/proc/task_mmu.c~fs-proc-task_mmuc-dont-read-mapcount-for-migration-entry-v4 > +++ a/fs/proc/task_mmu.c > @@ -469,9 +469,12 @@ static void smaps_account(struct mem_siz > * If any subpage of the compound page mapped with PTE it would elevate > * page_count(). > * > - * Treated regular migration entries as mapcount == 1 without reading > - * mapcount since calling page_mapcount() for migration entries is > - * racy against THP splitting. > + * The page_mapcount() is called to get a snapshot of the mapcount. > + * Without holding the page lock this snapshot can be slightly wrong as > + * we cannot always read the mapcount atomically. It is not safe to > + * call page_mapcount() even with PTL held if the page is not mapped, > + * especially for migration entries. Treat regular migration entries > + * as mapcount == 1. > */ > if ((page_count(page) == 1) || migration) { > smaps_page_accumulate(mss, page, size, size << PSS_SHIFT, dirty, > @@ -1393,6 +1396,7 @@ static pagemap_entry_t pte_to_pagemap_en > { > u64 frame = 0, flags = 0; > struct page *page = NULL; > + bool migration = false; > > if (pte_present(pte)) { > if (pm->show_pfn) > @@ -1414,13 +1418,14 @@ static pagemap_entry_t pte_to_pagemap_en > frame = swp_type(entry) | > (swp_offset(entry) << MAX_SWAPFILES_SHIFT); > flags |= PM_SWAP; > + migration = is_migration_entry(entry); > if (is_pfn_swap_entry(entry)) > page = pfn_swap_entry_to_page(entry); > } > > if (page && !PageAnon(page)) > flags |= PM_FILE; > - if (page && page_mapcount(page) == 1) > + if (page && !migration && page_mapcount(page) == 1) > flags |= PM_MMAP_EXCLUSIVE; > if (vma->vm_flags & VM_SOFTDIRTY) > flags |= PM_SOFT_DIRTY; > @@ -1436,6 +1441,7 @@ static int pagemap_pmd_range(pmd_t *pmdp > spinlock_t *ptl; > pte_t *pte, *orig_pte; > int err = 0; > + bool migration = false; > > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > ptl = pmd_trans_huge_lock(pmdp, vma); > @@ -1476,11 +1482,12 @@ static int pagemap_pmd_range(pmd_t *pmdp > if (pmd_swp_uffd_wp(pmd)) > flags |= PM_UFFD_WP; > VM_BUG_ON(!is_pmd_migration_entry(pmd)); > + migration = is_migration_entry(entry); > page = pfn_swap_entry_to_page(entry); > } > #endif > > - if (page && page_mapcount(page) == 1) > + if (page && !migration && page_mapcount(page) == 1) > flags |= PM_MMAP_EXCLUSIVE; > > for (; addr != end; addr += PAGE_SIZE) { > _ >