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 mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 919CEC433F5 for ; Mon, 27 Sep 2021 11:55:11 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 165B160F9B for ; Mon, 27 Sep 2021 11:55:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 165B160F9B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=shutemov.name Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvack.org Received: by kanga.kvack.org (Postfix) id 671706B0071; Mon, 27 Sep 2021 07:55:10 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 622656B0072; Mon, 27 Sep 2021 07:55:10 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 4E92C6B0073; Mon, 27 Sep 2021 07:55:10 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0040.hostedemail.com [216.40.44.40]) by kanga.kvack.org (Postfix) with ESMTP id 3C1D36B0071 for ; Mon, 27 Sep 2021 07:55:10 -0400 (EDT) Received: from smtpin08.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id D8C09181B04AD for ; Mon, 27 Sep 2021 11:55:09 +0000 (UTC) X-FDA: 78633197538.08.525B082 Received: from mail-lf1-f50.google.com (mail-lf1-f50.google.com [209.85.167.50]) by imf14.hostedemail.com (Postfix) with ESMTP id 90E89600198B for ; Mon, 27 Sep 2021 11:55:09 +0000 (UTC) Received: by mail-lf1-f50.google.com with SMTP id x27so76348192lfu.5 for ; Mon, 27 Sep 2021 04:55:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=shutemov-name.20210112.gappssmtp.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=DS5KVI0MI3urzxy+Dr1c8uCppaGchpddwzrmXVrMjZw=; b=cQvdOnUkyhSPNzgh4Wudd6h8B02zdpU4K7tSFEUUhp0dws6UouuWJi+cxD0kvJFMoZ NwMiIC/K24a4LRk6LE2ewO8tO1YgqceTgui7RHon2GlaZ5bk6v4bL+wBVX6EpJoQkPaV WYyhwxWv6r40e6cMQyPT8+qPaCfj//7a8RGg8O905rCqUvL/ufW+fx1w8BDNuxA7uSe9 FRF8+xgRNxR25AFQpGRRobbWp+VWribppnUjhJQ5mvbL1arcTkfJ74mcT9qmxhEPnOvW F/+w0VEXbr3dOVwplmKTzVnFkgQbKd8o5P9vj9dH6lj10g6Vxri4I7yg90cGTxMEXZiI 7kKQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=DS5KVI0MI3urzxy+Dr1c8uCppaGchpddwzrmXVrMjZw=; b=1nMZpGSwVQKBGo6V39H3Z9u65ysLvkwbbq2UjQqZjIwXjrKkNMlOCQq85J3MMdvFgr wEvTR9dR/kzpWyLpHLO7RLukA1R3/CS2Vobxe2MDjr1wSsa6DykYdu2RAlJvob6t6318 9Hz/CLokG9E/wEgxtLGLpank9euGMCrMq1dQXOGe4eQZkqZJaTVdmK+UO0EJk3jNVuaX uFINlhkt3TkLBOkWwlthpifqsTACM2UKV9rEqbeRF6vFXO2u1eb6nxOwtp7tn79E/XVO rcD26siAPwsGLgAhfKoboSAHXSHcM1OXsVyUj8xJPaLodEJ8iWyjeK8nFSxzu//Fev/r MM1A== X-Gm-Message-State: AOAM53013rNMxQITGDIZSkMb6BTv7BwDjVUrq3tp+TDZXWnjuFw765m9 1B7ZMP7kkDp+pOhTeZtWztIj1Q== X-Google-Smtp-Source: ABdhPJxk5GpozFMxWdpW/k7DbdIGJqQW2CyjZzhWKCVp8cH1dBvyXn+qf5X9RIP4VUFMj9EiPhdCKw== X-Received: by 2002:a05:6512:b0f:: with SMTP id w15mr23568038lfu.164.1632743708091; Mon, 27 Sep 2021 04:55:08 -0700 (PDT) Received: from box.localdomain ([86.57.175.117]) by smtp.gmail.com with ESMTPSA id v26sm1954224lja.22.2021.09.27.04.55.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 27 Sep 2021 04:55:07 -0700 (PDT) Received: by box.localdomain (Postfix, from userid 1000) id 1AD8F102FD9; Mon, 27 Sep 2021 14:55:07 +0300 (+03) Date: Mon, 27 Sep 2021 14:55:07 +0300 From: "Kirill A. Shutemov" To: Nadav Amit Cc: Andrew Morton , Linux-MM , Linux Kernel Mailing List , Peter Xu , Andrea Arcangeli , Minchan Kim , Colin Cross , Suren Baghdasarya , Mike Rapoport Subject: Re: [RFC PATCH 1/8] mm/madvise: propagate vma->vm_end changes Message-ID: <20210927115507.6xfpugeg3swookbh@box> References: <20210926161259.238054-1-namit@vmware.com> <20210926161259.238054-2-namit@vmware.com> <20210927090852.sc5u65ufwvfx57rl@box.shutemov.name> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 90E89600198B X-Stat-Signature: pcuw491g8w95pruwy8m6e4q81gam55rz Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=shutemov-name.20210112.gappssmtp.com header.s=20210112 header.b=cQvdOnUk; dmarc=none; spf=none (imf14.hostedemail.com: domain of kirill@shutemov.name has no SPF policy when checking 209.85.167.50) smtp.mailfrom=kirill@shutemov.name X-HE-Tag: 1632743709-744137 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 Mon, Sep 27, 2021 at 03:11:20AM -0700, Nadav Amit wrote: > > > On Sep 27, 2021, at 2:08 AM, Kirill A. Shutemov wrote: > > > > On Sun, Sep 26, 2021 at 09:12:52AM -0700, Nadav Amit wrote: > >> From: Nadav Amit > >> > >> The comment in madvise_dontneed_free() says that vma splits that occur > >> while the mmap-lock is dropped, during userfaultfd_remove(), should be > >> handled correctly, but nothing in the code indicates that it is so: prev > >> is invalidated, and do_madvise() will therefore continue to update VMAs > >> from the "obsolete" end (i.e., the one before the split). > >> > >> Propagate the changes to end from madvise_dontneed_free() back to > >> do_madvise() and continue the updates from the new end accordingly. > > > > Could you describe in details a race that would lead to wrong behaviour? > > Thanks for the quick response. > > For instance, madvise(MADV_DONTNEED) can race with mprotect() and cause > the VMA to split. > > Something like: > > CPU0 CPU1 > ---- ---- > madvise(0x10000, 0x2000, MADV_DONTNEED) > -> userfaultfd_remove() > [ mmap-lock dropped ] > mprotect(0x11000, 0x1000, PROT_READ) > [splitting the VMA] > > read(uffd) > [unblocking userfaultfd_remove()] > > [ resuming ] > end = vma->vm_end > [end == 0x11000] > > madvise_dontneed_single_vma(vma, 0x10000, 0x11000) > > Following this operation, 0x11000-0x12000 would not be zapped. Okay, fair enough. Wouldn't something like this work too: diff --git a/mm/madvise.c b/mm/madvise.c index 0734db8d53a7..0898120c5c04 100644 --- a/mm/madvise.c +++ b/mm/madvise.c @@ -796,6 +796,7 @@ static long madvise_dontneed_free(struct vm_area_struct *vma, */ return -ENOMEM; } + *prev = vma; if (!can_madv_lru_vma(vma)) return -EINVAL; if (end > vma->vm_end) { -- Kirill A. Shutemov