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=-5.3 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 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 CDDB6CA9ECF for ; Fri, 1 Nov 2019 18:31:44 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 093E321855 for ; Fri, 1 Nov 2019 18:31:43 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=cmpxchg-org.20150623.gappssmtp.com header.i=@cmpxchg-org.20150623.gappssmtp.com header.b="fz/PD9PF" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 093E321855 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=cmpxchg.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 78D466B0007; Fri, 1 Nov 2019 14:31:43 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 73D566B0008; Fri, 1 Nov 2019 14:31:43 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 62D5F6B000A; Fri, 1 Nov 2019 14:31:43 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0224.hostedemail.com [216.40.44.224]) by kanga.kvack.org (Postfix) with ESMTP id 4E1A66B0007 for ; Fri, 1 Nov 2019 14:31:43 -0400 (EDT) Received: from smtpin08.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with SMTP id EDC648131 for ; Fri, 1 Nov 2019 18:31:42 +0000 (UTC) X-FDA: 76108552044.08.woman54_edb679bbbd03 X-HE-Tag: woman54_edb679bbbd03 X-Filterd-Recvd-Size: 8521 Received: from mail-pf1-f194.google.com (mail-pf1-f194.google.com [209.85.210.194]) by imf15.hostedemail.com (Postfix) with ESMTP for ; Fri, 1 Nov 2019 18:31:41 +0000 (UTC) Received: by mail-pf1-f194.google.com with SMTP id c13so7614770pfp.5 for ; Fri, 01 Nov 2019 11:31:41 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cmpxchg-org.20150623.gappssmtp.com; s=20150623; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to:user-agent; bh=nKmNaX3Bm57vluvQWH/wfQwbui3Ian44PSlBzlCFoD4=; b=fz/PD9PFl6ekTjYUmJD/g4zRqdYHda4/CgtW11fwQbFlxcq3igPoDj9Dovl1iPMK+O kj58/32TT49pRwKuo/m3IfTUG9dtaHPekq4bDWXtF1/6LjNpJhDWdDsPJogRwOBg+33o sKp/yCWoFN2yYBlQ4Kc7xWJmejF20FGZC3IVUbFIRmMOokrE4fTDBZHiRYlAYeDSkS9B IRAAOVTpYJulcHpC+07SKOtK5kwUGclL/sL03eNSttAHohmU3N3xyBApscir6aVfH/BU T7nB8kwqO9qLYiA52C7XTNv8kyvEXSekfMK81p13Lc5+9Vd1w2eVpok2Gs7wtUFHdlH/ GJuw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to:user-agent; bh=nKmNaX3Bm57vluvQWH/wfQwbui3Ian44PSlBzlCFoD4=; b=BX+4McEHXNVBSXQJmvye1LBVhqoC1yVHrGCzMMb3uoctR1jPXDsxsoRgQfFTHY+Ugd +OsG2hql0Mx61hF2oq8XplmQvXbEQfp52741lgeXP/8vCmv44ejHPmhhj0SWu+ojeCsa D89kYEl58IsA9add0hT5tE2EvUbp5ETWEUtarJiG5q8Rs8OrFxWIAw4IWUuXwsITA6j6 9KVZA01Bqo2IEDRYaY6ofgek3xW43fgaWHXOJOVV12Oucj3dX1/5iN5d3L8ZjMYkHz5A ftA8Lxmg/VBieqaGeaBI5R4OZ0pRPmTg2rqGSrWMlpuaVF9zwynMT6AOG3g35ghlCZs1 LNxg== X-Gm-Message-State: APjAAAXLpoasuPi96Ui407Adjy2jjtksPqQ5kEk4EpaGHRyN7yoc6Pvw NWXHDr2HrVr4l6zc9/YlpDnbHQ== X-Google-Smtp-Source: APXvYqzHJe3uYgQyaLfXJHmegWpfEtQrzWrXAQy06sJtWaKQlALRmESRcnuZg2xTKL9iYyfc4rlOww== X-Received: by 2002:a17:90a:178e:: with SMTP id q14mr1467731pja.134.1572633100145; Fri, 01 Nov 2019 11:31:40 -0700 (PDT) Received: from localhost ([2620:10d:c090:180::1d92]) by smtp.gmail.com with ESMTPSA id f7sm8274457pfa.150.2019.11.01.11.31.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 01 Nov 2019 11:31:39 -0700 (PDT) Date: Fri, 1 Nov 2019 14:31:37 -0400 From: Johannes Weiner To: Andrew Morton Cc: Song Liu , linux-mm@kvack.org, kernel-team@fb.com, "Kirill A . Shutemov" , Hugh Dickins , William Kucharski , Matthew Wilcox Subject: Re: [PATCH] mm/thp: flush file for !is_shmem PageDirty() case in collapse_file() Message-ID: <20191101183137.GA16977@cmpxchg.org> References: <20191030200736.3455046-1-songliubraving@fb.com> <20191030185115.ad780e74c66b6286789559fd@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191030185115.ad780e74c66b6286789559fd@linux-foundation.org> User-Agent: Mutt/1.12.2 (2019-09-21) 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 Wed, Oct 30, 2019 at 06:51:15PM -0700, Andrew Morton wrote: > To that end, here's the combination of > mmthp-recheck-each-page-before-collapsing-file-thp.patch and this > patch: > > From: Song Liu > Subject: mm,thp: recheck each page before collapsing file THP > > In collapse_file(), for !is_shmem case, current check cannot guarantee > the locked page is up-to-date. Specifically, xas_unlock_irq() should > not be called before lock_page() and get_page(); and it is necessary to > recheck PageUptodate() after locking the page. > > With this bug and CONFIG_READ_ONLY_THP_FOR_FS=y, madvise(HUGE)'ed .text > may contain corrupted data. This is because khugepaged mistakenly > collapses some not up-to-date sub pages into a huge page, and assumes > the huge page is up-to-date. This will NOT corrupt data in the disk, > because the page is read-only and never written back. Fix this by > properly checking PageUptodate() after locking the page. This check > replaces "VM_BUG_ON_PAGE(!PageUptodate(page), page);". > > Also, move PageDirty() check after locking the page. Current > khugepaged should not try to collapse dirty file THP, because it is > limited to read-only .text. Add a warning with the PageDirty() check > as it should not happen. This warning is added after page_mapping() > check, because if the page is truncated, it might be dirty. > > [songliubraving@fb.com: flush file for !is_shmem PageDirty() case in collapse_file()] > Link: http://lkml.kernel.org/r/20191030200736.3455046-1-songliubraving@fb.com > [songliubraving@fb.com: v4] > Link: http://lkml.kernel.org/r/20191022191006.411277-1-songliubraving@fb.com > [songliubraving@fb.com: fix deadlock in collapse_file()] > Link: http://lkml.kernel.org/r/20191028221414.3685035-1-songliubraving@fb.com > Link: http://lkml.kernel.org/r/20191018180345.4188310-1-songliubraving@fb.com > Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS") > Signed-off-by: Song Liu > Acked-by: Johannes Weiner > Cc: Kirill A. Shutemov > Cc: Hugh Dickins > Cc: William Kucharski > Signed-off-by: Andrew Morton > --- > > mm/khugepaged.c | 49 +++++++++++++++++++++++++++++++++++++--------- > 1 file changed, 40 insertions(+), 9 deletions(-) > > --- a/mm/khugepaged.c~mmthp-recheck-each-page-before-collapsing-file-thp > +++ a/mm/khugepaged.c > @@ -1601,17 +1601,33 @@ static void collapse_file(struct mm_stru > result = SCAN_FAIL; > goto xa_unlocked; > } > - } else if (!PageUptodate(page)) { > - xas_unlock_irq(&xas); > - wait_on_page_locked(page); > - if (!trylock_page(page)) { > - result = SCAN_PAGE_LOCK; > - goto xa_unlocked; > + if (WARN_ON_ONCE(PageDirty(page))) { > + /* > + * page from readahead should not > + * be dirty. Show warning if this > + * somehow happens. > + */ > + result = SCAN_FAIL; > + goto out_unlock; I'm not sure we need this check here. We have a dirty check on the locked page below, and it's not clear why there is a suspicion of readahead producing dirty pages...? > } > - get_page(page); > } else if (PageDirty(page)) { > + /* > + * khugepaged only works on read-only fd, > + * so this page is dirty because it hasn't > + * been flushed since first write. There > + * won't be new dirty pages. > + * > + * Trigger async flush here and hope the > + * writeback is done when khugepaged > + * revisits this page. > + * > + * This is a one-off situation. We are not > + * forcing writeback in loop. > + */ > + xas_unlock_irq(&xas); > + filemap_flush(mapping); > result = SCAN_FAIL; > - goto xa_locked; > + goto xa_unlocked; We should do this to improve the file THP success rate. But we shouldn't conflate it with the data corruption bug fixed in the hunks below: > } else if (trylock_page(page)) { > get_page(page); > xas_unlock_irq(&xas); > @@ -1626,7 +1642,12 @@ static void collapse_file(struct mm_stru > * without racing with truncate. > */ > VM_BUG_ON_PAGE(!PageLocked(page), page); > - VM_BUG_ON_PAGE(!PageUptodate(page), page); > + > + /* double check the page is up to date */ > + if (unlikely(!PageUptodate(page))) { > + result = SCAN_FAIL; > + goto out_unlock; > + } This... > @@ -1642,6 +1663,16 @@ static void collapse_file(struct mm_stru > goto out_unlock; > } > > + if (!is_shmem && PageDirty(page)) { > + /* > + * khugepaged only works on read-only fd, so this > + * page is dirty because it hasn't been flushed > + * since first write. > + */ > + result = SCAN_FAIL; > + goto out_unlock; > + } ...and this are pretty urgent chunks because they protect the integrity of the page cache. They should go in asap. So I suggest we do two patches instead: 1. These two locked page checks to fix the corruption in 5.4 2. The filemap_flush() bit to improve THP coverage in 5.5