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=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED autolearn=no 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 6F4FEC34022 for ; Wed, 19 Feb 2020 21:22:42 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 273C82465D for ; Wed, 19 Feb 2020 21:22:42 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="TwGo8139" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 273C82465D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linux-foundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id C53856B000D; Wed, 19 Feb 2020 16:22:41 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id C05026B0096; Wed, 19 Feb 2020 16:22:41 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id B19226B0098; Wed, 19 Feb 2020 16:22:41 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0112.hostedemail.com [216.40.44.112]) by kanga.kvack.org (Postfix) with ESMTP id 985016B000D for ; Wed, 19 Feb 2020 16:22:41 -0500 (EST) Received: from smtpin09.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with ESMTP id 62747181AEF10 for ; Wed, 19 Feb 2020 21:22:41 +0000 (UTC) X-FDA: 76508150922.09.slave44_348b849764b2f X-HE-Tag: slave44_348b849764b2f X-Filterd-Recvd-Size: 3055 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by imf01.hostedemail.com (Postfix) with ESMTP for ; Wed, 19 Feb 2020 21:22:40 +0000 (UTC) Received: from X1 (nat-ab2241.sltdut.senawave.net [162.218.216.4]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id ECAE124656; Wed, 19 Feb 2020 21:22:39 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1582147360; bh=SMT83HTbhfyboCPhfsiX1K20ihz6gLD6srtGATEOVI0=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=TwGo8139M7PeZk7Ov1iEDzoLrm1mJZkY3kstaz84xgWoJbRuTjVmp5aqfcHPmKG9M kjI4/Wm5JwTpg8UlU9udwUB24H1NaXig16E9n0t/Nki27LU2HfkQKbuzg2Jtq74Mt0 KMSow4Ne76+p2IgcExEruN5IHkGzH2vIxV1CL3dI= Date: Wed, 19 Feb 2020 13:22:39 -0800 From: Andrew Morton To: "Kirill A. Shutemov" Cc: Dan Williams , Justin He , linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Kirill A. Shutemov" , Jeff Moyer Subject: Re: [PATCH] mm: Avoid data corruption on CoW fault into PFN-mapped VMA Message-Id: <20200219132239.92a22479e4bff7ec73ae6bdb@linux-foundation.org> In-Reply-To: <20200218154151.13349-1-kirill.shutemov@linux.intel.com> References: <20200218154151.13349-1-kirill.shutemov@linux.intel.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.32; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit 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 Tue, 18 Feb 2020 18:41:51 +0300 "Kirill A. Shutemov" wrote: > Jeff Moyer has reported that one of xfstests triggers a warning when run > on DAX-enabled filesystem: > > WARNING: CPU: 76 PID: 51024 at mm/memory.c:2317 wp_page_copy+0xc40/0xd50 > ... > wp_page_copy+0x98c/0xd50 (unreliable) > do_wp_page+0xd8/0xad0 > __handle_mm_fault+0x748/0x1b90 > handle_mm_fault+0x120/0x1f0 > __do_page_fault+0x240/0xd70 > do_page_fault+0x38/0xd0 > handle_page_fault+0x10/0x30 > > The warning happens on failed __copy_from_user_inatomic() which tries to > copy data into a CoW page. > > This happens because of race between MADV_DONTNEED and CoW page fault: > > CPU0 CPU1 > handle_mm_fault() > do_wp_page() > wp_page_copy() > do_wp_page() > madvise(MADV_DONTNEED) > zap_page_range() > zap_pte_range() > ptep_get_and_clear_full() > > __copy_from_user_inatomic() > sees empty PTE and fails > WARN_ON_ONCE(1) > clear_page() > > The solution is to re-try __copy_from_user_inatomic() under PTL after > checking that PTE is matches the orig_pte. > > The second copy attempt can still fail, like due to non-readable PTE, > but there's nothing reasonable we can do about, except clearing the CoW > page. You don't think this is worthy of a cc:stable?