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=-2.0 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 C95DEC47E49 for ; Mon, 28 Oct 2019 10:11:25 +0000 (UTC) Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 8FF8820873 for ; Mon, 28 Oct 2019 10:11:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="IXkn2osI" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8FF8820873 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:52276 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iP1zg-0000d8-OT for qemu-devel@archiver.kernel.org; Mon, 28 Oct 2019 06:11:24 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:36490) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iP1yv-0008MX-5y for qemu-devel@nongnu.org; Mon, 28 Oct 2019 06:10:38 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iP1yt-0005v4-T5 for qemu-devel@nongnu.org; Mon, 28 Oct 2019 06:10:37 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:45291 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iP1yt-0005uP-No for qemu-devel@nongnu.org; Mon, 28 Oct 2019 06:10:35 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1572257434; 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:autocrypt:autocrypt; bh=jkoqH6JMDSwbfzE0qrtZ9Er5pG60NuTsLfm9p/EwgK8=; b=IXkn2osIRiJoIvISYaqFYw/fOqe70unCYAgC0noARirfG2YAo7fcQN+E4oPzkSvfZq7cci 9TDYUhkUTLi6MATl6mkidE+dAWkofXrlNJ/JTQSvDmWsFauhDg0K1MwkIRiFcPQih5aJke L/fKWr/ezIawKeEXPTsOBTJ8zwD4un4= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-431-RTraHrUqM2uA2A9JxbyHZA-1; Mon, 28 Oct 2019 06:10:31 -0400 X-MC-Unique: RTraHrUqM2uA2A9JxbyHZA-1 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 90FB85E4; Mon, 28 Oct 2019 10:10:30 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-117-83.ams2.redhat.com [10.36.117.83]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6310C1001B30; Mon, 28 Oct 2019 10:10:25 +0000 (UTC) Subject: Re: [RFC 0/3] block/file-posix: Work around XFS bug To: Vladimir Sementsov-Ogievskiy , Stefan Hajnoczi References: <20191025095849.25283-1-mreitz@redhat.com> <20191027123555.GN4472@stefanha-x1.localdomain> <81bb0f91-2671-c9e5-f791-c7470dfd75ce@redhat.com> <0f81f678-7d0d-56d3-d236-c077e4251f1a@redhat.com> From: Max Reitz Autocrypt: addr=mreitz@redhat.com; prefer-encrypt=mutual; keydata= mQENBFXOJlcBCADEyyhOTsoa/2ujoTRAJj4MKA21dkxxELVj3cuILpLTmtachWj7QW+TVG8U /PsMCFbpwsQR7oEy8eHHZwuGQsNpEtNC2G/L8Yka0BIBzv7dEgrPzIu+W3anZXQW4702+uES U29G8TP/NGfXRRHGlbBIH9KNUnOSUD2vRtpOLXkWsV5CN6vQFYgQfFvmp5ZpPeUe6xNplu8V mcTw8OSEDW/ZnxJc8TekCKZSpdzYoxfzjm7xGmZqB18VFwgJZlIibt1HE0EB4w5GsD7x5ekh awIe3RwoZgZDLQMdOitJ1tUc8aqaxvgA4tz6J6st8D8pS//m1gAoYJWGwwIVj1DjTYLtABEB AAG0HU1heCBSZWl0eiA8bXJlaXR6QHJlZGhhdC5jb20+iQFTBBMBCAA9AhsDBQkSzAMABQsJ CAcCBhUICQoLAgQWAgMBAh4BAheABQJVzie5FRhoa3A6Ly9rZXlzLmdudXBnLm5ldAAKCRD0 B9sAYdXPQDcIB/9uNkbYEex1rHKz3mr12uxYMwLOOFY9fstP5aoVJQ1nWQVB6m2cfKGdcRe1 2/nFaHSNAzT0NnKz2MjhZVmcrpyd2Gp2QyISCfb1FbT82GMtXFj1wiHmPb3CixYmWGQUUh+I AvUqsevLA+WihgBUyaJq/vuDVM1/K9Un+w+Tz5vpeMidlIsTYhcsMhn0L9wlCjoucljvbDy/ 8C9L2DUdgi3XTa0ORKeflUhdL4gucWoAMrKX2nmPjBMKLgU7WLBc8AtV+84b9OWFML6NEyo4 4cP7cM/07VlJK53pqNg5cHtnWwjHcbpGkQvx6RUx6F1My3y52vM24rNUA3+ligVEgPYBuQEN BFXOJlcBCADAmcVUNTWT6yLWQHvxZ0o47KCP8OcLqD+67T0RCe6d0LP8GsWtrJdeDIQk+T+F xO7DolQPS6iQ6Ak2/lJaPX8L0BkEAiMuLCKFU6Bn3lFOkrQeKp3u05wCSV1iKnhg0UPji9V2 W5eNfy8F4ZQHpeGUGy+liGXlxqkeRVhLyevUqfU0WgNqAJpfhHSGpBgihUupmyUg7lfUPeRM DzAN1pIqoFuxnN+BRHdAecpsLcbR8sQddXmDg9BpSKozO/JyBmaS1RlquI8HERQoe6EynJhd 64aICHDfj61rp+/0jTIcevxIIAzW70IadoS/y3DVIkuhncgDBvGbF3aBtjrJVP+5ABEBAAGJ ASUEGAEIAA8FAlXOJlcCGwwFCRLMAwAACgkQ9AfbAGHVz0CbFwf9F/PXxQR9i4N0iipISYjU sxVdjJOM2TMut+ZZcQ6NSMvhZ0ogQxJ+iEQ5OjnIputKvPVd5U7WRh+4lF1lB/NQGrGZQ1ic alkj6ocscQyFwfib+xIe9w8TG1CVGkII7+TbS5pXHRxZH1niaRpoi/hYtgzkuOPp35jJyqT/ /ELbqQTDAWcqtJhzxKLE/ugcOMK520dJDeb6x2xVES+S5LXby0D4juZlvUj+1fwZu+7Io5+B bkhSVPb/QdOVTpnz7zWNyNw+OONo1aBUKkhq2UIByYXgORPFnbfMY7QWHcjpBVw9MgC4tGeF R4bv+1nAMMxKmb5VvQCExr0eFhJUAHAhVg== Message-ID: Date: Mon, 28 Oct 2019 11:10:23 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-Mimecast-Spam-Score: 0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="wGImOGD3BfXqalnzaAE0Oji32y7UsBmOs" X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.81 X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Kevin Wolf , Anton Nefedov , Alberto Garcia , "qemu-devel@nongnu.org" , "qemu-block@nongnu.org" Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --wGImOGD3BfXqalnzaAE0Oji32y7UsBmOs Content-Type: multipart/mixed; boundary="5kwEvpp4v6yetQsQkeFJpDNGeeafliIwb" --5kwEvpp4v6yetQsQkeFJpDNGeeafliIwb Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 28.10.19 11:07, Vladimir Sementsov-Ogievskiy wrote: > 28.10.2019 12:56, Max Reitz wrote: >> On 28.10.19 10:30, Max Reitz wrote: >>> On 28.10.19 10:24, Max Reitz wrote: >>>> On 27.10.19 13:35, Stefan Hajnoczi wrote: >>>>> On Fri, Oct 25, 2019 at 11:58:46AM +0200, Max Reitz wrote: >>>>>> As for how we can address the issue, I see three ways: >>>>>> (1) The one presented in this series: On XFS with aio=3Dnative, we e= xtend >>>>>> tracked requests for post-EOF fallocate() calls (i.e., write-ze= ro >>>>>> operations) to reach until infinity (INT64_MAX in practice), ma= rk >>>>>> them serializing and wait for other conflicting requests. >>>>>> >>>>>> Advantages: >>>>>> + Limits the impact to very specific cases >>>>>> (And that means it wouldn=E2=80=99t hurt too much to keep thi= s workaround >>>>>> even when the XFS driver has been fixed) >>>>>> + Works around the bug where it happens, namely in file-posix >>>>>> >>>>>> Disadvantages: >>>>>> - A bit complex >>>>>> - A bit of a layering violation (should file-posix have access = to >>>>>> tracked requests?) >>>>> >>>>> Your patch series is reasonable. I don't think it's too bad. >>>>> >>>>> The main question is how to detect the XFS fix once it ships. XFS >>>>> already has a ton of ioctls, so maybe they don't mind adding a >>>>> feature/quirk bit map ioctl for publishing information about bug fixe= s >>>>> to userspace. I didn't see another obvious way of doing it, maybe a >>>>> mount option that the kernel automatically sets and that gets reporte= d >>>>> to userspace? >>>> >>>> I=E2=80=99ll add a note to the RH BZ. >>>> >>>>> If we imagine that XFS will not provide a mechanism to detect the >>>>> presence of the fix, then could we ask QEMU package maintainers to >>>>> ./configure --disable-xfs-fallocate-beyond-eof-workaround at some poi= nt >>>>> in the future when their distro has been shipping a fixed kernel for = a >>>>> while? It's ugly because it doesn't work if the user installs an old= er >>>>> custom-built kernel on the host. But at least it will cover 98% of >>>>> users... >>>> >>>> :-/ >>>> >>>> I don=E2=80=99t like it, but I suppose it would work. We could also >>>> automatically enable this disabling option in configure when we detect >>>> uname to report a kernel version that must include the fix. (This >>>> wouldn=E2=80=99t work for kernel with backported fixes, but those disa= ppear over >>>> time...) >>> I just realized that none of this is going to work for the gluster case >>> brought up by Nir. The affected kernel is the remote one and we have n= o >>> insight into that. I don=E2=80=99t think we can do ioctls to XFS over = gluster, >>> can we? >> >> On third thought, we could try to detect whether the file is on a remote >> filesystem, and if so enable the workaround unconditionally. I suppose >> it wouldn=E2=80=99t hurt performance-wise, given that it=E2=80=99s a rem= ote filesystem >> anyway. >> >=20 > I think, for remote, the difference may be even higher than for local, as= cost > of writing real zeroes through the wire vs fast zero command is high. I was speaking of a workaround in general, and that includes the workaround presented in this series. > Really, can we live with simple config option, is it so bad? The config option won=E2=80=99t work for remote hosts, though. That=E2=80= =99s exactly the problem. Max --5kwEvpp4v6yetQsQkeFJpDNGeeafliIwb-- --wGImOGD3BfXqalnzaAE0Oji32y7UsBmOs Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl22vo8ACgkQ9AfbAGHV z0ABUgf/eQ3khmJEFlBdAxyTRSkeQnO2moV9+Ygu00p89O718pkv8vl2VV7ZIjoj Zl95UvkXKcEKTWyftuS6nE4JfkphQvPKrbiyJYIs8WK3B4L12laI2IsokgsDSYVW wr2OqT9r2YF+O8hOiTvUWmT8dwo4yv7qghRPk0bTlhb/RL62Slrky2OdhZt3Oski qeWzP3vRrpuywdixoUsEQ9lhIcauyX9jStXe7fy6DvREs1gnJ3vAwEc2GEYu2a62 mKovxQHYKK4DdvxjrrIqJNLnhtfqKT7HnZXvh6qOvnPeHHXTfj8p2m5407JZp6MJ vApRuAimKRm1UlpxRzkAJx2FCWplGQ== =x3Ss -----END PGP SIGNATURE----- --wGImOGD3BfXqalnzaAE0Oji32y7UsBmOs--