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Mon, 28 Oct 2019 09:57:04 +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 9861160923; Mon, 28 Oct 2019 09:57:00 +0000 (UTC) Subject: Re: [RFC 0/3] block/file-posix: Work around XFS bug From: Max Reitz To: Stefan Hajnoczi References: <20191025095849.25283-1-mreitz@redhat.com> <20191027123555.GN4472@stefanha-x1.localdomain> <81bb0f91-2671-c9e5-f791-c7470dfd75ce@redhat.com> 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: <0f81f678-7d0d-56d3-d236-c077e4251f1a@redhat.com> Date: Mon, 28 Oct 2019 10:56:58 +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 2.79 on 10.5.11.13 X-Mimecast-Spam-Score: 0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="7XjDDcRSTz63y09OZ0OP6bBU44g6EgQxM" X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 207.211.31.120 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-block@nongnu.org, qemu-devel@nongnu.org, Vladimir Sementsov-Ogievskiy 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) --7XjDDcRSTz63y09OZ0OP6bBU44g6EgQxM Content-Type: multipart/mixed; boundary="VxlxTtBdPKRnUPbeRoyNFtpaQ4QukDrPb" --VxlxTtBdPKRnUPbeRoyNFtpaQ4QukDrPb Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable 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 ext= end >>>> tracked requests for post-EOF fallocate() calls (i.e., write-zero >>>> operations) to reach until infinity (INT64_MAX in practice), mark >>>> 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 this w= orkaround >>>> 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 fixes >>> to userspace. I didn't see another obvious way of doing it, maybe a >>> mount option that the kernel automatically sets and that gets reported >>> 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 point >>> 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 older >>> 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 disapp= ear 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 no > insight into that. I don=E2=80=99t think we can do ioctls to XFS over gl= uster, > 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 remote= filesystem anyway. Max --VxlxTtBdPKRnUPbeRoyNFtpaQ4QukDrPb-- --7XjDDcRSTz63y09OZ0OP6bBU44g6EgQxM Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl22u2sACgkQ9AfbAGHV z0DgZQf/W8ZaM+FYgzrriPUeZVP598ObkUJQagCmnyW3ak0XfSOn0s22D2kGu4eY /SOsYz3YI2lC4jFFXXn0WWn4aXj63HKBOGC4NlGxRU8DmXG0Z7cQJ4oUaXKKmrwM Kp/Jqn4EVD3vk2YLXjT2UJeT1Ob0F8iJ6jT1NRC7qdlK4avosgRnNUWj79JLJ+6A Tu3P09p+9BxhhPanMqTj50IkVeg4iThWCLKywaXPv4AYLdDMchqkGIV/s3ONzzes 7oBDh2nba/ncXEhbJiRMZhOEx7Xsmp/Ke/wHlo1cODYaK0JBVvlENZrKXPcum5W5 2oTpdOpg/Iv3cLDIDhAU7mPW9A2ejg== =geWA -----END PGP SIGNATURE----- --7XjDDcRSTz63y09OZ0OP6bBU44g6EgQxM--