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=-8.1 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,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 B5349C43331 for ; Thu, 26 Mar 2020 18:28:17 +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 8046720719 for ; Thu, 26 Mar 2020 18:28:17 +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="TChAy4y5" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 8046720719 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]:57512 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jHXEm-0001qN-Kj for qemu-devel@archiver.kernel.org; Thu, 26 Mar 2020 14:28:16 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:49929) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jHXDx-000153-9E for qemu-devel@nongnu.org; Thu, 26 Mar 2020 14:27:26 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1jHXDv-0002x3-4W for qemu-devel@nongnu.org; Thu, 26 Mar 2020 14:27:24 -0400 Received: from us-smtp-delivery-74.mimecast.com ([63.128.21.74]:34555) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1jHXDu-0002w0-O7 for qemu-devel@nongnu.org; Thu, 26 Mar 2020 14:27:23 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1585247241; 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=wd+Wa71uTGKZJFeWCrqDj97TiA4DwHCn0PvYsSkBlfk=; b=TChAy4y5TCGBDBqoHOkAFeCcn6nRAqLwzA9KQQmg3CAa/PwrTMQm3aMr0JJlcUHfYelIMZ WBUpAZB1Ig0gz2oE6PdR3EiP2RI9OLFGb6mjwqzp2rC+J9bYJveSVy6QjDuvHaMyPDveH9 7WHer/iHns8nJo9rMBmqJHoWIk+btU0= 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-370-npXt21bkNKWszIHhh3yR3w-1; Thu, 26 Mar 2020 14:27:19 -0400 X-MC-Unique: npXt21bkNKWszIHhh3yR3w-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id D7CA7107ACC7; Thu, 26 Mar 2020 18:27:18 +0000 (UTC) Received: from dresden.str.redhat.com (ovpn-112-132.ams2.redhat.com [10.36.112.132]) by smtp.corp.redhat.com (Postfix) with ESMTPS id F41F65C1BA; Thu, 26 Mar 2020 18:27:16 +0000 (UTC) Subject: Re: [PATCH v2 2/2] mirror: Wait only for in-flight operations To: Kevin Wolf , qemu-block@nongnu.org References: <20200326153628.4869-1-kwolf@redhat.com> <20200326153628.4869-3-kwolf@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: <09eee5b4-71aa-97a2-1ea9-c6bfc313e77f@redhat.com> Date: Thu, 26 Mar 2020 19:27:14 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <20200326153628.4869-3-kwolf@redhat.com> X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="4gpxe1jZ0NdxBSHrOB4EGz9PM7xrs4S89" X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 63.128.21.74 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: jsnow@redhat.com, qemu-devel@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) --4gpxe1jZ0NdxBSHrOB4EGz9PM7xrs4S89 Content-Type: multipart/mixed; boundary="DclIpgKjNjBUOL36CsYxCFtuAaHGOyICh" --DclIpgKjNjBUOL36CsYxCFtuAaHGOyICh Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 26.03.20 16:36, Kevin Wolf wrote: > mirror_wait_for_free_in_flight_slot() just picks a random operation to > wait for. However, a MirrorOp is already in s->ops_in_flight when > mirror_co_read() waits for free slots, so if not enough slots are > immediately available, an operation can end up waiting for itself, or > two or more operations can wait for each other to complete, which > results in a hang. >=20 > Fix this by adding a flag to MirrorOp that tells us if the request is > already in flight (and therefore occupies slots that it will later > free), and picking only such operations for waiting. >=20 > Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=3D1794692 > Signed-off-by: Kevin Wolf > --- > block/mirror.c | 9 ++++++++- > 1 file changed, 8 insertions(+), 1 deletion(-) >=20 > diff --git a/block/mirror.c b/block/mirror.c > index 393131b135..88414d1653 100644 > --- a/block/mirror.c > +++ b/block/mirror.c [...] > @@ -1318,6 +1324,7 @@ static MirrorOp *coroutine_fn active_write_prepare(= MirrorBlockJob *s, > .offset =3D offset, > .bytes =3D bytes, > .is_active_write =3D true, > + .is_in_flight =3D true, > }; > qemu_co_queue_init(&op->waiting_requests); > QTAILQ_INSERT_TAIL(&s->ops_in_flight, op, next); >=20 There is a mirror_wait_on_conflicts() call after this. I was a bit worried about dependencies there. But I don=E2=80=99t think there=E2=80=99= s any problem, because mirror_wait_for_any_operation() is only called by: (1) mirror_wait_for_free_in_flight_slot(), which makes it look for non-active operations only, and (2) mirror_run(), which specifically waits for all active operations to settle, so it makes sense to wait for all of them, even when they are still doing their own dependency-waiting. But still, I=E2=80=99m not sure whether this is conceptually the best thing= to do. I think what we actually want is for mirror_wait_for_free_in_flight_slot() to only wait for in-flight operations; but the call in mirror_run() that waits for active-mirror operations wants to wait for all active-mirror operations, not just the ones that are in flight. So I think conceptually it would make more sense to set is_in_flight only after mirror_wait_on_conflicts(), and ensure that the mirror_wait_for_any_operation() call from mirror_run() ignores is_in_flight. E.g. by having another parameter =E2=80=9Cbool in_flight=E2= =80=9D for mirror_wait_for_any_operation() that chooses whether to check is_in_flight or whether to ignore it. In practice, @in_flight would always be the same as @active, but they are different things. But that would mean we would always ignore is_in_flight for active-mirror operations. In practice, there=E2=80=99s no difference to what this patch does, i.e. to= just let active-mirror operations have is_in_flight to be always true and let mirror_wait_for_any_operation() check is_in_flight unconditionally. So I don=E2=80=99t know. Maybe this is a start: Functionally-reviewed-by: Max Reitz Max --DclIpgKjNjBUOL36CsYxCFtuAaHGOyICh-- --4gpxe1jZ0NdxBSHrOB4EGz9PM7xrs4S89 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEEkb62CjDbPohX0Rgp9AfbAGHVz0AFAl589AIACgkQ9AfbAGHV z0B4qgf9HWlSoHmqH4XEip7iGk6NA3kZHD54I/+5NATNEamZkY5IjG4wNDARGhlF ezjhf6i6PlzRsHJ0Idx+6OhkWF2XkJqy1mB0A62F9uKx+Xk6ZLvAcEy/jGym6fi4 7jXuKRIA1ysiXWP3mvOH3IH5VPACi2KaYeq903iIs9gcH89Xm+158evT+4ZkAvFA NMOPe5K0E142whGV78qXv6tjqLiSPFAiZGR35KVmB9W5nWEvx2bpVPQJuIbzLiBb a6bjhwhGSPm/F8BPPRucdkRzaK7iePMisiYGb8tSkikAnNQKg3Iip+6faC0AUtc4 CZlPoNhlwMDZj9RTm5fHbR94C085OQ== =op5Y -----END PGP SIGNATURE----- --4gpxe1jZ0NdxBSHrOB4EGz9PM7xrs4S89--