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=-8.5 required=3.0 tests=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 5D0DDC5ACAE for ; Thu, 12 Sep 2019 10:33:23 +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 339FB20692 for ; Thu, 12 Sep 2019 10:33:23 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 339FB20692 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]:60500 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i8MPh-00012u-QH for qemu-devel@archiver.kernel.org; Thu, 12 Sep 2019 06:33:21 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:54743) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1i8MIc-00043q-Cz for qemu-devel@nongnu.org; Thu, 12 Sep 2019 06:26:04 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1i8MIa-0001S3-AE for qemu-devel@nongnu.org; Thu, 12 Sep 2019 06:26:02 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43796) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1i8MIR-0001PU-Mw; Thu, 12 Sep 2019 06:25:51 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id EDDAF3B464; Thu, 12 Sep 2019 10:25:50 +0000 (UTC) Received: from linux.fritz.box (ovpn-116-179.ams2.redhat.com [10.36.116.179]) by smtp.corp.redhat.com (Postfix) with ESMTPS id DE3E6194B9; Thu, 12 Sep 2019 10:25:47 +0000 (UTC) Date: Thu, 12 Sep 2019 12:25:46 +0200 From: Kevin Wolf To: Sergio Lopez Message-ID: <20190912102546.GF5383@linux.fritz.box> References: <20190911161521.59261-1-slp@redhat.com> <20190912082322.GD5383@linux.fritz.box> <87zhj9x1ov.fsf@redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="adJ1OR3c6QgCpb/j" Content-Disposition: inline In-Reply-To: <87zhj9x1ov.fsf@redhat.com> User-Agent: Mutt/1.12.1 (2019-06-15) X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Thu, 12 Sep 2019 10:25:51 +0000 (UTC) X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: Re: [Qemu-devel] [PATCH] nbd/server: attach client channel to the export's AioContext 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: qemu-devel@nongnu.org, qemu-block@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" --adJ1OR3c6QgCpb/j Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Am 12.09.2019 um 12:13 hat Sergio Lopez geschrieben: >=20 > Kevin Wolf writes: >=20 > > Am 11.09.2019 um 18:15 hat Sergio Lopez geschrieben: > >> On creation, the export's AioContext is set to the same one as the > >> BlockBackend, while the AioContext in the client QIOChannel is left > >> untouched. > >>=20 > >> As a result, when using data-plane, nbd_client_receive_next_request() > >> schedules coroutines in the IOThread AioContext, while the client's > >> QIOChannel is serviced from the main_loop, potentially triggering the > >> assertion at qio_channel_restart_[read|write]. > >>=20 > >> To fix this, as soon we have the export corresponding to the client, > >> we call qio_channel_attach_aio_context() to attach the QIOChannel > >> context to the export's AioContext. This matches with the logic in > >> blk_aio_attached(). > >>=20 > >> RHBZ: https://bugzilla.redhat.com/show_bug.cgi?id=3D1748253 > >> Signed-off-by: Sergio Lopez > > > > Oh, looks like I only fixed switching the AioContext after the fact, but > > not starting the NBD server for a node that is already in a different > > AioContext... :-/ > > > >> diff --git a/nbd/server.c b/nbd/server.c > >> index 10faedcfc5..51322e2343 100644 > >> --- a/nbd/server.c > >> +++ b/nbd/server.c > >> @@ -471,6 +471,7 @@ static int nbd_negotiate_handle_export_name(NBDCli= ent *client, > >> QTAILQ_INSERT_TAIL(&client->exp->clients, client, next); > >> nbd_export_get(client->exp); > >> nbd_check_meta_export(client); > >> + qio_channel_attach_aio_context(client->ioc, client->exp->ctx); > >> =20 > >> return 0; > >> } > >> @@ -673,6 +674,7 @@ static int nbd_negotiate_handle_info(NBDClient *cl= ient, uint16_t myflags, > >> QTAILQ_INSERT_TAIL(&client->exp->clients, client, next); > >> nbd_export_get(client->exp); > >> nbd_check_meta_export(client); > >> + qio_channel_attach_aio_context(client->ioc, exp->ctx); > >> rc =3D 1; > >> } > >> return rc; > > > > I think I would rather do this once at the end of nbd_negotiate() > > instead of duplicating it across the different way to open an export. > > During the negotiation phase, we don't start requests yet, so doing > > everything from the main thread should be fine. >=20 > OK. >=20 > > Actually, not doing everything from the main thread sounds nasty because > > I think the next QIOChannel callback could then already be executed in > > the iothread while this one hasn't completed yet. Or do we have any > > locking in place for the negotiation? >=20 > This is the first time I look at NBD code, but IIUC all the negotiation > is done with synchronous nbd_[read|write]() calls, so even if the > coroutine yields due to EWOULDBLOCK, nothing else should be making > progress. Ah, yes, you're right. We don't even have fd handlers installed if we aren't currently waiting for the coroutine to be re-entered. So as everything is tied to the one coroutine, this should not be a problem. Let's avoid the duplication anyway. 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