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=-8.3 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 D25DCC742AE for ; Fri, 12 Jul 2019 09:24:39 +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 A620620838 for ; Fri, 12 Jul 2019 09:24:39 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A620620838 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]:47728 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hlrnC-0007Ts-RY for qemu-devel@archiver.kernel.org; Fri, 12 Jul 2019 05:24:38 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:42242) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hlrn2-00071v-UX for qemu-devel@nongnu.org; Fri, 12 Jul 2019 05:24:29 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hlrn1-0002pj-VX for qemu-devel@nongnu.org; Fri, 12 Jul 2019 05:24:28 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44476) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hlrmz-0002iU-LA; Fri, 12 Jul 2019 05:24:25 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 6D3B04ACDF; Fri, 12 Jul 2019 09:24:24 +0000 (UTC) Received: from dhcp-200-226.str.redhat.com (dhcp-200-226.str.redhat.com [10.33.200.226]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 3C6825DD91; Fri, 12 Jul 2019 09:24:21 +0000 (UTC) Date: Fri, 12 Jul 2019 11:24:19 +0200 From: Kevin Wolf To: Max Reitz Message-ID: <20190712092419.GB4514@dhcp-200-226.str.redhat.com> References: <20190711195804.30703-1-mreitz@redhat.com> <20190711195804.30703-2-mreitz@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190711195804.30703-2-mreitz@redhat.com> User-Agent: Mutt/1.11.3 (2019-02-01) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Fri, 12 Jul 2019 09:24:24 +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] [RFC 1/5] block/nbd: Fix hang in .bdrv_close() 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: Stefan Hajnoczi , qemu-devel@nongnu.org, qemu-block@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Am 11.07.2019 um 21:58 hat Max Reitz geschrieben: > When nbd_close() is called from a coroutine, the connection_co never > gets to run, and thus nbd_teardown_connection() hangs. > > This is because aio_co_enter() only puts the connection_co into the main > coroutine's wake-up queue, so this main coroutine needs to yield and > reschedule itself to let the connection_co run. > > Signed-off-by: Max Reitz > --- > block/nbd.c | 12 +++++++++++- > 1 file changed, 11 insertions(+), 1 deletion(-) > > diff --git a/block/nbd.c b/block/nbd.c > index 81edabbf35..b83b6cd43e 100644 > --- a/block/nbd.c > +++ b/block/nbd.c > @@ -135,7 +135,17 @@ static void nbd_teardown_connection(BlockDriverState *bs) > qio_channel_shutdown(s->ioc, > QIO_CHANNEL_SHUTDOWN_BOTH, > NULL); > - BDRV_POLL_WHILE(bs, s->connection_co); > + > + if (qemu_in_coroutine()) { > + /* Let our caller poll and just yield until connection_co is done */ > + while (s->connection_co) { > + aio_co_schedule(qemu_get_current_aio_context(), > + qemu_coroutine_self()); > + qemu_coroutine_yield(); > + } Isn't this busy waiting? Why not let s->connection_co wake us up when it's about to terminate instead of immediately rescheduling ourselves? > + } else { > + BDRV_POLL_WHILE(bs, s->connection_co); > + } > > nbd_client_detach_aio_context(bs); > object_unref(OBJECT(s->sioc)); Kevin