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=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS 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 9D394C76188 for ; Mon, 22 Jul 2019 13:31:39 +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 6D8F72190F for ; Mon, 22 Jul 2019 13:31:39 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6D8F72190F 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]:33582 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hpYPi-0004CY-9c for qemu-devel@archiver.kernel.org; Mon, 22 Jul 2019 09:31:38 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:51914) by lists.gnu.org with esmtp (Exim 4.86_2) (envelope-from ) id 1hpYPK-00037m-Sf for qemu-devel@nongnu.org; Mon, 22 Jul 2019 09:31:15 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1hpYPJ-00026o-Sb for qemu-devel@nongnu.org; Mon, 22 Jul 2019 09:31:14 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43692) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1hpYPH-00021t-J3; Mon, 22 Jul 2019 09:31:11 -0400 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 mx1.redhat.com (Postfix) with ESMTPS id DDC9A307D88C; Mon, 22 Jul 2019 13:31:10 +0000 (UTC) Received: from localhost (unknown [10.40.205.2]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 6F8F5646CD; Mon, 22 Jul 2019 13:31:08 +0000 (UTC) From: Max Reitz To: qemu-block@nongnu.org Date: Mon, 22 Jul 2019 15:30:53 +0200 Message-Id: <20190722133054.21781-2-mreitz@redhat.com> In-Reply-To: <20190722133054.21781-1-mreitz@redhat.com> References: <20190722133054.21781-1-mreitz@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.48]); Mon, 22 Jul 2019 13:31:10 +0000 (UTC) Content-Transfer-Encoding: quoted-printable X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] X-Received-From: 209.132.183.28 Subject: [Qemu-devel] [PATCH for-4.1 1/2] block: Dec. drained_end_counter before bdrv_wakeup 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 , qemu-devel@nongnu.org, Max Reitz Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Decrementing drained_end_counter after bdrv_dec_in_flight() (which in turn invokes bdrv_wakeup() and thus aio_wait_kick()) is not very clever. We should decrement it beforehand, so that any waiting aio_poll() that is woken by bdrv_dec_in_flight() sees the decremented drained_end_counter. Because the time window between decrementing drained_end_counter and aio_wait_kick() is very small, I cannot supply a reliable regression test. However, running e.g. the /bdrv-drain/blockjob/iothread/drain_all test in test-bdrv-drain has a small chance of hanging without this patch (about 1/200 or so; it gets to nearly 100 % if you add e.g. an fputc(' ', stderr); after the bdrv_dec_flight()). Fixes: e037c09c78520cbdb6da7cfc6ad0256d5870b814 Signed-off-by: Max Reitz --- block/io.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/block/io.c b/block/io.c index b89e155d21..06305c6ea6 100644 --- a/block/io.c +++ b/block/io.c @@ -217,13 +217,12 @@ static void coroutine_fn bdrv_drain_invoke_entry(vo= id *opaque) bs->drv->bdrv_co_drain_end(bs); } =20 - /* Set data->done before reading bs->wakeup. */ + /* Set data->done and decrement drained_end_counter before bdrv_wake= up() */ atomic_mb_set(&data->done, true); - bdrv_dec_in_flight(bs); - if (!data->begin) { atomic_dec(data->drained_end_counter); } + bdrv_dec_in_flight(bs); =20 g_free(data); } --=20 2.21.0