From patchwork Fri Aug 3 15:49:55 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Fam Zheng X-Patchwork-Id: 10555255 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id EA9B2157D for ; Fri, 3 Aug 2018 15:50:57 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id CDFD92C854 for ; Fri, 3 Aug 2018 15:50:57 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id C028F2C850; Fri, 3 Aug 2018 15:50:57 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from lists.gnu.org (lists.gnu.org [208.118.235.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 6567E2C850 for ; Fri, 3 Aug 2018 15:50:57 +0000 (UTC) Received: from localhost ([::1]:51996 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1flcLw-0000AQ-9f for patchwork-qemu-devel@patchwork.kernel.org; Fri, 03 Aug 2018 11:50:56 -0400 Received: from eggs.gnu.org ([2001:4830:134:3::10]:39650) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1flcLH-0008FR-3v for qemu-devel@nongnu.org; Fri, 03 Aug 2018 11:50:15 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1flcLG-0005zq-4p for qemu-devel@nongnu.org; Fri, 03 Aug 2018 11:50:15 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:44134 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1flcLB-0005pb-OX; Fri, 03 Aug 2018 11:50:09 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id B6C117788E; Fri, 3 Aug 2018 15:50:08 +0000 (UTC) Received: from lemon.usersys.redhat.com (ovpn-12-124.pek2.redhat.com [10.72.12.124]) by smtp.corp.redhat.com (Postfix) with ESMTP id 1310A2142F20; Fri, 3 Aug 2018 15:50:04 +0000 (UTC) From: Fam Zheng To: qemu-devel@nongnu.org Date: Fri, 3 Aug 2018 23:49:55 +0800 Message-Id: <20180803154955.25251-1-famz@redhat.com> X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.1]); Fri, 03 Aug 2018 15:50:08 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.1]); Fri, 03 Aug 2018 15:50:08 +0000 (UTC) for IP:'10.11.54.6' DOMAIN:'int-mx06.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'famz@redhat.com' RCPT:'' X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 66.187.233.73 Subject: [Qemu-devel] [RFC PATCH] async: Fix aio_notify_accept X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: pbonzini@redhat.com, Fam Zheng , qemu-block@nongnu.org, Stefan Hajnoczi Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" X-Virus-Scanned: ClamAV using ClamSMTP From main loop, bdrv_set_aio_context() can call IOThread's aio_poll(). That breaks aio_notify() because the ctx->notifier event can get cleared too early by this which causes IOThread hanging. See https://bugzilla.redhat.com/show_bug.cgi?id=1562750 for details. Signed-off-by: Fam Zheng --- util/async.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/util/async.c b/util/async.c index 05979f8014..c6e8aebc3a 100644 --- a/util/async.c +++ b/util/async.c @@ -355,7 +355,11 @@ void aio_notify(AioContext *ctx) void aio_notify_accept(AioContext *ctx) { - if (atomic_xchg(&ctx->notified, false)) { + /* If ctx->notify_me >= 2, another aio_poll() is waiting which may need the + * ctx->notifier event to wake up, so don't already clear it just because "we" are + * done iterating. */ + if (atomic_read(&ctx->notify_me) < 2 + && atomic_xchg(&ctx->notified, false)) { event_notifier_test_and_clear(&ctx->notifier); } }