From patchwork Wed Oct 2 08:30:03 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Wolfgang Bumiller X-Patchwork-Id: 1170529 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=pass (mailfrom) smtp.mailfrom=nongnu.org (client-ip=209.51.188.17; helo=lists.gnu.org; envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org; receiver=) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=proxmox.com 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 ozlabs.org (Postfix) with ESMTPS id 46jqKh40X1z9sDB for ; Wed, 2 Oct 2019 18:38:30 +1000 (AEST) Received: from localhost ([::1]:52568 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iFa9T-0005MP-0R for incoming@patchwork.ozlabs.org; Wed, 02 Oct 2019 04:38:27 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:38389) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iFa8q-0005MH-EF for qemu-devel@nongnu.org; Wed, 02 Oct 2019 04:37:49 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iFa8p-0005u6-5H for qemu-devel@nongnu.org; Wed, 02 Oct 2019 04:37:48 -0400 Received: from proxmox-new.maurer-it.com ([212.186.127.180]:41519) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iFa8o-0005tj-Ue; Wed, 02 Oct 2019 04:37:47 -0400 Received: from proxmox-new.maurer-it.com (localhost.localdomain [127.0.0.1]) by proxmox-new.maurer-it.com (Proxmox) with ESMTP id 4187C468A7; Wed, 2 Oct 2019 10:30:04 +0200 (CEST) From: Wolfgang Bumiller To: qemu-devel@nongnu.org Subject: [PATCH] monitor/qmp: resume monitor when clearing its queue Date: Wed, 2 Oct 2019 10:30:03 +0200 Message-Id: <20191002083003.21556-1-w.bumiller@proxmox.com> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 X-detected-operating-system: by eggs.gnu.org: GNU/Linux 2.2.x-3.x [generic] [fuzzy] X-Received-From: 212.186.127.180 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: Michael Roth , Markus Armbruster , qemu-stable@nongnu.org Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: "Qemu-devel" When a monitor's queue is filled up in handle_qmp_command() it gets suspended. It's the dispatcher bh's job currently to resume the monitor, which it does after processing an event from the queue. However, it is possible for a CHR_EVENT_CLOSED event to be processed before before the bh is scheduled, which will clear the queue without resuming the monitor, thereby preventing the dispatcher from reaching the resume() call. Fix this by resuming the monitor when clearing a queue which was filled up. Signed-off-by: Wolfgang Bumiller --- @Michael, we ran into this with qemu 4.0, so if the logic in this patch is correct it may make sense to include it in the 4.0.1 roundup. A backport is at [1] as 4.0 was before the monitor/ dir split. [1] https://gitlab.com/wbumiller/qemu/commit/9d8bbb5294ed084f282174b0c91e1a614e0a0714 monitor/qmp.c | 10 ++++++++++ 1 file changed, 10 insertions(+) diff --git a/monitor/qmp.c b/monitor/qmp.c index 9d9e5d8b27..c1db5bf940 100644 --- a/monitor/qmp.c +++ b/monitor/qmp.c @@ -70,9 +70,19 @@ static void qmp_request_free(QMPRequest *req) /* Caller must hold mon->qmp.qmp_queue_lock */ static void monitor_qmp_cleanup_req_queue_locked(MonitorQMP *mon) { + bool need_resume = (!qmp_oob_enabled(mon) && mon->qmp_requests->length > 0) + || mon->qmp_requests->length == QMP_REQ_QUEUE_LEN_MAX; while (!g_queue_is_empty(mon->qmp_requests)) { qmp_request_free(g_queue_pop_head(mon->qmp_requests)); } + if (need_resume) { + /* + * Pairs with the monitor_suspend() in handle_qmp_command() in case the + * queue gets cleared from a CH_EVENT_CLOSED event before the dispatch + * bh got scheduled. + */ + monitor_resume(&mon->common); + } } static void monitor_qmp_cleanup_queues(MonitorQMP *mon)