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=-9.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_GIT 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 63C49CA9EAF for ; Thu, 24 Oct 2019 08:49:38 +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 36D2120684 for ; Thu, 24 Oct 2019 08:49:38 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 36D2120684 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=proxmox.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Received: from localhost ([::1]:35312 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iNYoL-00077g-Cl for qemu-devel@archiver.kernel.org; Thu, 24 Oct 2019 04:49:37 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:37480) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1iNYOC-0004SO-8D for qemu-devel@nongnu.org; Thu, 24 Oct 2019 04:22:37 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1iNYOA-0000lE-U9 for qemu-devel@nongnu.org; Thu, 24 Oct 2019 04:22:35 -0400 Received: from proxmox-new.maurer-it.com ([212.186.127.180]:3405) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1iNYOA-0000jC-Mq; Thu, 24 Oct 2019 04:22:34 -0400 Received: from proxmox-new.maurer-it.com (localhost.localdomain [127.0.0.1]) by proxmox-new.maurer-it.com (Proxmox) with ESMTP id AE566407FB; Thu, 24 Oct 2019 10:12:32 +0200 (CEST) From: Wolfgang Bumiller To: qemu-devel@nongnu.org Subject: [PATCH v2] monitor/qmp: resume monitor when clearing its queue Date: Thu, 24 Oct 2019 10:12:31 +0200 Message-Id: <20191024081231.19087-1-w.bumiller@proxmox.com> X-Mailer: git-send-email 2.20.1 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable 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 , =?UTF-8?q?Marc-Andr=C3=A9=20Lureau?= , Gerd Hoffmann , Markus Armbruster , qemu-stable@nongnu.org Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.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. Any new connections to the qmp socket will be accept()ed and show the greeting, but will not respond to any messages sent afterwards (as they will not be read from the still-suspended socket). Fix this by resuming the monitor when clearing a queue which was filled up. Signed-off-by: Wolfgang Bumiller --- Changes to v1: * Update commit message to include the resulting symptoms. * Moved the resume code from `monitor_qmp_cleanup_req_queue_locked` to `monitor_qmp_cleanup_queues` to avoid an unnecessary resume when destroying the monitor (as the `_locked` version is also used by `monitor_data_destroy()`. * Renamed `monitor_qmp_cleanup_queues` to `monitor_qmp_cleanup_queues_and_resume` to reflect the change and be verbose about it for potential future users of the function. Currently the only user is `monitor_qmp_event()` in the `CHR_EVENT_CLOSED` case, which is exactly the problematic case curren= tly. Sorry for the deleay :| monitor/qmp.c | 24 ++++++++++++++++++++++-- 1 file changed, 22 insertions(+), 2 deletions(-) diff --git a/monitor/qmp.c b/monitor/qmp.c index 9d9e5d8b27..df689aa95e 100644 --- a/monitor/qmp.c +++ b/monitor/qmp.c @@ -75,10 +75,30 @@ static void monitor_qmp_cleanup_req_queue_locked(Moni= torQMP *mon) } } =20 -static void monitor_qmp_cleanup_queues(MonitorQMP *mon) +static void monitor_qmp_cleanup_queues_and_resume(MonitorQMP *mon) { qemu_mutex_lock(&mon->qmp_queue_lock); + + /* + * Same condition as in monitor_qmp_bh_dispatcher(), but before remo= ving an + * element from the queue (hence no `- 1`), also, the queue should n= ot be + * empty either, otherwise the monitor hasn't been suspended yet (or= was + * already resumed). + */ + bool need_resume =3D (!qmp_oob_enabled(mon) && mon->qmp_requests->le= ngth > 0) + || mon->qmp_requests->length =3D=3D QMP_REQ_QUEUE_LEN_MAX; + monitor_qmp_cleanup_req_queue_locked(mon); + + if (need_resume) { + /* + * Pairs with the monitor_suspend() in handle_qmp_command() in c= ase the + * queue gets cleared from a CH_EVENT_CLOSED event before the di= spatch + * bh got scheduled. + */ + monitor_resume(&mon->common); + } + qemu_mutex_unlock(&mon->qmp_queue_lock); } =20 @@ -332,7 +352,7 @@ static void monitor_qmp_event(void *opaque, int event= ) * stdio, it's possible that stdout is still open when stdin * is closed. */ - monitor_qmp_cleanup_queues(mon); + monitor_qmp_cleanup_queues_and_resume(mon); json_message_parser_destroy(&mon->parser); json_message_parser_init(&mon->parser, handle_qmp_command, mon, NULL); --=20 2.20.1