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 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 smtp.lore.kernel.org (Postfix) with ESMTPS id DAE5DD116E2 for ; Mon, 1 Dec 2025 06:01:06 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vPwxX-0006BW-Ch; Mon, 01 Dec 2025 01:00:27 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1vPwxV-000694-Ki for qemu-devel@nongnu.org; Mon, 01 Dec 2025 01:00:25 -0500 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1vPwxP-0004fx-Kn for qemu-devel@nongnu.org; Mon, 01 Dec 2025 01:00:24 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1764568815; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=XBPBpbsS2JyvptKS0jTD17AI3l/fBMkx7rikPQaQ/aE=; b=gOhR8TPUruXun6Hg92lL6gwP8DBF12DOF9mQ4Rk0szkwmH+olugf7jO81FVJneRuzTwkTB TJc3FqdfFO0RCoP7B/KaMFzhnlajyvWKlJ+emfHv5HlnUva3gUaajBp2lvAX6ja3fwHPo9 KRrAkQzRM5cc9cXnVly5cUusOfqTRi0= Received: from mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-22-9F9v1LzsP4WRje1esxdb1g-1; Mon, 01 Dec 2025 01:00:11 -0500 X-MC-Unique: 9F9v1LzsP4WRje1esxdb1g-1 X-Mimecast-MFC-AGG-ID: 9F9v1LzsP4WRje1esxdb1g_1764568810 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 602C61955F2A; Mon, 1 Dec 2025 06:00:10 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.45.242.7]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id B9A55195608E; Mon, 1 Dec 2025 06:00:09 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id DCF1321E6A27; Mon, 01 Dec 2025 07:00:06 +0100 (CET) From: Markus Armbruster To: Jie Song Cc: marcandre.lureau@gmail.com, eblake@redhat.com, berrange@redhat.com, qemu-devel@nongnu.org, songjie_yewu@cmss.chinamobile.com, =?utf-8?Q?Ma?= =?utf-8?Q?rc-Andr=C3=A9?= Lureau Subject: Re: [PATCH v4] monitor/qmp: cleanup SocketChardev listener sources early to avoid fd handling race In-Reply-To: <20251125140706.114197-1-mail@jiesong.me> (Jie Song's message of "Tue, 25 Nov 2025 22:07:06 +0800") References: <20251125140706.114197-1-mail@jiesong.me> Date: Mon, 01 Dec 2025 07:00:06 +0100 Message-ID: <87ms424u8p.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Received-SPF: pass client-ip=170.10.133.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H3=-0.01, RCVD_IN_MSPIKE_WL=-0.01, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Jie Song, Marc-Andr=C3=A9, is this bug serious enough and the fix safe enou= gh to still go into 10.2? Jie Song writes: > From: Jie Song > > When starting a dummy QEMU process with virsh version, monitor_init_qmp() > enables IOThread monitoring of the QMP fd by default. However, a race > condition exists during the initialization phase: the IOThread only remov= es > the main thread's fd watch when it reaches qio_net_listener_set_client_fu= nc_full(), > which may be delayed under high system load. > > This creates a window between monitor_qmp_setup_handlers_bh() and > qio_net_listener_set_client_func_full() where both the main thread and > IOThread are simultaneously monitoring the same fd and processing events. > This race can cause either the main thread or the IOThread to hang and > become unresponsive. > > Fix this by proactively cleaning up the listener's IO sources in > monitor_init_qmp() before the IOThread initializes QMP monitoring, > ensuring exclusive fd ownership and eliminating the race condition. > > Signed-off-by: Jie Song > Reviewed-by: Marc-Andr=C3=A9 Lureau