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=-0.9 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS autolearn=no 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 3B481C28CBC for ; Wed, 6 May 2020 06:40:50 +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 04704206E6 for ; Wed, 6 May 2020 06:40:49 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="E5zoreIw" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 04704206E6 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]:55904 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jWDjd-0002EQ-35 for qemu-devel@archiver.kernel.org; Wed, 06 May 2020 02:40:49 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:43848) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jWDib-0001VR-Dq for qemu-devel@nongnu.org; Wed, 06 May 2020 02:39:45 -0400 Received: from us-smtp-1.mimecast.com ([207.211.31.81]:44049 helo=us-smtp-delivery-1.mimecast.com) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1jWDiY-0006tH-R5 for qemu-devel@nongnu.org; Wed, 06 May 2020 02:39:44 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1588747180; 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=uHEDi7QUzdfPppoODZMKZNkQcWEBzFTL5ac4jf/Q5iI=; b=E5zoreIwyg/JVZzm+Yi6wMlBUjuu8QJk2D2Yf751c40X2uArMEUdTaFCLHDUUGHYbx/ab/ /A2vL0mWQvdDO+DbCvYf4SZuu023j3wbqxj2KymUNNxrBTmxfUtb11p4faM8S6nSzMqU+X yp2oZf4anCG8YNRgerGeD26c6v6/vSY= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-495-q7-Cs1zMPSuh4h5c3CMk_w-1; Wed, 06 May 2020 02:39:39 -0400 X-MC-Unique: q7-Cs1zMPSuh4h5c3CMk_w-1 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 46CAE100CCC2 for ; Wed, 6 May 2020 06:39:38 +0000 (UTC) Received: from blackfin.pond.sub.org (ovpn-113-6.ams2.redhat.com [10.36.113.6]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 134DB25277; Wed, 6 May 2020 06:39:37 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 81C3E11358BC; Wed, 6 May 2020 08:39:36 +0200 (CEST) From: Markus Armbruster To: Paolo Bonzini Subject: Re: Infinite loop in bus_unparent(), qdev bug or qdev misuse? References: <87tv0vzrwj.fsf@dusky.pond.sub.org> <6fc8633a-6d91-b83a-e6cd-5f714ccaf9ea@redhat.com> <875zda8j3m.fsf@dusky.pond.sub.org> Date: Wed, 06 May 2020 08:39:36 +0200 In-Reply-To: (Paolo Bonzini's message of "Tue, 5 May 2020 18:26:57 +0200") Message-ID: <87zhal4lef.fsf@dusky.pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.3 (gnu/linux) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain Content-Transfer-Encoding: quoted-printable Received-SPF: pass client-ip=207.211.31.81; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/06 02:39:40 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] [fuzzy] 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_H2=-0.001, SPF_PASS=-0.001 autolearn=_AUTOLEARN X-Spam_action: no action 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: "Daniel P. Berrange" , qemu-devel@nongnu.org, Eduardo Habkost Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" Paolo Bonzini writes: > On 05/05/20 18:03, Markus Armbruster wrote: >>> That's a good one, and especially a safe one, since it matches >>> qdev_device_add. It has the disadvantage of having to touch all >>> qdev_create() calls. >>=20 >> Also, it moves onboard devices from /machine/unattached/ to >> /machine/peripheral-anon/. > > Uh indeed. No that's too ugly. > >>> Even better however would be to move the bus argument (and thus >>> qdev_set_parent_bus) to qdev_init, and likewise in qdev_device_add move >>> qdev_set_id after qemu_opt_foreach. I looked at the property setters >>> and couldn't find anything suspicious (somewhat to my surprise), but I >>> haven't honestly tried. >>=20 >> Thus, we satisfy bus_unparent()'s precondition "bus children have a QOM >> parent"[*] by moving "add to parent bus" next to the place where we >> ensure "has QOM parent" by putting orphans under /machine/unattached/. >> Makes sense. >>=20 >> If we add to the bus first, the precondition ceases to hold until we >> realize. Ugly, but harmless unless we manage to actually call the >> function then. > > Shouldn't be a big deal, since users should call either qdev_set_id or > object_property_add_child before device_set_realized. The issue isn't neglecting to set a QOM parent, it's destroying a device before its bus children get their QOM parent. Mostly harmless: by delaying "add to bus" until right before realize, we narrow the window where the trap is armed, and keep it completely within qdev_init_nofail(), qdev_device_add(), and possibly code that duplicates their work. Ensuring qdev_init_nofail() and qdev_device_add() don't fail in this window should be easy enough (except for writing the comment explaining it). The duplicates, though... I guess we need to double-check users of qdev_set_parent_bus(). Ugly: yes, compared to the pretty invariant "bus children all have QOM parents". >> I suspect we can't realize first, because the realize method may want to >> use the parent bus. > > Right. > > Moving the bus to qdev_init would be quite large but hopefully scriptable= . Feels feasible. [*] We might want to look into deduplicating: the string "realized" occurs more than 450 times, and I figure almost always as property name.