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=-1.0 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 40ED0CA90AF for ; Tue, 12 May 2020 15:59:40 +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 F12C02054F for ; Tue, 12 May 2020 15:59:39 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="XZYPIrNC" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org F12C02054F 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]:51542 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jYXJj-0008I0-4w for qemu-devel@archiver.kernel.org; Tue, 12 May 2020 11:59:39 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:43486) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jYXIr-0007GQ-Qf for qemu-devel@nongnu.org; Tue, 12 May 2020 11:58:45 -0400 Received: from us-smtp-2.mimecast.com ([207.211.31.81]:42358 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 1jYXIq-0003aA-UC for qemu-devel@nongnu.org; Tue, 12 May 2020 11:58:45 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1589299123; 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: in-reply-to:in-reply-to:references:references; bh=jvnz7FX33H6HQ6Cb1lKhjYigd52Yp7dFl7bV/HpbkeA=; b=XZYPIrNCYGAKX1yIMPlMursakIIs6bOCuV0nZfQ6nlvvJ0uUWFByNKhkwol6h/HYjLfJNs kjAovxkndCJO75I6vXw39MzW8VRDAyUCMTLx4CW8j2+m8ImH7BJQGo7lI2JlmTLQck4EAD xSOTWVA2ODHMGCGZAYeDHYjPEwlB5QI= 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-427-SnIlkeh5Msmtrbxsj3yW1w-1; Tue, 12 May 2020 11:58:41 -0400 X-MC-Unique: SnIlkeh5Msmtrbxsj3yW1w-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.phx2.redhat.com [10.5.11.16]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 9F9148005B7 for ; Tue, 12 May 2020 15:58:40 +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 6CD665C1B2; Tue, 12 May 2020 15:58:40 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id EFA4F11358BC; Tue, 12 May 2020 17:58:38 +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> <87zhal4lef.fsf@dusky.pond.sub.org> Date: Tue, 12 May 2020 17:58:38 +0200 In-Reply-To: <87zhal4lef.fsf@dusky.pond.sub.org> (Markus Armbruster's message of "Wed, 06 May 2020 08:39:36 +0200") Message-ID: <87o8qttaa9.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 2.79 on 10.5.11.16 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain 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 = 2020/05/12 01:41:59 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" Markus Armbruster writes: > 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. >>> >>> 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. >>> >>> 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. >>> >>> 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. Look, a rabbit hole :) I got rough patches, with several more to do. There's one thing worth mentioning. Unrealize is recursive: unrealizing a qdev recurses into its qbuses, and unrealizing a qbus recurses into its qdevs. Realize, however, is TODO recursive :) See your commit 5942a19040 "qdev: recursively unrealize devices when unrealizing bus", 2014-06-19. Moving "put on qbus" from qdev_create() (and its wrappers) to qdev_init_nofail() means we put on bus by realizing. No use to recursive realization then, > [*] We might want to look into deduplicating: the string "realized" > occurs more than 450 times, and I figure almost always as property name. I wield a sharp hatchet.