From nobody Sat May 18 04:46:21 2024 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; dkim=fail; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail(p=none dis=none) header.from=redhat.com ARC-Seal: i=1; a=rsa-sha256; t=1588603207; cv=none; d=zohomail.com; s=zohoarc; b=JS3WMXS3EL+sph507P7U1MBB44pFhIR38GVWZ1lKUSRKQm+LeuPAv1/BOMdUegNgDMgS4yDZLAIsxjQ+k208/wEFI+gQUN9sSVRdL93/7n3HH+5Dn4FzCYbcXl1RJdp/6Kr2JXwFY6KgyGpQwuIltESfi5GFlbUdva/0OnVzMFU= ARC-Message-Signature: i=1; a=rsa-sha256; c=relaxed/relaxed; d=zohomail.com; s=zohoarc; t=1588603207; h=Content-Type:Content-Transfer-Encoding:Cc:Date:From:List-Subscribe:List-Post:List-Id:List-Archive:List-Help:List-Unsubscribe:MIME-Version:Message-ID:Sender:Subject:To; bh=H6YrDImHZnPxnhU2Gnx1G1rCpKwVZdPNBfoXlIT6i8g=; b=eFPJd+zC74R9plHm6dtWGP5G1UTo0KQvJexzKiqxKZBHcZE/9wsBnYcCjQIxGIQrO2nqNcm3W108vNkjBqTN98koIzrdyeRxiNgb1XBx0Oyep0MZgH7zXtMuIZ1tZKkN56TwlmynUm8RAMp/R/XHHfSTs+AV6YVl60wektcdrj0= ARC-Authentication-Results: i=1; mx.zohomail.com; dkim=fail; spf=pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) smtp.mailfrom=qemu-devel-bounces+importer=patchew.org@nongnu.org; dmarc=fail header.from= (p=none dis=none) header.from= Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1588603207716281.85257417354535; Mon, 4 May 2020 07:40:07 -0700 (PDT) Received: from localhost ([::1]:38240 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1jVcGM-0007fh-Eo for importer@patchew.org; Mon, 04 May 2020 10:40:06 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:48976) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1jVcFH-0005x1-KP for qemu-devel@nongnu.org; Mon, 04 May 2020 10:38:59 -0400 Received: from us-smtp-2.mimecast.com ([205.139.110.61]:34490 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 1jVcFG-0003LH-3u for qemu-devel@nongnu.org; Mon, 04 May 2020 10:38:58 -0400 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-310-Av9AdGBlOyqRk-eXXJ0kCA-1; Mon, 04 May 2020 10:38:55 -0400 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 2574A8014D5 for ; Mon, 4 May 2020 14:38:54 +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 E76465D9D5; Mon, 4 May 2020 14:38:53 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 7973E11358BC; Mon, 4 May 2020 16:38:52 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1588603136; 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; bh=H6YrDImHZnPxnhU2Gnx1G1rCpKwVZdPNBfoXlIT6i8g=; b=gv+JBYKHahHJfEYrBUnNAfZ6ss2AAc+0qGHDBBFhCHHnnwgpugLRIIRl8CRNr4uP/VlXpJ XQjC3KO9WdYcRkn7cs4zCbN+VSUxZ5NXCmrSE+3A3VXc7iZf/7bPJ49MRzAyLM+jPNlsWi M/xNKjp02UsMa+P4ruWhsREADMB7ogA= X-MC-Unique: Av9AdGBlOyqRk-eXXJ0kCA-1 From: Markus Armbruster To: qemu-devel@nongnu.org Subject: Infinite loop in bus_unparent(), qdev bug or qdev misuse? Date: Mon, 04 May 2020 16:38:52 +0200 Message-ID: <87tv0vzrwj.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 10.5.11.14 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Transfer-Encoding: quoted-printable Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; envelope-from=qemu-devel-bounces+importer=patchew.org@nongnu.org; helo=lists.gnu.org; Received-SPF: pass client-ip=205.139.110.61; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-1.mimecast.com X-detected-operating-system: by eggs.gnu.org: First seen = 2020/05/04 01:21:32 X-ACL-Warn: Detected OS = Linux 2.2.x-3.x [generic] 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: Paolo Bonzini , "Daniel P. Berrange" , Eduardo Habkost Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: "Qemu-devel" X-ZohoMail-DKIM: fail (Header signature does not verify) Content-Type: text/plain; charset="utf-8" I stumbled over this while working on a feature branch. Instead of throwing the whole branch at you as a reproducer, I give you a mock up. This is fdctrl_connect_drives(): dev =3D qdev_create(&fdctrl->bus.bus, "floppy"); qdev_prop_set_uint32(dev, "unit", i); qdev_prop_set_enum(dev, "drive-type", fdctrl->qdev_for_drives[i].ty= pe); blk_ref(blk); blk_detach_dev(blk, fdc_dev); fdctrl->qdev_for_drives[i].blk =3D NULL; qdev_prop_set_drive(dev, "drive", blk, &local_err); blk_unref(blk); if (local_err) { error_propagate(errp, local_err); return; } object_property_set_bool(OBJECT(dev), true, "realized", &local_err); if (local_err) { error_propagate(errp, local_err); return; } What if qdev_prop_set_drive() fails? I don't have a reproducer ready (I do on my feature branch), so let's mock it, and also instrument the place where things go wrong. Patch appended. To try it, run qemu-system-x86_64 without arguments. Turns out the failure bubbles up into device_set_realized() for the isa-fdc, where the cleanup code calls object_unparent(). This unparents children, and ends up in bus_unparent() for the isa-fdc's floppy-bus: #4 0x0000555555abdb7f in bus_unparent (obj=3D0x55555675a9f0) at /work/armbru/qemu/hw/core/bus.c:148 #5 0x0000555555d2aea6 in object_finalize_child_property (obj=3D0x55555675a800, name=3D0x555557281230 "floppy-bus.0", opaque= =3D0x55555675a9f0) at /work/armbru/qemu/qom/object.c:1672 #6 0x0000555555d2872b in object_property_del_child (obj=3D0x55555675a800, child=3D0x55555675a9f0, errp=3D0x0) at /work/armbru/qemu/qom/object.c:628 #7 0x0000555555d2880b in object_unparent (obj=3D0x55555675a9f0) at /work/armbru/qemu/qom/object.c:647 #8 0x0000555555ab9e10 in device_unparent (obj=3D0x55555675a800) at /work/armbru/qemu/hw/core/qdev.c:1101 This loop there while ((kid =3D QTAILQ_FIRST(&bus->children)) !=3D NULL) { DeviceState *dev =3D kid->child; object_unparent(OBJECT(dev)); } makes no progreess because OBJECT(dev)->parent is still null, and therefore object_unparent() does nothing. Possible culprit: qdev_try_create() calls qdev_set_parent_bus(), which adds the device to the bus, but leaves ->parent null. If this isn't wrong outright, it's at least a dangerous state. Work-around: call qdev_set_id(dev, NULL) right after qdev_create(). This sets ->parent. From 2554db096866138a85482d683e57a38166bb425b Mon Sep 17 00:00:00 2001 From: Markus Armbruster Date: Mon, 4 May 2020 15:58:10 +0200 Subject: [PATCH] qdev: Hack to reproduce infinite loop in bus_unparent() --- hw/block/fdc.c | 4 ++++ hw/core/bus.c | 5 +++++ 2 files changed, 9 insertions(+) diff --git a/hw/block/fdc.c b/hw/block/fdc.c index 9628cc171e..f57558eea4 100644 --- a/hw/block/fdc.c +++ b/hw/block/fdc.c @@ -2523,7 +2523,11 @@ static void fdctrl_connect_drives(FDCtrl *fdctrl, De= viceState *fdc_dev, blk_ref(blk); blk_detach_dev(blk, fdc_dev); fdctrl->qdev_for_drives[i].blk =3D NULL; +#if 0 qdev_prop_set_drive(dev, "drive", blk, &local_err); +#else + error_setg(&local_err, "hack"); +#endif blk_unref(blk); =20 if (local_err) { diff --git a/hw/core/bus.c b/hw/core/bus.c index 3dc0a825f0..3620a7be54 100644 --- a/hw/core/bus.c +++ b/hw/core/bus.c @@ -135,12 +135,17 @@ static void bus_unparent(Object *obj) BusState *bus =3D BUS(obj); BusChild *kid; =20 + printf("### %s bus=3D%p %s\n", + __func__, obj, object_get_typename(obj)); /* Only the main system bus has no parent, and that bus is never freed= */ assert(bus->parent); =20 while ((kid =3D QTAILQ_FIRST(&bus->children)) !=3D NULL) { DeviceState *dev =3D kid->child; + printf("### %s kid=3D%p %s\n", + __func__, OBJECT(dev), object_get_typename(OBJECT(dev))); object_unparent(OBJECT(dev)); + assert(kid !=3D QTAILQ_FIRST(&bus->children)); } QLIST_REMOVE(bus, sibling); bus->parent->num_child_bus--; --=20 2.21.1