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=-15.1 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 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 C1BC6C4361B for ; Wed, 16 Dec 2020 09:57:08 +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 44D5C2313B for ; Wed, 16 Dec 2020 09:57:08 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 44D5C2313B 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]:53204 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1kpTYQ-00005A-Tu for qemu-devel@archiver.kernel.org; Wed, 16 Dec 2020 04:57:07 -0500 Received: from eggs.gnu.org ([2001:470:142:3::10]:38938) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1kpTWs-0007Be-5H for qemu-devel@nongnu.org; Wed, 16 Dec 2020 04:55:30 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:21831) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA1:256) (Exim 4.90_1) (envelope-from ) id 1kpTWl-00052e-FJ for qemu-devel@nongnu.org; Wed, 16 Dec 2020 04:55:29 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1608112521; h=from:from:reply-to: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=F/G5Qwcyc3XcVFWZGtVGBOI15QH7aQ0Kbb1AxyHJTIg=; b=CKZ1Jy/LdeZxP+A0ma4cEr8s5wOfQsh4CjotSkxDBs+yxUfe1QkDX2gNES0wiFyFhpDR3u Da9yciJZGHL/X+WEuAkevCdhSDRw0Wco7EWpEz8UyT38jwINvcUZvcbzp8bVAUq5EJbdyO MJlDQnLc/MjLzrm2CD0dc1MAcHfr0KA= 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-64-FC1QcPuXMRGgGPzv1Uvpig-1; Wed, 16 Dec 2020 04:55:19 -0500 X-MC-Unique: FC1QcPuXMRGgGPzv1Uvpig-1 Received: from smtp.corp.redhat.com (int-mx03.intmail.prod.int.phx2.redhat.com [10.5.11.13]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 15D80800D62; Wed, 16 Dec 2020 09:55:18 +0000 (UTC) Received: from redhat.com (ovpn-115-177.ams2.redhat.com [10.36.115.177]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 22EB260C5E; Wed, 16 Dec 2020 09:55:12 +0000 (UTC) Date: Wed, 16 Dec 2020 09:55:09 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: =?utf-8?Q?Marc-Andr=C3=A9?= Lureau Subject: Re: [PATCH 2/2] qom: Assert that objects being destroyed have no parent Message-ID: <20201216095509.GD189795@redhat.com> References: <20201215224133.3545901-1-ehabkost@redhat.com> <20201215224133.3545901-3-ehabkost@redhat.com> MIME-Version: 1.0 In-Reply-To: User-Agent: Mutt/1.14.6 (2020-07-11) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.13 Authentication-Results: relay.mimecast.com; auth=pass smtp.auth=CUSA124A263 smtp.mailfrom=berrange@redhat.com X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=63.128.21.124; envelope-from=berrange@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_H4=0.001, RCVD_IN_MSPIKE_WL=0.001, SPF_HELO_NONE=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: 2.1.23 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Cc: Paolo Bonzini , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Eduardo Habkost , qemu-devel Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Wed, Dec 16, 2020 at 11:53:06AM +0400, Marc-André Lureau wrote: > Hi > > On Wed, Dec 16, 2020 at 2:41 AM Eduardo Habkost wrote: > > > QOM reference counting bugs are often hard to detect, but there's > > one kind of bug that's easier: if we are freeing an object but is > > still attached to a parent, it means the reference count is wrong > > (because the parent always hold a reference to their children). > > > > Add an assertion to make sure we detect those cases. > > > > Signed-off-by: Eduardo Habkost > > > > On the principle, I fully agree. But the risk is high to introduce > regression if objects are manipulated in strange ways. Isn't the point that we're broken already. We have a QOM instance in the tree which has a zero reference count and has been freed. As soon as something touches that object in the tree, we're liable to crash & burn touching free'd memory. So it seems the choices are between crash fast where we see the problem, or crash eventually at a place where we can't easily trace back to the root cause. > I remember I wanted object_unref() to automatically remove itself from the > parent when the last ref is dropped. I think there were similar concerns. Automatically removing itself would be hiding the bug in whatever code has mistakenly removed a reference it didn't own. > > Maybe with --enable-qom-debug ? (removing the -cast) > > --- > > qom/object.c | 1 + > > 1 file changed, 1 insertion(+) > > > > diff --git a/qom/object.c b/qom/object.c > > index f2ae6e6b2a..5cfed6d7c6 100644 > > --- a/qom/object.c > > +++ b/qom/object.c > > @@ -685,6 +685,7 @@ static void object_finalize(void *data) > > object_deinit(obj, ti); > > > > g_assert(obj->ref == 0); > > + g_assert(obj->parent == NULL); > > if (obj->free) { > > obj->free(obj); > > } > > -- > > 2.28.0 > > > > Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|