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 26094D0E6C7 for ; Tue, 25 Nov 2025 11:26:19 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1vNrBM-0002x1-Ka; Tue, 25 Nov 2025 06:26:05 -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 1vNrB7-0002ry-7C for qemu-devel@nongnu.org; Tue, 25 Nov 2025 06:25:50 -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 1vNrB3-00061R-33 for qemu-devel@nongnu.org; Tue, 25 Nov 2025 06:25:47 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1764069942; 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=eaJ1fjXvEaOH2Zur89dMYlyW9B7jikufbkMJcB7OxTQ=; b=Hfr2j0LWRkTZrzPuPYQA5z8y9xkhbBipzVs0YCaqwAqjh448uYVYoSKda2ynTx62EeZ4TT vl9rUyaS7vgUr9ZTy7o+EKwr/LUQeVXEN4k0jpzrI30gRW0jaAlrvUPxgckByRbbu2bFtn U6TVM172EtW7niagLQ6Rtg/VbIEUlkE= 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-634-3V0nEY_vN4iYEjlXgScoIg-1; Tue, 25 Nov 2025 06:25:38 -0500 X-MC-Unique: 3V0nEY_vN4iYEjlXgScoIg-1 X-Mimecast-MFC-AGG-ID: 3V0nEY_vN4iYEjlXgScoIg_1764069937 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (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 56B4D195606D; Tue, 25 Nov 2025 11:25:37 +0000 (UTC) Received: from redhat.com (unknown [10.42.28.80]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 77133180049F; Tue, 25 Nov 2025 11:25:35 +0000 (UTC) Date: Tue, 25 Nov 2025 11:25:32 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Markus Armbruster Cc: qemu-devel@nongnu.org, peterx@redhat.com, farosas@suse.de, peter.maydell@linaro.org Subject: Re: g_autoptr(Error) (was: [PATCH] migration: Fix double-free on error path) Message-ID: References: <20251125070554.2256181-1-armbru@redhat.com> <871plmk1bc.fsf@pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <871plmk1bc.fsf@pond.sub.org> User-Agent: Mutt/2.2.14 (2025-02-20) X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.075, 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=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On Tue, Nov 25, 2025 at 08:40:07AM +0100, Markus Armbruster wrote: > g_autoptr(T) is quite useful when the object's extent matches the > function's. > > This isn't the case for an Error object the function propagates to its > caller. It is the case for an Error object the function reports or > handles itself. However, the functions to report Error also free it. > > Thus, g_autoptr(Error) is rarely applicable. We have just three > instances out of >1100 local Error variables, all in migration code. > > Two want to move the error to the MigrationState for later handling / > reporting. Since migrate_set_error() doesn't move, but stores a copy, > the original needs to be freed, and g_autoptr() is correct there. We > have 17 more that instead manually free with error_free() or > error_report_err() right after migrate_set_error(). > > We recently discussed storing a copy vs. move the original: > > From: Peter Xu > Subject: Re: [PATCH 0/3] migration: Error fixes and improvements > Date: Mon, 17 Nov 2025 11:03:37 -0500 > Message-ID: > > The two g_autoptr() gave me pause when I investigated this topic, simply > because they deviate from the common pattern migrate_set_error(s, err) > followed by error_free() or error_report_err(). > > The third one became wrong when I cleaned up the reporting (missed in > the cleanup patch, fixed in the patch I'm replying to). I suspect my > mistake escaped review for the same reason I made it: g_autoptr(Error) > is unusual and not visible in the patch hunk. > > Would you like me to replace the two correct uses of g_autoptr(Error) by > more common usage? I had previously proposed g_autoptr(Error) a year or two back and you rejected it then, so I'm surprised to see that it got into the code, because it requires explicit opt-in via a G_DEFINE_AUTOPTR_CLEANUP_FUNC. Unfortunately it appears exactly that was added earlier this year in commit 18eb55546a54e443d94a4c49286348176ad4b00a Author: Maciej S. Szmigiero Date: Tue Mar 4 23:03:35 2025 +0100 error: define g_autoptr() cleanup function for the Error type Automatic memory management helps avoid memory safety issues. Reviewed-by: Peter Xu Signed-off-by: Maciej S. Szmigiero Link: https://lore.kernel.org/qemu-devel/a5843c5fa64d7e5239a4316092ec0ef0d10c2320.1741124640.git.maciej.szmigiero@oracle.com Signed-off-by: Cédric Le Goater When removing this usage, ensure that commit is reverted too, which will prevent anyone unwittingly re-introducing g_autoptr(Error) usage With 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 :|