From nobody Thu Oct 30 23:13:05 2025 Delivered-To: importer@patchew.org Authentication-Results: mx.zohomail.com; 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=reject dis=none) header.from=rsg.ci.i.u-tokyo.ac.jp Return-Path: Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) by mx.zohomail.com with SMTPS id 1758104258630357.70668919364005; Wed, 17 Sep 2025 03:17:38 -0700 (PDT) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1uypE9-0001RX-Ai; Wed, 17 Sep 2025 06:17:29 -0400 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 1uypCu-0000bc-Ow; Wed, 17 Sep 2025 06:16:15 -0400 Received: from www3579.sakura.ne.jp ([49.212.243.89]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1uypCk-0003IL-PZ; Wed, 17 Sep 2025 06:16:12 -0400 Received: from h205.csg.ci.i.u-tokyo.ac.jp (h205.csg.ci.i.u-tokyo.ac.jp [133.11.54.205]) (authenticated bits=0) by www3579.sakura.ne.jp (8.16.1/8.16.1) with ESMTPSA id 58HAE8s9093528 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Wed, 17 Sep 2025 19:14:22 +0900 (JST) (envelope-from odaki@rsg.ci.i.u-tokyo.ac.jp) DKIM-Signature: a=rsa-sha256; bh=tbKbnY2EjTKUHaLtZsZLQXCBZoyFNJpVfMbynsbGNqo=; c=relaxed/relaxed; d=rsg.ci.i.u-tokyo.ac.jp; h=From:Date:Subject:Message-Id:To; s=rs20250326; t=1758104062; v=1; b=L8qA32CUCpnM5wR9hyBKh3E3/yVIENsagGU1hOnAgvAMMqlfFWNsMEt2aZTPndT1 789WFVfvIMnTmjILQ2a/n6nU42rVSG1NwIR23FhPpG2CBeMmrKgzeI5p6qgROC5L NBrIr4Xb9ur7ofaNTCvw3IZHWSwJ8n3ReSrCn6YIv/vGP86RhHKGK7ito8oLS6xv mhfGB0exEQKh1wFHt2ToijtgXVJRDHSE6hyg1tz+Q4MEV404KUYgN5PZa5xhUt7y CDWjSftHQBO/8M3Teael6SsSbVBhBDSPHvF0ko20sHKelxLfwsz7aXE/sqDR1kt9 3UY9vvUiMSInhL8GYh3TQA== From: Akihiko Odaki Date: Wed, 17 Sep 2025 19:13:26 +0900 Subject: [PATCH v3 1/7] docs/devel: Do not unparent in instance_finalize() MIME-Version: 1.0 Content-Type: text/plain; charset="utf-8" Content-Transfer-Encoding: quoted-printable Message-Id: <20250917-use-v3-1-72c2a6887c6c@rsg.ci.i.u-tokyo.ac.jp> References: <20250917-use-v3-0-72c2a6887c6c@rsg.ci.i.u-tokyo.ac.jp> In-Reply-To: <20250917-use-v3-0-72c2a6887c6c@rsg.ci.i.u-tokyo.ac.jp> To: qemu-devel@nongnu.org Cc: Alex Williamson , =?utf-8?q?C=C3=A9dric_Le_Goater?= , Paolo Bonzini , =?utf-8?q?Daniel_P=2E_Berrang=C3=A9?= , Eduardo Habkost , Peter Xu , David Hildenbrand , =?utf-8?q?Philippe_Mathieu-Daud=C3=A9?= , Richard Henderson , Helge Deller , =?utf-8?q?Marc-Andr=C3=A9_Lureau?= , "Michael S. Tsirkin" , Gerd Hoffmann , John Snow , qemu-block@nongnu.org, Keith Busch , Klaus Jensen , Jesper Devantier , Marcel Apfelbaum , Nicholas Piggin , qemu-ppc@nongnu.org, John Levon , Thanos Makatos , Yanan Wang , BALATON Zoltan , Jiaxun Yang , Daniel Henrique Barboza , David Gibson , Harsh Prateek Bora , Alexey Kardashevskiy , =?utf-8?q?Alex_Benn=C3=A9e?= , Fabiano Rosas , Thomas Huth , Laurent Vivier , Peter Maydell , Aurelien Jarno , Aleksandar Rikalo , Max Filippov , =?utf-8?q?Herv=C3=A9_Poussineau?= , Mark Cave-Ayland , Artyom Tarasenko , Alistair Francis , "Maciej S. Szmigiero" , Bin Meng , Stefano Stabellini , Anthony PERARD , Paul Durrant , "Edgar E. Iglesias" , xen-devel@lists.xenproject.org, Akihiko Odaki X-Mailer: b4 0.15-dev-179e8 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=49.212.243.89; envelope-from=odaki@rsg.ci.i.u-tokyo.ac.jp; helo=www3579.sakura.ne.jp X-Spam_score_int: -16 X-Spam_score: -1.7 X-Spam_bar: - X-Spam_report: (-1.7 / 5.0 requ) BAYES_00=-1.9, DKIM_INVALID=0.1, DKIM_SIGNED=0.1, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=no 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: , Errors-To: qemu-devel-bounces+importer=patchew.org@nongnu.org Sender: qemu-devel-bounces+importer=patchew.org@nongnu.org X-ZM-MESSAGEID: 1758104260949116600 Children are automatically unparented so manually unparenting is unnecessary. Worse, automatic unparenting happens before the instance_finalize() callback of the parent gets called, so object_unparent() calls in the callback will refer to objects that are already unparented, which is semantically incorrect. Remove the instruction to call object_unparent(), and the exception of the "do not call object_unparent()" rule for instance_finalize(). Signed-off-by: Akihiko Odaki Reviewed-by: Daniel P. Berrang=C3=A9 --- docs/devel/memory.rst | 19 ++++++------------- 1 file changed, 6 insertions(+), 13 deletions(-) diff --git a/docs/devel/memory.rst b/docs/devel/memory.rst index 57fb2aec76e0..749f11d8a4dd 100644 --- a/docs/devel/memory.rst +++ b/docs/devel/memory.rst @@ -161,18 +161,11 @@ or never. Destruction of a memory region happens automatically when the owner object dies. =20 -If however the memory region is part of a dynamically allocated data -structure, you should call object_unparent() to destroy the memory region -before the data structure is freed. For an example see VFIOMSIXInfo -and VFIOQuirk in hw/vfio/pci.c. - You must not destroy a memory region as long as it may be in use by a device or CPU. In order to do this, as a general rule do not create or -destroy memory regions dynamically during a device's lifetime, and only -call object_unparent() in the memory region owner's instance_finalize -callback. The dynamically allocated data structure that contains the -memory region then should obviously be freed in the instance_finalize -callback as well. +destroy memory regions dynamically during a device's lifetime. +The dynamically allocated data structure that contains the +memory region should be freed in the instance_finalize callback. =20 If you break this rule, the following situation can happen: =20 @@ -198,9 +191,9 @@ this exception is rarely necessary, and therefore it is= discouraged, but nevertheless it is used in a few places. =20 For regions that "have no owner" (NULL is passed at creation time), the -machine object is actually used as the owner. Since instance_finalize is -never called for the machine object, you must never call object_unparent -on regions that have no owner, unless they are aliases or containers. +machine object is actually used as the owner. You must never call +object_unparent on regions that have no owner, unless they are aliases +or containers. =20 =20 Overlapping regions and priority --=20 2.51.0