{"id":2215387,"url":"http://patchwork.ozlabs.org/api/patches/2215387/?format=json","web_url":"http://patchwork.ozlabs.org/project/linux-tegra/patch/20260324-drm-bridge-atomic-vs-remove-private_obj-v3-1-64deefe84044@bootlin.com/","project":{"id":21,"url":"http://patchwork.ozlabs.org/api/projects/21/?format=json","name":"Linux Tegra Development","link_name":"linux-tegra","list_id":"linux-tegra.vger.kernel.org","list_email":"linux-tegra@vger.kernel.org","web_url":null,"scm_url":null,"webscm_url":null,"list_archive_url":"","list_archive_url_format":"","commit_url_format":""},"msgid":"<20260324-drm-bridge-atomic-vs-remove-private_obj-v3-1-64deefe84044@bootlin.com>","list_archive_url":null,"date":"2026-03-24T13:07:30","name":"[v3] drm/atomic: drm_atomic_private_obj_fini: protect private_obj removal from list","commit_ref":null,"pull_url":null,"state":"new","archived":false,"hash":"6c5436de95d463405a22b14047c3cd56c855cdb3","submitter":{"id":83908,"url":"http://patchwork.ozlabs.org/api/people/83908/?format=json","name":"Luca Ceresoli","email":"luca.ceresoli@bootlin.com"},"delegate":null,"mbox":"http://patchwork.ozlabs.org/project/linux-tegra/patch/20260324-drm-bridge-atomic-vs-remove-private_obj-v3-1-64deefe84044@bootlin.com/mbox/","series":[{"id":497287,"url":"http://patchwork.ozlabs.org/api/series/497287/?format=json","web_url":"http://patchwork.ozlabs.org/project/linux-tegra/list/?series=497287","date":"2026-03-24T13:07:30","name":"[v3] drm/atomic: drm_atomic_private_obj_fini: protect private_obj removal from list","version":3,"mbox":"http://patchwork.ozlabs.org/series/497287/mbox/"}],"comments":"http://patchwork.ozlabs.org/api/patches/2215387/comments/","check":"pending","checks":"http://patchwork.ozlabs.org/api/patches/2215387/checks/","tags":{},"related":[],"headers":{"Return-Path":"\n ","X-Original-To":["incoming@patchwork.ozlabs.org","linux-tegra@vger.kernel.org"],"Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (2048-bit key;\n unprotected) header.d=bootlin.com header.i=@bootlin.com header.a=rsa-sha256\n header.s=dkim header.b=QcbodRRZ;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org\n (client-ip=104.64.211.4; helo=sin.lore.kernel.org;\n envelope-from=linux-tegra+bounces-13117-incoming=patchwork.ozlabs.org@vger.kernel.org;\n receiver=patchwork.ozlabs.org)","smtp.subspace.kernel.org;\n\tdkim=pass (2048-bit key) header.d=bootlin.com header.i=@bootlin.com\n header.b=\"QcbodRRZ\"","smtp.subspace.kernel.org;\n arc=none smtp.client-ip=185.246.84.56","smtp.subspace.kernel.org;\n dmarc=pass (p=reject dis=none) header.from=bootlin.com","smtp.subspace.kernel.org;\n spf=pass smtp.mailfrom=bootlin.com"],"Received":["from sin.lore.kernel.org (sin.lore.kernel.org [104.64.211.4])\n\t(using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits)\n\t key-exchange x25519 server-signature ECDSA (secp384r1) server-digest SHA384)\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4fg9hm4sGrz1xy1\n\tfor ; Wed, 25 Mar 2026 00:23:20 +1100 (AEDT)","from smtp.subspace.kernel.org (conduit.subspace.kernel.org\n [100.90.174.1])\n\tby sin.lore.kernel.org (Postfix) with ESMTP id D755A3040F33\n\tfor ; Tue, 24 Mar 2026 13:07:56 +0000 (UTC)","from localhost.localdomain (localhost.localdomain [127.0.0.1])\n\tby smtp.subspace.kernel.org (Postfix) with ESMTP id 739083F7AB2;\n\tTue, 24 Mar 2026 13:07:56 +0000 (UTC)","from smtpout-02.galae.net (smtpout-02.galae.net [185.246.84.56])\n\t(using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits))\n\t(No client certificate requested)\n\tby smtp.subspace.kernel.org (Postfix) with ESMTPS id 82D7C3F87FE;\n\tTue, 24 Mar 2026 13:07:54 +0000 (UTC)","from smtpout-01.galae.net (smtpout-01.galae.net [212.83.139.233])\n\tby smtpout-02.galae.net (Postfix) with ESMTPS id 1EBBE1A2FC6;\n\tTue, 24 Mar 2026 13:07:53 +0000 (UTC)","from mail.galae.net (mail.galae.net [212.83.136.155])\n\tby smtpout-01.galae.net (Postfix) with ESMTPS id E5B506011D;\n\tTue, 24 Mar 2026 13:07:52 +0000 (UTC)","from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon)\n with ESMTPSA id CC98510451277;\n\tTue, 24 Mar 2026 14:07:44 +0100 (CET)"],"ARC-Seal":"i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116;\n\tt=1774357676; cv=none;\n b=ikL3FvCbx9/u820CApNroKI4gKEf6EAO3IYZ46OTnABbyaioHjSDEFZ5xIdDugEABujkgl0bLVy7Y0ImD/X2pUxcVhhi5qfJqu2mROrkKLQg2X/ifqmEexXSBymzt+/CeiLpKjJEf9tiXaFmxOd4YbKHhvN2Ys3OpCU+6EcN4GM=","ARC-Message-Signature":"i=1; a=rsa-sha256; d=subspace.kernel.org;\n\ts=arc-20240116; t=1774357676; c=relaxed/simple;\n\tbh=3gcDvKDiofu5+UBNldcs7iRDdzjLiu7N536dnvCCZcA=;\n\th=From:Date:Subject:MIME-Version:Content-Type:Message-Id:References:\n\t In-Reply-To:To:Cc;\n b=tKs7ytyoAQ+yUhqVmz/qiNTxGUEDD2Iac7V2BMZuBH+sCEQwQh+j0opvzanKC89JnHUE3+UnNm4kcU/6R2hti85QYDel3SRIDbWNmwfddddwES3dDzc8ap1stC+5z5z8xd4QsstzVHikIc/1eO6G/upY9gAmzFGtsZGDym5eM34=","ARC-Authentication-Results":"i=1; smtp.subspace.kernel.org;\n dmarc=pass (p=reject dis=none) header.from=bootlin.com;\n spf=pass smtp.mailfrom=bootlin.com;\n dkim=pass (2048-bit key) header.d=bootlin.com header.i=@bootlin.com\n header.b=QcbodRRZ; arc=none smtp.client-ip=185.246.84.56","DKIM-Signature":"v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=dkim;\n\tt=1774357670; h=from:subject:date:message-id:to:cc:mime-version:content-type:\n\t content-transfer-encoding:in-reply-to:references;\n\tbh=fzs1pWNycSsS39sE+twHeUSR+qT4+7glSHwX8hsiv/I=;\n\tb=QcbodRRZQ7IqeUKtkAQoCsXRCzX49zCQ7c/T+hCSVAXapnmgLoW9sIiyhNT46+mtFpU61J\n\tgJKeSKsjZKwJOSysmrVxJF3olbTeDJZ2DqVTCNwCP9TRBajYIcDIENx5tLs+7THxp2dWu0\n\tG/nuEQt7uiBb0r0BIkhRCZVn6pXSbqYfjcLzD/L4CbpSNR9WLcFeTQpZ4rS6QK/GzA8nkX\n\th9C6LEGO1+qyCWSTqAgOYNv4hY+3xqTMYTAflOF0bmF5eF20QckGAirTPjA+Op1MqF0Nv7\n\t40zg4pJn5YPXFwI/uVYiiJu5XpAy2TfiMXAYQmP7sGyJ6NVFPthK0xMFXjZ6wA==","From":"Luca Ceresoli ","Date":"Tue, 24 Mar 2026 14:07:30 +0100","Subject":"[PATCH v3] drm/atomic: drm_atomic_private_obj_fini: protect\n private_obj removal from list","Precedence":"bulk","X-Mailing-List":"linux-tegra@vger.kernel.org","List-Id":"","List-Subscribe":"","List-Unsubscribe":"","MIME-Version":"1.0","Content-Type":"text/plain; charset=\"utf-8\"","Content-Transfer-Encoding":"7bit","Message-Id":"\n <20260324-drm-bridge-atomic-vs-remove-private_obj-v3-1-64deefe84044@bootlin.com>","References":"\n <20260324-drm-bridge-atomic-vs-remove-private_obj-v3-0-64deefe84044@bootlin.com>","In-Reply-To":"\n <20260324-drm-bridge-atomic-vs-remove-private_obj-v3-0-64deefe84044@bootlin.com>","To":"Harry Wentland , Leo Li ,\n Rodrigo Siqueira ,\n Alex Deucher ,\n =?utf-8?q?Christian_K=C3=B6nig?= ,\n David Airlie , Simona Vetter ,\n Liviu Dudau ,\n Maarten Lankhorst ,\n Maxime Ripard , Thomas Zimmermann ,\n Andrzej Hajda ,\n Neil Armstrong , Robert Foss ,\n Laurent Pinchart ,\n Jonas Karlman , Jernej Skrabec ,\n Paul Cercueil ,\n Rob Clark ,\n Dmitry Baryshkov ,\n Abhinav Kumar , Sean Paul ,\n Marijn Suijten ,\n Tomi Valkeinen ,\n Thierry Reding ,\n Mikko Perttunen ,\n Jonathan Hunter ,\n Dave Stevenson , =?utf-8?q?Ma=C3=ADra_Cana?=\n\t=?utf-8?q?l?= ,\n Raspberry Pi Kernel Maintenance ","Cc":"Hui Pu ,\n Thomas Petazzoni ,\n amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,\n linux-kernel@vger.kernel.org, linux-mips@vger.kernel.org,\n linux-arm-msm@vger.kernel.org, freedreno@lists.freedesktop.org,\n linux-tegra@vger.kernel.org, Ian Ray ,\n Luca Ceresoli ","X-Mailer":"b4 0.15.0","X-Last-TLS-Session-Version":"TLSv1.3"},"content":"Currently drm_bridge_detach() expects that the bridge private_obj is not\nlocked by a drm_modeset_acquire_ctx, and it warns in case that happens:\n\n drm_bridge_detach()\n -> drm_atomic_private_obj_fini()\n -> list_del(&obj->head) // removes priv_obj from\n // dev->mode_config.privobj_list\n -> obj->funcs->atomic_destroy_state()\n -> drm_modeset_lock_fini(&obj->lock)\n -> WARN_ON(!list_empty(&lock->head)) // warn if priv_obj->lock\n\t // is still in ctx->locked\n\nThe expectation is not respected when introducing bridge hot-plugging. In\nsuch case the warning triggers if the bridge is being removed concurrently\nto an operation that locks the private object using a\ndrm_modeset_acquire_ctx, such as in this execution scenario:\n\n CPU0:\n drm_mode_obj_get_properties_ioctl() // userspace request\n -> DRM_MODESET_LOCK_ALL_BEGIN()\n . -> drm_for_each_privobj() // loop on dev->mode_config.privobj_list\n . - lock the privobj mutex\n .\t- add priv_obj->lock to ctx->locked\n .\t (list of locks to be released later)\n .\n . CPU1:\n . drm_bridge_detach() // bridge hot-unplug\n .\t\t -> WARN triggers!\n .\n -> DRM_MODESET_LOCK_ALL_END()\n -> for each lock in ctx->locked\n\t- remove priv_obj->lock from ctx->locked\n - unlock the privobj mutex\n\nPrevent this potential deadlock by using DRM_MODESET_LOCK_ALL_BEGIN/END()\naround the list removal in drm_atomic_private_obj_fini(). This ensures that\nexactly one of these happens:\n\n * the concurrent code (e.g. drm_mode_obj_get_properties_ioctl()) acquires\n all the locks first, so it can execute fully and release the\n privobj->lock before drm_atomic_private_obj_fini() calls list_del() and\n before the WARN_ON()\n * drm_atomic_private_obj_fini() acquires all the locks first, so it\n removes its privobj->lock from the dev->mode_config.privobj_list; the\n concurrent code will run afterwards and not acquire that lock because it\n is not present anymore\n\nSigned-off-by: Luca Ceresoli \n\n---\n\nChanges in v3:\n- Rebased on current drm-misc-next (on 7.0-rc3)\n- Small commit message clarification\n\nChanges in v2:\n- added 'drm/atomic:' prefix to commit title\n- Adapted to work on top of \"drm/atomic: Add dev pointer to drm_private_obj\"\n- Slightly improved commit message\n---\n drivers/gpu/drm/drm_atomic.c | 6 ++++++\n 1 file changed, 6 insertions(+)","diff":"diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c\nindex 41c57063f3b4..0f9c2528c9ee 100644\n--- a/drivers/gpu/drm/drm_atomic.c\n+++ b/drivers/gpu/drm/drm_atomic.c\n@@ -962,7 +962,13 @@ EXPORT_SYMBOL(drm_atomic_private_obj_init);\n void\n drm_atomic_private_obj_fini(struct drm_private_obj *obj)\n {\n+\tstruct drm_modeset_acquire_ctx ctx;\n+\tint ret = 0;\n+\n+\tDRM_MODESET_LOCK_ALL_BEGIN(obj->dev, ctx, 0, ret);\n \tlist_del(&obj->head);\n+\tDRM_MODESET_LOCK_ALL_END(obj->dev, ctx, ret);\n+\n \tobj->funcs->atomic_destroy_state(obj, obj->state);\n \tdrm_modeset_lock_fini(&obj->lock);\n }\n","prefixes":["v3"]}