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 gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (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 A4C82C982ED for ; Mon, 21 Sep 2026 16:51:51 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id F36C810E3D0; Mon, 21 Sep 2026 16:51:50 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=bootlin.com header.i=@bootlin.com header.b="IjYWD3xI"; dkim-atps=neutral Received: from smtpout-03.galae.net (smtpout-03.galae.net [185.246.85.4]) by gabe.freedesktop.org (Postfix) with ESMTPS id 124CD10E3C8 for ; Mon, 21 Sep 2026 16:51:49 +0000 (UTC) Received: from smtpout-01.galae.net (smtpout-01.galae.net [212.83.139.233]) by smtpout-03.galae.net (Postfix) with ESMTPS id 46F5E4E40755; Mon, 21 Sep 2026 16:51:48 +0000 (UTC) Received: from mail.galae.net (mail.galae.net [212.83.136.155]) by smtpout-01.galae.net (Postfix) with ESMTPS id 04BCA5FFB2; Mon, 21 Sep 2026 16:51:48 +0000 (UTC) Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPSA id 59E35103291BD; Mon, 21 Sep 2026 18:51:26 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=dkim; t=1790009502; h=from:subject:date:message-id:to:cc:mime-version:content-type: content-transfer-encoding:in-reply-to:references; bh=cSwoV7JYFKwWDkDL4IDFclIBqtgIii8ZsKhV2r0CgdE=; b=IjYWD3xIKW0KiAwSGgakYrxt0r+vUYd0qxiCiN/UWCsb/Lzv6F9MRJMiln7kdo9fS0L97I MsXakBjOTJ1+zKqPla6JTpP36tNNijKQuc05p4N/sYCzdy/c7URDCf+uJa5rryyF/pGD5K CvqGwT/3RpwqR10lvWnK934ts0XBX+qWLGQw+t4WaJu2BG8/qPF+HiQ1510dHvF6L28CmX ioTpVmqh4beeqW3L3IIl55sutm8DOpW/zT1po1oe7QbGwrjZOVXRXmuApmKzwv2DLncD2H 1SpLtpGpNxBgOe0ek/Ku+tmxFQw0ujiCLjuQSMInGOlC5v95Mxni3AZCvi3qHg== Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Mon, 21 Sep 2026 18:51:25 +0200 Message-Id: Cc: , , , , , , , "Sashiko" To: "Luca Ceresoli" , "Cristian Ciocaltea" , "Maarten Lankhorst" , "Maxime Ripard" , "Thomas Zimmermann" , "David Airlie" , "Simona Vetter" , "Dave Stevenson" , "Dmitry Baryshkov" , "Andrzej Hajda" , "Neil Armstrong" , "Robert Foss" , "Laurent Pinchart" , "Jonas Karlman" , "Jernej Skrabec" , "Chen-Yu Tsai" , "Samuel Holland" , =?utf-8?q?Ma=C3=ADra_Canal?= , "Raspberry Pi Kernel Maintenance" , "Raphael Gallais-Pou" , "Sandy Huang" , =?utf-8?q?Heiko_St=C3=BCbner?= , "Andy Yan" , "Algea Cao" , "Daniel Stone" , "Liu Ying" , "Phong LE" , "Helge Deller" From: "Luca Ceresoli" Subject: Re: [PATCH v11 12/74] drm/bridge: Fix unlocked list_del in drm_bridge_add() X-Mailer: aerc 0.22.0 References: <20260901-dw-hdmi-qp-scramb-v11-0-bc12954a0688@collabora.com> <20260901-dw-hdmi-qp-scramb-v11-12-bc12954a0688@collabora.com> In-Reply-To: X-Last-TLS-Session-Version: TLSv1.3 X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Mon Sep 21, 2026 at 9:21 AM CEST, Luca Ceresoli wrote: > On Mon Sep 21, 2026 at 9:16 AM CEST, Luca Ceresoli wrote: >> Hello Cristian, >> >> On Tue Sep 1, 2026 at 8:50 PM CEST, Cristian Ciocaltea wrote: >>> When re-adding a bridge that was previously removed, drm_bridge_add() >>> drops it from bridge_lingering_list without holding bridge_lock. >>> >>> Both bridge_list and bridge_lingering_list are protected by bridge_lock= , >>> as they are concurrently modified by drm_bridge_remove() and >>> __drm_bridge_free(), and walked by the debugfs 'bridges' file. Running >>> the list_empty() test and the list_del_init() outside of the lock may >>> therefore corrupt either list. >> >> The analysis appears correct, with a small nit: __drm_bridge_free() cann= ot >> touch the list concurrently to other functions, because it only runs whe= n >> the refcount is 0, and all other functions tounch the lists only when th= ey >> have a reference. (Should this sentence be wrong, that would be a big bu= g!) > > Ah, no, I just realized my concern does not stand. Indeed > __drm_bridge_free() can run concurrently on a different bridge than the o= ne > being handled by other functions, ending up in modifying the same list. S= o > your comment is fully correct: > > Reviewed-by: Luca Ceresoli And tested with bridge hotplug: Tested-by: Luca Ceresoli -- Luca Ceresoli, Bootlin Embedded Linux and Kernel engineering https://bootlin.com