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 1E379C982DE for ; Mon, 21 Sep 2026 07:21:24 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 5CF2D10E090; Mon, 21 Sep 2026 07:21:23 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=bootlin.com header.i=@bootlin.com header.b="zHnAy6Yh"; dkim-atps=neutral Received: from smtpout-02.galae.net (smtpout-02.galae.net [185.246.84.56]) by gabe.freedesktop.org (Postfix) with ESMTPS id 4943F10E090 for ; Mon, 21 Sep 2026 07:21:22 +0000 (UTC) Received: from smtpout-01.galae.net (smtpout-01.galae.net [212.83.139.233]) by smtpout-02.galae.net (Postfix) with ESMTPS id A9E2A1A0DEF; Mon, 21 Sep 2026 07:21:20 +0000 (UTC) Received: from mail.galae.net (mail.galae.net [212.83.136.155]) by smtpout-01.galae.net (Postfix) with ESMTPS id 76DA460339; Mon, 21 Sep 2026 07:21:20 +0000 (UTC) Received: from [127.0.0.1] (localhost [127.0.0.1]) by localhost (Mailerdaemon) with ESMTPSA id 4D6C61032800A; Mon, 21 Sep 2026 09:21:05 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=bootlin.com; s=dkim; t=1789975277; h=from:subject:date:message-id:to:cc:mime-version:content-type: content-transfer-encoding:in-reply-to:references; bh=nxoDYhmIzh2JJPIArEyFT+HN+oVRry6II7QzeYp2Ns8=; b=zHnAy6YhRwPKGEf0y9dvmZY6PdyuCehyShuLCcQ9hRcoCEFxRx6BMqRv8J/NByWFUTsOPO UybaskuxoT1S6hcjn+xsLjoN+6jng6MfTBuO5xYPusGsKOsfcltFGCd8hmOVwuvALGc3V0 xftL6l0nCepix/p2nb+MZHpik/f1U2Kye8vARp3Pa/djqdjtwJ/dnZYQp+XUYAB55Rof0s Ut/KyIf5rzHYGLrPdtLZmUmGXlE5329asARgMt2Hd1t7zwpB58v1iuHV0FQfDsYazTgD2Y Hn9NI9L8z87aSohbMMp24WzHI1zro2CeqOZxWYuGQqFE/Fhxvj5KmIfS67tOsw== Mime-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset=UTF-8 Date: Mon, 21 Sep 2026 09:21:04 +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 9:16 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() canno= t > touch the list concurrently to other functions, because it only runs when > the refcount is 0, and all other functions tounch the lists only when the= y > have a reference. (Should this sentence be wrong, that would be a big bug= !) Ah, no, I just realized my concern does not stand. Indeed __drm_bridge_free() can run concurrently on a different bridge than the one being handled by other functions, ending up in modifying the same list. So your comment is fully correct: Reviewed-by: Luca Ceresoli Apologies for the noise. Luca -- Luca Ceresoli, Bootlin Embedded Linux and Kernel engineering https://bootlin.com