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 vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 16E81C433EF for ; Fri, 18 Mar 2022 10:22:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234980AbiCRKX3 (ORCPT ); Fri, 18 Mar 2022 06:23:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:40034 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234966AbiCRKXV (ORCPT ); Fri, 18 Mar 2022 06:23:21 -0400 Received: from bhuna.collabora.co.uk (bhuna.collabora.co.uk [46.235.227.227]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 02DB01ED07F for ; Fri, 18 Mar 2022 03:22:02 -0700 (PDT) Received: from [127.0.0.1] (localhost [127.0.0.1]) (Authenticated sender: kholk11) with ESMTPSA id 362351F45DF3 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1647598921; bh=W1u39IUbe6otztE9r97TmBCaSkIJMT4WAPdgwQbuLz4=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=iyNSFjkU8INvl3lzVLbYVltGn9Ljcetd9s8dl/V8f5DVEU00xl0ZDrqbXRsL65QYc UoeyDwjqn2KUdwJYnh2luQ44Ht+3XAgexrigTM7hX0WFQwVZFoY6kyhOAHAj7xn1UN uwcXJkRlIm/z0mP82WxrdoYQeCNZ4pjawzoLTPZpRC9vBB4NUFLXMJJIUcJwAp1Rrw 45qYx9I4aN+L8o8FrQ6sR70thPKtHdlYwfCY89nbYDEJMtJkminYYjuULIgIuK6Gsk 5iQbJZfsZDXGcjQckZrH245rhABMCJAiZ+VD9Xae84TfHqV13qmye6VmojaJWYAE8Q m6U05UKxQXLTw== Message-ID: Date: Fri, 18 Mar 2022 11:21:59 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.1 Subject: Re: [PATCH 1/2 RESEND] drm/bridge: parade-ps8640: avoid race condition on driver unbinding Content-Language: en-US To: =?UTF-8?Q?Ricardo_Ca=c3=b1uelo?= , dri-devel@lists.freedesktop.org Cc: linux-kernel@vger.kernel.org, linux-mediatek@lists.infradead.org, kernel@collabora.com, andrzej.hajda@intel.com, narmstrong@baylibre.com, maarten.lankhorst@linux.intel.com, mripard@kernel.org References: <20220311093406.4068019-1-ricardo.canuelo@collabora.com> <20220311093406.4068019-2-ricardo.canuelo@collabora.com> From: AngeloGioacchino Del Regno In-Reply-To: <20220311093406.4068019-2-ricardo.canuelo@collabora.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Il 11/03/22 10:34, Ricardo Cañuelo ha scritto: > When unbinding a DRM master driver there's a race condition that > sometimes results in an invalid vm access when userspace (gnome-shell) > issues a DRM_IOCTL_MODE_GETCONNECTOR ioctl right after a bridge has been > removed from an encoder's bridge chain. > > This means that once a bridge has been disabled and gone through > ps8640_post_disable(), if ps8640_bridge_get_edid() runs afterwards as a > result of that ioctl call it will call drm_bridge_chain_pre_enable() > and drm_bridge_chain_post_disable() again in a bridge that has been > already detached. > > Setting `ps_bridge->pre_enabled = false` at a later stage of the > bringdown path and calling drm_bridge_chain_pre_enable() inside > ps8640_bridge_get_edid() only if needed avoid this, although a proper > subsystem-wide fix would be the proper solution, since the same type of > race conditions might happen somewhere else. > > Tested on an Acer Chromebook R13 (Elm, MT8173) with Debian Sid. > > Signed-off-by: Ricardo Cañuelo Reviewed-by: AngeloGioacchino Del Regno > --- > drivers/gpu/drm/bridge/parade-ps8640.c | 6 +++--- > 1 file changed, 3 insertions(+), 3 deletions(-) >