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 A7A17C54F51 for ; Wed, 29 Jul 2026 15:16:43 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 055B810EC9E; Wed, 29 Jul 2026 15:16:43 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=intel.com header.i=@intel.com header.b="A9YEkYzJ"; dkim-atps=neutral Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.17]) by gabe.freedesktop.org (Postfix) with ESMTPS id 84C8F10ECA5 for ; Wed, 29 Jul 2026 15:16:41 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1785338202; x=1816874202; h=from:to:cc:subject:in-reply-to:references:date: message-id:mime-version; bh=ylNlrwd5I+ocZZ9hMiT1FUoQDTuD4qsR1sCf+aIRzN4=; b=A9YEkYzJMqbBv4c5j+Z4KIEf2SC0geSFzQMRT97VVICyrlmckFffMw0m sYwPUanaJZ7W0A9teVkcq+mHjIhK6Z1qJBTTl7hMumlN2EEshQ+VOAz/u N5n3t8cTEy4NsBAO4c6GdxZ7XYFtebvjTrBceGnwhkaG9gfyP+t2D8emA rRSzdOmIe8kXcSC9BlkKgO5pDlHV5ryoFKKL/tB0pzYb6u4o7S1llyZ02 aBz73vq7xiR4AgWgY81JT3aetFQsgEXNpYKnGHPFre0yyURTT3wJH/Zba 6D6fi3PyESAe1k7tBfJ3/FlxNqpBJ0VvNbM7jEUpoKGCF21B5K2LZ9c6i Q==; X-CSE-ConnectionGUID: 8hSUbKnkRc+FpICtOWr/IA== X-CSE-MsgGUID: ndakj0OaQ9OzyQm60iM6Yg== X-IronPort-AV: E=McAfee;i="6800,10657,11859"; a="85962506" X-IronPort-AV: E=Sophos;i="6.25,192,1779174000"; d="scan'208";a="85962506" Received: from fmviesa010.fm.intel.com ([10.60.135.150]) by orvoesa109.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Jul 2026 08:16:41 -0700 X-CSE-ConnectionGUID: J+Qd/klSQyaD8SwYvHWYuA== X-CSE-MsgGUID: 724wJqkxT76KpKAiokNrXw== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.25,192,1779174000"; d="scan'208";a="256104711" Received: from slindbla-desk.ger.corp.intel.com (HELO localhost) ([10.245.244.212]) by fmviesa010-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 29 Jul 2026 08:16:37 -0700 From: Jani Nikula To: Jocelyn Falempe , oushixiong1025@163.com Cc: Javier Martinez Canillas , Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter , dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Shixiong Ou Subject: Re: [PATCH v2] drm/log: Fix division by zero when scale module parameter is 0 In-Reply-To: <8012b9ea-a39d-437a-8539-9e4c3836d1bd@redhat.com> Organization: Intel Finland Oy - BIC 0357606-4 - c/o Alberga Business Park, 6 krs Bertel Jungin Aukio 5, 02600 Espoo, Finland References: <20260729105840.865696-1-oushixiong1025@163.com> <8012b9ea-a39d-437a-8539-9e4c3836d1bd@redhat.com> Date: Wed, 29 Jul 2026 18:16:35 +0300 Message-ID: <11999f4020869c7094a718f4762a0fc475a8a8d1@intel.com> MIME-Version: 1.0 Content-Type: text/plain 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 Wed, 29 Jul 2026, Jocelyn Falempe wrote: > On 29/07/2026 12:58, oushixiong1025@163.com wrote: >> From: Shixiong Ou >> >> The scale module parameter can be set to 0 via kernel command line or >> sysfs. When scale is 0, scaled_font_h and scaled_font_w become 0, >> causing a division by zero in the rows/columns calculation. >> >> Introduce a drm_log_scale() helper that returns scale ?: 1, and use it >> at all read sites. This avoids a race that a setter-based clamp would >> have between param_set_uint() and the subsequent check, where another >> CPU could observe scale == 0. > > The scale module parameter is read only (that's the meaning of 0444 in > module_param()) so it can't be set by sysfs, or change at runtime. > > So this check can be done only once in drm_log_register(). Oops, missed this in my review completely, thanks! -- Jani Nikula, Intel