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 X-Spam-Level: X-Spam-Status: No, score=-10.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7EDE9C4338F for ; Fri, 13 Aug 2021 07:33:05 +0000 (UTC) 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 mail.kernel.org (Postfix) with ESMTPS id 6F63A60720 for ; Fri, 13 Aug 2021 07:33:04 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 6F63A60720 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=daenzer.net Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.freedesktop.org Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id D53B36E526; Fri, 13 Aug 2021 07:33:03 +0000 (UTC) Received: from netline-mail3.netline.ch (mail.netline.ch [148.251.143.180]) by gabe.freedesktop.org (Postfix) with ESMTP id E02176E526 for ; Fri, 13 Aug 2021 07:33:02 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by netline-mail3.netline.ch (Postfix) with ESMTP id BFB9420201B; Fri, 13 Aug 2021 09:33:01 +0200 (CEST) X-Virus-Scanned: Debian amavisd-new at netline-mail3.netline.ch Received: from netline-mail3.netline.ch ([127.0.0.1]) by localhost (netline-mail3.netline.ch [127.0.0.1]) (amavisd-new, port 10024) with LMTP id VN5sTBzV7V1P; Fri, 13 Aug 2021 09:32:57 +0200 (CEST) Received: from thor (24.99.2.85.dynamic.wline.res.cust.swisscom.ch [85.2.99.24]) by netline-mail3.netline.ch (Postfix) with ESMTPA id 44D5A20201A; Fri, 13 Aug 2021 09:32:57 +0200 (CEST) Received: from [::1] by thor with esmtp (Exim 4.94.2) (envelope-from ) id 1mERgW-000B0f-6u; Fri, 13 Aug 2021 09:32:56 +0200 Subject: Re: [PATCH v2] drm: Copy drm_wait_vblank to user before returning To: Mark Yacoub , dri-devel@lists.freedesktop.org Cc: seanpaul@chromium.org, abhinavk@codeaurora.org, robdclark@chromium.org, airlied@linux.ie, Mark Yacoub References: <20210811175525.2125964-1-markyacoub@chromium.org> <20210812194917.1703356-1-markyacoub@chromium.org> From: =?UTF-8?Q?Michel_D=c3=a4nzer?= Message-ID: <4ab4548f-34fc-27cb-928e-af2b8ab78b1b@daenzer.net> Date: Fri, 13 Aug 2021 09:32:56 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 MIME-Version: 1.0 In-Reply-To: <20210812194917.1703356-1-markyacoub@chromium.org> Content-Type: text/plain; charset=utf-8 Content-Language: en-CA Content-Transfer-Encoding: 8bit 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 2021-08-12 9:49 p.m., Mark Yacoub wrote: > From: Mark Yacoub > > [Why] > Userspace should get back a copy of drm_wait_vblank that's been modified > even when drm_wait_vblank_ioctl returns a failure. > > Rationale: > drm_wait_vblank_ioctl modifies the request and expects the user to read > it back. When the type is RELATIVE, it modifies it to ABSOLUTE and updates > the sequence to become current_vblank_count + sequence (which was > RELATIVE), but now it became ABSOLUTE. > drmWaitVBlank (in libdrm) expects this to be the case as it modifies > the request to be Absolute so it expects the sequence to would have been > updated. > > The change is in compat_drm_wait_vblank, which is called by > drm_compat_ioctl. This change of copying the data back regardless of the > return number makes it en par with drm_ioctl, which always copies the > data before returning. > > [How] > Return from the function after everything has been copied to user. > > Fixes: IGT:kms_flip::modeset-vs-vblank-race-interruptible > Tested on ChromeOS Trogdor(msm) > > Signed-off-by: Mark Yacoub > Change-Id: I98da279a5f1329c66a9d1e06b88d40b247b51313 With the Gerrit Change-Id removed, Reviewed-by: Michel Dänzer -- Earthling Michel Dänzer | https://redhat.com Libre software enthusiast | Mesa and X developer