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=-16.2 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable 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 09CAFC4320A for ; Wed, 18 Aug 2021 14:50:12 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D7ABC610CF for ; Wed, 18 Aug 2021 14:50:11 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238637AbhHROup (ORCPT ); Wed, 18 Aug 2021 10:50:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55282 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S239019AbhHROun (ORCPT ); Wed, 18 Aug 2021 10:50:43 -0400 Received: from mail-pl1-x62d.google.com (mail-pl1-x62d.google.com [IPv6:2607:f8b0:4864:20::62d]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 42904C061764; Wed, 18 Aug 2021 07:50:09 -0700 (PDT) Received: by mail-pl1-x62d.google.com with SMTP id u1so1981169plr.1; Wed, 18 Aug 2021 07:50:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=subject:to:references:from:message-id:date:user-agent:mime-version :in-reply-to:content-language:content-transfer-encoding; bh=6Uh8FBGFVJ1JdTCeddx1mUTf33ZOu2+YFROQAiC4wXw=; b=FvxDgvbsWlWgiHHfo1cKELhnM2uSeTuVKkYL2a8NcwGFJLwbeRWzgzRHZ8LWuG5NXb VBDbxFm+4D48ZsM+JzqFGDXsR8/MRg7RcLNCTLAb/qRBj0LrTjF+EoGTNZ/5UDl0VIDs yi4RDyhBIfbtt4V0QSVU8m8PekoGAmb/y6FaL5QMxUynMoAF/3DGPMkYnvRX6SgglbFZ mawgbJD1NySe74n5M2h+iekGuME65Y14JCyXEVYJd5jWsZfD64RfyzT5lmyWIQiHuHpx 6qgGkSn19WksDxegdxPDTs/Iv798MUgIt59ehxFNZZl8bO57ZUqixbljydZbbWhvJK47 ZaSA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:subject:to:references:from:message-id:date :user-agent:mime-version:in-reply-to:content-language :content-transfer-encoding; bh=6Uh8FBGFVJ1JdTCeddx1mUTf33ZOu2+YFROQAiC4wXw=; b=LmVKhYuw9xSJWpUQgC/8mumtYGtfOFQlkrShH9+iZG7u73DDawAe8U5lhFCeeLVter mHfB0v5pYsgM80+0tfOv0YTbGJu3xQ0U8Jm07mzrZH0NICCVxcIRnac8/12d/LCW0mTQ oetPHAMGM7YVIt9KwnX7xFl/gD2aWKjhSH58eAWA0JNWHYrmJvdX5UZ9EERxQMs7WsQR dpT6f27CZyIFKBM08x8rjDaDMyaRQo58llP0n2QWsr6BJYPWe5uvPU4W/mtXiB6KTJR/ /azLhOxiFGelmkvcoI/Fru6/ZgzTpdpZmcqvCysLnfJvK9Mh7pu0HNE+gqDoRQjrjy8J FTSA== X-Gm-Message-State: AOAM531PNLpwqCQ1+ewaFJntYf6e98FRmOjzdADvEzj/sOM9E271mME0 PTT537Usl6antXQsh3mDWSU= X-Google-Smtp-Source: ABdhPJwK6zZDS5MxiSPQQly8zibq21bpqwtpHyPoIGe12pbxG6FIcKasukxZTM8/HiLQS9uS1RYPEQ== X-Received: by 2002:a17:90b:3784:: with SMTP id mz4mr9897189pjb.127.1629298208817; Wed, 18 Aug 2021 07:50:08 -0700 (PDT) Received: from [192.168.1.237] ([118.200.190.93]) by smtp.gmail.com with ESMTPSA id 64sm6780126pfy.114.2021.08.18.07.50.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 18 Aug 2021 07:50:08 -0700 (PDT) Subject: Re: [PATCH v3 2/9] drm: hold master_lookup_lock when releasing a drm_file's master To: maarten.lankhorst@linux.intel.com, mripard@kernel.org, tzimmermann@suse.de, airlied@linux.ie, sumit.semwal@linaro.org, christian.koenig@amd.com, axboe@kernel.dk, oleg@redhat.com, tglx@linutronix.de, dvyukov@google.com, walter-zh.wu@mediatek.com, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, intel-gfx@lists.freedesktop.org, linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org, skhan@linuxfoundation.org, gregkh@linuxfoundation.org, linux-kernel-mentees@lists.linuxfoundation.org References: <20210818073824.1560124-1-desmondcheongzx@gmail.com> <20210818073824.1560124-3-desmondcheongzx@gmail.com> From: Desmond Cheong Zhi Xi Message-ID: Date: Wed, 18 Aug 2021 22:50:00 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.11.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 18/8/21 6:05 pm, Daniel Vetter wrote: > On Wed, Aug 18, 2021 at 03:38:17PM +0800, Desmond Cheong Zhi Xi wrote: >> When drm_file.master changes value, the corresponding >> drm_device.master_lookup_lock should be held. >> >> In drm_master_release, a call to drm_master_put sets the >> file_priv->master to NULL, so we protect this section with >> drm_device.master_lookup_lock. >> >> Signed-off-by: Desmond Cheong Zhi Xi > > At this points all refcounts to drm_file have disappeared, so yeah this is > a lockless access, but also no one can observe it anymore. See also next > patch. > > Hence I think the current code is fine. > -Daniel > Ah ok got it, I didn't realize that. I'll drop patch 2 and 3 from the series then. >> --- >> drivers/gpu/drm/drm_auth.c | 5 ++++- >> 1 file changed, 4 insertions(+), 1 deletion(-) >> >> diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c >> index 8efb58aa7d95..8c0e0dba1611 100644 >> --- a/drivers/gpu/drm/drm_auth.c >> +++ b/drivers/gpu/drm/drm_auth.c >> @@ -373,8 +373,11 @@ void drm_master_release(struct drm_file *file_priv) >> } >> >> /* drop the master reference held by the file priv */ >> - if (file_priv->master) >> + if (file_priv->master) { >> + spin_lock(&dev->master_lookup_lock); >> drm_master_put(&file_priv->master); >> + spin_unlock(&dev->master_lookup_lock); >> + } >> mutex_unlock(&dev->master_mutex); >> } >> >> -- >> 2.25.1 >> >