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=-13.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED 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 14022C4338F for ; Wed, 18 Aug 2021 10:05:33 +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 CC8206109F for ; Wed, 18 Aug 2021 10:05:32 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org CC8206109F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ffwll.ch 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 273B66E50B; Wed, 18 Aug 2021 10:05:32 +0000 (UTC) Received: from mail-ej1-x62c.google.com (mail-ej1-x62c.google.com [IPv6:2a00:1450:4864:20::62c]) by gabe.freedesktop.org (Postfix) with ESMTPS id 019F76E51C for ; Wed, 18 Aug 2021 10:05:06 +0000 (UTC) Received: by mail-ej1-x62c.google.com with SMTP id z20so3861636ejf.5 for ; Wed, 18 Aug 2021 03:05:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ffwll.ch; s=google; h=date:from:to:cc:subject:message-id:mail-followup-to:references :mime-version:content-disposition:in-reply-to; bh=+UugXJNovZ2vqktgPlIQAdEvTrXzjK5N1Cr++nIj3DA=; b=R42e8IjQDth0gJLIVgsbrUrhAc6d0ey998kv2PQoRChb7eJx00eZ1Gm0c/EhfBivkC IBNmrGkJ8ApCpeW2C+4cEd65TeabJc9SlX1xYSqdk72h0IEQ+khLKq7zNM6jv5wHaBvB ZXdjx0ctrHer5bc0vfxlwQtTRpuI1JQHIunWU= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id :mail-followup-to:references:mime-version:content-disposition :in-reply-to; bh=+UugXJNovZ2vqktgPlIQAdEvTrXzjK5N1Cr++nIj3DA=; b=ls3Uyk6i1Kigy8nlfCW5GBucihNZwjHX2gTYzjM7W+90qfCrYwF+CyJ9f78kgmAbnw He6jUXC1RW4iSv3QTa3wdcd/NrbdZCNCk7smPikDJpuW8Ew16Md4bB0EUD1sVKLfvOfK YC11fEU1iGnRg0Hi2pgzsKwEB7yQ/73qEejZqaq9XSsbvZBZoiuUB/VDprTt6UKzO/JT S0SA/N8+gqojw24/hOQ1f0Bt8qszWMyVBVzyyZ+l9ESCwQdClIe444gEh3Y8vIM1xowR KfkHgDq88Eh9OYB+sAVMhPQLxPEzHMeTwp9Zj0EBOgedNJUT18SS7+oR+URun8ie0p4Z Q11w== X-Gm-Message-State: AOAM530urxzve/hWoVtsBeyUXjOJ+c5MeKcHNZG5dVpLZeClFTPaX/yp ZYc9JuC7yc83MnNPNvu2ZEyx8w== X-Google-Smtp-Source: ABdhPJyCL0wNSTVtmCi+TFUYXg5lqc4ePLGIxn2k+rFjGuAVDwSBiMK9lqUgzHWBYJDOF+Ij9NGXdA== X-Received: by 2002:a17:906:150c:: with SMTP id b12mr8875986ejd.275.1629281104548; Wed, 18 Aug 2021 03:05:04 -0700 (PDT) Received: from phenom.ffwll.local ([2a02:168:57f4:0:efd0:b9e5:5ae6:c2fa]) by smtp.gmail.com with ESMTPSA id e22sm2384475eds.45.2021.08.18.03.05.03 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Aug 2021 03:05:03 -0700 (PDT) Date: Wed, 18 Aug 2021 12:05:01 +0200 From: Daniel Vetter To: Desmond Cheong Zhi Xi Cc: maarten.lankhorst@linux.intel.com, mripard@kernel.org, tzimmermann@suse.de, airlied@linux.ie, daniel@ffwll.ch, 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 Message-ID: Mail-Followup-To: Desmond Cheong Zhi Xi , 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> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210818073824.1560124-3-desmondcheongzx@gmail.com> X-Operating-System: Linux phenom 5.10.0-7-amd64 Subject: Re: [Intel-gfx] [PATCH v3 2/9] drm: hold master_lookup_lock when releasing a drm_file's master X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" 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 > --- > 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 > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch