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=-15.8 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,SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT 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 CF30FC11F6A for ; Thu, 1 Jul 2021 16:54:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B0F59613E2 for ; Thu, 1 Jul 2021 16:54:56 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232630AbhGAQ50 (ORCPT ); Thu, 1 Jul 2021 12:57:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37800 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229987AbhGAQ5Z (ORCPT ); Thu, 1 Jul 2021 12:57:25 -0400 Received: from mail-pf1-x42b.google.com (mail-pf1-x42b.google.com [IPv6:2607:f8b0:4864:20::42b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 113A9C061762; Thu, 1 Jul 2021 09:54:54 -0700 (PDT) Received: by mail-pf1-x42b.google.com with SMTP id 17so6200360pfz.4; Thu, 01 Jul 2021 09:54:54 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=a/frhO6FmtYyjDjb4pEipIaBwOJXfhDMByIQ78NnCHs=; b=TCW+FmOiZG+i+Z/ZlOr4Z4hcJh9xukuhv0/R3u0l56bjD/mt47x8ru3BiFnaysVube BOUcvz1JQgMxOHNt0IWw3jlnPvMxWXA1DfutI6KdoBQhgOpDF3ctqkcr+4i+xDB4xu5b yYgdSENSWRrO1Auokd1gD8y1w94GkqMSBdWRsTXZuJqY3x9dtRRLYuZ5nCZBiN2LiT/w 9Rfo9A9aw1K0zLKHVq5WupUS16wTSTwPpmesf8COEpqYZULJvGvTyrK1CnWv/V+OaPvC mWaDw6zsuAuTEjutPfyaN3GDLdFd/GuWlGJ1zdqrLedQT3+rppzgkjbzWV+C+xPnWSL+ xZ/w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references:mime-version:content-transfer-encoding; bh=a/frhO6FmtYyjDjb4pEipIaBwOJXfhDMByIQ78NnCHs=; b=B20SnFDmdLTeWvURO1UIiz4yXVafCKnpu2Z2cGCLzeNQXq+0NCuEd7vqAZUG2R7B1h mHcNUvfifDCG2MZDPKHjdJqJLj1NqGcCCoCgznt/YH+SNl4h/jAlUJn8DXcuHozW+Ysp a8eOMgUt3QZmvMltOagQTJimU6+eLsJVHrSK9t6cYin9gd2mtpp0SjIaruPqEpksYOR0 EqpNu3xwDPzuTwS3MFkpdIcTIrFi5LSCzEnzHbJpGmDuSXITPycllTCvRybSqd2P56cb KXJQZj/tCK5fFd/eY0mnn4qaBi+3GtqEgHKH+q7oPPnVgpZH+Llq2RdKH0BYTZKSyt+f B4og== X-Gm-Message-State: AOAM533HJ7R6Q+lXvE3RhiH9nXQvRq0Akshv53pZFxVG4+2LdWWp06xn qrJP5x+8L8JX8EtTFMX0dgU= X-Google-Smtp-Source: ABdhPJwE3OxMy8uOFmjcS/bajY7yrTC64aL5hOZ8sTBWSSVzlSL/vKTNf2leR7iswBH2WOcYCpq88g== X-Received: by 2002:a63:65c5:: with SMTP id z188mr555583pgb.174.1625158493587; Thu, 01 Jul 2021 09:54:53 -0700 (PDT) Received: from localhost.localdomain ([118.200.190.93]) by smtp.gmail.com with ESMTPSA id s20sm398738pgv.1.2021.07.01.09.54.48 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 01 Jul 2021 09:54:53 -0700 (PDT) From: Desmond Cheong Zhi Xi To: 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 Cc: Desmond Cheong Zhi Xi , dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org, linux-kernel@vger.kernel.org, linux-media@vger.kernel.org, linaro-mm-sig@lists.linaro.org, skhan@linuxfoundation.org, gregkh@linuxfoundation.org, linux-kernel-mentees@lists.linuxfoundation.org, emil.l.velikov@gmail.com, Daniel Vetter Subject: [PATCH v7 4/5] drm: serialize drm_file.master with a master lock Date: Fri, 2 Jul 2021 00:53:57 +0800 Message-Id: <20210701165358.19053-5-desmondcheongzx@gmail.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210701165358.19053-1-desmondcheongzx@gmail.com> References: <20210701165358.19053-1-desmondcheongzx@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Currently, drm_file.master pointers should be protected by drm_device.master_mutex when being dereferenced. This is because drm_file.master is not invariant for the lifetime of drm_file. If drm_file is not the creator of master, then drm_file.is_master is false, and a call to drm_setmaster_ioctl will invoke drm_new_set_master, which then allocates a new master for drm_file and puts the old master. Thus, without holding drm_device.master_mutex, the old value of drm_file.master could be freed while it is being used by another concurrent process. However, it is not always possible to lock drm_device.master_mutex to dereference drm_file.master. Through the fbdev emulation code, this might occur in a deep nest of other locks. But drm_device.master_mutex is also the outermost lock in the nesting hierarchy, so this leads to potential deadlocks. To address this, we introduce a new mutex at the bottom of the lock hierarchy that only serializes drm_file.master. With this change, the value of drm_file.master changes only when both drm_device.master_mutex and drm_file.master_lock are held. Hence, any process holding either of those locks can ensure that the value of drm_file.master will not change concurrently. Since no lock depends on the new drm_file.master_lock, when drm_file.master is dereferenced, but drm_device.master_mutex cannot be held, we can safely protect the master pointer with drm_file.master_lock. Reported-by: Daniel Vetter Signed-off-by: Desmond Cheong Zhi Xi --- Since our lock inversions were a result of dev->master_mutex being used to serialize many other things, perhaps a finer grained lock will solve the lockdep issues. drivers/gpu/drm/drm_auth.c | 10 ++++++++-- drivers/gpu/drm/drm_file.c | 1 + include/drm/drm_file.h | 12 +++++++++--- 3 files changed, 18 insertions(+), 5 deletions(-) diff --git a/drivers/gpu/drm/drm_auth.c b/drivers/gpu/drm/drm_auth.c index ab1863c5a5a0..fe5b6adc6133 100644 --- a/drivers/gpu/drm/drm_auth.c +++ b/drivers/gpu/drm/drm_auth.c @@ -169,11 +169,14 @@ static int drm_new_set_master(struct drm_device *dev, struct drm_file *fpriv) WARN_ON(fpriv->is_master); old_master = fpriv->master; + mutex_lock(&fpriv->master_lock); fpriv->master = drm_master_create(dev); if (!fpriv->master) { fpriv->master = old_master; + mutex_unlock(&fpriv->master_lock); return -ENOMEM; } + mutex_unlock(&fpriv->master_lock); fpriv->is_master = 1; fpriv->authenticated = 1; @@ -332,10 +335,13 @@ int drm_master_open(struct drm_file *file_priv) * any master object for render clients */ mutex_lock(&dev->master_mutex); - if (!dev->master) + if (!dev->master) { ret = drm_new_set_master(dev, file_priv); - else + } else { + mutex_lock(&file_priv->master_lock); file_priv->master = drm_master_get(dev->master); + mutex_unlock(&file_priv->master_lock); + } mutex_unlock(&dev->master_mutex); return ret; diff --git a/drivers/gpu/drm/drm_file.c b/drivers/gpu/drm/drm_file.c index d4f0bac6f8f8..8ccadfa1c752 100644 --- a/drivers/gpu/drm/drm_file.c +++ b/drivers/gpu/drm/drm_file.c @@ -176,6 +176,7 @@ struct drm_file *drm_file_alloc(struct drm_minor *minor) init_waitqueue_head(&file->event_wait); file->event_space = 4096; /* set aside 4k for event buffer */ + mutex_init(&file->master_lock); mutex_init(&file->event_read_lock); if (drm_core_check_feature(dev, DRIVER_GEM)) diff --git a/include/drm/drm_file.h b/include/drm/drm_file.h index b81b3bfb08c8..88539f93fc8e 100644 --- a/include/drm/drm_file.h +++ b/include/drm/drm_file.h @@ -226,15 +226,21 @@ struct drm_file { /** * @master: * - * Master this node is currently associated with. Only relevant if - * drm_is_primary_client() returns true. Note that this only - * matches &drm_device.master if the master is the currently active one. + * Master this node is currently associated with. Protected by struct + * &drm_device.master_mutex, and serialized by @master_lock. + * + * Only relevant if drm_is_primary_client() returns true. Note that + * this only matches &drm_device.master if the master is the currently + * active one. * * See also @authentication and @is_master and the :ref:`section on * primary nodes and authentication `. */ struct drm_master *master; + /** @master_lock: Serializes @master. */ + struct mutex master_lock; + /** @pid: Process that opened this file. */ struct pid *pid; -- 2.25.1