From patchwork Wed Aug 18 07:38:22 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Desmond Cheong Zhi Xi X-Patchwork-Id: 12443523 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=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 79A9DC4338F for ; Wed, 18 Aug 2021 07:41:16 +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 4AE0160FDA for ; Wed, 18 Aug 2021 07:41:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 4AE0160FDA Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=gmail.com 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 873EF6E471; Wed, 18 Aug 2021 07:41:15 +0000 (UTC) Received: from mail-pl1-x634.google.com (mail-pl1-x634.google.com [IPv6:2607:f8b0:4864:20::634]) by gabe.freedesktop.org (Postfix) with ESMTPS id EC0646E463; Wed, 18 Aug 2021 07:41:13 +0000 (UTC) Received: by mail-pl1-x634.google.com with SMTP id l11so1270121plk.6; Wed, 18 Aug 2021 00:41:13 -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=6qsW0sYS+QWl9YqcEcKPcEnVn6HLCKGFheZ9UsQK7Pw=; b=UOFTIL4BlsedoXnh4zHxO1Ey3z7ZulzCS5A0HofF4Pdc6KSOphdAQfUboSXTigN3QJ KV9GWvBIpiqXwe2DDYu2nmNE8CrFkYYFXVATDHFQup4d7oi9AssfF8qYtWT9XhKXgvqV hI0Q1Gq8wgxyphDTnoroV9F5koJtJ59wKMcWiCPDa1Bkq6RqPGY9N3aa8EV6KItNemMa gP5HwtFGnKuqLIsbCWkrhhrBrq+ZV++p+8hZ1RmRx/QEg7TYVGg0v9wiGESj2m60zwuM E0/lsPiZhzcN7BbB6TNJh84nkcOUcRh6VEIOKIcuc4++u7nT6silUQXPZR4R/jFnhWG0 eMWA== 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=6qsW0sYS+QWl9YqcEcKPcEnVn6HLCKGFheZ9UsQK7Pw=; b=g+Npq/MX2XsEG8jd+joxLUMK7y+uaBcQAEe94GEVB+Me0G07efhiJZIVuztvsgdgSl nSUwQHc+Qa+yL1Ztnw3TSeTdLwI5iwweYpJxSoId/wwZnbIR+aaXUbq8hQnm/EO6n2Ae P4Go5nVPbW3cj9NiOoW00C7Mwm5rJFaWfq4R6O2tH58Ufm6NQgvhqiju5c/NmBKj0qtQ rDQcuL6p5azm4WxK5TE3GWPgareO+tb2Bqx8HfRirpRsFdvySHjUqg4nJR9C6Uf6aKNn QppAGuuPtkiqKaHloBGtf0Zf6kbXV1asYBvAZEfFljsM8VK++i1OZh3NHrAu4GaN91HR sbdw== X-Gm-Message-State: AOAM530cKCFqw8WpLpKf+Gqx6hBW1/SJ5FN/Y4lKp+E+F+b/knbP+6mY qVQbOyX5zRyrEBhx03WLEdc= X-Google-Smtp-Source: ABdhPJyoRQikktAIIYzk2SdRrsIHolgC6+oIsd/deH794I59G6Uc3YKKU+oqVIrW58xvLjcm506Y1A== X-Received: by 2002:a17:902:d713:b029:12d:5b1a:c49 with SMTP id w19-20020a170902d713b029012d5b1a0c49mr6051047ply.70.1629272473538; Wed, 18 Aug 2021 00:41:13 -0700 (PDT) Received: from localhost.localdomain ([118.200.190.93]) by smtp.gmail.com with ESMTPSA id u3sm3886729pjr.2.2021.08.18.00.41.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Aug 2021 00:41:13 -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, axboe@kernel.dk, oleg@redhat.com, tglx@linutronix.de, dvyukov@google.com, walter-zh.wu@mediatek.com Cc: Desmond Cheong Zhi Xi , 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 Subject: [PATCH v3 7/9] drm: update global mutex lock in the ioctl handler Date: Wed, 18 Aug 2021 15:38:22 +0800 Message-Id: <20210818073824.1560124-8-desmondcheongzx@gmail.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210818073824.1560124-1-desmondcheongzx@gmail.com> References: <20210818073824.1560124-1-desmondcheongzx@gmail.com> MIME-Version: 1.0 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" In a future patch, a read lock on drm_device.master_rwsem is held in the ioctl handler before the check for ioctl permissions. However, this produces the following lockdep splat: ====================================================== WARNING: possible circular locking dependency detected 5.14.0-rc6-CI-Patchwork_20831+ #1 Tainted: G U ------------------------------------------------------ kms_lease/1752 is trying to acquire lock: ffffffff827bad88 (drm_global_mutex){+.+.}-{3:3}, at: drm_open+0x64/0x280 but task is already holding lock: ffff88812e350108 (&dev->master_rwsem){++++}-{3:3}, at: drm_ioctl_kernel+0xfb/0x1a0 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&dev->master_rwsem){++++}-{3:3}: lock_acquire+0xd3/0x310 down_read+0x3b/0x140 drm_master_internal_acquire+0x1d/0x60 drm_client_modeset_commit+0x10/0x40 __drm_fb_helper_restore_fbdev_mode_unlocked+0x88/0xb0 drm_fb_helper_set_par+0x34/0x40 intel_fbdev_set_par+0x11/0x40 [i915] fbcon_init+0x270/0x4f0 visual_init+0xc6/0x130 do_bind_con_driver+0x1de/0x2c0 do_take_over_console+0x10e/0x180 do_fbcon_takeover+0x53/0xb0 register_framebuffer+0x22d/0x310 __drm_fb_helper_initial_config_and_unlock+0x36c/0x540 intel_fbdev_initial_config+0xf/0x20 [i915] async_run_entry_fn+0x28/0x130 process_one_work+0x26d/0x5c0 worker_thread+0x37/0x390 kthread+0x13b/0x170 ret_from_fork+0x1f/0x30 -> #1 (&helper->lock){+.+.}-{3:3}: lock_acquire+0xd3/0x310 __mutex_lock+0xa8/0x930 __drm_fb_helper_restore_fbdev_mode_unlocked+0x44/0xb0 intel_fbdev_restore_mode+0x2b/0x50 [i915] drm_lastclose+0x27/0x50 drm_release_noglobal+0x42/0x60 __fput+0x9e/0x250 task_work_run+0x6b/0xb0 exit_to_user_mode_prepare+0x1c5/0x1d0 syscall_exit_to_user_mode+0x19/0x50 do_syscall_64+0x46/0xb0 entry_SYSCALL_64_after_hwframe+0x44/0xae -> #0 (drm_global_mutex){+.+.}-{3:3}: validate_chain+0xb39/0x1e70 __lock_acquire+0x5a1/0xb70 lock_acquire+0xd3/0x310 __mutex_lock+0xa8/0x930 drm_open+0x64/0x280 drm_stub_open+0x9f/0x100 chrdev_open+0x9f/0x1d0 do_dentry_open+0x14a/0x3a0 dentry_open+0x53/0x70 drm_mode_create_lease_ioctl+0x3cb/0x970 drm_ioctl_kernel+0xc9/0x1a0 drm_ioctl+0x201/0x3d0 __x64_sys_ioctl+0x6a/0xa0 do_syscall_64+0x37/0xb0 entry_SYSCALL_64_after_hwframe+0x44/0xae other info that might help us debug this: Chain exists of: drm_global_mutex --> &helper->lock --> &dev->master_rwsem Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&dev->master_rwsem); lock(&helper->lock); lock(&dev->master_rwsem); lock(drm_global_mutex); *** DEADLOCK *** The lock hierarchy inversion happens because we grab the drm_global_mutex while already holding on to master_rwsem. To avoid this, we do some prep work to grab the drm_global_mutex before checking for ioctl permissions. At the same time, we update the check for the global mutex to use the drm_dev_needs_global_mutex helper function. Signed-off-by: Desmond Cheong Zhi Xi --- drivers/gpu/drm/drm_ioctl.c | 18 +++++++++--------- 1 file changed, 9 insertions(+), 9 deletions(-) diff --git a/drivers/gpu/drm/drm_ioctl.c b/drivers/gpu/drm/drm_ioctl.c index 880fc565d599..2cb57378a787 100644 --- a/drivers/gpu/drm/drm_ioctl.c +++ b/drivers/gpu/drm/drm_ioctl.c @@ -779,19 +779,19 @@ long drm_ioctl_kernel(struct file *file, drm_ioctl_t *func, void *kdata, if (drm_dev_is_unplugged(dev)) return -ENODEV; + /* Enforce sane locking for modern driver ioctls. */ + if (unlikely(drm_dev_needs_global_mutex(dev)) && !(flags & DRM_UNLOCKED)) + mutex_lock(&drm_global_mutex); + retcode = drm_ioctl_permit(flags, file_priv); if (unlikely(retcode)) - return retcode; + goto out; - /* Enforce sane locking for modern driver ioctls. */ - if (likely(!drm_core_check_feature(dev, DRIVER_LEGACY)) || - (flags & DRM_UNLOCKED)) - retcode = func(dev, kdata, file_priv); - else { - mutex_lock(&drm_global_mutex); - retcode = func(dev, kdata, file_priv); + retcode = func(dev, kdata, file_priv); + +out: + if (unlikely(drm_dev_needs_global_mutex(dev)) && !(flags & DRM_UNLOCKED)) mutex_unlock(&drm_global_mutex); - } return retcode; } EXPORT_SYMBOL(drm_ioctl_kernel);