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 3EFD4C11F68 for ; Tue, 29 Jun 2021 03:38:04 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 240D461D3D for ; Tue, 29 Jun 2021 03:38:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231980AbhF2Dk3 (ORCPT ); Mon, 28 Jun 2021 23:40:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42230 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231952AbhF2Dk1 (ORCPT ); Mon, 28 Jun 2021 23:40:27 -0400 Received: from mail-pg1-x533.google.com (mail-pg1-x533.google.com [IPv6:2607:f8b0:4864:20::533]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 2B00AC061574; Mon, 28 Jun 2021 20:38:01 -0700 (PDT) Received: by mail-pg1-x533.google.com with SMTP id a2so17241733pgi.6; Mon, 28 Jun 2021 20:38:01 -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=VkOFQf/536RNFMu+xaArckMzz68g/ujSW9t2Sns7i4U=; b=JBmBwYA7IT4xcNcqZ9oTxNv+fduy88l+lRYwHyOxAT4d74hZiHK2BqgFd8CRqzVKWB QqH/TArCcsaSc2CM3xquE3JQcDTzNsqJ/wPCtDhzJOeilygI9OWtGJkWX8HyEz0z46Cm EbqGpLPFrw0wICXehaI2HGKBXEfRARjdLK763N4wtu8JTZKvdfYgeu9fv9aafp43/C9b xYq2U8pRKQC9+mEt2mpiuDm7muP9zXvZyBZsP/V65CRGuTis5rxUtcNzI0nNSO45/3Fn UTrt6aLZw4qjfklyG7LB9ZxUNGfanmy8IyG05hdvWk10oFOdA9zUFtIDfptk/VRddVRY 3Mkg== 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=VkOFQf/536RNFMu+xaArckMzz68g/ujSW9t2Sns7i4U=; b=CC6wFL/xA8n/0Qp3eVm/IFWby83msFp6Jfpgmx7t9QoHWKWMJpAFO5zsnNjKv1w2nj i2xU8FDqfk2BgxczYWt0y4smyBMfsgPF72G3d3s8Ny2da0PQLzJgx7VD0O79wpPrNlmI p07uXKbp/eWRV1OjMyjvQYfWLg4m8ANrH/8z5Eo442lpVEix4Cuk488aqlD8N5kxIeap Uq9wZHes+BSgoiXo/i17bc445nCaH9S3wJCkSzdoaLDBVIAmQRYxjhDaq5oh7YPyBZgo GSXlSo+fURwih9MdVzr0iuAZYZtkiWr9kThX0lnGyJviMyULBA+XUCbRpH/bLWbbiJVC cSwQ== X-Gm-Message-State: AOAM530vAoqsCazS1CYCXttppeNcHRMjBWtAFtxs3V6U3vXdOqozBUGB S+3dJdCrQmCv+drRRvh6qg0= X-Google-Smtp-Source: ABdhPJyFDojKWVkhV0CV0B2CVgV3KJ4T9IPd2rw0iLhik1NNTjHtlY4m556JI3QqbHPac0YSuAv1xQ== X-Received: by 2002:a63:d909:: with SMTP id r9mr26737857pgg.285.1624937880177; Mon, 28 Jun 2021 20:38:00 -0700 (PDT) Received: from localhost.localdomain ([118.200.190.93]) by smtp.gmail.com with ESMTPSA id d129sm14769076pfd.218.2021.06.28.20.37.55 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 28 Jun 2021 20:37:59 -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 v5 1/3] drm: avoid circular locks in drm_mode_getconnector Date: Tue, 29 Jun 2021 11:37:04 +0800 Message-Id: <20210629033706.20537-2-desmondcheongzx@gmail.com> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20210629033706.20537-1-desmondcheongzx@gmail.com> References: <20210629033706.20537-1-desmondcheongzx@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org In preparation for a future patch to take a lock on drm_device.master_mutex inside drm_is_current_master(), we first move the call to drm_is_current_master() in drm_mode_getconnector out from the section locked by &dev->mode_config.mutex. This avoids creating a circular lock dependency. Failing to avoid this lock dependency produces the following lockdep splat: ====================================================== WARNING: possible circular locking dependency detected 5.13.0-rc7-CI-CI_DRM_10254+ #1 Not tainted ------------------------------------------------------ kms_frontbuffer/1087 is trying to acquire lock: ffff88810dcd01a8 (&dev->master_mutex){+.+.}-{3:3}, at: drm_is_current_master+0x1b/0x40 but task is already holding lock: ffff88810dcd0488 (&dev->mode_config.mutex){+.+.}-{3:3}, at: drm_mode_getconnector+0x1c6/0x4a0 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #2 (&dev->mode_config.mutex){+.+.}-{3:3}: __mutex_lock+0xab/0x970 drm_client_modeset_probe+0x22e/0xca0 __drm_fb_helper_initial_config_and_unlock+0x42/0x540 intel_fbdev_initial_config+0xf/0x20 [i915] async_run_entry_fn+0x28/0x130 process_one_work+0x26d/0x5c0 worker_thread+0x37/0x380 kthread+0x144/0x170 ret_from_fork+0x1f/0x30 -> #1 (&client->modeset_mutex){+.+.}-{3:3}: __mutex_lock+0xab/0x970 drm_client_modeset_commit_locked+0x1c/0x180 drm_client_modeset_commit+0x1c/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+0x1e5/0x2d0 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+0x37/0x380 kthread+0x144/0x170 ret_from_fork+0x1f/0x30 -> #0 (&dev->master_mutex){+.+.}-{3:3}: __lock_acquire+0x151e/0x2590 lock_acquire+0xd1/0x3d0 __mutex_lock+0xab/0x970 drm_is_current_master+0x1b/0x40 drm_mode_getconnector+0x37e/0x4a0 drm_ioctl_kernel+0xa8/0xf0 drm_ioctl+0x1e8/0x390 __x64_sys_ioctl+0x6a/0xa0 do_syscall_64+0x39/0xb0 entry_SYSCALL_64_after_hwframe+0x44/0xae other info that might help us debug this: Chain exists of: &dev->master_mutex --> &client->modeset_mutex --> &dev->mode_config.mutex Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(&dev->mode_config.mutex); lock(&client->modeset_mutex); lock(&dev->mode_config.mutex); lock(&dev->master_mutex); *** DEADLOCK *** 1 lock held by kms_frontbuffer/1087: #0: ffff88810dcd0488 (&dev->mode_config.mutex){+.+.}-{3:3}, at: drm_mode_getconnector+0x1c6/0x4a0 stack backtrace: CPU: 7 PID: 1087 Comm: kms_frontbuffer Not tainted 5.13.0-rc7-CI-CI_DRM_10254+ #1 Hardware name: Intel Corporation Ice Lake Client Platform/IceLake U DDR4 SODIMM PD RVP TLC, BIOS ICLSFWR1.R00.3234.A01.1906141750 06/14/2019 Call Trace: dump_stack+0x7f/0xad check_noncircular+0x12e/0x150 __lock_acquire+0x151e/0x2590 lock_acquire+0xd1/0x3d0 __mutex_lock+0xab/0x970 drm_is_current_master+0x1b/0x40 drm_mode_getconnector+0x37e/0x4a0 drm_ioctl_kernel+0xa8/0xf0 drm_ioctl+0x1e8/0x390 __x64_sys_ioctl+0x6a/0xa0 do_syscall_64+0x39/0xb0 entry_SYSCALL_64_after_hwframe+0x44/0xae Reported-by: Daniel Vetter Signed-off-by: Desmond Cheong Zhi Xi --- drivers/gpu/drm/drm_connector.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c index da39e7ff6965..2ba257b1ae20 100644 --- a/drivers/gpu/drm/drm_connector.c +++ b/drivers/gpu/drm/drm_connector.c @@ -2414,6 +2414,7 @@ int drm_mode_getconnector(struct drm_device *dev, void *data, struct drm_mode_modeinfo u_mode; struct drm_mode_modeinfo __user *mode_ptr; uint32_t __user *encoder_ptr; + bool is_current_master; if (!drm_core_check_feature(dev, DRIVER_MODESET)) return -EOPNOTSUPP; @@ -2444,9 +2445,11 @@ int drm_mode_getconnector(struct drm_device *dev, void *data, out_resp->connector_type = connector->connector_type; out_resp->connector_type_id = connector->connector_type_id; + is_current_master = drm_is_current_master(file_priv); + mutex_lock(&dev->mode_config.mutex); if (out_resp->count_modes == 0) { - if (drm_is_current_master(file_priv)) + if (is_current_master) connector->funcs->fill_modes(connector, dev->mode_config.max_width, dev->mode_config.max_height); -- 2.25.1