From patchwork Thu Nov 17 16:53:11 2022 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Maxime Ripard X-Patchwork-Id: 13047123 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org 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 smtp.lore.kernel.org (Postfix) with ESMTPS id 6A888C4332F for ; Thu, 17 Nov 2022 16:53:29 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 9BD0810E198; Thu, 17 Nov 2022 16:53:26 +0000 (UTC) Received: from wout4-smtp.messagingengine.com (wout4-smtp.messagingengine.com [64.147.123.20]) by gabe.freedesktop.org (Postfix) with ESMTPS id 56F4C10E0E5 for ; Thu, 17 Nov 2022 16:53:19 +0000 (UTC) Received: from compute2.internal (compute2.nyi.internal [10.202.2.46]) by mailout.west.internal (Postfix) with ESMTP id 989633201B69; Thu, 17 Nov 2022 11:53:15 -0500 (EST) Received: from mailfrontend2 ([10.202.2.163]) by compute2.internal (MEProxy); Thu, 17 Nov 2022 11:53:16 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=cerno.tech; h=cc :cc:content-type:date:date:from:from:in-reply-to:message-id :mime-version:reply-to:sender:subject:subject:to:to; s=fm2; t= 1668703995; x=1668790395; bh=FbzlDkkhhsRtKSZiUm2xWhCcXLtVXKnc1W3 izJLploc=; b=Q/266Oy+xDLeuIV4Kf5CL1NHL7bAxNsInYyW4KsyQ3HCpNw9cHE dGhwAppw14wJKRPMUhL3OCzPc4MHEajCb5+7UHkc4XUvHtLWHFYmyMVc8nKnF2jH TA/jE/wJirFQ4yctUTYNyW9c7JbP4rx/rpWmzpiUubEG/o8xtXt037To+G/QqBra 009fhxDNboiMNF0A3vvEfzZ95B3jk2ZqSnOxdXNY1XJSOF8cF/g/7n3o64qprOGJ YEELav7az3jiUO2w5VLF6RcNkjMvpewKeB7Ix1ySwFDvdxKHhbe+68fhfIxn8NNj hHQYCqAE89CoZjk7qf1vuoZYMlwIr0OlZtg== DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d= messagingengine.com; h=cc:cc:content-type:date:date:feedback-id :feedback-id:from:from:in-reply-to:message-id:mime-version :reply-to:sender:subject:subject:to:to:x-me-proxy:x-me-proxy :x-me-sender:x-me-sender:x-sasl-enc; s=fm1; t=1668703995; x= 1668790395; bh=FbzlDkkhhsRtKSZiUm2xWhCcXLtVXKnc1W3izJLploc=; b=w kH5BeJJ0sxtl3xiySYdhYXXot1xbFrHsakf599nx+1VS0Wp9N8XtcwZSZDeHebpv 5iO113iphsejg6/oZRiQnUjznHRBwLZv17HRs35gFEg9WkGZDBqO8FvE43lyNeoY +U+VxaO+8J07/4hvimbbyHK7r6cmOxdVsXHIr1OpwUSRgr9oX9xPM5L9l/SNMDkC bNok6KkBXuu8bwNxhGDU7qkdI3EKOinFSSNSmEIKq71hisZ6i6drfzUG5D8Imt96 oD0zj022aw0D2/CWrI0eMT5SFohIcDSmaU84y312vSytcyWSOMAPkzuRgQKne23h 9WW1y5ufVgJHT5G8l8GWw== X-ME-Sender: X-ME-Received: X-ME-Proxy-Cause: gggruggvucftvghtrhhoucdtuddrgedvgedrgeekgdelvdcutefuodetggdotefrodftvf curfhrohhfihhlvgemucfhrghsthforghilhdpqfgfvfdpuffrtefokffrpgfnqfghnecu uegrihhlohhuthemuceftddtnecusecvtfgvtghiphhivghnthhsucdlqddutddtmdenuc fjughrpeffhffvvefukfggtggusehgtderredttddvnecuhfhrohhmpeforgigihhmvgcu tfhiphgrrhguuceomhgrgihimhgvsegtvghrnhhordhtvggthheqnecuggftrfgrthhtvg hrnhepteeifeeigeetgfffgedufeefheekgfevuefgtdehffefheelleejveeviefhgfek necuffhomhgrihhnpehfrhgvvgguvghskhhtohhprdhorhhgpdgsohhothhlihhnrdgtoh hmnecuvehluhhsthgvrhfuihiivgeptdenucfrrghrrghmpehmrghilhhfrhhomhepmhgr gihimhgvsegtvghrnhhordhtvggthh X-ME-Proxy: Feedback-ID: i8771445c:Fastmail Received: by mail.messagingengine.com (Postfix) with ESMTPA; Thu, 17 Nov 2022 11:53:14 -0500 (EST) Date: Thu, 17 Nov 2022 17:53:11 +0100 From: Maxime Ripard To: Daniel Vetter , David Airlie , Maarten Lankhorst , Thomas Zimmermann , Maxime Ripard , Greg Kroah-Hartman , "Rafael J. Wysocki" Subject: DRM-managed resources / devm_drm_dev_alloc leaking resources Message-ID: <20221117165311.vovrc7usy4efiytl@houat> MIME-Version: 1.0 Content-Disposition: inline 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: , Cc: linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" Hi, After trying to get more kunit tests for KMS, I found out that the recent kunit helpers we merged to create a DRM device [1] are broken and won't free their device-managed and DRM-managed resources. With some help from Thomas, we've dug into this and it turns out that if we allocate a device with root_device_register, initialise our drm device with devm_drm_dev_alloc(), register it using drm_dev_register(), unregister it using drm_dev_unregister/drm_dev_unplug and then remove the parent device, neither the device managed nor the DRM managed actions are run. root_device_register initializes the device by eventually calling device_initialize() which sets the initial reference count of the root device to 1 [2]. devm_drm_dev_alloc() then comes in, drm_dev_init() will increase the root device refcount [3] and initialize our DRM device to 1 [4]. drm_dev_register(), through drm_minor_register() and device_add(), will increase the root device refcount [5]. When unrolling things, drm_dev_unregister(), through drm_minor_unregister() and device_del(), will give up its reference [6]. root_device_unregister(), through device_unregister(), will also give up its own [7]. So we end up with this for the reference counts: +------------------------+-------------+------------+ | funcs | root device | DRM device | +------------------------+-------------+------------+ | root_device_register | 1 | N/A | | devm_drm_dev_alloc | 2 | 1 | | drm_dev_register | 3 | 1 | | drm_dev_unregister | 2 | 1 | | root_device_unregister | 1 | 1 | +------------------------+-------------+------------+ If we go back to the list of reference taken, the root device reference and the initial drm_device reference, both taken by devm_drm_dev_alloc() through drm_dev_init(), haven't been put back. If we look at the drm_dev_init code(), we can see that it sets up a DRM-managed action [8] that will put back the device reference [9]. The DRM-managed code is executed by the drm_managed_cleanup() function, that is executed as part of a release hook [10] executed once we give up the final reference to the DRM device [11]. If we go back a little, the final reference to the DRM device is actually the initial one setup by devm_drm_dev_alloc(). This function has superseded drm_dev_alloc(), with the documentation that we do need a final drm_dev_put() to put back our final reference [12]. devm_drm_dev_alloc() is a more convenient variant that has been introduced explicitly to not require that drm_dev_put(), and states it as such in the documentation [13]. It does so by adding a device-managed action that will call drm_dev_put() [14]. Device-managed actions are ran as part devres_release_all() that is called by device_release() [15], itself being run when the last reference on the device is put back [16][17][18]. So if we sum things up, the DRM device will only give its last root device reference when the last DRM device reference will be put back, and the last DRM device reference will be put back when the last device reference will be put back, which sounds very circular to me, with both ending up in a deadlock scenario. I've added two kunit tests that demonstrate the issue: we register a device, allocate and register a DRM device, register a DRM-managed action, remove the DRM device and the parent device, and wait for the action to execute. drm_register_unregister_with_devm_test() uses the broken(?) devm_drm_dev_alloc and is failing. drm_register_unregister_test uses the deprecated drm_dev_alloc() that requires an explicit call to drm_dev_put() which works fine. It's also worth noting that Thomas tested with simpledrm and it seems to work fine. Using a platform_device instead of the root_device doesn't change anything to the outcome in my tests, so there might be a more subtle behaviour involved. Thanks, Maxime --------- 8< ----------- --------- 8< ----------- 1: https://cgit.freedesktop.org/drm-misc/tree/drivers/gpu/drm/tests/drm_kunit_helpers.c 2: https://elixir.bootlin.com/linux/latest/source/drivers/base/core.c#L2979 3: https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_drv.c#L597 4: https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_drv.c#L596 5: https://elixir.bootlin.com/linux/latest/source/drivers/base/core.c#L3437 6: https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_drv.c#L201 7: https://elixir.bootlin.com/linux/latest/source/drivers/base/core.c#L3737 8: https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_drv.c#L618 9: https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_drv.c#L570 10: https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_drv.c#L751 11: https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_drv.c#L785 12: https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_drv.c#L259 13: https://elixir.bootlin.com/linux/latest/source/include/drm/drm_drv.h#L505 14: https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_drv.c#L682 15: https://elixir.bootlin.com/linux/latest/source/drivers/base/core.c#L2321 16: https://elixir.bootlin.com/linux/latest/source/drivers/base/core.c#L2357 17: https://elixir.bootlin.com/linux/latest/source/lib/kobject.c#L721 18: https://elixir.bootlin.com/linux/latest/source/lib/kobject.c#L647 diff --git a/drivers/gpu/drm/tests/drm_register_test.c b/drivers/gpu/drm/tests/drm_register_test.c new file mode 100644 index 000000000000..3256b53d08f2 --- /dev/null +++ b/drivers/gpu/drm/tests/drm_register_test.c @@ -0,0 +1,117 @@ +// SPDX-License-Identifier: GPL-2.0 + +#include +#include + +#include + +#include +#include + +#include "drm_kunit_helpers.h" + +struct test_priv { + bool release_done; + wait_queue_head_t release_wq; +}; + +static const struct drm_mode_config_funcs drm_mode_config_funcs = { +}; + +static const struct drm_driver drm_driver = { + .driver_features = DRIVER_MODESET, +}; + +static void drm_release(struct drm_device *drm, void *ptr) +{ + struct test_priv *priv = ptr; + + priv->release_done = true; + wake_up_interruptible(&priv->release_wq); +} + +#define RELEASE_TIMEOUT_MS 500 + +static void drm_register_unregister_test(struct kunit *test) +{ + struct test_priv *priv; + struct drm_device *drm; + struct device *dev; + int ret; + + priv = kunit_kzalloc(test, sizeof(*priv), GFP_KERNEL); + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, priv); + init_waitqueue_head(&priv->release_wq); + + dev = root_device_register("test"); + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, dev); + + drm = drm_dev_alloc(&drm_driver, dev); + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, drm); + + drm->mode_config.funcs = &drm_mode_config_funcs; + ret = drmm_mode_config_init(drm); + KUNIT_ASSERT_EQ(test, ret, 0); + + ret = drmm_add_action_or_reset(drm, drm_release, priv); + KUNIT_ASSERT_EQ(test, ret, 0); + + ret = drm_dev_register(drm, 0); + KUNIT_ASSERT_EQ(test, ret, 0); + + drm_dev_unregister(drm); + drm_dev_put(drm); + root_device_unregister(dev); + + ret = wait_event_interruptible_timeout(priv->release_wq, priv->release_done, + msecs_to_jiffies(RELEASE_TIMEOUT_MS)); + KUNIT_EXPECT_GT(test, ret, 0); +} + +static void drm_register_unregister_with_devm_test(struct kunit *test) +{ + struct test_priv *priv; + struct drm_device *drm; + struct device *dev; + int ret; + + priv = kunit_kzalloc(test, sizeof(*priv), GFP_KERNEL); + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, priv); + init_waitqueue_head(&priv->release_wq); + + dev = root_device_register("test"); + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, dev); + + drm = __devm_drm_dev_alloc(dev, &drm_driver, sizeof(*drm), 0); + KUNIT_ASSERT_NOT_ERR_OR_NULL(test, drm); + + drm->mode_config.funcs = &drm_mode_config_funcs; + ret = drmm_mode_config_init(drm); + KUNIT_ASSERT_EQ(test, ret, 0); + + ret = drmm_add_action_or_reset(drm, drm_release, priv); + KUNIT_ASSERT_EQ(test, ret, 0); + + ret = drm_dev_register(drm, 0); + KUNIT_ASSERT_EQ(test, ret, 0); + + drm_dev_unregister(drm); + root_device_unregister(dev); + + ret = wait_event_interruptible_timeout(priv->release_wq, priv->release_done, + msecs_to_jiffies(RELEASE_TIMEOUT_MS)); + KUNIT_EXPECT_GT(test, ret, 0); +} + +static struct kunit_case drm_register_tests[] = { + KUNIT_CASE(drm_register_unregister_test), + KUNIT_CASE(drm_register_unregister_with_devm_test), + {} +}; + +static struct kunit_suite drm_register_test_suite = { + .name = "drm-test-register", + .test_cases = drm_register_tests +}; + +kunit_test_suite(drm_register_test_suite);