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Wysocki" , ACPI Devel Maling List , Linux Kernel Mailing List References: <20210716101602.1891-1-laurentiu.tudor@nxp.com> <2a0f7fa6-b164-eeb4-118a-acd57d79a484@nxp.com> From: Laurentiu Tudor Message-ID: Date: Mon, 26 Jul 2021 10:59:20 +0300 User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101 Thunderbird/78.12.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-ClientProxiedBy: AM0PR03CA0072.eurprd03.prod.outlook.com (2603:10a6:208::49) To VI1PR0402MB3405.eurprd04.prod.outlook.com (2603:10a6:803:3::26) MIME-Version: 1.0 X-MS-Exchange-MessageSentRepresentingType: 1 Received: from [192.168.1.109] (86.123.59.131) by AM0PR03CA0072.eurprd03.prod.outlook.com (2603:10a6:208::49) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.4352.25 via Frontend Transport; Mon, 26 Jul 2021 07:59:21 +0000 X-MS-PublicTrafficType: Email X-MS-Office365-Filtering-Correlation-Id: 9b43c454-fb18-4b29-338c-08d9500b4787 X-MS-TrafficTypeDiagnostic: VI1PR0402MB2816: X-Microsoft-Antispam-PRVS: X-MS-Oob-TLC-OOBClassifiers: OLM:9508; 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Balance the refcount by >>>>>>> bumping it in the device_create_managed_software_node() function. >>>>>>> >>>>>>> The error [1] was encountered after adding a .shutdown() op to our >>>>>>> fsl-mc-bus driver. >>>>>> >>>>>> Looking into the history of adding ->shutdown() to dwc3 driver (it got reverted >>>>>> later on), I can tell that probably something is wrong in the ->shutdown() >>>>>> method itself. >>>>> >>>>> Isn't the other alternative to just remove the second kobject_put from >>>>> KOBJ_REMOVE ? >>>> >>>> Or maybe on top of Heikki's suggestion, replace the calls to >>>> sysfs_create_link() from KOBJ_ADD with sysfs_create_link_nowarn()? >>> >>> _noearn will hide the problem. It was there, it was removed from there. >>> Perhaps we have to understand the root cause better (some specific flow?). >>> >>> Any insight from you on the flow when the issue appears? I.o.w. what happened >>> on the big picture that we got into the warning you see? >> >> I encountered the initial issue when trying to shut down a system booted >> with ACPI but only after adding a .shutdown() callback to our bus driver >> so that the devices are properly taken down. The problem was that >> software_node_notify(), on KOBJ_REMOVE was dropping the reference count >> twice leading to an underflow error. My initial proposal was to just >> bump the refcount in device_create_managed_software_node(). The device >> properties that triggered the problem are created here [1]. >> >> Heikko suggested that instead of manually incrementing the refcount to >> use software_node_notify(KOBJ_ADD). This triggered the second issue, a >> duplicated sysfs entry warning originating in the usb subsystem: >> device_create_managed_software_node() ends up being called twice, once >> here [2] and secondly, the place I previous mentioned [1]. > > This [3] is what I have reported against DWC3 when ->shutdown() has > been added there. And here [4] is another thread about the issue with > that callback. The ->release() callback is called at put_device() [5] > and ->shutdown() is called before that [6]. That said, can you inspect > your ->shutdown() implementation once more time and perhaps see if > there is anything that can be amended? > Will do, thanks for the pointers. It could be that we mess something out in how we use the driver model. --- Best Regards, Laurentiu