linux-kernel - [PATCH 4.9 75/86] mei: bus: dont clean driver pointer

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Message-Id: <20200720152756.978576850@linuxfoundation.org>
Date:   Mon, 20 Jul 2020 17:37:11 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Andy Whitcroft <apw@...onical.com>,
        Alexander Usyskin <alexander.usyskin@...el.com>,
        Tomas Winkler <tomas.winkler@...el.com>
Subject: [PATCH 4.9 75/86] mei: bus: dont clean driver pointer

From: Alexander Usyskin <alexander.usyskin@...el.com>

commit e852c2c251ed9c23ae6e3efebc5ec49adb504207 upstream.

It's not needed to set driver to NULL in mei_cl_device_remove()
which is bus_type remove() handler as this is done anyway
in __device_release_driver().

Actually this is causing an endless loop in driver_detach()
on ubuntu patched kernel, while removing (rmmod) the mei_hdcp module.
The reason list_empty(&drv->p->klist_devices.k_list) is always not-empty.
as the check is always true in  __device_release_driver()
	if (dev->driver != drv)
		return;

The non upstream patch is causing this behavior, titled:
'vfio -- release device lock before userspace requests'

Nevertheless the fix is correct also for the upstream.

Link: https://patchwork.ozlabs.org/project/ubuntu-kernel/patch/20180912085046.3401-2-apw@canonical.com/
Cc: <stable@...r.kernel.org>
Cc: Andy Whitcroft <apw@...onical.com>
Signed-off-by: Alexander Usyskin <alexander.usyskin@...el.com>
Signed-off-by: Tomas Winkler <tomas.winkler@...el.com>
Link: https://lore.kernel.org/r/20200628225359.2185929-1-tomas.winkler@intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

---
 drivers/misc/mei/bus.c |    3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

--- a/drivers/misc/mei/bus.c
+++ b/drivers/misc/mei/bus.c
@@ -639,9 +639,8 @@ static int mei_cl_device_remove(struct d
 		ret = cldrv->remove(cldev);
 
 	module_put(THIS_MODULE);
-	dev->driver = NULL;
-	return ret;
 
+	return ret;
 }
 
 static ssize_t name_show(struct device *dev, struct device_attribute *a,