mei: bus: need to unlink client before freeing

In case a client fails to connect in mei_cldev_enable(), the
caller won't call the mei_cldev_disable leaving the client
in a linked stated. Upon driver unload the client structure
will be freed in  mei_cl_bus_dev_release(), leaving a stale pointer
on a fail_list.  This will eventually end up in crash
during power down flow in mei_cl_set_disonnected().

RIP:  mei_cl_set_disconnected+0x5/0x260[mei]
Call trace:
mei_cl_all_disconnect+0x22/0x30
mei_reset+0x194/0x250
__synchronize_hardirq+0x43/0x50
_cond_resched+0x15/0x30
mei_me_intr_clear+0x20/0x100
mei_stop+0x76/0xb0
mei_me_shutdown+0x3f/0x80
pci_device_shutdown+0x34/0x60
kernel_restart+0x0e/0x30

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=200455
Fixes: 'c110cdb1 ("mei: bus: make a client pointer always available")'
Cc: <stable@vger.kernel.org> 4.10+
Tested-by: Georg Müller <georgmueller@gmx.net>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/mei/bus.c

@@ -521,17 +521,15 @@ int mei_cldev_enable(struct mei_cl_device *cldev)
 
 	cl = cldev->cl;
 
-	if (cl->state == MEI_FILE_UNINITIALIZED) {
 	mutex_lock(&bus->device_lock);
+	if (cl->state == MEI_FILE_UNINITIALIZED) {
 		ret = mei_cl_link(cl);
-		mutex_unlock(&bus->device_lock);
 		if (ret)
-			return ret;
+			goto out;
 		/* update pointers */
 		cl->cldev = cldev;
 	}
 
-	mutex_lock(&bus->device_lock);
 	if (mei_cl_is_connected(cl)) {
 		ret = 0;
 		goto out;
@@ -875,6 +873,7 @@ static void mei_cl_bus_dev_release(struct device *dev)
 
 	mei_me_cl_put(cldev->me_cl);
 	mei_dev_bus_put(cldev->bus);
+	mei_cl_unlink(cldev->cl);
 	kfree(cldev->cl);
 	kfree(cldev);
 }