i40e: Fix a bug where a client close can be called before an open is complete

The client->open call in this path was not protected with the
client instance mutex, and hence the client->close can get initiated
before the open completes.

Change-Id: I0ed60c38868dd3f44966b6ed49a063d0e5b7edf5
Signed-off-by: Anjali Singhai Jain <anjali.singhai@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40e/i40e_client.c

@@ -541,6 +541,7 @@ void i40e_client_subtask(struct i40e_pf *pf)
 			 client->name, pf->hw.pf_id,
 			 pf->hw.bus.device, pf->hw.bus.func);
 
+		mutex_lock(&i40e_client_instance_mutex);
 		/* Send an Open request to the client */
 		atomic_inc(&cdev->ref_cnt);
 		if (client->ops && client->ops->open)
@@ -554,6 +555,7 @@ void i40e_client_subtask(struct i40e_pf *pf)
 			atomic_dec(&client->ref_cnt);
 			continue;
 		}
+		mutex_unlock(&i40e_client_instance_mutex);
 	}
 	mutex_unlock(&i40e_client_mutex);
 }