nvmet-loop: Flush nvme_delete_wq when removing the port

After calling nvme_loop_delete_ctrl(), the controllers will not
yet be deleted because nvme_delete_ctrl() only schedules work
to do the delete.

This means a race can occur if a port is removed but there
are still active controllers trying to access that memory.

To fix this, flush the nvme_delete_wq before returning from
nvme_loop_remove_port() so that any controllers that might
be in the process of being deleted won't access a freed port.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Max Gurtovoy <maxg@mellanox.com>
Reviewed-by : Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>

drivers/nvme/target/loop.c

@@ -654,6 +654,14 @@ static void nvme_loop_remove_port(struct nvmet_port *port)
  mutex_lock(&nvme_loop_ports_mutex);
  list_del_init(&port->entry);
  mutex_unlock(&nvme_loop_ports_mutex);
+
+ /*
+ * Ensure any ctrls that are in the process of being
+ * deleted are in fact deleted before we return
+ * and free the port. This is to prevent active
+ * ctrls from using a port after it's freed.
+ */
+ flush_workqueue(nvme_delete_wq);
 }
 
 static const struct nvmet_fabrics_ops nvme_loop_ops = {