workqueue: add pool ID to the names of unbound kworkers

There are gonna be multiple unbound pools.  Include pool ID in the
name of unbound kworkers.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Lai Jiangshan <laijs@cn.fujitsu.com>

kernel/workqueue.c

@@ -1707,7 +1707,8 @@ static struct worker *create_worker(struct worker_pool *pool)
 					"kworker/%d:%d%s", pool->cpu, id, pri);
 	else
 		worker->task = kthread_create(worker_thread, worker,
-					      "kworker/u:%d%s", id, pri);
+					      "kworker/u%d:%d%s",
+					      pool->id, id, pri);
 	if (IS_ERR(worker->task))
 		goto fail;