workqueue: Fix an use after free in init_rescuer()

We need to preserve error code before freeing "rescuer".

Fixes: f187b697 ("workqueue: Use IS_ERR and PTR_ERR instead of PTR_ERR_OR_ZERO.")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Lai Jiangshan <jiangshanlai@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

kernel/workqueue.c

@@ -4197,6 +4197,7 @@ static int wq_clamp_max_active(int max_active, unsigned int flags,
 static int init_rescuer(struct workqueue_struct *wq)
 {
 	struct worker *rescuer;
+	int ret;
 
 	if (!(wq->flags & WQ_MEM_RECLAIM))
 		return 0;
@@ -4208,8 +4209,9 @@ static int init_rescuer(struct workqueue_struct *wq)
 	rescuer->rescue_wq = wq;
 	rescuer->task = kthread_create(rescuer_thread, rescuer, "%s", wq->name);
 	if (IS_ERR(rescuer->task)) {
+		ret = PTR_ERR(rescuer->task);
 		kfree(rescuer);
-		return PTR_ERR(rescuer->task);
+		return ret;
 	}
 
 	wq->rescuer = rescuer;