SUNRPC: fix a list corruption issue in xprt_release()

We remove the request from the receive list before we call
xprt_wait_on_pinned_rqst(), and so we need to use list_del_init().
Otherwise, we will see list corruption when xprt_complete_rqst()
is called.

Reported-by: Emre Celebi <emre@primarydata.com>
Fixes: ce7c252a8c741 ("SUNRPC: Add a separate spinlock to protect...")
Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>

net/sunrpc/xprt.c

@@ -1333,7 +1333,7 @@ void xprt_release(struct rpc_task *task)
 		rpc_count_iostats(task, task->tk_client->cl_metrics);
 	spin_lock(&xprt->recv_lock);
 	if (!list_empty(&req->rq_list)) {
-		list_del(&req->rq_list);
+		list_del_init(&req->rq_list);
 		xprt_wait_on_pinned_rqst(req);
 	}
 	spin_unlock(&xprt->recv_lock);