[RFC PATCH v1 2/8] sunrpc: fail only the RPC a transport refuses

[Pranjal Shrivastava <praan@google.com>]

A transport returns -EREMOTEIO from ->send_request() for a request
whose P2PDMA pages it cannot move. Retrying doesn't help, but today
the error stops xprt_transmit(), finds whichever task is draining
the transmit queue, and leaves the refused request queued.

Dequeue the request, on -EREMOTEIO, cancel only its own task with
rpc_task_try_cancel(), and keep draining. Setting tk_status instead
would not work, a dequeued task looks transmitted and would wait for
a reply that never comes.

Signed-off-by: Pranjal Shrivastava <praan@google.com>
---
 net/sunrpc/xprt.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/net/sunrpc/xprt.c b/net/sunrpc/xprt.c
index 48a3618cbb29..084d5a508357 100644
--- a/net/sunrpc/xprt.c
+++ b/net/sunrpc/xprt.c
@@ -1579,6 +1579,15 @@ xprt_request_transmit(struct rpc_rqst *req, struct rpc_task *snd_task)
 	if (status != 0) {
 		req->rq_ntrans--;
 		trace_xprt_transmit(req, status);
+		if (status == -EREMOTEIO) {
+			/*
+			 * This transport will never send req. Fail only
+			 * its task, and let the caller keep draining.
+			 */
+			xprt_request_dequeue_transmit(task);
+			rpc_task_try_cancel(task, status);
+			return 0;
+		}
 		return status;
 	}
 
-- 
2.56.0.rc1.315.gc6ed9934b7-goog