[PATCH v2] SUNRPC: Fix backchannel reply, again

[cel@kernel.org]

From: Chuck Lever <chuck.lever@oracle.com>

I still see "RPC: Could not send backchannel reply error: -110"
quite often, along with slow-running tests. Debugging shows that the
backchannel is still stumbling when it has to queue a callback reply
on a busy transport.

Note that every one of these timeouts causes a connection loss by
virtue of the xprt_conditional_disconnect() call in that arm of
call_cb_transmit_status().

I found that setting to_maxval is necessary to get the RPC timeout
logic to behave whenever to_exponential is not set.

Fixes: 57331a59ac0d ("NFSv4.1: Use the nfs_client's rpc timeouts for backchannel")
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
---
 net/sunrpc/svc.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/net/sunrpc/svc.c b/net/sunrpc/svc.c
index 965a27806bfd..e03f14024e47 100644
--- a/net/sunrpc/svc.c
+++ b/net/sunrpc/svc.c
@@ -1588,9 +1588,11 @@ void svc_process(struct svc_rqst *rqstp)
  */
 void svc_process_bc(struct rpc_rqst *req, struct svc_rqst *rqstp)
 {
+	struct rpc_timeout timeout = {
+		.to_increment		= 0,
+	};
 	struct rpc_task *task;
 	int proc_error;
-	struct rpc_timeout timeout;
 
 	/* Build the svc_rqst used by the common processing routine */
 	rqstp->rq_xid = req->rq_xid;
@@ -1643,6 +1645,7 @@ void svc_process_bc(struct rpc_rqst *req, struct svc_rqst *rqstp)
 		timeout.to_initval = req->rq_xprt->timeout->to_initval;
 		timeout.to_retries = req->rq_xprt->timeout->to_retries;
 	}
+	timeout.to_maxval = timeout.to_initval;
 	memcpy(&req->rq_snd_buf, &rqstp->rq_res, sizeof(req->rq_snd_buf));
 	task = rpc_run_bc_task(req, &timeout);
 
-- 
2.45.1