SUNRPC: Move xpt_mutex into socket xpo_sendto methods

It appears that the RPC/RDMA transport does not need serialization
of calls to its xpo_sendto method. Move the mutex into the socket
methods that still need that serialization.

Tail latencies are unambiguously better with this patch applied.
fio randrw 8KB 70/30 on NFSv3, smaller numbers are better:

    clat percentiles (usec):

With xpt_mutex:
r    | 99.99th=[ 8848]
w    | 99.99th=[ 9634]

Without xpt_mutex:
r    | 99.99th=[ 8586]
w    | 99.99th=[ 8979]

Serializing the construction of RPC/RDMA transport headers is not
really necessary at this point, because the Linux NFS server
implementation never changes its credit grant on a connection. If
that should change, then svc_rdma_sendto will need to serialize
access to the transport's credit grant fields.

Reported-by: kbuild test robot <lkp@intel.com>
[ cel: fix uninitialized variable warning ]
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

1 files changed, 25 insertions, 0 deletions

diff --git a/net/sunrpc/svcsock.c b/net/sunrpc/svcsock.c
index 023514e392b3..3e7b6445e317 100644
--- a/net/sunrpc/svcsock.c
+++ b/net/sunrpc/svcsock.c
@@ -506,6 +506,9 @@ out_free:
  * svc_udp_sendto - Send out a reply on a UDP socket
  * @rqstp: completed svc_rqst
  *
+ * xpt_mutex ensures @rqstp's whole message is written to the socket
+ * without interruption.
+ *
  * Returns the number of bytes sent, or a negative errno.
  */
 static int svc_udp_sendto(struct svc_rqst *rqstp)
@@ -531,6 +534,11 @@ static int svc_udp_sendto(struct svc_rqst *rqstp)
 
 	svc_set_cmsg_data(rqstp, cmh);
 
+	mutex_lock(&xprt->xpt_mutex);
+
+	if (svc_xprt_is_dead(xprt))
+		goto out_notconn;
+
 	err = xprt_sock_sendmsg(svsk->sk_sock, &msg, xdr, 0, 0, &sent);
 	xdr_free_bvec(xdr);
 	if (err == -ECONNREFUSED) {
@@ -538,9 +546,15 @@ static int svc_udp_sendto(struct svc_rqst *rqstp)
 		err = xprt_sock_sendmsg(svsk->sk_sock, &msg, xdr, 0, 0, &sent);
 		xdr_free_bvec(xdr);
 	}
+
+	mutex_unlock(&xprt->xpt_mutex);
 	if (err < 0)
 		return err;
 	return sent;
+
+out_notconn:
+	mutex_unlock(&xprt->xpt_mutex);
+	return -ENOTCONN;
 }
 
 static int svc_udp_has_wspace(struct svc_xprt *xprt)
@@ -1063,6 +1077,9 @@ err_noclose:
  * svc_tcp_sendto - Send out a reply on a TCP socket
  * @rqstp: completed svc_rqst
  *
+ * xpt_mutex ensures @rqstp's whole message is written to the socket
+ * without interruption.
+ *
  * Returns the number of bytes sent, or a negative errno.
  */
 static int svc_tcp_sendto(struct svc_rqst *rqstp)
@@ -1080,12 +1097,19 @@ static int svc_tcp_sendto(struct svc_rqst *rqstp)
 
 	svc_release_skb(rqstp);
 
+	mutex_lock(&xprt->xpt_mutex);
+	if (svc_xprt_is_dead(xprt))
+		goto out_notconn;
 	err = xprt_sock_sendmsg(svsk->sk_sock, &msg, xdr, 0, marker, &sent);
 	xdr_free_bvec(xdr);
 	if (err < 0 || sent != (xdr->len + sizeof(marker)))
 		goto out_close;
+	mutex_unlock(&xprt->xpt_mutex);
 	return sent;
 
+out_notconn:
+	mutex_unlock(&xprt->xpt_mutex);
+	return -ENOTCONN;
 out_close:
 	pr_notice("rpc-srv/tcp: %s: %s %d when sending %d bytes - shutting down socket\n",
 		  xprt->xpt_server->sv_name,
@@ -1093,6 +1117,7 @@ out_close:
 		  (err < 0) ? err : sent, xdr->len);
 	set_bit(XPT_CLOSE, &xprt->xpt_flags);
 	svc_xprt_enqueue(xprt);
+	mutex_unlock(&xprt->xpt_mutex);
 	return -EAGAIN;
 }