backchannel.c

  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Copyright (c) 2015-2020, Oracle and/or its affiliates.
  4 *
  5 * Support for reverse-direction RPCs on RPC/RDMA.
  6 */
  7
  8#include <linux/sunrpc/xprt.h>
  9#include <linux/sunrpc/svc.h>
 10#include <linux/sunrpc/svc_xprt.h>
 11#include <linux/sunrpc/svc_rdma.h>
 12#include <linux/sunrpc/bc_xprt.h>
 13
 14#include "xprt_rdma.h"
 15#include <trace/events/rpcrdma.h>
 16
 17#undef RPCRDMA_BACKCHANNEL_DEBUG
 18
 19/**
 20 * xprt_rdma_bc_setup - Pre-allocate resources for handling backchannel requests
 21 * @xprt: transport associated with these backchannel resources
 22 * @reqs: number of concurrent incoming requests to expect
 23 *
 24 * Returns 0 on success; otherwise a negative errno
 25 */
 26int xprt_rdma_bc_setup(struct rpc_xprt *xprt, unsigned int reqs)
 27{
 28	struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(xprt);
 29
 30	r_xprt->rx_buf.rb_bc_srv_max_requests = RPCRDMA_BACKWARD_WRS >> 1;
 31	trace_xprtrdma_cb_setup(r_xprt, reqs);
 32	return 0;
 33}
 34
 35/**
 36 * xprt_rdma_bc_maxpayload - Return maximum backchannel message size
 37 * @xprt: transport
 38 *
 39 * Returns maximum size, in bytes, of a backchannel message
 40 */
 41size_t xprt_rdma_bc_maxpayload(struct rpc_xprt *xprt)
 42{
 43	struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(xprt);
 44	struct rpcrdma_ep *ep = r_xprt->rx_ep;
 45	size_t maxmsg;
 46
 47	maxmsg = min_t(unsigned int, ep->re_inline_send, ep->re_inline_recv);
 48	maxmsg = min_t(unsigned int, maxmsg, PAGE_SIZE);
 49	return maxmsg - RPCRDMA_HDRLEN_MIN;
 50}
 51
 52unsigned int xprt_rdma_bc_max_slots(struct rpc_xprt *xprt)
 53{
 54	return RPCRDMA_BACKWARD_WRS >> 1;
 55}
 56
 57static int rpcrdma_bc_marshal_reply(struct rpc_rqst *rqst)
 58{
 59	struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(rqst->rq_xprt);
 60	struct rpcrdma_req *req = rpcr_to_rdmar(rqst);
 61	__be32 *p;
 62
 63	rpcrdma_set_xdrlen(&req->rl_hdrbuf, 0);
 64	xdr_init_encode(&req->rl_stream, &req->rl_hdrbuf,
 65			rdmab_data(req->rl_rdmabuf), rqst);
 66
 67	p = xdr_reserve_space(&req->rl_stream, 28);
 68	if (unlikely(!p))
 69		return -EIO;
 70	*p++ = rqst->rq_xid;
 71	*p++ = rpcrdma_version;
 72	*p++ = cpu_to_be32(r_xprt->rx_buf.rb_bc_srv_max_requests);
 73	*p++ = rdma_msg;
 74	*p++ = xdr_zero;
 75	*p++ = xdr_zero;
 76	*p = xdr_zero;
 77
 78	if (rpcrdma_prepare_send_sges(r_xprt, req, RPCRDMA_HDRLEN_MIN,
 79				      &rqst->rq_snd_buf, rpcrdma_noch_pullup))
 80		return -EIO;
 81
 82	trace_xprtrdma_cb_reply(r_xprt, rqst);
 83	return 0;
 84}
 85
 86/**
 87 * xprt_rdma_bc_send_reply - marshal and send a backchannel reply
 88 * @rqst: RPC rqst with a backchannel RPC reply in rq_snd_buf
 89 *
 90 * Caller holds the transport's write lock.
 91 *
 92 * Returns:
 93 *	%0 if the RPC message has been sent
 94 *	%-ENOTCONN if the caller should reconnect and call again
 95 *	%-EIO if a permanent error occurred and the request was not
 96 *		sent. Do not try to send this message again.
 97 */
 98int xprt_rdma_bc_send_reply(struct rpc_rqst *rqst)
 99{
100	struct rpc_xprt *xprt = rqst->rq_xprt;
101	struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(xprt);
102	struct rpcrdma_req *req = rpcr_to_rdmar(rqst);
103	int rc;
104
105	if (!xprt_connected(xprt))
106		return -ENOTCONN;
107
108	if (!xprt_request_get_cong(xprt, rqst))
109		return -EBADSLT;
110
111	rc = rpcrdma_bc_marshal_reply(rqst);
112	if (rc < 0)
113		goto failed_marshal;
114
115	if (frwr_send(r_xprt, req))
116		goto drop_connection;
117	return 0;
118
119failed_marshal:
120	if (rc != -ENOTCONN)
121		return rc;
122drop_connection:
123	xprt_rdma_close(xprt);
124	return -ENOTCONN;
125}
126
127/**
128 * xprt_rdma_bc_destroy - Release resources for handling backchannel requests
129 * @xprt: transport associated with these backchannel resources
130 * @reqs: number of incoming requests to destroy; ignored
131 */
132void xprt_rdma_bc_destroy(struct rpc_xprt *xprt, unsigned int reqs)
133{
134	struct rpc_rqst *rqst, *tmp;
135
136	spin_lock(&xprt->bc_pa_lock);
137	list_for_each_entry_safe(rqst, tmp, &xprt->bc_pa_list, rq_bc_pa_list) {
138		list_del(&rqst->rq_bc_pa_list);
139		spin_unlock(&xprt->bc_pa_lock);
140
141		rpcrdma_req_destroy(rpcr_to_rdmar(rqst));
142
143		spin_lock(&xprt->bc_pa_lock);
144	}
145	spin_unlock(&xprt->bc_pa_lock);
146}
147
148/**
149 * xprt_rdma_bc_free_rqst - Release a backchannel rqst
150 * @rqst: request to release
151 */
152void xprt_rdma_bc_free_rqst(struct rpc_rqst *rqst)
153{
154	struct rpcrdma_req *req = rpcr_to_rdmar(rqst);
155	struct rpcrdma_rep *rep = req->rl_reply;
156	struct rpc_xprt *xprt = rqst->rq_xprt;
157	struct rpcrdma_xprt *r_xprt = rpcx_to_rdmax(xprt);
158
159	rpcrdma_rep_put(&r_xprt->rx_buf, rep);
160	req->rl_reply = NULL;
161
162	spin_lock(&xprt->bc_pa_lock);
163	list_add_tail(&rqst->rq_bc_pa_list, &xprt->bc_pa_list);
164	spin_unlock(&xprt->bc_pa_lock);
165	xprt_put(xprt);
166}
167
168static struct rpc_rqst *rpcrdma_bc_rqst_get(struct rpcrdma_xprt *r_xprt)
169{
170	struct rpc_xprt *xprt = &r_xprt->rx_xprt;
171	struct rpcrdma_req *req;
172	struct rpc_rqst *rqst;
173	size_t size;
174
175	spin_lock(&xprt->bc_pa_lock);
176	rqst = list_first_entry_or_null(&xprt->bc_pa_list, struct rpc_rqst,
177					rq_bc_pa_list);
178	if (!rqst)
179		goto create_req;
180	list_del(&rqst->rq_bc_pa_list);
181	spin_unlock(&xprt->bc_pa_lock);
182	return rqst;
183
184create_req:
185	spin_unlock(&xprt->bc_pa_lock);
186
187	/* Set a limit to prevent a remote from overrunning our resources.
188	 */
189	if (xprt->bc_alloc_count >= RPCRDMA_BACKWARD_WRS)
190		return NULL;
191
192	size = min_t(size_t, r_xprt->rx_ep->re_inline_recv, PAGE_SIZE);
193	req = rpcrdma_req_create(r_xprt, size);
194	if (!req)
195		return NULL;
196	if (rpcrdma_req_setup(r_xprt, req)) {
197		rpcrdma_req_destroy(req);
198		return NULL;
199	}
200
201	xprt->bc_alloc_count++;
202	rqst = &req->rl_slot;
203	rqst->rq_xprt = xprt;
204	__set_bit(RPC_BC_PA_IN_USE, &rqst->rq_bc_pa_state);
205	xdr_buf_init(&rqst->rq_snd_buf, rdmab_data(req->rl_sendbuf), size);
206	return rqst;
207}
208
209/**
210 * rpcrdma_bc_receive_call - Handle a reverse-direction Call
211 * @r_xprt: transport receiving the call
212 * @rep: receive buffer containing the call
213 *
214 * Operational assumptions:
215 *    o Backchannel credits are ignored, just as the NFS server
216 *      forechannel currently does
217 *    o The ULP manages a replay cache (eg, NFSv4.1 sessions).
218 *      No replay detection is done at the transport level
219 */
220void rpcrdma_bc_receive_call(struct rpcrdma_xprt *r_xprt,
221			     struct rpcrdma_rep *rep)
222{
223	struct rpc_xprt *xprt = &r_xprt->rx_xprt;
224	struct rpcrdma_req *req;
225	struct rpc_rqst *rqst;
226	struct xdr_buf *buf;
227	size_t size;
228	__be32 *p;
229
230	p = xdr_inline_decode(&rep->rr_stream, 0);
231	size = xdr_stream_remaining(&rep->rr_stream);
232
233#ifdef RPCRDMA_BACKCHANNEL_DEBUG
234	pr_info("RPC:       %s: callback XID %08x, length=%u\n",
235		__func__, be32_to_cpup(p), size);
236	pr_info("RPC:       %s: %*ph\n", __func__, size, p);
237#endif
238
239	rqst = rpcrdma_bc_rqst_get(r_xprt);
240	if (!rqst)
241		goto out_overflow;
242
243	rqst->rq_reply_bytes_recvd = 0;
244	rqst->rq_xid = *p;
245
246	rqst->rq_private_buf.len = size;
247
248	buf = &rqst->rq_rcv_buf;
249	memset(buf, 0, sizeof(*buf));
250	buf->head[0].iov_base = p;
251	buf->head[0].iov_len = size;
252	buf->len = size;
253
254	/* The receive buffer has to be hooked to the rpcrdma_req
255	 * so that it is not released while the req is pointing
256	 * to its buffer, and so that it can be reposted after
257	 * the Upper Layer is done decoding it.
258	 */
259	req = rpcr_to_rdmar(rqst);
260	req->rl_reply = rep;
261	trace_xprtrdma_cb_call(r_xprt, rqst);
262
263	/* Queue rqst for ULP's callback service */
264	xprt_enqueue_bc_request(rqst);
265
266	r_xprt->rx_stats.bcall_count++;
267	return;
268
269out_overflow:
270	pr_warn("RPC/RDMA backchannel overflow\n");
271	xprt_force_disconnect(xprt);
272	/* This receive buffer gets reposted automatically
273	 * when the connection is re-established.
274	 */
275	return;
276}