frwr_ops.c

  1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Copyright (c) 2015, 2017 Oracle.  All rights reserved.
  4 * Copyright (c) 2003-2007 Network Appliance, Inc. All rights reserved.
  5 */
  6
  7/* Lightweight memory registration using Fast Registration Work
  8 * Requests (FRWR).
  9 *
 10 * FRWR features ordered asynchronous registration and invalidation
 11 * of arbitrarily-sized memory regions. This is the fastest and safest
 12 * but most complex memory registration mode.
 13 */
 14
 15/* Normal operation
 16 *
 17 * A Memory Region is prepared for RDMA Read or Write using a FAST_REG
 18 * Work Request (frwr_map). When the RDMA operation is finished, this
 19 * Memory Region is invalidated using a LOCAL_INV Work Request
 20 * (frwr_unmap_async and frwr_unmap_sync).
 21 *
 22 * Typically FAST_REG Work Requests are not signaled, and neither are
 23 * RDMA Send Work Requests (with the exception of signaling occasionally
 24 * to prevent provider work queue overflows). This greatly reduces HCA
 25 * interrupt workload.
 26 */
 27
 28/* Transport recovery
 29 *
 30 * frwr_map and frwr_unmap_* cannot run at the same time the transport
 31 * connect worker is running. The connect worker holds the transport
 32 * send lock, just as ->send_request does. This prevents frwr_map and
 33 * the connect worker from running concurrently. When a connection is
 34 * closed, the Receive completion queue is drained before the allowing
 35 * the connect worker to get control. This prevents frwr_unmap and the
 36 * connect worker from running concurrently.
 37 *
 38 * When the underlying transport disconnects, MRs that are in flight
 39 * are flushed and are likely unusable. Thus all MRs are destroyed.
 40 * New MRs are created on demand.
 41 */
 42
 43#include <linux/sunrpc/svc_rdma.h>
 44
 45#include "xprt_rdma.h"
 46#include <trace/events/rpcrdma.h>
 47
 48static void frwr_cid_init(struct rpcrdma_ep *ep,
 49			  struct rpcrdma_mr *mr)
 50{
 51	struct rpc_rdma_cid *cid = &mr->mr_cid;
 52
 53	cid->ci_queue_id = ep->re_attr.send_cq->res.id;
 54	cid->ci_completion_id = mr->mr_ibmr->res.id;
 55}
 56
 57static void frwr_mr_unmap(struct rpcrdma_mr *mr)
 58{
 59	if (mr->mr_device) {
 60		trace_xprtrdma_mr_unmap(mr);
 61		ib_dma_unmap_sg(mr->mr_device, mr->mr_sg, mr->mr_nents,
 62				mr->mr_dir);
 63		mr->mr_device = NULL;
 64	}
 65}
 66
 67/**
 68 * frwr_mr_release - Destroy one MR
 69 * @mr: MR allocated by frwr_mr_init
 70 *
 71 */
 72void frwr_mr_release(struct rpcrdma_mr *mr)
 73{
 74	int rc;
 75
 76	frwr_mr_unmap(mr);
 77
 78	rc = ib_dereg_mr(mr->mr_ibmr);
 79	if (rc)
 80		trace_xprtrdma_frwr_dereg(mr, rc);
 81	kfree(mr->mr_sg);
 82	kfree(mr);
 83}
 84
 85static void frwr_mr_put(struct rpcrdma_mr *mr)
 86{
 87	frwr_mr_unmap(mr);
 88
 89	/* The MR is returned to the req's MR free list instead
 90	 * of to the xprt's MR free list. No spinlock is needed.
 91	 */
 92	rpcrdma_mr_push(mr, &mr->mr_req->rl_free_mrs);
 93}
 94
 95/**
 96 * frwr_reset - Place MRs back on @req's free list
 97 * @req: request to reset
 98 *
 99 * Used after a failed marshal. For FRWR, this means the MRs
100 * don't have to be fully released and recreated.
101 *
102 * NB: This is safe only as long as none of @req's MRs are
103 * involved with an ongoing asynchronous FAST_REG or LOCAL_INV
104 * Work Request.
105 */
106void frwr_reset(struct rpcrdma_req *req)
107{
108	struct rpcrdma_mr *mr;
109
110	while ((mr = rpcrdma_mr_pop(&req->rl_registered)))
111		frwr_mr_put(mr);
112}
113
114/**
115 * frwr_mr_init - Initialize one MR
116 * @r_xprt: controlling transport instance
117 * @mr: generic MR to prepare for FRWR
118 *
119 * Returns zero if successful. Otherwise a negative errno
120 * is returned.
121 */
122int frwr_mr_init(struct rpcrdma_xprt *r_xprt, struct rpcrdma_mr *mr)
123{
124	struct rpcrdma_ep *ep = r_xprt->rx_ep;
125	unsigned int depth = ep->re_max_fr_depth;
126	struct scatterlist *sg;
127	struct ib_mr *frmr;
128
129	sg = kcalloc_node(depth, sizeof(*sg), XPRTRDMA_GFP_FLAGS,
130			  ibdev_to_node(ep->re_id->device));
131	if (!sg)
132		return -ENOMEM;
133
134	frmr = ib_alloc_mr(ep->re_pd, ep->re_mrtype, depth);
135	if (IS_ERR(frmr))
136		goto out_mr_err;
137
138	mr->mr_xprt = r_xprt;
139	mr->mr_ibmr = frmr;
140	mr->mr_device = NULL;
141	INIT_LIST_HEAD(&mr->mr_list);
142	init_completion(&mr->mr_linv_done);
143	frwr_cid_init(ep, mr);
144
145	sg_init_table(sg, depth);
146	mr->mr_sg = sg;
147	return 0;
148
149out_mr_err:
150	kfree(sg);
151	trace_xprtrdma_frwr_alloc(mr, PTR_ERR(frmr));
152	return PTR_ERR(frmr);
153}
154
155/**
156 * frwr_query_device - Prepare a transport for use with FRWR
157 * @ep: endpoint to fill in
158 * @device: RDMA device to query
159 *
160 * On success, sets:
161 *	ep->re_attr
162 *	ep->re_max_requests
163 *	ep->re_max_rdma_segs
164 *	ep->re_max_fr_depth
165 *	ep->re_mrtype
166 *
167 * Return values:
168 *   On success, returns zero.
169 *   %-EINVAL - the device does not support FRWR memory registration
170 *   %-ENOMEM - the device is not sufficiently capable for NFS/RDMA
171 */
172int frwr_query_device(struct rpcrdma_ep *ep, const struct ib_device *device)
173{
174	const struct ib_device_attr *attrs = &device->attrs;
175	int max_qp_wr, depth, delta;
176	unsigned int max_sge;
177
178	if (!(attrs->device_cap_flags & IB_DEVICE_MEM_MGT_EXTENSIONS) ||
179	    attrs->max_fast_reg_page_list_len == 0) {
180		pr_err("rpcrdma: 'frwr' mode is not supported by device %s\n",
181		       device->name);
182		return -EINVAL;
183	}
184
185	max_sge = min_t(unsigned int, attrs->max_send_sge,
186			RPCRDMA_MAX_SEND_SGES);
187	if (max_sge < RPCRDMA_MIN_SEND_SGES) {
188		pr_err("rpcrdma: HCA provides only %u send SGEs\n", max_sge);
189		return -ENOMEM;
190	}
191	ep->re_attr.cap.max_send_sge = max_sge;
192	ep->re_attr.cap.max_recv_sge = 1;
193
194	ep->re_mrtype = IB_MR_TYPE_MEM_REG;
195	if (attrs->kernel_cap_flags & IBK_SG_GAPS_REG)
196		ep->re_mrtype = IB_MR_TYPE_SG_GAPS;
197
198	/* Quirk: Some devices advertise a large max_fast_reg_page_list_len
199	 * capability, but perform optimally when the MRs are not larger
200	 * than a page.
201	 */
202	if (attrs->max_sge_rd > RPCRDMA_MAX_HDR_SEGS)
203		ep->re_max_fr_depth = attrs->max_sge_rd;
204	else
205		ep->re_max_fr_depth = attrs->max_fast_reg_page_list_len;
206	if (ep->re_max_fr_depth > RPCRDMA_MAX_DATA_SEGS)
207		ep->re_max_fr_depth = RPCRDMA_MAX_DATA_SEGS;
208
209	/* Add room for frwr register and invalidate WRs.
210	 * 1. FRWR reg WR for head
211	 * 2. FRWR invalidate WR for head
212	 * 3. N FRWR reg WRs for pagelist
213	 * 4. N FRWR invalidate WRs for pagelist
214	 * 5. FRWR reg WR for tail
215	 * 6. FRWR invalidate WR for tail
216	 * 7. The RDMA_SEND WR
217	 */
218	depth = 7;
219
220	/* Calculate N if the device max FRWR depth is smaller than
221	 * RPCRDMA_MAX_DATA_SEGS.
222	 */
223	if (ep->re_max_fr_depth < RPCRDMA_MAX_DATA_SEGS) {
224		delta = RPCRDMA_MAX_DATA_SEGS - ep->re_max_fr_depth;
225		do {
226			depth += 2; /* FRWR reg + invalidate */
227			delta -= ep->re_max_fr_depth;
228		} while (delta > 0);
229	}
230
231	max_qp_wr = attrs->max_qp_wr;
232	max_qp_wr -= RPCRDMA_BACKWARD_WRS;
233	max_qp_wr -= 1;
234	if (max_qp_wr < RPCRDMA_MIN_SLOT_TABLE)
235		return -ENOMEM;
236	if (ep->re_max_requests > max_qp_wr)
237		ep->re_max_requests = max_qp_wr;
238	ep->re_attr.cap.max_send_wr = ep->re_max_requests * depth;
239	if (ep->re_attr.cap.max_send_wr > max_qp_wr) {
240		ep->re_max_requests = max_qp_wr / depth;
241		if (!ep->re_max_requests)
242			return -ENOMEM;
243		ep->re_attr.cap.max_send_wr = ep->re_max_requests * depth;
244	}
245	ep->re_attr.cap.max_send_wr += RPCRDMA_BACKWARD_WRS;
246	ep->re_attr.cap.max_send_wr += 1; /* for ib_drain_sq */
247	ep->re_attr.cap.max_recv_wr = ep->re_max_requests;
248	ep->re_attr.cap.max_recv_wr += RPCRDMA_BACKWARD_WRS;
249	ep->re_attr.cap.max_recv_wr += RPCRDMA_MAX_RECV_BATCH;
250	ep->re_attr.cap.max_recv_wr += 1; /* for ib_drain_rq */
251
252	ep->re_max_rdma_segs =
253		DIV_ROUND_UP(RPCRDMA_MAX_DATA_SEGS, ep->re_max_fr_depth);
254	/* Reply chunks require segments for head and tail buffers */
255	ep->re_max_rdma_segs += 2;
256	if (ep->re_max_rdma_segs > RPCRDMA_MAX_HDR_SEGS)
257		ep->re_max_rdma_segs = RPCRDMA_MAX_HDR_SEGS;
258
259	/* Ensure the underlying device is capable of conveying the
260	 * largest r/wsize NFS will ask for. This guarantees that
261	 * failing over from one RDMA device to another will not
262	 * break NFS I/O.
263	 */
264	if ((ep->re_max_rdma_segs * ep->re_max_fr_depth) < RPCRDMA_MAX_SEGS)
265		return -ENOMEM;
266
267	return 0;
268}
269
270/**
271 * frwr_map - Register a memory region
272 * @r_xprt: controlling transport
273 * @seg: memory region co-ordinates
274 * @nsegs: number of segments remaining
275 * @writing: true when RDMA Write will be used
276 * @xid: XID of RPC using the registered memory
277 * @mr: MR to fill in
278 *
279 * Prepare a REG_MR Work Request to register a memory region
280 * for remote access via RDMA READ or RDMA WRITE.
281 *
282 * Returns the next segment or a negative errno pointer.
283 * On success, @mr is filled in.
284 */
285struct rpcrdma_mr_seg *frwr_map(struct rpcrdma_xprt *r_xprt,
286				struct rpcrdma_mr_seg *seg,
287				int nsegs, bool writing, __be32 xid,
288				struct rpcrdma_mr *mr)
289{
290	struct rpcrdma_ep *ep = r_xprt->rx_ep;
291	struct ib_reg_wr *reg_wr;
292	int i, n, dma_nents;
293	struct ib_mr *ibmr;
294	u8 key;
295
296	if (nsegs > ep->re_max_fr_depth)
297		nsegs = ep->re_max_fr_depth;
298	for (i = 0; i < nsegs;) {
299		sg_set_page(&mr->mr_sg[i], seg->mr_page,
300			    seg->mr_len, seg->mr_offset);
301
302		++seg;
303		++i;
304		if (ep->re_mrtype == IB_MR_TYPE_SG_GAPS)
305			continue;
306		if ((i < nsegs && seg->mr_offset) ||
307		    offset_in_page((seg-1)->mr_offset + (seg-1)->mr_len))
308			break;
309	}
310	mr->mr_dir = rpcrdma_data_dir(writing);
311	mr->mr_nents = i;
312
313	dma_nents = ib_dma_map_sg(ep->re_id->device, mr->mr_sg, mr->mr_nents,
314				  mr->mr_dir);
315	if (!dma_nents)
316		goto out_dmamap_err;
317	mr->mr_device = ep->re_id->device;
318
319	ibmr = mr->mr_ibmr;
320	n = ib_map_mr_sg(ibmr, mr->mr_sg, dma_nents, NULL, PAGE_SIZE);
321	if (n != dma_nents)
322		goto out_mapmr_err;
323
324	ibmr->iova &= 0x00000000ffffffff;
325	ibmr->iova |= ((u64)be32_to_cpu(xid)) << 32;
326	key = (u8)(ibmr->rkey & 0x000000FF);
327	ib_update_fast_reg_key(ibmr, ++key);
328
329	reg_wr = &mr->mr_regwr;
330	reg_wr->mr = ibmr;
331	reg_wr->key = ibmr->rkey;
332	reg_wr->access = writing ?
333			 IB_ACCESS_REMOTE_WRITE | IB_ACCESS_LOCAL_WRITE :
334			 IB_ACCESS_REMOTE_READ;
335
336	mr->mr_handle = ibmr->rkey;
337	mr->mr_length = ibmr->length;
338	mr->mr_offset = ibmr->iova;
339	trace_xprtrdma_mr_map(mr);
340
341	return seg;
342
343out_dmamap_err:
344	trace_xprtrdma_frwr_sgerr(mr, i);
345	return ERR_PTR(-EIO);
346
347out_mapmr_err:
348	trace_xprtrdma_frwr_maperr(mr, n);
349	return ERR_PTR(-EIO);
350}
351
352/**
353 * frwr_wc_fastreg - Invoked by RDMA provider for a flushed FastReg WC
354 * @cq: completion queue
355 * @wc: WCE for a completed FastReg WR
356 *
357 * Each flushed MR gets destroyed after the QP has drained.
358 */
359static void frwr_wc_fastreg(struct ib_cq *cq, struct ib_wc *wc)
360{
361	struct ib_cqe *cqe = wc->wr_cqe;
362	struct rpcrdma_mr *mr = container_of(cqe, struct rpcrdma_mr, mr_cqe);
363
364	/* WARNING: Only wr_cqe and status are reliable at this point */
365	trace_xprtrdma_wc_fastreg(wc, &mr->mr_cid);
366
367	rpcrdma_flush_disconnect(cq->cq_context, wc);
368}
369
370/**
371 * frwr_send - post Send WRs containing the RPC Call message
372 * @r_xprt: controlling transport instance
373 * @req: prepared RPC Call
374 *
375 * For FRWR, chain any FastReg WRs to the Send WR. Only a
376 * single ib_post_send call is needed to register memory
377 * and then post the Send WR.
378 *
379 * Returns the return code from ib_post_send.
380 *
381 * Caller must hold the transport send lock to ensure that the
382 * pointers to the transport's rdma_cm_id and QP are stable.
383 */
384int frwr_send(struct rpcrdma_xprt *r_xprt, struct rpcrdma_req *req)
385{
386	struct ib_send_wr *post_wr, *send_wr = &req->rl_wr;
387	struct rpcrdma_ep *ep = r_xprt->rx_ep;
388	struct rpcrdma_mr *mr;
389	unsigned int num_wrs;
390	int ret;
391
392	num_wrs = 1;
393	post_wr = send_wr;
394	list_for_each_entry(mr, &req->rl_registered, mr_list) {
395		trace_xprtrdma_mr_fastreg(mr);
396
397		mr->mr_cqe.done = frwr_wc_fastreg;
398		mr->mr_regwr.wr.next = post_wr;
399		mr->mr_regwr.wr.wr_cqe = &mr->mr_cqe;
400		mr->mr_regwr.wr.num_sge = 0;
401		mr->mr_regwr.wr.opcode = IB_WR_REG_MR;
402		mr->mr_regwr.wr.send_flags = 0;
403		post_wr = &mr->mr_regwr.wr;
404		++num_wrs;
405	}
406
407	if ((kref_read(&req->rl_kref) > 1) || num_wrs > ep->re_send_count) {
408		send_wr->send_flags |= IB_SEND_SIGNALED;
409		ep->re_send_count = min_t(unsigned int, ep->re_send_batch,
410					  num_wrs - ep->re_send_count);
411	} else {
412		send_wr->send_flags &= ~IB_SEND_SIGNALED;
413		ep->re_send_count -= num_wrs;
414	}
415
416	trace_xprtrdma_post_send(req);
417	ret = ib_post_send(ep->re_id->qp, post_wr, NULL);
418	if (ret)
419		trace_xprtrdma_post_send_err(r_xprt, req, ret);
420	return ret;
421}
422
423/**
424 * frwr_reminv - handle a remotely invalidated mr on the @mrs list
425 * @rep: Received reply
426 * @mrs: list of MRs to check
427 *
428 */
429void frwr_reminv(struct rpcrdma_rep *rep, struct list_head *mrs)
430{
431	struct rpcrdma_mr *mr;
432
433	list_for_each_entry(mr, mrs, mr_list)
434		if (mr->mr_handle == rep->rr_inv_rkey) {
435			list_del_init(&mr->mr_list);
436			trace_xprtrdma_mr_reminv(mr);
437			frwr_mr_put(mr);
438			break;	/* only one invalidated MR per RPC */
439		}
440}
441
442static void frwr_mr_done(struct ib_wc *wc, struct rpcrdma_mr *mr)
443{
444	if (likely(wc->status == IB_WC_SUCCESS))
445		frwr_mr_put(mr);
446}
447
448/**
449 * frwr_wc_localinv - Invoked by RDMA provider for a LOCAL_INV WC
450 * @cq: completion queue
451 * @wc: WCE for a completed LocalInv WR
452 *
453 */
454static void frwr_wc_localinv(struct ib_cq *cq, struct ib_wc *wc)
455{
456	struct ib_cqe *cqe = wc->wr_cqe;
457	struct rpcrdma_mr *mr = container_of(cqe, struct rpcrdma_mr, mr_cqe);
458
459	/* WARNING: Only wr_cqe and status are reliable at this point */
460	trace_xprtrdma_wc_li(wc, &mr->mr_cid);
461	frwr_mr_done(wc, mr);
462
463	rpcrdma_flush_disconnect(cq->cq_context, wc);
464}
465
466/**
467 * frwr_wc_localinv_wake - Invoked by RDMA provider for a LOCAL_INV WC
468 * @cq: completion queue
469 * @wc: WCE for a completed LocalInv WR
470 *
471 * Awaken anyone waiting for an MR to finish being fenced.
472 */
473static void frwr_wc_localinv_wake(struct ib_cq *cq, struct ib_wc *wc)
474{
475	struct ib_cqe *cqe = wc->wr_cqe;
476	struct rpcrdma_mr *mr = container_of(cqe, struct rpcrdma_mr, mr_cqe);
477
478	/* WARNING: Only wr_cqe and status are reliable at this point */
479	trace_xprtrdma_wc_li_wake(wc, &mr->mr_cid);
480	frwr_mr_done(wc, mr);
481	complete(&mr->mr_linv_done);
482
483	rpcrdma_flush_disconnect(cq->cq_context, wc);
484}
485
486/**
487 * frwr_unmap_sync - invalidate memory regions that were registered for @req
488 * @r_xprt: controlling transport instance
489 * @req: rpcrdma_req with a non-empty list of MRs to process
490 *
491 * Sleeps until it is safe for the host CPU to access the previously mapped
492 * memory regions. This guarantees that registered MRs are properly fenced
493 * from the server before the RPC consumer accesses the data in them. It
494 * also ensures proper Send flow control: waking the next RPC waits until
495 * this RPC has relinquished all its Send Queue entries.
496 */
497void frwr_unmap_sync(struct rpcrdma_xprt *r_xprt, struct rpcrdma_req *req)
498{
499	struct ib_send_wr *first, **prev, *last;
500	struct rpcrdma_ep *ep = r_xprt->rx_ep;
501	const struct ib_send_wr *bad_wr;
502	struct rpcrdma_mr *mr;
503	int rc;
504
505	/* ORDER: Invalidate all of the MRs first
506	 *
507	 * Chain the LOCAL_INV Work Requests and post them with
508	 * a single ib_post_send() call.
509	 */
510	prev = &first;
511	mr = rpcrdma_mr_pop(&req->rl_registered);
512	do {
513		trace_xprtrdma_mr_localinv(mr);
514		r_xprt->rx_stats.local_inv_needed++;
515
516		last = &mr->mr_invwr;
517		last->next = NULL;
518		last->wr_cqe = &mr->mr_cqe;
519		last->sg_list = NULL;
520		last->num_sge = 0;
521		last->opcode = IB_WR_LOCAL_INV;
522		last->send_flags = IB_SEND_SIGNALED;
523		last->ex.invalidate_rkey = mr->mr_handle;
524
525		last->wr_cqe->done = frwr_wc_localinv;
526
527		*prev = last;
528		prev = &last->next;
529	} while ((mr = rpcrdma_mr_pop(&req->rl_registered)));
530
531	mr = container_of(last, struct rpcrdma_mr, mr_invwr);
532
533	/* Strong send queue ordering guarantees that when the
534	 * last WR in the chain completes, all WRs in the chain
535	 * are complete.
536	 */
537	last->wr_cqe->done = frwr_wc_localinv_wake;
538	reinit_completion(&mr->mr_linv_done);
539
540	/* Transport disconnect drains the receive CQ before it
541	 * replaces the QP. The RPC reply handler won't call us
542	 * unless re_id->qp is a valid pointer.
543	 */
544	bad_wr = NULL;
545	rc = ib_post_send(ep->re_id->qp, first, &bad_wr);
546
547	/* The final LOCAL_INV WR in the chain is supposed to
548	 * do the wake. If it was never posted, the wake will
549	 * not happen, so don't wait in that case.
550	 */
551	if (bad_wr != first)
552		wait_for_completion(&mr->mr_linv_done);
553	if (!rc)
554		return;
555
556	/* On error, the MRs get destroyed once the QP has drained. */
557	trace_xprtrdma_post_linv_err(req, rc);
558
559	/* Force a connection loss to ensure complete recovery.
560	 */
561	rpcrdma_force_disconnect(ep);
562}
563
564/**
565 * frwr_wc_localinv_done - Invoked by RDMA provider for a signaled LOCAL_INV WC
566 * @cq:	completion queue
567 * @wc:	WCE for a completed LocalInv WR
568 *
569 */
570static void frwr_wc_localinv_done(struct ib_cq *cq, struct ib_wc *wc)
571{
572	struct ib_cqe *cqe = wc->wr_cqe;
573	struct rpcrdma_mr *mr = container_of(cqe, struct rpcrdma_mr, mr_cqe);
574	struct rpcrdma_rep *rep;
575
576	/* WARNING: Only wr_cqe and status are reliable at this point */
577	trace_xprtrdma_wc_li_done(wc, &mr->mr_cid);
578
579	/* Ensure that @rep is generated before the MR is released */
580	rep = mr->mr_req->rl_reply;
581	smp_rmb();
582
583	if (wc->status != IB_WC_SUCCESS) {
584		if (rep)
585			rpcrdma_unpin_rqst(rep);
586		rpcrdma_flush_disconnect(cq->cq_context, wc);
587		return;
588	}
589	frwr_mr_put(mr);
590	rpcrdma_complete_rqst(rep);
591}
592
593/**
594 * frwr_unmap_async - invalidate memory regions that were registered for @req
595 * @r_xprt: controlling transport instance
596 * @req: rpcrdma_req with a non-empty list of MRs to process
597 *
598 * This guarantees that registered MRs are properly fenced from the
599 * server before the RPC consumer accesses the data in them. It also
600 * ensures proper Send flow control: waking the next RPC waits until
601 * this RPC has relinquished all its Send Queue entries.
602 */
603void frwr_unmap_async(struct rpcrdma_xprt *r_xprt, struct rpcrdma_req *req)
604{
605	struct ib_send_wr *first, *last, **prev;
606	struct rpcrdma_ep *ep = r_xprt->rx_ep;
607	struct rpcrdma_mr *mr;
608	int rc;
609
610	/* Chain the LOCAL_INV Work Requests and post them with
611	 * a single ib_post_send() call.
612	 */
613	prev = &first;
614	mr = rpcrdma_mr_pop(&req->rl_registered);
615	do {
616		trace_xprtrdma_mr_localinv(mr);
617		r_xprt->rx_stats.local_inv_needed++;
618
619		last = &mr->mr_invwr;
620		last->next = NULL;
621		last->wr_cqe = &mr->mr_cqe;
622		last->sg_list = NULL;
623		last->num_sge = 0;
624		last->opcode = IB_WR_LOCAL_INV;
625		last->send_flags = IB_SEND_SIGNALED;
626		last->ex.invalidate_rkey = mr->mr_handle;
627
628		last->wr_cqe->done = frwr_wc_localinv;
629
630		*prev = last;
631		prev = &last->next;
632	} while ((mr = rpcrdma_mr_pop(&req->rl_registered)));
633
634	/* Strong send queue ordering guarantees that when the
635	 * last WR in the chain completes, all WRs in the chain
636	 * are complete. The last completion will wake up the
637	 * RPC waiter.
638	 */
639	last->wr_cqe->done = frwr_wc_localinv_done;
640
641	/* Transport disconnect drains the receive CQ before it
642	 * replaces the QP. The RPC reply handler won't call us
643	 * unless re_id->qp is a valid pointer.
644	 */
645	rc = ib_post_send(ep->re_id->qp, first, NULL);
646	if (!rc)
647		return;
648
649	/* On error, the MRs get destroyed once the QP has drained. */
650	trace_xprtrdma_post_linv_err(req, rc);
651
652	/* The final LOCAL_INV WR in the chain is supposed to
653	 * do the wake. If it was never posted, the wake does
654	 * not happen. Unpin the rqst in preparation for its
655	 * retransmission.
656	 */
657	rpcrdma_unpin_rqst(req->rl_reply);
658
659	/* Force a connection loss to ensure complete recovery.
660	 */
661	rpcrdma_force_disconnect(ep);
662}
663
664/**
665 * frwr_wp_create - Create an MR for padding Write chunks
666 * @r_xprt: transport resources to use
667 *
668 * Return 0 on success, negative errno on failure.
669 */
670int frwr_wp_create(struct rpcrdma_xprt *r_xprt)
671{
672	struct rpcrdma_ep *ep = r_xprt->rx_ep;
673	struct rpcrdma_mr_seg seg;
674	struct rpcrdma_mr *mr;
675
676	mr = rpcrdma_mr_get(r_xprt);
677	if (!mr)
678		return -EAGAIN;
679	mr->mr_req = NULL;
680	ep->re_write_pad_mr = mr;
681
682	seg.mr_len = XDR_UNIT;
683	seg.mr_page = virt_to_page(ep->re_write_pad);
684	seg.mr_offset = offset_in_page(ep->re_write_pad);
685	if (IS_ERR(frwr_map(r_xprt, &seg, 1, true, xdr_zero, mr)))
686		return -EIO;
687	trace_xprtrdma_mr_fastreg(mr);
688
689	mr->mr_cqe.done = frwr_wc_fastreg;
690	mr->mr_regwr.wr.next = NULL;
691	mr->mr_regwr.wr.wr_cqe = &mr->mr_cqe;
692	mr->mr_regwr.wr.num_sge = 0;
693	mr->mr_regwr.wr.opcode = IB_WR_REG_MR;
694	mr->mr_regwr.wr.send_flags = 0;
695
696	return ib_post_send(ep->re_id->qp, &mr->mr_regwr.wr, NULL);
697}