xref: /linux/net/sunrpc/xprtrdma/frwr_ops.c (revision 5e3c6a312a0946d2d83e32359612cbb925a8bed0)
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/rpc_rdma.h>
44 #include <linux/sunrpc/svc_rdma.h>
45 
46 #include "xprt_rdma.h"
47 #include <trace/events/rpcrdma.h>
48 
49 #if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
50 # define RPCDBG_FACILITY	RPCDBG_TRANS
51 #endif
52 
53 /**
54  * frwr_release_mr - Destroy one MR
55  * @mr: MR allocated by frwr_init_mr
56  *
57  */
58 void frwr_release_mr(struct rpcrdma_mr *mr)
59 {
60 	int rc;
61 
62 	rc = ib_dereg_mr(mr->frwr.fr_mr);
63 	if (rc)
64 		trace_xprtrdma_frwr_dereg(mr, rc);
65 	kfree(mr->mr_sg);
66 	kfree(mr);
67 }
68 
69 static void frwr_mr_recycle(struct rpcrdma_mr *mr)
70 {
71 	struct rpcrdma_xprt *r_xprt = mr->mr_xprt;
72 
73 	trace_xprtrdma_mr_recycle(mr);
74 
75 	if (mr->mr_dir != DMA_NONE) {
76 		trace_xprtrdma_mr_unmap(mr);
77 		ib_dma_unmap_sg(r_xprt->rx_ia.ri_id->device,
78 				mr->mr_sg, mr->mr_nents, mr->mr_dir);
79 		mr->mr_dir = DMA_NONE;
80 	}
81 
82 	spin_lock(&r_xprt->rx_buf.rb_lock);
83 	list_del(&mr->mr_all);
84 	r_xprt->rx_stats.mrs_recycled++;
85 	spin_unlock(&r_xprt->rx_buf.rb_lock);
86 
87 	frwr_release_mr(mr);
88 }
89 
90 /* frwr_reset - Place MRs back on the free list
91  * @req: request to reset
92  *
93  * Used after a failed marshal. For FRWR, this means the MRs
94  * don't have to be fully released and recreated.
95  *
96  * NB: This is safe only as long as none of @req's MRs are
97  * involved with an ongoing asynchronous FAST_REG or LOCAL_INV
98  * Work Request.
99  */
100 void frwr_reset(struct rpcrdma_req *req)
101 {
102 	struct rpcrdma_mr *mr;
103 
104 	while ((mr = rpcrdma_mr_pop(&req->rl_registered)))
105 		rpcrdma_mr_put(mr);
106 }
107 
108 /**
109  * frwr_init_mr - Initialize one MR
110  * @ia: interface adapter
111  * @mr: generic MR to prepare for FRWR
112  *
113  * Returns zero if successful. Otherwise a negative errno
114  * is returned.
115  */
116 int frwr_init_mr(struct rpcrdma_ia *ia, struct rpcrdma_mr *mr)
117 {
118 	unsigned int depth = ia->ri_max_frwr_depth;
119 	struct scatterlist *sg;
120 	struct ib_mr *frmr;
121 	int rc;
122 
123 	frmr = ib_alloc_mr(ia->ri_pd, ia->ri_mrtype, depth);
124 	if (IS_ERR(frmr))
125 		goto out_mr_err;
126 
127 	sg = kcalloc(depth, sizeof(*sg), GFP_NOFS);
128 	if (!sg)
129 		goto out_list_err;
130 
131 	mr->frwr.fr_mr = frmr;
132 	mr->mr_dir = DMA_NONE;
133 	INIT_LIST_HEAD(&mr->mr_list);
134 	init_completion(&mr->frwr.fr_linv_done);
135 
136 	sg_init_table(sg, depth);
137 	mr->mr_sg = sg;
138 	return 0;
139 
140 out_mr_err:
141 	rc = PTR_ERR(frmr);
142 	trace_xprtrdma_frwr_alloc(mr, rc);
143 	return rc;
144 
145 out_list_err:
146 	ib_dereg_mr(frmr);
147 	return -ENOMEM;
148 }
149 
150 /**
151  * frwr_query_device - Prepare a transport for use with FRWR
152  * @r_xprt: controlling transport instance
153  * @device: RDMA device to query
154  *
155  * On success, sets:
156  *	ep->rep_attr
157  *	ep->rep_max_requests
158  *	ia->ri_max_rdma_segs
159  *
160  * And these FRWR-related fields:
161  *	ia->ri_max_frwr_depth
162  *	ia->ri_mrtype
163  *
164  * Return values:
165  *   On success, returns zero.
166  *   %-EINVAL - the device does not support FRWR memory registration
167  *   %-ENOMEM - the device is not sufficiently capable for NFS/RDMA
168  */
169 int frwr_query_device(struct rpcrdma_xprt *r_xprt,
170 		      const struct ib_device *device)
171 {
172 	const struct ib_device_attr *attrs = &device->attrs;
173 	struct rpcrdma_ia *ia = &r_xprt->rx_ia;
174 	struct rpcrdma_ep *ep = &r_xprt->rx_ep;
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->rep_attr.cap.max_send_sge = max_sge;
192 	ep->rep_attr.cap.max_recv_sge = 1;
193 
194 	ia->ri_mrtype = IB_MR_TYPE_MEM_REG;
195 	if (attrs->device_cap_flags & IB_DEVICE_SG_GAPS_REG)
196 		ia->ri_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 		ia->ri_max_frwr_depth = attrs->max_sge_rd;
204 	else
205 		ia->ri_max_frwr_depth = attrs->max_fast_reg_page_list_len;
206 	if (ia->ri_max_frwr_depth > RPCRDMA_MAX_DATA_SEGS)
207 		ia->ri_max_frwr_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 (ia->ri_max_frwr_depth < RPCRDMA_MAX_DATA_SEGS) {
224 		delta = RPCRDMA_MAX_DATA_SEGS - ia->ri_max_frwr_depth;
225 		do {
226 			depth += 2; /* FRWR reg + invalidate */
227 			delta -= ia->ri_max_frwr_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->rep_max_requests > max_qp_wr)
237 		ep->rep_max_requests = max_qp_wr;
238 	ep->rep_attr.cap.max_send_wr = ep->rep_max_requests * depth;
239 	if (ep->rep_attr.cap.max_send_wr > max_qp_wr) {
240 		ep->rep_max_requests = max_qp_wr / depth;
241 		if (!ep->rep_max_requests)
242 			return -ENOMEM;
243 		ep->rep_attr.cap.max_send_wr = ep->rep_max_requests * depth;
244 	}
245 	ep->rep_attr.cap.max_send_wr += RPCRDMA_BACKWARD_WRS;
246 	ep->rep_attr.cap.max_send_wr += 1; /* for ib_drain_sq */
247 	ep->rep_attr.cap.max_recv_wr = ep->rep_max_requests;
248 	ep->rep_attr.cap.max_recv_wr += RPCRDMA_BACKWARD_WRS;
249 	ep->rep_attr.cap.max_recv_wr += 1; /* for ib_drain_rq */
250 
251 	ia->ri_max_rdma_segs =
252 		DIV_ROUND_UP(RPCRDMA_MAX_DATA_SEGS, ia->ri_max_frwr_depth);
253 	/* Reply chunks require segments for head and tail buffers */
254 	ia->ri_max_rdma_segs += 2;
255 	if (ia->ri_max_rdma_segs > RPCRDMA_MAX_HDR_SEGS)
256 		ia->ri_max_rdma_segs = RPCRDMA_MAX_HDR_SEGS;
257 
258 	/* Ensure the underlying device is capable of conveying the
259 	 * largest r/wsize NFS will ask for. This guarantees that
260 	 * failing over from one RDMA device to another will not
261 	 * break NFS I/O.
262 	 */
263 	if ((ia->ri_max_rdma_segs * ia->ri_max_frwr_depth) < RPCRDMA_MAX_SEGS)
264 		return -ENOMEM;
265 
266 	return 0;
267 }
268 
269 /**
270  * frwr_map - Register a memory region
271  * @r_xprt: controlling transport
272  * @seg: memory region co-ordinates
273  * @nsegs: number of segments remaining
274  * @writing: true when RDMA Write will be used
275  * @xid: XID of RPC using the registered memory
276  * @mr: MR to fill in
277  *
278  * Prepare a REG_MR Work Request to register a memory region
279  * for remote access via RDMA READ or RDMA WRITE.
280  *
281  * Returns the next segment or a negative errno pointer.
282  * On success, @mr is filled in.
283  */
284 struct rpcrdma_mr_seg *frwr_map(struct rpcrdma_xprt *r_xprt,
285 				struct rpcrdma_mr_seg *seg,
286 				int nsegs, bool writing, __be32 xid,
287 				struct rpcrdma_mr *mr)
288 {
289 	struct rpcrdma_ia *ia = &r_xprt->rx_ia;
290 	struct ib_reg_wr *reg_wr;
291 	int i, n, dma_nents;
292 	struct ib_mr *ibmr;
293 	u8 key;
294 
295 	if (nsegs > ia->ri_max_frwr_depth)
296 		nsegs = ia->ri_max_frwr_depth;
297 	for (i = 0; i < nsegs;) {
298 		if (seg->mr_page)
299 			sg_set_page(&mr->mr_sg[i],
300 				    seg->mr_page,
301 				    seg->mr_len,
302 				    offset_in_page(seg->mr_offset));
303 		else
304 			sg_set_buf(&mr->mr_sg[i], seg->mr_offset,
305 				   seg->mr_len);
306 
307 		++seg;
308 		++i;
309 		if (ia->ri_mrtype == IB_MR_TYPE_SG_GAPS)
310 			continue;
311 		if ((i < nsegs && offset_in_page(seg->mr_offset)) ||
312 		    offset_in_page((seg-1)->mr_offset + (seg-1)->mr_len))
313 			break;
314 	}
315 	mr->mr_dir = rpcrdma_data_dir(writing);
316 	mr->mr_nents = i;
317 
318 	dma_nents = ib_dma_map_sg(ia->ri_id->device, mr->mr_sg, mr->mr_nents,
319 				  mr->mr_dir);
320 	if (!dma_nents)
321 		goto out_dmamap_err;
322 
323 	ibmr = mr->frwr.fr_mr;
324 	n = ib_map_mr_sg(ibmr, mr->mr_sg, dma_nents, NULL, PAGE_SIZE);
325 	if (n != dma_nents)
326 		goto out_mapmr_err;
327 
328 	ibmr->iova &= 0x00000000ffffffff;
329 	ibmr->iova |= ((u64)be32_to_cpu(xid)) << 32;
330 	key = (u8)(ibmr->rkey & 0x000000FF);
331 	ib_update_fast_reg_key(ibmr, ++key);
332 
333 	reg_wr = &mr->frwr.fr_regwr;
334 	reg_wr->mr = ibmr;
335 	reg_wr->key = ibmr->rkey;
336 	reg_wr->access = writing ?
337 			 IB_ACCESS_REMOTE_WRITE | IB_ACCESS_LOCAL_WRITE :
338 			 IB_ACCESS_REMOTE_READ;
339 
340 	mr->mr_handle = ibmr->rkey;
341 	mr->mr_length = ibmr->length;
342 	mr->mr_offset = ibmr->iova;
343 	trace_xprtrdma_mr_map(mr);
344 
345 	return seg;
346 
347 out_dmamap_err:
348 	mr->mr_dir = DMA_NONE;
349 	trace_xprtrdma_frwr_sgerr(mr, i);
350 	return ERR_PTR(-EIO);
351 
352 out_mapmr_err:
353 	trace_xprtrdma_frwr_maperr(mr, n);
354 	return ERR_PTR(-EIO);
355 }
356 
357 /**
358  * frwr_wc_fastreg - Invoked by RDMA provider for a flushed FastReg WC
359  * @cq:	completion queue (ignored)
360  * @wc:	completed WR
361  *
362  */
363 static void frwr_wc_fastreg(struct ib_cq *cq, struct ib_wc *wc)
364 {
365 	struct ib_cqe *cqe = wc->wr_cqe;
366 	struct rpcrdma_frwr *frwr =
367 		container_of(cqe, struct rpcrdma_frwr, fr_cqe);
368 
369 	/* WARNING: Only wr_cqe and status are reliable at this point */
370 	trace_xprtrdma_wc_fastreg(wc, frwr);
371 	/* The MR will get recycled when the associated req is retransmitted */
372 }
373 
374 /**
375  * frwr_send - post Send WR containing the RPC Call message
376  * @ia: interface adapter
377  * @req: Prepared RPC Call
378  *
379  * For FRWR, chain any FastReg WRs to the Send WR. Only a
380  * single ib_post_send call is needed to register memory
381  * and then post the Send WR.
382  *
383  * Returns the result of ib_post_send.
384  */
385 int frwr_send(struct rpcrdma_ia *ia, struct rpcrdma_req *req)
386 {
387 	struct ib_send_wr *post_wr;
388 	struct rpcrdma_mr *mr;
389 
390 	post_wr = &req->rl_wr;
391 	list_for_each_entry(mr, &req->rl_registered, mr_list) {
392 		struct rpcrdma_frwr *frwr;
393 
394 		frwr = &mr->frwr;
395 
396 		frwr->fr_cqe.done = frwr_wc_fastreg;
397 		frwr->fr_regwr.wr.next = post_wr;
398 		frwr->fr_regwr.wr.wr_cqe = &frwr->fr_cqe;
399 		frwr->fr_regwr.wr.num_sge = 0;
400 		frwr->fr_regwr.wr.opcode = IB_WR_REG_MR;
401 		frwr->fr_regwr.wr.send_flags = 0;
402 
403 		post_wr = &frwr->fr_regwr.wr;
404 	}
405 
406 	return ib_post_send(ia->ri_id->qp, post_wr, NULL);
407 }
408 
409 /**
410  * frwr_reminv - handle a remotely invalidated mr on the @mrs list
411  * @rep: Received reply
412  * @mrs: list of MRs to check
413  *
414  */
415 void frwr_reminv(struct rpcrdma_rep *rep, struct list_head *mrs)
416 {
417 	struct rpcrdma_mr *mr;
418 
419 	list_for_each_entry(mr, mrs, mr_list)
420 		if (mr->mr_handle == rep->rr_inv_rkey) {
421 			list_del_init(&mr->mr_list);
422 			trace_xprtrdma_mr_remoteinv(mr);
423 			rpcrdma_mr_put(mr);
424 			break;	/* only one invalidated MR per RPC */
425 		}
426 }
427 
428 static void __frwr_release_mr(struct ib_wc *wc, struct rpcrdma_mr *mr)
429 {
430 	if (wc->status != IB_WC_SUCCESS)
431 		frwr_mr_recycle(mr);
432 	else
433 		rpcrdma_mr_put(mr);
434 }
435 
436 /**
437  * frwr_wc_localinv - Invoked by RDMA provider for a LOCAL_INV WC
438  * @cq:	completion queue (ignored)
439  * @wc:	completed WR
440  *
441  */
442 static void frwr_wc_localinv(struct ib_cq *cq, struct ib_wc *wc)
443 {
444 	struct ib_cqe *cqe = wc->wr_cqe;
445 	struct rpcrdma_frwr *frwr =
446 		container_of(cqe, struct rpcrdma_frwr, fr_cqe);
447 	struct rpcrdma_mr *mr = container_of(frwr, struct rpcrdma_mr, frwr);
448 
449 	/* WARNING: Only wr_cqe and status are reliable at this point */
450 	trace_xprtrdma_wc_li(wc, frwr);
451 	__frwr_release_mr(wc, mr);
452 }
453 
454 /**
455  * frwr_wc_localinv_wake - Invoked by RDMA provider for a LOCAL_INV WC
456  * @cq:	completion queue (ignored)
457  * @wc:	completed WR
458  *
459  * Awaken anyone waiting for an MR to finish being fenced.
460  */
461 static void frwr_wc_localinv_wake(struct ib_cq *cq, struct ib_wc *wc)
462 {
463 	struct ib_cqe *cqe = wc->wr_cqe;
464 	struct rpcrdma_frwr *frwr =
465 		container_of(cqe, struct rpcrdma_frwr, fr_cqe);
466 	struct rpcrdma_mr *mr = container_of(frwr, struct rpcrdma_mr, frwr);
467 
468 	/* WARNING: Only wr_cqe and status are reliable at this point */
469 	trace_xprtrdma_wc_li_wake(wc, frwr);
470 	__frwr_release_mr(wc, mr);
471 	complete(&frwr->fr_linv_done);
472 }
473 
474 /**
475  * frwr_unmap_sync - invalidate memory regions that were registered for @req
476  * @r_xprt: controlling transport instance
477  * @req: rpcrdma_req with a non-empty list of MRs to process
478  *
479  * Sleeps until it is safe for the host CPU to access the previously mapped
480  * memory regions. This guarantees that registered MRs are properly fenced
481  * from the server before the RPC consumer accesses the data in them. It
482  * also ensures proper Send flow control: waking the next RPC waits until
483  * this RPC has relinquished all its Send Queue entries.
484  */
485 void frwr_unmap_sync(struct rpcrdma_xprt *r_xprt, struct rpcrdma_req *req)
486 {
487 	struct ib_send_wr *first, **prev, *last;
488 	const struct ib_send_wr *bad_wr;
489 	struct rpcrdma_frwr *frwr;
490 	struct rpcrdma_mr *mr;
491 	int rc;
492 
493 	/* ORDER: Invalidate all of the MRs first
494 	 *
495 	 * Chain the LOCAL_INV Work Requests and post them with
496 	 * a single ib_post_send() call.
497 	 */
498 	frwr = NULL;
499 	prev = &first;
500 	while ((mr = rpcrdma_mr_pop(&req->rl_registered))) {
501 
502 		trace_xprtrdma_mr_localinv(mr);
503 		r_xprt->rx_stats.local_inv_needed++;
504 
505 		frwr = &mr->frwr;
506 		frwr->fr_cqe.done = frwr_wc_localinv;
507 		last = &frwr->fr_invwr;
508 		last->next = NULL;
509 		last->wr_cqe = &frwr->fr_cqe;
510 		last->sg_list = NULL;
511 		last->num_sge = 0;
512 		last->opcode = IB_WR_LOCAL_INV;
513 		last->send_flags = IB_SEND_SIGNALED;
514 		last->ex.invalidate_rkey = mr->mr_handle;
515 
516 		*prev = last;
517 		prev = &last->next;
518 	}
519 
520 	/* Strong send queue ordering guarantees that when the
521 	 * last WR in the chain completes, all WRs in the chain
522 	 * are complete.
523 	 */
524 	frwr->fr_cqe.done = frwr_wc_localinv_wake;
525 	reinit_completion(&frwr->fr_linv_done);
526 
527 	/* Transport disconnect drains the receive CQ before it
528 	 * replaces the QP. The RPC reply handler won't call us
529 	 * unless ri_id->qp is a valid pointer.
530 	 */
531 	bad_wr = NULL;
532 	rc = ib_post_send(r_xprt->rx_ia.ri_id->qp, first, &bad_wr);
533 
534 	/* The final LOCAL_INV WR in the chain is supposed to
535 	 * do the wake. If it was never posted, the wake will
536 	 * not happen, so don't wait in that case.
537 	 */
538 	if (bad_wr != first)
539 		wait_for_completion(&frwr->fr_linv_done);
540 	if (!rc)
541 		return;
542 
543 	/* Recycle MRs in the LOCAL_INV chain that did not get posted.
544 	 */
545 	trace_xprtrdma_post_linv(req, rc);
546 	while (bad_wr) {
547 		frwr = container_of(bad_wr, struct rpcrdma_frwr,
548 				    fr_invwr);
549 		mr = container_of(frwr, struct rpcrdma_mr, frwr);
550 		bad_wr = bad_wr->next;
551 
552 		list_del_init(&mr->mr_list);
553 		frwr_mr_recycle(mr);
554 	}
555 }
556 
557 /**
558  * frwr_wc_localinv_done - Invoked by RDMA provider for a signaled LOCAL_INV WC
559  * @cq:	completion queue (ignored)
560  * @wc:	completed WR
561  *
562  */
563 static void frwr_wc_localinv_done(struct ib_cq *cq, struct ib_wc *wc)
564 {
565 	struct ib_cqe *cqe = wc->wr_cqe;
566 	struct rpcrdma_frwr *frwr =
567 		container_of(cqe, struct rpcrdma_frwr, fr_cqe);
568 	struct rpcrdma_mr *mr = container_of(frwr, struct rpcrdma_mr, frwr);
569 	struct rpcrdma_rep *rep = mr->mr_req->rl_reply;
570 
571 	/* WARNING: Only wr_cqe and status are reliable at this point */
572 	trace_xprtrdma_wc_li_done(wc, frwr);
573 	__frwr_release_mr(wc, mr);
574 
575 	/* Ensure @rep is generated before __frwr_release_mr */
576 	smp_rmb();
577 	rpcrdma_complete_rqst(rep);
578 }
579 
580 /**
581  * frwr_unmap_async - invalidate memory regions that were registered for @req
582  * @r_xprt: controlling transport instance
583  * @req: rpcrdma_req with a non-empty list of MRs to process
584  *
585  * This guarantees that registered MRs are properly fenced from the
586  * server before the RPC consumer accesses the data in them. It also
587  * ensures proper Send flow control: waking the next RPC waits until
588  * this RPC has relinquished all its Send Queue entries.
589  */
590 void frwr_unmap_async(struct rpcrdma_xprt *r_xprt, struct rpcrdma_req *req)
591 {
592 	struct ib_send_wr *first, *last, **prev;
593 	const struct ib_send_wr *bad_wr;
594 	struct rpcrdma_frwr *frwr;
595 	struct rpcrdma_mr *mr;
596 	int rc;
597 
598 	/* Chain the LOCAL_INV Work Requests and post them with
599 	 * a single ib_post_send() call.
600 	 */
601 	frwr = NULL;
602 	prev = &first;
603 	while ((mr = rpcrdma_mr_pop(&req->rl_registered))) {
604 
605 		trace_xprtrdma_mr_localinv(mr);
606 		r_xprt->rx_stats.local_inv_needed++;
607 
608 		frwr = &mr->frwr;
609 		frwr->fr_cqe.done = frwr_wc_localinv;
610 		last = &frwr->fr_invwr;
611 		last->next = NULL;
612 		last->wr_cqe = &frwr->fr_cqe;
613 		last->sg_list = NULL;
614 		last->num_sge = 0;
615 		last->opcode = IB_WR_LOCAL_INV;
616 		last->send_flags = IB_SEND_SIGNALED;
617 		last->ex.invalidate_rkey = mr->mr_handle;
618 
619 		*prev = last;
620 		prev = &last->next;
621 	}
622 
623 	/* Strong send queue ordering guarantees that when the
624 	 * last WR in the chain completes, all WRs in the chain
625 	 * are complete. The last completion will wake up the
626 	 * RPC waiter.
627 	 */
628 	frwr->fr_cqe.done = frwr_wc_localinv_done;
629 
630 	/* Transport disconnect drains the receive CQ before it
631 	 * replaces the QP. The RPC reply handler won't call us
632 	 * unless ri_id->qp is a valid pointer.
633 	 */
634 	bad_wr = NULL;
635 	rc = ib_post_send(r_xprt->rx_ia.ri_id->qp, first, &bad_wr);
636 	if (!rc)
637 		return;
638 
639 	/* Recycle MRs in the LOCAL_INV chain that did not get posted.
640 	 */
641 	trace_xprtrdma_post_linv(req, rc);
642 	while (bad_wr) {
643 		frwr = container_of(bad_wr, struct rpcrdma_frwr, fr_invwr);
644 		mr = container_of(frwr, struct rpcrdma_mr, frwr);
645 		bad_wr = bad_wr->next;
646 
647 		frwr_mr_recycle(mr);
648 	}
649 
650 	/* The final LOCAL_INV WR in the chain is supposed to
651 	 * do the wake. If it was never posted, the wake will
652 	 * not happen, so wake here in that case.
653 	 */
654 	rpcrdma_complete_rqst(req->rl_reply);
655 }
656