net/sunrpc/xprtrdma/svc_rdma_recvfrom.c

   1 /*
   2  * Copyright (c) 2014 Open Grid Computing, Inc. All rights reserved.
   3  * Copyright (c) 2005-2006 Network Appliance, Inc. All rights reserved.
   4  *
   5  * This software is available to you under a choice of one of two
   6  * licenses.  You may choose to be licensed under the terms of the GNU
   7  * General Public License (GPL) Version 2, available from the file
   8  * COPYING in the main directory of this source tree, or the BSD-type
   9  * license below:
  10  *
  11  * Redistribution and use in source and binary forms, with or without
  12  * modification, are permitted provided that the following conditions
  13  * are met:
  14  *
  15  *      Redistributions of source code must retain the above copyright
  16  *      notice, this list of conditions and the following disclaimer.
  17  *
  18  *      Redistributions in binary form must reproduce the above
  19  *      copyright notice, this list of conditions and the following
  20  *      disclaimer in the documentation and/or other materials provided
  21  *      with the distribution.
  22  *
  23  *      Neither the name of the Network Appliance, Inc. nor the names of
  24  *      its contributors may be used to endorse or promote products
  25  *      derived from this software without specific prior written
  26  *      permission.
  27  *
  28  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
  29  * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
  30  * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
  31  * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
  32  * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
  33  * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
  34  * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  35  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  36  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  37  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  38  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  39  *
  40  * Author: Tom Tucker <tom@opengridcomputing.com>
  41  */
  42
  43 #include <linux/sunrpc/debug.h>
  44 #include <linux/sunrpc/rpc_rdma.h>
  45 #include <linux/spinlock.h>
  46 #include <linux/highmem.h>
  47 #include <asm/unaligned.h>
  48 #include <rdma/ib_verbs.h>
  49 #include <rdma/rdma_cm.h>
  50 #include <linux/sunrpc/svc_rdma.h>
  51
  52 #define RPCDBG_FACILITY RPCDBG_SVCXPRT
  53
  54 /*
  55  * Replace the pages in the rq_argpages array with the pages from the SGE in
  56  * the RDMA_RECV completion. The SGL should contain full pages up until the
  57  * last one.
  58  */
  59 static void rdma_build_arg_xdr(struct svc_rqst *rqstp,
  60                                struct svc_rdma_op_ctxt *ctxt,
  61                                u32 byte_count)
  62 {
  63         struct page *page;
  64         u32 bc;
  65         int sge_no;
  66
  67         /* Swap the page in the SGE with the page in argpages */
  68         page = ctxt->pages[0];
  69         put_page(rqstp->rq_pages[0]);
  70         rqstp->rq_pages[0] = page;
  71
  72         /* Set up the XDR head */
  73         rqstp->rq_arg.head[0].iov_base = page_address(page);
  74         rqstp->rq_arg.head[0].iov_len =
  75                 min_t(size_t, byte_count, ctxt->sge[0].length);
  76         rqstp->rq_arg.len = byte_count;
  77         rqstp->rq_arg.buflen = byte_count;
  78
  79         /* Compute bytes past head in the SGL */
  80         bc = byte_count - rqstp->rq_arg.head[0].iov_len;
  81
  82         /* If data remains, store it in the pagelist */
  83         rqstp->rq_arg.page_len = bc;
  84         rqstp->rq_arg.page_base = 0;
  85         rqstp->rq_arg.pages = &rqstp->rq_pages[1];
  86         sge_no = 1;
  87         while (bc && sge_no < ctxt->count) {
  88                 page = ctxt->pages[sge_no];
  89                 put_page(rqstp->rq_pages[sge_no]);
  90                 rqstp->rq_pages[sge_no] = page;
  91                 bc -= min_t(u32, bc, ctxt->sge[sge_no].length);
  92                 rqstp->rq_arg.buflen += ctxt->sge[sge_no].length;
  93                 sge_no++;
  94         }
  95         rqstp->rq_respages = &rqstp->rq_pages[sge_no];
  96         rqstp->rq_next_page = rqstp->rq_respages + 1;
  97
  98         /* We should never run out of SGE because the limit is defined to
  99          * support the max allowed RPC data length
 100          */
 101         BUG_ON(bc && (sge_no == ctxt->count));
 102         BUG_ON((rqstp->rq_arg.head[0].iov_len + rqstp->rq_arg.page_len)
 103                != byte_count);
 104         BUG_ON(rqstp->rq_arg.len != byte_count);
 105
 106         /* If not all pages were used from the SGL, free the remaining ones */
 107         bc = sge_no;
 108         while (sge_no < ctxt->count) {
 109                 page = ctxt->pages[sge_no++];
 110                 put_page(page);
 111         }
 112         ctxt->count = bc;
 113
 114         /* Set up tail */
 115         rqstp->rq_arg.tail[0].iov_base = NULL;
 116         rqstp->rq_arg.tail[0].iov_len = 0;
 117 }
 118
 119 static int rdma_read_max_sge(struct svcxprt_rdma *xprt, int sge_count)
 120 {
 121         if (rdma_node_get_transport(xprt->sc_cm_id->device->node_type) ==
 122              RDMA_TRANSPORT_IWARP)
 123                 return 1;
 124         else
 125                 return min_t(int, sge_count, xprt->sc_max_sge);
 126 }
 127
 128 typedef int (*rdma_reader_fn)(struct svcxprt_rdma *xprt,
 129                               struct svc_rqst *rqstp,
 130                               struct svc_rdma_op_ctxt *head,
 131                               int *page_no,
 132                               u32 *page_offset,
 133                               u32 rs_handle,
 134                               u32 rs_length,
 135                               u64 rs_offset,
 136                               int last);
 137
 138 /* Issue an RDMA_READ using the local lkey to map the data sink */
 139 static int rdma_read_chunk_lcl(struct svcxprt_rdma *xprt,
 140                                struct svc_rqst *rqstp,
 141                                struct svc_rdma_op_ctxt *head,
 142                                int *page_no,
 143                                u32 *page_offset,
 144                                u32 rs_handle,
 145                                u32 rs_length,
 146                                u64 rs_offset,
 147                                int last)
 148 {
 149         struct ib_send_wr read_wr;
 150         int pages_needed = PAGE_ALIGN(*page_offset + rs_length) >> PAGE_SHIFT;
 151         struct svc_rdma_op_ctxt *ctxt = svc_rdma_get_context(xprt);
 152         int ret, read, pno;
 153         u32 pg_off = *page_offset;
 154         u32 pg_no = *page_no;
 155
 156         ctxt->direction = DMA_FROM_DEVICE;
 157         ctxt->read_hdr = head;
 158         pages_needed =
 159                 min_t(int, pages_needed, rdma_read_max_sge(xprt, pages_needed));
 160         read = min_t(int, pages_needed << PAGE_SHIFT, rs_length);
 161
 162         for (pno = 0; pno < pages_needed; pno++) {
 163                 int len = min_t(int, rs_length, PAGE_SIZE - pg_off);
 164
 165                 head->arg.pages[pg_no] = rqstp->rq_arg.pages[pg_no];
 166                 head->arg.page_len += len;
 167                 head->arg.len += len;
 168                 if (!pg_off)
 169                         head->count++;
 170                 rqstp->rq_respages = &rqstp->rq_arg.pages[pg_no+1];
 171                 rqstp->rq_next_page = rqstp->rq_respages + 1;
 172                 ctxt->sge[pno].addr =
 173                         ib_dma_map_page(xprt->sc_cm_id->device,
 174                                         head->arg.pages[pg_no], pg_off,
 175                                         PAGE_SIZE - pg_off,
 176                                         DMA_FROM_DEVICE);
 177                 ret = ib_dma_mapping_error(xprt->sc_cm_id->device,
 178                                            ctxt->sge[pno].addr);
 179                 if (ret)
 180                         goto err;
 181                 atomic_inc(&xprt->sc_dma_used);
 182
 183                 /* The lkey here is either a local dma lkey or a dma_mr lkey */
 184                 ctxt->sge[pno].lkey = xprt->sc_dma_lkey;
 185                 ctxt->sge[pno].length = len;
 186                 ctxt->count++;
 187
 188                 /* adjust offset and wrap to next page if needed */
 189                 pg_off += len;
 190                 if (pg_off == PAGE_SIZE) {
 191                         pg_off = 0;
 192                         pg_no++;
 193                 }
 194                 rs_length -= len;
 195         }
 196
 197         if (last && rs_length == 0)
 198                 set_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags);
 199         else
 200                 clear_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags);
 201
 202         memset(&read_wr, 0, sizeof(read_wr));
 203         read_wr.wr_id = (unsigned long)ctxt;
 204         read_wr.opcode = IB_WR_RDMA_READ;
 205         ctxt->wr_op = read_wr.opcode;
 206         read_wr.send_flags = IB_SEND_SIGNALED;
 207         read_wr.wr.rdma.rkey = rs_handle;
 208         read_wr.wr.rdma.remote_addr = rs_offset;
 209         read_wr.sg_list = ctxt->sge;
 210         read_wr.num_sge = pages_needed;
 211
 212         ret = svc_rdma_send(xprt, &read_wr);
 213         if (ret) {
 214                 pr_err("svcrdma: Error %d posting RDMA_READ\n", ret);
 215                 set_bit(XPT_CLOSE, &xprt->sc_xprt.xpt_flags);
 216                 goto err;
 217         }
 218
 219         /* return current location in page array */
 220         *page_no = pg_no;
 221         *page_offset = pg_off;
 222         ret = read;
 223         atomic_inc(&rdma_stat_read);
 224         return ret;
 225  err:
 226         svc_rdma_unmap_dma(ctxt);
 227         svc_rdma_put_context(ctxt, 0);
 228         return ret;
 229 }
 230
 231 /* Issue an RDMA_READ using an FRMR to map the data sink */
 232 static int rdma_read_chunk_frmr(struct svcxprt_rdma *xprt,
 233                                 struct svc_rqst *rqstp,
 234                                 struct svc_rdma_op_ctxt *head,
 235                                 int *page_no,
 236                                 u32 *page_offset,
 237                                 u32 rs_handle,
 238                                 u32 rs_length,
 239                                 u64 rs_offset,
 240                                 int last)
 241 {
 242         struct ib_send_wr read_wr;
 243         struct ib_send_wr inv_wr;
 244         struct ib_send_wr fastreg_wr;
 245         u8 key;
 246         int pages_needed = PAGE_ALIGN(*page_offset + rs_length) >> PAGE_SHIFT;
 247         struct svc_rdma_op_ctxt *ctxt = svc_rdma_get_context(xprt);
 248         struct svc_rdma_fastreg_mr *frmr = svc_rdma_get_frmr(xprt);
 249         int ret, read, pno;
 250         u32 pg_off = *page_offset;
 251         u32 pg_no = *page_no;
 252
 253         if (IS_ERR(frmr))
 254                 return -ENOMEM;
 255
 256         ctxt->direction = DMA_FROM_DEVICE;
 257         ctxt->frmr = frmr;
 258         pages_needed = min_t(int, pages_needed, xprt->sc_frmr_pg_list_len);
 259         read = min_t(int, pages_needed << PAGE_SHIFT, rs_length);
 260
 261         frmr->kva = page_address(rqstp->rq_arg.pages[pg_no]);
 262         frmr->direction = DMA_FROM_DEVICE;
 263         frmr->access_flags = (IB_ACCESS_LOCAL_WRITE|IB_ACCESS_REMOTE_WRITE);
 264         frmr->map_len = pages_needed << PAGE_SHIFT;
 265         frmr->page_list_len = pages_needed;
 266
 267         for (pno = 0; pno < pages_needed; pno++) {
 268                 int len = min_t(int, rs_length, PAGE_SIZE - pg_off);
 269
 270                 head->arg.pages[pg_no] = rqstp->rq_arg.pages[pg_no];
 271                 head->arg.page_len += len;
 272                 head->arg.len += len;
 273                 if (!pg_off)
 274                         head->count++;
 275                 rqstp->rq_respages = &rqstp->rq_arg.pages[pg_no+1];
 276                 rqstp->rq_next_page = rqstp->rq_respages + 1;
 277                 frmr->page_list->page_list[pno] =
 278                         ib_dma_map_page(xprt->sc_cm_id->device,
 279                                         head->arg.pages[pg_no], 0,
 280                                         PAGE_SIZE, DMA_FROM_DEVICE);
 281                 ret = ib_dma_mapping_error(xprt->sc_cm_id->device,
 282                                            frmr->page_list->page_list[pno]);
 283                 if (ret)
 284                         goto err;
 285                 atomic_inc(&xprt->sc_dma_used);
 286
 287                 /* adjust offset and wrap to next page if needed */
 288                 pg_off += len;
 289                 if (pg_off == PAGE_SIZE) {
 290                         pg_off = 0;
 291                         pg_no++;
 292                 }
 293                 rs_length -= len;
 294         }
 295
 296         if (last && rs_length == 0)
 297                 set_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags);
 298         else
 299                 clear_bit(RDMACTXT_F_LAST_CTXT, &ctxt->flags);
 300
 301         /* Bump the key */
 302         key = (u8)(frmr->mr->lkey & 0x000000FF);
 303         ib_update_fast_reg_key(frmr->mr, ++key);
 304
 305         ctxt->sge[0].addr = (unsigned long)frmr->kva + *page_offset;
 306         ctxt->sge[0].lkey = frmr->mr->lkey;
 307         ctxt->sge[0].length = read;
 308         ctxt->count = 1;
 309         ctxt->read_hdr = head;
 310
 311         /* Prepare FASTREG WR */
 312         memset(&fastreg_wr, 0, sizeof(fastreg_wr));
 313         fastreg_wr.opcode = IB_WR_FAST_REG_MR;
 314         fastreg_wr.send_flags = IB_SEND_SIGNALED;
 315         fastreg_wr.wr.fast_reg.iova_start = (unsigned long)frmr->kva;
 316         fastreg_wr.wr.fast_reg.page_list = frmr->page_list;
 317         fastreg_wr.wr.fast_reg.page_list_len = frmr->page_list_len;
 318         fastreg_wr.wr.fast_reg.page_shift = PAGE_SHIFT;
 319         fastreg_wr.wr.fast_reg.length = frmr->map_len;
 320         fastreg_wr.wr.fast_reg.access_flags = frmr->access_flags;
 321         fastreg_wr.wr.fast_reg.rkey = frmr->mr->lkey;
 322         fastreg_wr.next = &read_wr;
 323
 324         /* Prepare RDMA_READ */
 325         memset(&read_wr, 0, sizeof(read_wr));
 326         read_wr.send_flags = IB_SEND_SIGNALED;
 327         read_wr.wr.rdma.rkey = rs_handle;
 328         read_wr.wr.rdma.remote_addr = rs_offset;
 329         read_wr.sg_list = ctxt->sge;
 330         read_wr.num_sge = 1;
 331         if (xprt->sc_dev_caps & SVCRDMA_DEVCAP_READ_W_INV) {
 332                 read_wr.opcode = IB_WR_RDMA_READ_WITH_INV;
 333                 read_wr.wr_id = (unsigned long)ctxt;
 334                 read_wr.ex.invalidate_rkey = ctxt->frmr->mr->lkey;
 335         } else {
 336                 read_wr.opcode = IB_WR_RDMA_READ;
 337                 read_wr.next = &inv_wr;
 338                 /* Prepare invalidate */
 339                 memset(&inv_wr, 0, sizeof(inv_wr));
 340                 inv_wr.wr_id = (unsigned long)ctxt;
 341                 inv_wr.opcode = IB_WR_LOCAL_INV;
 342                 inv_wr.send_flags = IB_SEND_SIGNALED | IB_SEND_FENCE;
 343                 inv_wr.ex.invalidate_rkey = frmr->mr->lkey;
 344         }
 345         ctxt->wr_op = read_wr.opcode;
 346
 347         /* Post the chain */
 348         ret = svc_rdma_send(xprt, &fastreg_wr);
 349         if (ret) {
 350                 pr_err("svcrdma: Error %d posting RDMA_READ\n", ret);
 351                 set_bit(XPT_CLOSE, &xprt->sc_xprt.xpt_flags);
 352                 goto err;
 353         }
 354
 355         /* return current location in page array */
 356         *page_no = pg_no;
 357         *page_offset = pg_off;
 358         ret = read;
 359         atomic_inc(&rdma_stat_read);
 360         return ret;
 361  err:
 362         svc_rdma_unmap_dma(ctxt);
 363         svc_rdma_put_context(ctxt, 0);
 364         svc_rdma_put_frmr(xprt, frmr);
 365         return ret;
 366 }
 367
 368 static int rdma_read_chunks(struct svcxprt_rdma *xprt,
 369                             struct rpcrdma_msg *rmsgp,
 370                             struct svc_rqst *rqstp,
 371                             struct svc_rdma_op_ctxt *head)
 372 {
 373         int page_no, ch_count, ret;
 374         struct rpcrdma_read_chunk *ch;
 375         u32 page_offset, byte_count;
 376         u64 rs_offset;
 377         rdma_reader_fn reader;
 378
 379         /* If no read list is present, return 0 */
 380         ch = svc_rdma_get_read_chunk(rmsgp);
 381         if (!ch)
 382                 return 0;
 383
 384         svc_rdma_rcl_chunk_counts(ch, &ch_count, &byte_count);
 385         if (ch_count > RPCSVC_MAXPAGES)
 386                 return -EINVAL;
 387
 388         /* The request is completed when the RDMA_READs complete. The
 389          * head context keeps all the pages that comprise the
 390          * request.
 391          */
 392         head->arg.head[0] = rqstp->rq_arg.head[0];
 393         head->arg.tail[0] = rqstp->rq_arg.tail[0];
 394         head->arg.pages = &head->pages[head->count];
 395         head->hdr_count = head->count;
 396         head->arg.page_base = 0;
 397         head->arg.page_len = 0;
 398         head->arg.len = rqstp->rq_arg.len;
 399         head->arg.buflen = rqstp->rq_arg.buflen;
 400
 401         /* Use FRMR if supported */
 402         if (xprt->sc_dev_caps & SVCRDMA_DEVCAP_FAST_REG)
 403                 reader = rdma_read_chunk_frmr;
 404         else
 405                 reader = rdma_read_chunk_lcl;
 406
 407         page_no = 0; page_offset = 0;
 408         for (ch = (struct rpcrdma_read_chunk *)&rmsgp->rm_body.rm_chunks[0];
 409              ch->rc_discrim != 0; ch++) {
 410
 411                 xdr_decode_hyper((__be32 *)&ch->rc_target.rs_offset,
 412                                  &rs_offset);
 413                 byte_count = ntohl(ch->rc_target.rs_length);
 414
 415                 while (byte_count > 0) {
 416                         ret = reader(xprt, rqstp, head,
 417                                      &page_no, &page_offset,
 418                                      ntohl(ch->rc_target.rs_handle),
 419                                      byte_count, rs_offset,
 420                                      ((ch+1)->rc_discrim == 0) /* last */
 421                                      );
 422                         if (ret < 0)
 423                                 goto err;
 424                         byte_count -= ret;
 425                         rs_offset += ret;
 426                         head->arg.buflen += ret;
 427                 }
 428         }
 429         ret = 1;
 430  err:
 431         /* Detach arg pages. svc_recv will replenish them */
 432         for (page_no = 0;
 433              &rqstp->rq_pages[page_no] < rqstp->rq_respages; page_no++)
 434                 rqstp->rq_pages[page_no] = NULL;
 435
 436         return ret;
 437 }
 438
 439 /*
 440  * To avoid a separate RDMA READ just for a handful of zero bytes,
 441  * RFC 5666 section 3.7 allows the client to omit the XDR zero pad
 442  * in chunk lists.
 443  */
 444 static void
 445 rdma_fix_xdr_pad(struct xdr_buf *buf)
 446 {
 447         unsigned int page_len = buf->page_len;
 448         unsigned int size = (XDR_QUADLEN(page_len) << 2) - page_len;
 449         unsigned int offset, pg_no;
 450         char *p;
 451
 452         if (size == 0)
 453                 return;
 454
 455         pg_no = page_len >> PAGE_SHIFT;
 456         offset = page_len & ~PAGE_MASK;
 457         p = page_address(buf->pages[pg_no]);
 458         memset(p + offset, 0, size);
 459
 460         buf->page_len += size;
 461         buf->buflen += size;
 462         buf->len += size;
 463 }
 464
 465 static int rdma_read_complete(struct svc_rqst *rqstp,
 466                               struct svc_rdma_op_ctxt *head)
 467 {
 468         int page_no;
 469         int ret;
 470
 471         BUG_ON(!head);
 472
 473         /* Copy RPC pages */
 474         for (page_no = 0; page_no < head->count; page_no++) {
 475                 put_page(rqstp->rq_pages[page_no]);
 476                 rqstp->rq_pages[page_no] = head->pages[page_no];
 477         }
 478         /* Point rq_arg.pages past header */
 479         rdma_fix_xdr_pad(&head->arg);
 480         rqstp->rq_arg.pages = &rqstp->rq_pages[head->hdr_count];
 481         rqstp->rq_arg.page_len = head->arg.page_len;
 482         rqstp->rq_arg.page_base = head->arg.page_base;
 483
 484         /* rq_respages starts after the last arg page */
 485         rqstp->rq_respages = &rqstp->rq_arg.pages[page_no];
 486         rqstp->rq_next_page = rqstp->rq_respages + 1;
 487
 488         /* Rebuild rq_arg head and tail. */
 489         rqstp->rq_arg.head[0] = head->arg.head[0];
 490         rqstp->rq_arg.tail[0] = head->arg.tail[0];
 491         rqstp->rq_arg.len = head->arg.len;
 492         rqstp->rq_arg.buflen = head->arg.buflen;
 493
 494         /* Free the context */
 495         svc_rdma_put_context(head, 0);
 496
 497         /* XXX: What should this be? */
 498         rqstp->rq_prot = IPPROTO_MAX;
 499         svc_xprt_copy_addrs(rqstp, rqstp->rq_xprt);
 500
 501         ret = rqstp->rq_arg.head[0].iov_len
 502                 + rqstp->rq_arg.page_len
 503                 + rqstp->rq_arg.tail[0].iov_len;
 504         dprintk("svcrdma: deferred read ret=%d, rq_arg.len =%d, "
 505                 "rq_arg.head[0].iov_base=%p, rq_arg.head[0].iov_len = %zd\n",
 506                 ret, rqstp->rq_arg.len, rqstp->rq_arg.head[0].iov_base,
 507                 rqstp->rq_arg.head[0].iov_len);
 508
 509         return ret;
 510 }
 511
 512 /*
 513  * Set up the rqstp thread context to point to the RQ buffer. If
 514  * necessary, pull additional data from the client with an RDMA_READ
 515  * request.
 516  */
 517 int svc_rdma_recvfrom(struct svc_rqst *rqstp)
 518 {
 519         struct svc_xprt *xprt = rqstp->rq_xprt;
 520         struct svcxprt_rdma *rdma_xprt =
 521                 container_of(xprt, struct svcxprt_rdma, sc_xprt);
 522         struct svc_rdma_op_ctxt *ctxt = NULL;
 523         struct rpcrdma_msg *rmsgp;
 524         int ret = 0;
 525         int len;
 526
 527         dprintk("svcrdma: rqstp=%p\n", rqstp);
 528
 529         spin_lock_bh(&rdma_xprt->sc_rq_dto_lock);
 530         if (!list_empty(&rdma_xprt->sc_read_complete_q)) {
 531                 ctxt = list_entry(rdma_xprt->sc_read_complete_q.next,
 532                                   struct svc_rdma_op_ctxt,
 533                                   dto_q);
 534                 list_del_init(&ctxt->dto_q);
 535                 spin_unlock_bh(&rdma_xprt->sc_rq_dto_lock);
 536                 return rdma_read_complete(rqstp, ctxt);
 537         } else if (!list_empty(&rdma_xprt->sc_rq_dto_q)) {
 538                 ctxt = list_entry(rdma_xprt->sc_rq_dto_q.next,
 539                                   struct svc_rdma_op_ctxt,
 540                                   dto_q);
 541                 list_del_init(&ctxt->dto_q);
 542         } else {
 543                 atomic_inc(&rdma_stat_rq_starve);
 544                 clear_bit(XPT_DATA, &xprt->xpt_flags);
 545                 ctxt = NULL;
 546         }
 547         spin_unlock_bh(&rdma_xprt->sc_rq_dto_lock);
 548         if (!ctxt) {
 549                 /* This is the EAGAIN path. The svc_recv routine will
 550                  * return -EAGAIN, the nfsd thread will go to call into
 551                  * svc_recv again and we shouldn't be on the active
 552                  * transport list
 553                  */
 554                 if (test_bit(XPT_CLOSE, &xprt->xpt_flags))
 555                         goto close_out;
 556
 557                 goto out;
 558         }
 559         dprintk("svcrdma: processing ctxt=%p on xprt=%p, rqstp=%p, status=%d\n",
 560                 ctxt, rdma_xprt, rqstp, ctxt->wc_status);
 561         BUG_ON(ctxt->wc_status != IB_WC_SUCCESS);
 562         atomic_inc(&rdma_stat_recv);
 563
 564         /* Build up the XDR from the receive buffers. */
 565         rdma_build_arg_xdr(rqstp, ctxt, ctxt->byte_len);
 566
 567         /* Decode the RDMA header. */
 568         len = svc_rdma_xdr_decode_req(&rmsgp, rqstp);
 569         rqstp->rq_xprt_hlen = len;
 570
 571         /* If the request is invalid, reply with an error */
 572         if (len < 0) {
 573                 if (len == -ENOSYS)
 574                         svc_rdma_send_error(rdma_xprt, rmsgp, ERR_VERS);
 575                 goto close_out;
 576         }
 577
 578         /* Read read-list data. */
 579         ret = rdma_read_chunks(rdma_xprt, rmsgp, rqstp, ctxt);
 580         if (ret > 0) {
 581                 /* read-list posted, defer until data received from client. */
 582                 goto defer;
 583         } else if (ret < 0) {
 584                 /* Post of read-list failed, free context. */
 585                 svc_rdma_put_context(ctxt, 1);
 586                 return 0;
 587         }
 588
 589         ret = rqstp->rq_arg.head[0].iov_len
 590                 + rqstp->rq_arg.page_len
 591                 + rqstp->rq_arg.tail[0].iov_len;
 592         svc_rdma_put_context(ctxt, 0);
 593  out:
 594         dprintk("svcrdma: ret = %d, rq_arg.len =%d, "
 595                 "rq_arg.head[0].iov_base=%p, rq_arg.head[0].iov_len = %zd\n",
 596                 ret, rqstp->rq_arg.len,
 597                 rqstp->rq_arg.head[0].iov_base,
 598                 rqstp->rq_arg.head[0].iov_len);
 599         rqstp->rq_prot = IPPROTO_MAX;
 600         svc_xprt_copy_addrs(rqstp, xprt);
 601         return ret;
 602
 603  close_out:
 604         if (ctxt)
 605                 svc_rdma_put_context(ctxt, 1);
 606         dprintk("svcrdma: transport %p is closing\n", xprt);
 607         /*
 608          * Set the close bit and enqueue it. svc_recv will see the
 609          * close bit and call svc_xprt_delete
 610          */
 611         set_bit(XPT_CLOSE, &xprt->xpt_flags);
 612 defer:
 613         return 0;
 614 }