drivers/block/drbd/drbd_req.c

   1 /*
   2    drbd_req.c
   3
   4    This file is part of DRBD by Philipp Reisner and Lars Ellenberg.
   5
   6    Copyright (C) 2001-2008, LINBIT Information Technologies GmbH.
   7    Copyright (C) 1999-2008, Philipp Reisner <philipp.reisner@linbit.com>.
   8    Copyright (C) 2002-2008, Lars Ellenberg <lars.ellenberg@linbit.com>.
   9
  10    drbd is free software; you can redistribute it and/or modify
  11    it under the terms of the GNU General Public License as published by
  12    the Free Software Foundation; either version 2, or (at your option)
  13    any later version.
  14
  15    drbd is distributed in the hope that it will be useful,
  16    but WITHOUT ANY WARRANTY; without even the implied warranty of
  17    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  18    GNU General Public License for more details.
  19
  20    You should have received a copy of the GNU General Public License
  21    along with drbd; see the file COPYING.  If not, write to
  22    the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
  23
  24  */
  25
  26 #include <linux/module.h>
  27
  28 #include <linux/slab.h>
  29 #include <linux/drbd.h>
  30 #include "drbd_int.h"
  31 #include "drbd_req.h"
  32
  33
  34 static bool drbd_may_do_local_read(struct drbd_device *device, sector_t sector, int size);
  35
  36 /* Update disk stats at start of I/O request */
  37 static void _drbd_start_io_acct(struct drbd_device *device, struct drbd_request *req)
  38 {
  39         struct request_queue *q = device->rq_queue;
  40
  41         generic_start_io_acct(q, bio_op(req->master_bio),
  42                                 req->i.size >> 9, &device->vdisk->part0);
  43 }
  44
  45 /* Update disk stats when completing request upwards */
  46 static void _drbd_end_io_acct(struct drbd_device *device, struct drbd_request *req)
  47 {
  48         struct request_queue *q = device->rq_queue;
  49
  50         generic_end_io_acct(q, bio_op(req->master_bio),
  51                             &device->vdisk->part0, req->start_jif);
  52 }
  53
  54 static struct drbd_request *drbd_req_new(struct drbd_device *device, struct bio *bio_src)
  55 {
  56         struct drbd_request *req;
  57
  58         req = mempool_alloc(&drbd_request_mempool, GFP_NOIO);
  59         if (!req)
  60                 return NULL;
  61         memset(req, 0, sizeof(*req));
  62
  63         drbd_req_make_private_bio(req, bio_src);
  64         req->rq_state = (bio_data_dir(bio_src) == WRITE ? RQ_WRITE : 0)
  65                       | (bio_op(bio_src) == REQ_OP_WRITE_SAME ? RQ_WSAME : 0)
  66                       | (bio_op(bio_src) == REQ_OP_WRITE_ZEROES ? RQ_UNMAP : 0)
  67                       | (bio_op(bio_src) == REQ_OP_DISCARD ? RQ_UNMAP : 0);
  68         req->device = device;
  69         req->master_bio = bio_src;
  70         req->epoch = 0;
  71
  72         drbd_clear_interval(&req->i);
  73         req->i.sector     = bio_src->bi_iter.bi_sector;
  74         req->i.size      = bio_src->bi_iter.bi_size;
  75         req->i.local = true;
  76         req->i.waiting = false;
  77
  78         INIT_LIST_HEAD(&req->tl_requests);
  79         INIT_LIST_HEAD(&req->w.list);
  80         INIT_LIST_HEAD(&req->req_pending_master_completion);
  81         INIT_LIST_HEAD(&req->req_pending_local);
  82
  83         /* one reference to be put by __drbd_make_request */
  84         atomic_set(&req->completion_ref, 1);
  85         /* one kref as long as completion_ref > 0 */
  86         kref_init(&req->kref);
  87         return req;
  88 }
  89
  90 static void drbd_remove_request_interval(struct rb_root *root,
  91                                          struct drbd_request *req)
  92 {
  93         struct drbd_device *device = req->device;
  94         struct drbd_interval *i = &req->i;
  95
  96         drbd_remove_interval(root, i);
  97
  98         /* Wake up any processes waiting for this request to complete.  */
  99         if (i->waiting)
 100                 wake_up(&device->misc_wait);
 101 }
 102
 103 void drbd_req_destroy(struct kref *kref)
 104 {
 105         struct drbd_request *req = container_of(kref, struct drbd_request, kref);
 106         struct drbd_device *device = req->device;
 107         const unsigned s = req->rq_state;
 108
 109         if ((req->master_bio && !(s & RQ_POSTPONED)) ||
 110                 atomic_read(&req->completion_ref) ||
 111                 (s & RQ_LOCAL_PENDING) ||
 112                 ((s & RQ_NET_MASK) && !(s & RQ_NET_DONE))) {
 113                 drbd_err(device, "drbd_req_destroy: Logic BUG rq_state = 0x%x, completion_ref = %d\n",
 114                                 s, atomic_read(&req->completion_ref));
 115                 return;
 116         }
 117
 118         /* If called from mod_rq_state (expected normal case) or
 119          * drbd_send_and_submit (the less likely normal path), this holds the
 120          * req_lock, and req->tl_requests will typicaly be on ->transfer_log,
 121          * though it may be still empty (never added to the transfer log).
 122          *
 123          * If called from do_retry(), we do NOT hold the req_lock, but we are
 124          * still allowed to unconditionally list_del(&req->tl_requests),
 125          * because it will be on a local on-stack list only. */
 126         list_del_init(&req->tl_requests);
 127
 128         /* finally remove the request from the conflict detection
 129          * respective block_id verification interval tree. */
 130         if (!drbd_interval_empty(&req->i)) {
 131                 struct rb_root *root;
 132
 133                 if (s & RQ_WRITE)
 134                         root = &device->write_requests;
 135                 else
 136                         root = &device->read_requests;
 137                 drbd_remove_request_interval(root, req);
 138         } else if (s & (RQ_NET_MASK & ~RQ_NET_DONE) && req->i.size != 0)
 139                 drbd_err(device, "drbd_req_destroy: Logic BUG: interval empty, but: rq_state=0x%x, sect=%llu, size=%u\n",
 140                         s, (unsigned long long)req->i.sector, req->i.size);
 141
 142         /* if it was a write, we may have to set the corresponding
 143          * bit(s) out-of-sync first. If it had a local part, we need to
 144          * release the reference to the activity log. */
 145         if (s & RQ_WRITE) {
 146                 /* Set out-of-sync unless both OK flags are set
 147                  * (local only or remote failed).
 148                  * Other places where we set out-of-sync:
 149                  * READ with local io-error */
 150
 151                 /* There is a special case:
 152                  * we may notice late that IO was suspended,
 153                  * and postpone, or schedule for retry, a write,
 154                  * before it even was submitted or sent.
 155                  * In that case we do not want to touch the bitmap at all.
 156                  */
 157                 if ((s & (RQ_POSTPONED|RQ_LOCAL_MASK|RQ_NET_MASK)) != RQ_POSTPONED) {
 158                         if (!(s & RQ_NET_OK) || !(s & RQ_LOCAL_OK))
 159                                 drbd_set_out_of_sync(device, req->i.sector, req->i.size);
 160
 161                         if ((s & RQ_NET_OK) && (s & RQ_LOCAL_OK) && (s & RQ_NET_SIS))
 162                                 drbd_set_in_sync(device, req->i.sector, req->i.size);
 163                 }
 164
 165                 /* one might be tempted to move the drbd_al_complete_io
 166                  * to the local io completion callback drbd_request_endio.
 167                  * but, if this was a mirror write, we may only
 168                  * drbd_al_complete_io after this is RQ_NET_DONE,
 169                  * otherwise the extent could be dropped from the al
 170                  * before it has actually been written on the peer.
 171                  * if we crash before our peer knows about the request,
 172                  * but after the extent has been dropped from the al,
 173                  * we would forget to resync the corresponding extent.
 174                  */
 175                 if (s & RQ_IN_ACT_LOG) {
 176                         if (get_ldev_if_state(device, D_FAILED)) {
 177                                 drbd_al_complete_io(device, &req->i);
 178                                 put_ldev(device);
 179                         } else if (__ratelimit(&drbd_ratelimit_state)) {
 180                                 drbd_warn(device, "Should have called drbd_al_complete_io(, %llu, %u), "
 181                                          "but my Disk seems to have failed :(\n",
 182                                          (unsigned long long) req->i.sector, req->i.size);
 183                         }
 184                 }
 185         }
 186
 187         mempool_free(req, &drbd_request_mempool);
 188 }
 189
 190 static void wake_all_senders(struct drbd_connection *connection)
 191 {
 192         wake_up(&connection->sender_work.q_wait);
 193 }
 194
 195 /* must hold resource->req_lock */
 196 void start_new_tl_epoch(struct drbd_connection *connection)
 197 {
 198         /* no point closing an epoch, if it is empty, anyways. */
 199         if (connection->current_tle_writes == 0)
 200                 return;
 201
 202         connection->current_tle_writes = 0;
 203         atomic_inc(&connection->current_tle_nr);
 204         wake_all_senders(connection);
 205 }
 206
 207 void complete_master_bio(struct drbd_device *device,
 208                 struct bio_and_error *m)
 209 {
 210         m->bio->bi_status = errno_to_blk_status(m->error);
 211         bio_endio(m->bio);
 212         dec_ap_bio(device);
 213 }
 214
 215
 216 /* Helper for __req_mod().
 217  * Set m->bio to the master bio, if it is fit to be completed,
 218  * or leave it alone (it is initialized to NULL in __req_mod),
 219  * if it has already been completed, or cannot be completed yet.
 220  * If m->bio is set, the error status to be returned is placed in m->error.
 221  */
 222 static
 223 void drbd_req_complete(struct drbd_request *req, struct bio_and_error *m)
 224 {
 225         const unsigned s = req->rq_state;
 226         struct drbd_device *device = req->device;
 227         int error, ok;
 228
 229         /* we must not complete the master bio, while it is
 230          *      still being processed by _drbd_send_zc_bio (drbd_send_dblock)
 231          *      not yet acknowledged by the peer
 232          *      not yet completed by the local io subsystem
 233          * these flags may get cleared in any order by
 234          *      the worker,
 235          *      the receiver,
 236          *      the bio_endio completion callbacks.
 237          */
 238         if ((s & RQ_LOCAL_PENDING && !(s & RQ_LOCAL_ABORTED)) ||
 239             (s & RQ_NET_QUEUED) || (s & RQ_NET_PENDING) ||
 240             (s & RQ_COMPLETION_SUSP)) {
 241                 drbd_err(device, "drbd_req_complete: Logic BUG rq_state = 0x%x\n", s);
 242                 return;
 243         }
 244
 245         if (!req->master_bio) {
 246                 drbd_err(device, "drbd_req_complete: Logic BUG, master_bio == NULL!\n");
 247                 return;
 248         }
 249
 250         /*
 251          * figure out whether to report success or failure.
 252          *
 253          * report success when at least one of the operations succeeded.
 254          * or, to put the other way,
 255          * only report failure, when both operations failed.
 256          *
 257          * what to do about the failures is handled elsewhere.
 258          * what we need to do here is just: complete the master_bio.
 259          *
 260          * local completion error, if any, has been stored as ERR_PTR
 261          * in private_bio within drbd_request_endio.
 262          */
 263         ok = (s & RQ_LOCAL_OK) || (s & RQ_NET_OK);
 264         error = PTR_ERR(req->private_bio);
 265
 266         /* Before we can signal completion to the upper layers,
 267          * we may need to close the current transfer log epoch.
 268          * We are within the request lock, so we can simply compare
 269          * the request epoch number with the current transfer log
 270          * epoch number.  If they match, increase the current_tle_nr,
 271          * and reset the transfer log epoch write_cnt.
 272          */
 273         if (op_is_write(bio_op(req->master_bio)) &&
 274             req->epoch == atomic_read(&first_peer_device(device)->connection->current_tle_nr))
 275                 start_new_tl_epoch(first_peer_device(device)->connection);
 276
 277         /* Update disk stats */
 278         _drbd_end_io_acct(device, req);
 279
 280         /* If READ failed,
 281          * have it be pushed back to the retry work queue,
 282          * so it will re-enter __drbd_make_request(),
 283          * and be re-assigned to a suitable local or remote path,
 284          * or failed if we do not have access to good data anymore.
 285          *
 286          * Unless it was failed early by __drbd_make_request(),
 287          * because no path was available, in which case
 288          * it was not even added to the transfer_log.
 289          *
 290          * read-ahead may fail, and will not be retried.
 291          *
 292          * WRITE should have used all available paths already.
 293          */
 294         if (!ok &&
 295             bio_op(req->master_bio) == REQ_OP_READ &&
 296             !(req->master_bio->bi_opf & REQ_RAHEAD) &&
 297             !list_empty(&req->tl_requests))
 298                 req->rq_state |= RQ_POSTPONED;
 299
 300         if (!(req->rq_state & RQ_POSTPONED)) {
 301                 m->error = ok ? 0 : (error ?: -EIO);
 302                 m->bio = req->master_bio;
 303                 req->master_bio = NULL;
 304                 /* We leave it in the tree, to be able to verify later
 305                  * write-acks in protocol != C during resync.
 306                  * But we mark it as "complete", so it won't be counted as
 307                  * conflict in a multi-primary setup. */
 308                 req->i.completed = true;
 309         }
 310
 311         if (req->i.waiting)
 312                 wake_up(&device->misc_wait);
 313
 314         /* Either we are about to complete to upper layers,
 315          * or we will restart this request.
 316          * In either case, the request object will be destroyed soon,
 317          * so better remove it from all lists. */
 318         list_del_init(&req->req_pending_master_completion);
 319 }
 320
 321 /* still holds resource->req_lock */
 322 static void drbd_req_put_completion_ref(struct drbd_request *req, struct bio_and_error *m, int put)
 323 {
 324         struct drbd_device *device = req->device;
 325         D_ASSERT(device, m || (req->rq_state & RQ_POSTPONED));
 326
 327         if (!put)
 328                 return;
 329
 330         if (!atomic_sub_and_test(put, &req->completion_ref))
 331                 return;
 332
 333         drbd_req_complete(req, m);
 334
 335         /* local completion may still come in later,
 336          * we need to keep the req object around. */
 337         if (req->rq_state & RQ_LOCAL_ABORTED)
 338                 return;
 339
 340         if (req->rq_state & RQ_POSTPONED) {
 341                 /* don't destroy the req object just yet,
 342                  * but queue it for retry */
 343                 drbd_restart_request(req);
 344                 return;
 345         }
 346
 347         kref_put(&req->kref, drbd_req_destroy);
 348 }
 349
 350 static void set_if_null_req_next(struct drbd_peer_device *peer_device, struct drbd_request *req)
 351 {
 352         struct drbd_connection *connection = peer_device ? peer_device->connection : NULL;
 353         if (!connection)
 354                 return;
 355         if (connection->req_next == NULL)
 356                 connection->req_next = req;
 357 }
 358
 359 static void advance_conn_req_next(struct drbd_peer_device *peer_device, struct drbd_request *req)
 360 {
 361         struct drbd_connection *connection = peer_device ? peer_device->connection : NULL;
 362         if (!connection)
 363                 return;
 364         if (connection->req_next != req)
 365                 return;
 366         list_for_each_entry_continue(req, &connection->transfer_log, tl_requests) {
 367                 const unsigned s = req->rq_state;
 368                 if (s & RQ_NET_QUEUED)
 369                         break;
 370         }
 371         if (&req->tl_requests == &connection->transfer_log)
 372                 req = NULL;
 373         connection->req_next = req;
 374 }
 375
 376 static void set_if_null_req_ack_pending(struct drbd_peer_device *peer_device, struct drbd_request *req)
 377 {
 378         struct drbd_connection *connection = peer_device ? peer_device->connection : NULL;
 379         if (!connection)
 380                 return;
 381         if (connection->req_ack_pending == NULL)
 382                 connection->req_ack_pending = req;
 383 }
 384
 385 static void advance_conn_req_ack_pending(struct drbd_peer_device *peer_device, struct drbd_request *req)
 386 {
 387         struct drbd_connection *connection = peer_device ? peer_device->connection : NULL;
 388         if (!connection)
 389                 return;
 390         if (connection->req_ack_pending != req)
 391                 return;
 392         list_for_each_entry_continue(req, &connection->transfer_log, tl_requests) {
 393                 const unsigned s = req->rq_state;
 394                 if ((s & RQ_NET_SENT) && (s & RQ_NET_PENDING))
 395                         break;
 396         }
 397         if (&req->tl_requests == &connection->transfer_log)
 398                 req = NULL;
 399         connection->req_ack_pending = req;
 400 }
 401
 402 static void set_if_null_req_not_net_done(struct drbd_peer_device *peer_device, struct drbd_request *req)
 403 {
 404         struct drbd_connection *connection = peer_device ? peer_device->connection : NULL;
 405         if (!connection)
 406                 return;
 407         if (connection->req_not_net_done == NULL)
 408                 connection->req_not_net_done = req;
 409 }
 410
 411 static void advance_conn_req_not_net_done(struct drbd_peer_device *peer_device, struct drbd_request *req)
 412 {
 413         struct drbd_connection *connection = peer_device ? peer_device->connection : NULL;
 414         if (!connection)
 415                 return;
 416         if (connection->req_not_net_done != req)
 417                 return;
 418         list_for_each_entry_continue(req, &connection->transfer_log, tl_requests) {
 419                 const unsigned s = req->rq_state;
 420                 if ((s & RQ_NET_SENT) && !(s & RQ_NET_DONE))
 421                         break;
 422         }
 423         if (&req->tl_requests == &connection->transfer_log)
 424                 req = NULL;
 425         connection->req_not_net_done = req;
 426 }
 427
 428 /* I'd like this to be the only place that manipulates
 429  * req->completion_ref and req->kref. */
 430 static void mod_rq_state(struct drbd_request *req, struct bio_and_error *m,
 431                 int clear, int set)
 432 {
 433         struct drbd_device *device = req->device;
 434         struct drbd_peer_device *peer_device = first_peer_device(device);
 435         unsigned s = req->rq_state;
 436         int c_put = 0;
 437
 438         if (drbd_suspended(device) && !((s | clear) & RQ_COMPLETION_SUSP))
 439                 set |= RQ_COMPLETION_SUSP;
 440
 441         /* apply */
 442
 443         req->rq_state &= ~clear;
 444         req->rq_state |= set;
 445
 446         /* no change? */
 447         if (req->rq_state == s)
 448                 return;
 449
 450         /* intent: get references */
 451
 452         kref_get(&req->kref);
 453
 454         if (!(s & RQ_LOCAL_PENDING) && (set & RQ_LOCAL_PENDING))
 455                 atomic_inc(&req->completion_ref);
 456
 457         if (!(s & RQ_NET_PENDING) && (set & RQ_NET_PENDING)) {
 458                 inc_ap_pending(device);
 459                 atomic_inc(&req->completion_ref);
 460         }
 461
 462         if (!(s & RQ_NET_QUEUED) && (set & RQ_NET_QUEUED)) {
 463                 atomic_inc(&req->completion_ref);
 464                 set_if_null_req_next(peer_device, req);
 465         }
 466
 467         if (!(s & RQ_EXP_BARR_ACK) && (set & RQ_EXP_BARR_ACK))
 468                 kref_get(&req->kref); /* wait for the DONE */
 469
 470         if (!(s & RQ_NET_SENT) && (set & RQ_NET_SENT)) {
 471                 /* potentially already completed in the ack_receiver thread */
 472                 if (!(s & RQ_NET_DONE)) {
 473                         atomic_add(req->i.size >> 9, &device->ap_in_flight);
 474                         set_if_null_req_not_net_done(peer_device, req);
 475                 }
 476                 if (req->rq_state & RQ_NET_PENDING)
 477                         set_if_null_req_ack_pending(peer_device, req);
 478         }
 479
 480         if (!(s & RQ_COMPLETION_SUSP) && (set & RQ_COMPLETION_SUSP))
 481                 atomic_inc(&req->completion_ref);
 482
 483         /* progress: put references */
 484
 485         if ((s & RQ_COMPLETION_SUSP) && (clear & RQ_COMPLETION_SUSP))
 486                 ++c_put;
 487
 488         if (!(s & RQ_LOCAL_ABORTED) && (set & RQ_LOCAL_ABORTED)) {
 489                 D_ASSERT(device, req->rq_state & RQ_LOCAL_PENDING);
 490                 ++c_put;
 491         }
 492
 493         if ((s & RQ_LOCAL_PENDING) && (clear & RQ_LOCAL_PENDING)) {
 494                 if (req->rq_state & RQ_LOCAL_ABORTED)
 495                         kref_put(&req->kref, drbd_req_destroy);
 496                 else
 497                         ++c_put;
 498                 list_del_init(&req->req_pending_local);
 499         }
 500
 501         if ((s & RQ_NET_PENDING) && (clear & RQ_NET_PENDING)) {
 502                 dec_ap_pending(device);
 503                 ++c_put;
 504                 req->acked_jif = jiffies;
 505                 advance_conn_req_ack_pending(peer_device, req);
 506         }
 507
 508         if ((s & RQ_NET_QUEUED) && (clear & RQ_NET_QUEUED)) {
 509                 ++c_put;
 510                 advance_conn_req_next(peer_device, req);
 511         }
 512
 513         if (!(s & RQ_NET_DONE) && (set & RQ_NET_DONE)) {
 514                 if (s & RQ_NET_SENT)
 515                         atomic_sub(req->i.size >> 9, &device->ap_in_flight);
 516                 if (s & RQ_EXP_BARR_ACK)
 517                         kref_put(&req->kref, drbd_req_destroy);
 518                 req->net_done_jif = jiffies;
 519
 520                 /* in ahead/behind mode, or just in case,
 521                  * before we finally destroy this request,
 522                  * the caching pointers must not reference it anymore */
 523                 advance_conn_req_next(peer_device, req);
 524                 advance_conn_req_ack_pending(peer_device, req);
 525                 advance_conn_req_not_net_done(peer_device, req);
 526         }
 527
 528         /* potentially complete and destroy */
 529
 530         /* If we made progress, retry conflicting peer requests, if any. */
 531         if (req->i.waiting)
 532                 wake_up(&device->misc_wait);
 533
 534         drbd_req_put_completion_ref(req, m, c_put);
 535         kref_put(&req->kref, drbd_req_destroy);
 536 }
 537
 538 static void drbd_report_io_error(struct drbd_device *device, struct drbd_request *req)
 539 {
 540         char b[BDEVNAME_SIZE];
 541
 542         if (!__ratelimit(&drbd_ratelimit_state))
 543                 return;
 544
 545         drbd_warn(device, "local %s IO error sector %llu+%u on %s\n",
 546                         (req->rq_state & RQ_WRITE) ? "WRITE" : "READ",
 547                         (unsigned long long)req->i.sector,
 548                         req->i.size >> 9,
 549                         bdevname(device->ldev->backing_bdev, b));
 550 }
 551
 552 /* Helper for HANDED_OVER_TO_NETWORK.
 553  * Is this a protocol A write (neither WRITE_ACK nor RECEIVE_ACK expected)?
 554  * Is it also still "PENDING"?
 555  * --> If so, clear PENDING and set NET_OK below.
 556  * If it is a protocol A write, but not RQ_PENDING anymore, neg-ack was faster
 557  * (and we must not set RQ_NET_OK) */
 558 static inline bool is_pending_write_protocol_A(struct drbd_request *req)
 559 {
 560         return (req->rq_state &
 561                    (RQ_WRITE|RQ_NET_PENDING|RQ_EXP_WRITE_ACK|RQ_EXP_RECEIVE_ACK))
 562                 == (RQ_WRITE|RQ_NET_PENDING);
 563 }
 564
 565 /* obviously this could be coded as many single functions
 566  * instead of one huge switch,
 567  * or by putting the code directly in the respective locations
 568  * (as it has been before).
 569  *
 570  * but having it this way
 571  *  enforces that it is all in this one place, where it is easier to audit,
 572  *  it makes it obvious that whatever "event" "happens" to a request should
 573  *  happen "atomically" within the req_lock,
 574  *  and it enforces that we have to think in a very structured manner
 575  *  about the "events" that may happen to a request during its life time ...
 576  */
 577 int __req_mod(struct drbd_request *req, enum drbd_req_event what,
 578                 struct bio_and_error *m)
 579 {
 580         struct drbd_device *const device = req->device;
 581         struct drbd_peer_device *const peer_device = first_peer_device(device);
 582         struct drbd_connection *const connection = peer_device ? peer_device->connection : NULL;
 583         struct net_conf *nc;
 584         int p, rv = 0;
 585
 586         if (m)
 587                 m->bio = NULL;
 588
 589         switch (what) {
 590         default:
 591                 drbd_err(device, "LOGIC BUG in %s:%u\n", __FILE__ , __LINE__);
 592                 break;
 593
 594         /* does not happen...
 595          * initialization done in drbd_req_new
 596         case CREATED:
 597                 break;
 598                 */
 599
 600         case TO_BE_SENT: /* via network */
 601                 /* reached via __drbd_make_request
 602                  * and from w_read_retry_remote */
 603                 D_ASSERT(device, !(req->rq_state & RQ_NET_MASK));
 604                 rcu_read_lock();
 605                 nc = rcu_dereference(connection->net_conf);
 606                 p = nc->wire_protocol;
 607                 rcu_read_unlock();
 608                 req->rq_state |=
 609                         p == DRBD_PROT_C ? RQ_EXP_WRITE_ACK :
 610                         p == DRBD_PROT_B ? RQ_EXP_RECEIVE_ACK : 0;
 611                 mod_rq_state(req, m, 0, RQ_NET_PENDING);
 612                 break;
 613
 614         case TO_BE_SUBMITTED: /* locally */
 615                 /* reached via __drbd_make_request */
 616                 D_ASSERT(device, !(req->rq_state & RQ_LOCAL_MASK));
 617                 mod_rq_state(req, m, 0, RQ_LOCAL_PENDING);
 618                 break;
 619
 620         case COMPLETED_OK:
 621                 if (req->rq_state & RQ_WRITE)
 622                         device->writ_cnt += req->i.size >> 9;
 623                 else
 624                         device->read_cnt += req->i.size >> 9;
 625
 626                 mod_rq_state(req, m, RQ_LOCAL_PENDING,
 627                                 RQ_LOCAL_COMPLETED|RQ_LOCAL_OK);
 628                 break;
 629
 630         case ABORT_DISK_IO:
 631                 mod_rq_state(req, m, 0, RQ_LOCAL_ABORTED);
 632                 break;
 633
 634         case WRITE_COMPLETED_WITH_ERROR:
 635                 drbd_report_io_error(device, req);
 636                 __drbd_chk_io_error(device, DRBD_WRITE_ERROR);
 637                 mod_rq_state(req, m, RQ_LOCAL_PENDING, RQ_LOCAL_COMPLETED);
 638                 break;
 639
 640         case READ_COMPLETED_WITH_ERROR:
 641                 drbd_set_out_of_sync(device, req->i.sector, req->i.size);
 642                 drbd_report_io_error(device, req);
 643                 __drbd_chk_io_error(device, DRBD_READ_ERROR);
 644                 /* fall through. */
 645         case READ_AHEAD_COMPLETED_WITH_ERROR:
 646                 /* it is legal to fail read-ahead, no __drbd_chk_io_error in that case. */
 647                 mod_rq_state(req, m, RQ_LOCAL_PENDING, RQ_LOCAL_COMPLETED);
 648                 break;
 649
 650         case DISCARD_COMPLETED_NOTSUPP:
 651         case DISCARD_COMPLETED_WITH_ERROR:
 652                 /* I'd rather not detach from local disk just because it
 653                  * failed a REQ_OP_DISCARD. */
 654                 mod_rq_state(req, m, RQ_LOCAL_PENDING, RQ_LOCAL_COMPLETED);
 655                 break;
 656
 657         case QUEUE_FOR_NET_READ:
 658                 /* READ, and
 659                  * no local disk,
 660                  * or target area marked as invalid,
 661                  * or just got an io-error. */
 662                 /* from __drbd_make_request
 663                  * or from bio_endio during read io-error recovery */
 664
 665                 /* So we can verify the handle in the answer packet.
 666                  * Corresponding drbd_remove_request_interval is in
 667                  * drbd_req_complete() */
 668                 D_ASSERT(device, drbd_interval_empty(&req->i));
 669                 drbd_insert_interval(&device->read_requests, &req->i);
 670
 671                 set_bit(UNPLUG_REMOTE, &device->flags);
 672
 673                 D_ASSERT(device, req->rq_state & RQ_NET_PENDING);
 674                 D_ASSERT(device, (req->rq_state & RQ_LOCAL_MASK) == 0);
 675                 mod_rq_state(req, m, 0, RQ_NET_QUEUED);
 676                 req->w.cb = w_send_read_req;
 677                 drbd_queue_work(&connection->sender_work,
 678                                 &req->w);
 679                 break;
 680
 681         case QUEUE_FOR_NET_WRITE:
 682                 /* assert something? */
 683                 /* from __drbd_make_request only */
 684
 685                 /* Corresponding drbd_remove_request_interval is in
 686                  * drbd_req_complete() */
 687                 D_ASSERT(device, drbd_interval_empty(&req->i));
 688                 drbd_insert_interval(&device->write_requests, &req->i);
 689
 690                 /* NOTE
 691                  * In case the req ended up on the transfer log before being
 692                  * queued on the worker, it could lead to this request being
 693                  * missed during cleanup after connection loss.
 694                  * So we have to do both operations here,
 695                  * within the same lock that protects the transfer log.
 696                  *
 697                  * _req_add_to_epoch(req); this has to be after the
 698                  * _maybe_start_new_epoch(req); which happened in
 699                  * __drbd_make_request, because we now may set the bit
 700                  * again ourselves to close the current epoch.
 701                  *
 702                  * Add req to the (now) current epoch (barrier). */
 703
 704                 /* otherwise we may lose an unplug, which may cause some remote
 705                  * io-scheduler timeout to expire, increasing maximum latency,
 706                  * hurting performance. */
 707                 set_bit(UNPLUG_REMOTE, &device->flags);
 708
 709                 /* queue work item to send data */
 710                 D_ASSERT(device, req->rq_state & RQ_NET_PENDING);
 711                 mod_rq_state(req, m, 0, RQ_NET_QUEUED|RQ_EXP_BARR_ACK);
 712                 req->w.cb =  w_send_dblock;
 713                 drbd_queue_work(&connection->sender_work,
 714                                 &req->w);
 715
 716                 /* close the epoch, in case it outgrew the limit */
 717                 rcu_read_lock();
 718                 nc = rcu_dereference(connection->net_conf);
 719                 p = nc->max_epoch_size;
 720                 rcu_read_unlock();
 721                 if (connection->current_tle_writes >= p)
 722                         start_new_tl_epoch(connection);
 723
 724                 break;
 725
 726         case QUEUE_FOR_SEND_OOS:
 727                 mod_rq_state(req, m, 0, RQ_NET_QUEUED);
 728                 req->w.cb =  w_send_out_of_sync;
 729                 drbd_queue_work(&connection->sender_work,
 730                                 &req->w);
 731                 break;
 732
 733         case READ_RETRY_REMOTE_CANCELED:
 734         case SEND_CANCELED:
 735         case SEND_FAILED:
 736                 /* real cleanup will be done from tl_clear.  just update flags
 737                  * so it is no longer marked as on the worker queue */
 738                 mod_rq_state(req, m, RQ_NET_QUEUED, 0);
 739                 break;
 740
 741         case HANDED_OVER_TO_NETWORK:
 742                 /* assert something? */
 743                 if (is_pending_write_protocol_A(req))
 744                         /* this is what is dangerous about protocol A:
 745                          * pretend it was successfully written on the peer. */
 746                         mod_rq_state(req, m, RQ_NET_QUEUED|RQ_NET_PENDING,
 747                                                 RQ_NET_SENT|RQ_NET_OK);
 748                 else
 749                         mod_rq_state(req, m, RQ_NET_QUEUED, RQ_NET_SENT);
 750                 /* It is still not yet RQ_NET_DONE until the
 751                  * corresponding epoch barrier got acked as well,
 752                  * so we know what to dirty on connection loss. */
 753                 break;
 754
 755         case OOS_HANDED_TO_NETWORK:
 756                 /* Was not set PENDING, no longer QUEUED, so is now DONE
 757                  * as far as this connection is concerned. */
 758                 mod_rq_state(req, m, RQ_NET_QUEUED, RQ_NET_DONE);
 759                 break;
 760
 761         case CONNECTION_LOST_WHILE_PENDING:
 762                 /* transfer log cleanup after connection loss */
 763                 mod_rq_state(req, m,
 764                                 RQ_NET_OK|RQ_NET_PENDING|RQ_COMPLETION_SUSP,
 765                                 RQ_NET_DONE);
 766                 break;
 767
 768         case CONFLICT_RESOLVED:
 769                 /* for superseded conflicting writes of multiple primaries,
 770                  * there is no need to keep anything in the tl, potential
 771                  * node crashes are covered by the activity log.
 772                  *
 773                  * If this request had been marked as RQ_POSTPONED before,
 774                  * it will actually not be completed, but "restarted",
 775                  * resubmitted from the retry worker context. */
 776                 D_ASSERT(device, req->rq_state & RQ_NET_PENDING);
 777                 D_ASSERT(device, req->rq_state & RQ_EXP_WRITE_ACK);
 778                 mod_rq_state(req, m, RQ_NET_PENDING, RQ_NET_DONE|RQ_NET_OK);
 779                 break;
 780
 781         case WRITE_ACKED_BY_PEER_AND_SIS:
 782                 req->rq_state |= RQ_NET_SIS;
 783         case WRITE_ACKED_BY_PEER:
 784                 /* Normal operation protocol C: successfully written on peer.
 785                  * During resync, even in protocol != C,
 786                  * we requested an explicit write ack anyways.
 787                  * Which means we cannot even assert anything here.
 788                  * Nothing more to do here.
 789                  * We want to keep the tl in place for all protocols, to cater
 790                  * for volatile write-back caches on lower level devices. */
 791                 goto ack_common;
 792         case RECV_ACKED_BY_PEER:
 793                 D_ASSERT(device, req->rq_state & RQ_EXP_RECEIVE_ACK);
 794                 /* protocol B; pretends to be successfully written on peer.
 795                  * see also notes above in HANDED_OVER_TO_NETWORK about
 796                  * protocol != C */
 797         ack_common:
 798                 mod_rq_state(req, m, RQ_NET_PENDING, RQ_NET_OK);
 799                 break;
 800
 801         case POSTPONE_WRITE:
 802                 D_ASSERT(device, req->rq_state & RQ_EXP_WRITE_ACK);
 803                 /* If this node has already detected the write conflict, the
 804                  * worker will be waiting on misc_wait.  Wake it up once this
 805                  * request has completed locally.
 806                  */
 807                 D_ASSERT(device, req->rq_state & RQ_NET_PENDING);
 808                 req->rq_state |= RQ_POSTPONED;
 809                 if (req->i.waiting)
 810                         wake_up(&device->misc_wait);
 811                 /* Do not clear RQ_NET_PENDING. This request will make further
 812                  * progress via restart_conflicting_writes() or
 813                  * fail_postponed_requests(). Hopefully. */
 814                 break;
 815
 816         case NEG_ACKED:
 817                 mod_rq_state(req, m, RQ_NET_OK|RQ_NET_PENDING, 0);
 818                 break;
 819
 820         case FAIL_FROZEN_DISK_IO:
 821                 if (!(req->rq_state & RQ_LOCAL_COMPLETED))
 822                         break;
 823                 mod_rq_state(req, m, RQ_COMPLETION_SUSP, 0);
 824                 break;
 825
 826         case RESTART_FROZEN_DISK_IO:
 827                 if (!(req->rq_state & RQ_LOCAL_COMPLETED))
 828                         break;
 829
 830                 mod_rq_state(req, m,
 831                                 RQ_COMPLETION_SUSP|RQ_LOCAL_COMPLETED,
 832                                 RQ_LOCAL_PENDING);
 833
 834                 rv = MR_READ;
 835                 if (bio_data_dir(req->master_bio) == WRITE)
 836                         rv = MR_WRITE;
 837
 838                 get_ldev(device); /* always succeeds in this call path */
 839                 req->w.cb = w_restart_disk_io;
 840                 drbd_queue_work(&connection->sender_work,
 841                                 &req->w);
 842                 break;
 843
 844         case RESEND:
 845                 /* Simply complete (local only) READs. */
 846                 if (!(req->rq_state & RQ_WRITE) && !req->w.cb) {
 847                         mod_rq_state(req, m, RQ_COMPLETION_SUSP, 0);
 848                         break;
 849                 }
 850
 851                 /* If RQ_NET_OK is already set, we got a P_WRITE_ACK or P_RECV_ACK
 852                    before the connection loss (B&C only); only P_BARRIER_ACK
 853                    (or the local completion?) was missing when we suspended.
 854                    Throwing them out of the TL here by pretending we got a BARRIER_ACK.
 855                    During connection handshake, we ensure that the peer was not rebooted. */
 856                 if (!(req->rq_state & RQ_NET_OK)) {
 857                         /* FIXME could this possibly be a req->dw.cb == w_send_out_of_sync?
 858                          * in that case we must not set RQ_NET_PENDING. */
 859
 860                         mod_rq_state(req, m, RQ_COMPLETION_SUSP, RQ_NET_QUEUED|RQ_NET_PENDING);
 861                         if (req->w.cb) {
 862                                 /* w.cb expected to be w_send_dblock, or w_send_read_req */
 863                                 drbd_queue_work(&connection->sender_work,
 864                                                 &req->w);
 865                                 rv = req->rq_state & RQ_WRITE ? MR_WRITE : MR_READ;
 866                         } /* else: FIXME can this happen? */
 867                         break;
 868                 }
 869                 /* else, fall through to BARRIER_ACKED */
 870
 871         case BARRIER_ACKED:
 872                 /* barrier ack for READ requests does not make sense */
 873                 if (!(req->rq_state & RQ_WRITE))
 874                         break;
 875
 876                 if (req->rq_state & RQ_NET_PENDING) {
 877                         /* barrier came in before all requests were acked.
 878                          * this is bad, because if the connection is lost now,
 879                          * we won't be able to clean them up... */
 880                         drbd_err(device, "FIXME (BARRIER_ACKED but pending)\n");
 881                 }
 882                 /* Allowed to complete requests, even while suspended.
 883                  * As this is called for all requests within a matching epoch,
 884                  * we need to filter, and only set RQ_NET_DONE for those that
 885                  * have actually been on the wire. */
 886                 mod_rq_state(req, m, RQ_COMPLETION_SUSP,
 887                                 (req->rq_state & RQ_NET_MASK) ? RQ_NET_DONE : 0);
 888                 break;
 889
 890         case DATA_RECEIVED:
 891                 D_ASSERT(device, req->rq_state & RQ_NET_PENDING);
 892                 mod_rq_state(req, m, RQ_NET_PENDING, RQ_NET_OK|RQ_NET_DONE);
 893                 break;
 894
 895         case QUEUE_AS_DRBD_BARRIER:
 896                 start_new_tl_epoch(connection);
 897                 mod_rq_state(req, m, 0, RQ_NET_OK|RQ_NET_DONE);
 898                 break;
 899         };
 900
 901         return rv;
 902 }
 903
 904 /* we may do a local read if:
 905  * - we are consistent (of course),
 906  * - or we are generally inconsistent,
 907  *   BUT we are still/already IN SYNC for this area.
 908  *   since size may be bigger than BM_BLOCK_SIZE,
 909  *   we may need to check several bits.
 910  */
 911 static bool drbd_may_do_local_read(struct drbd_device *device, sector_t sector, int size)
 912 {
 913         unsigned long sbnr, ebnr;
 914         sector_t esector, nr_sectors;
 915
 916         if (device->state.disk == D_UP_TO_DATE)
 917                 return true;
 918         if (device->state.disk != D_INCONSISTENT)
 919                 return false;
 920         esector = sector + (size >> 9) - 1;
 921         nr_sectors = drbd_get_capacity(device->this_bdev);
 922         D_ASSERT(device, sector  < nr_sectors);
 923         D_ASSERT(device, esector < nr_sectors);
 924
 925         sbnr = BM_SECT_TO_BIT(sector);
 926         ebnr = BM_SECT_TO_BIT(esector);
 927
 928         return drbd_bm_count_bits(device, sbnr, ebnr) == 0;
 929 }
 930
 931 static bool remote_due_to_read_balancing(struct drbd_device *device, sector_t sector,
 932                 enum drbd_read_balancing rbm)
 933 {
 934         struct backing_dev_info *bdi;
 935         int stripe_shift;
 936
 937         switch (rbm) {
 938         case RB_CONGESTED_REMOTE:
 939                 bdi = device->ldev->backing_bdev->bd_disk->queue->backing_dev_info;
 940                 return bdi_read_congested(bdi);
 941         case RB_LEAST_PENDING:
 942                 return atomic_read(&device->local_cnt) >
 943                         atomic_read(&device->ap_pending_cnt) + atomic_read(&device->rs_pending_cnt);
 944         case RB_32K_STRIPING:  /* stripe_shift = 15 */
 945         case RB_64K_STRIPING:
 946         case RB_128K_STRIPING:
 947         case RB_256K_STRIPING:
 948         case RB_512K_STRIPING:
 949         case RB_1M_STRIPING:   /* stripe_shift = 20 */
 950                 stripe_shift = (rbm - RB_32K_STRIPING + 15);
 951                 return (sector >> (stripe_shift - 9)) & 1;
 952         case RB_ROUND_ROBIN:
 953                 return test_and_change_bit(READ_BALANCE_RR, &device->flags);
 954         case RB_PREFER_REMOTE:
 955                 return true;
 956         case RB_PREFER_LOCAL:
 957         default:
 958                 return false;
 959         }
 960 }
 961
 962 /*
 963  * complete_conflicting_writes  -  wait for any conflicting write requests
 964  *
 965  * The write_requests tree contains all active write requests which we
 966  * currently know about.  Wait for any requests to complete which conflict with
 967  * the new one.
 968  *
 969  * Only way out: remove the conflicting intervals from the tree.
 970  */
 971 static void complete_conflicting_writes(struct drbd_request *req)
 972 {
 973         DEFINE_WAIT(wait);
 974         struct drbd_device *device = req->device;
 975         struct drbd_interval *i;
 976         sector_t sector = req->i.sector;
 977         int size = req->i.size;
 978
 979         for (;;) {
 980                 drbd_for_each_overlap(i, &device->write_requests, sector, size) {
 981                         /* Ignore, if already completed to upper layers. */
 982                         if (i->completed)
 983                                 continue;
 984                         /* Handle the first found overlap.  After the schedule
 985                          * we have to restart the tree walk. */
 986                         break;
 987                 }
 988                 if (!i) /* if any */
 989                         break;
 990
 991                 /* Indicate to wake up device->misc_wait on progress.  */
 992                 prepare_to_wait(&device->misc_wait, &wait, TASK_UNINTERRUPTIBLE);
 993                 i->waiting = true;
 994                 spin_unlock_irq(&device->resource->req_lock);
 995                 schedule();
 996                 spin_lock_irq(&device->resource->req_lock);
 997         }
 998         finish_wait(&device->misc_wait, &wait);
 999 }
1000
1001 /* called within req_lock */
1002 static void maybe_pull_ahead(struct drbd_device *device)
1003 {
1004         struct drbd_connection *connection = first_peer_device(device)->connection;
1005         struct net_conf *nc;
1006         bool congested = false;
1007         enum drbd_on_congestion on_congestion;
1008
1009         rcu_read_lock();
1010         nc = rcu_dereference(connection->net_conf);
1011         on_congestion = nc ? nc->on_congestion : OC_BLOCK;
1012         rcu_read_unlock();
1013         if (on_congestion == OC_BLOCK ||
1014             connection->agreed_pro_version < 96)
1015                 return;
1016
1017         if (on_congestion == OC_PULL_AHEAD && device->state.conn == C_AHEAD)
1018                 return; /* nothing to do ... */
1019
1020         /* If I don't even have good local storage, we can not reasonably try
1021          * to pull ahead of the peer. We also need the local reference to make
1022          * sure device->act_log is there.
1023          */
1024         if (!get_ldev_if_state(device, D_UP_TO_DATE))
1025                 return;
1026
1027         if (nc->cong_fill &&
1028             atomic_read(&device->ap_in_flight) >= nc->cong_fill) {
1029                 drbd_info(device, "Congestion-fill threshold reached\n");
1030                 congested = true;
1031         }
1032
1033         if (device->act_log->used >= nc->cong_extents) {
1034                 drbd_info(device, "Congestion-extents threshold reached\n");
1035                 congested = true;
1036         }
1037
1038         if (congested) {
1039                 /* start a new epoch for non-mirrored writes */
1040                 start_new_tl_epoch(first_peer_device(device)->connection);
1041
1042                 if (on_congestion == OC_PULL_AHEAD)
1043                         _drbd_set_state(_NS(device, conn, C_AHEAD), 0, NULL);
1044                 else  /*nc->on_congestion == OC_DISCONNECT */
1045                         _drbd_set_state(_NS(device, conn, C_DISCONNECTING), 0, NULL);
1046         }
1047         put_ldev(device);
1048 }
1049
1050 /* If this returns false, and req->private_bio is still set,
1051  * this should be submitted locally.
1052  *
1053  * If it returns false, but req->private_bio is not set,
1054  * we do not have access to good data :(
1055  *
1056  * Otherwise, this destroys req->private_bio, if any,
1057  * and returns true.
1058  */
1059 static bool do_remote_read(struct drbd_request *req)
1060 {
1061         struct drbd_device *device = req->device;
1062         enum drbd_read_balancing rbm;
1063
1064         if (req->private_bio) {
1065                 if (!drbd_may_do_local_read(device,
1066                                         req->i.sector, req->i.size)) {
1067                         bio_put(req->private_bio);
1068                         req->private_bio = NULL;
1069                         put_ldev(device);
1070                 }
1071         }
1072
1073         if (device->state.pdsk != D_UP_TO_DATE)
1074                 return false;
1075
1076         if (req->private_bio == NULL)
1077                 return true;
1078
1079         /* TODO: improve read balancing decisions, take into account drbd
1080          * protocol, pending requests etc. */
1081
1082         rcu_read_lock();
1083         rbm = rcu_dereference(device->ldev->disk_conf)->read_balancing;
1084         rcu_read_unlock();
1085
1086         if (rbm == RB_PREFER_LOCAL && req->private_bio)
1087                 return false; /* submit locally */
1088
1089         if (remote_due_to_read_balancing(device, req->i.sector, rbm)) {
1090                 if (req->private_bio) {
1091                         bio_put(req->private_bio);
1092                         req->private_bio = NULL;
1093                         put_ldev(device);
1094                 }
1095                 return true;
1096         }
1097
1098         return false;
1099 }
1100
1101 bool drbd_should_do_remote(union drbd_dev_state s)
1102 {
1103         return s.pdsk == D_UP_TO_DATE ||
1104                 (s.pdsk >= D_INCONSISTENT &&
1105                  s.conn >= C_WF_BITMAP_T &&
1106                  s.conn < C_AHEAD);
1107         /* Before proto 96 that was >= CONNECTED instead of >= C_WF_BITMAP_T.
1108            That is equivalent since before 96 IO was frozen in the C_WF_BITMAP*
1109            states. */
1110 }
1111
1112 static bool drbd_should_send_out_of_sync(union drbd_dev_state s)
1113 {
1114         return s.conn == C_AHEAD || s.conn == C_WF_BITMAP_S;
1115         /* pdsk = D_INCONSISTENT as a consequence. Protocol 96 check not necessary
1116            since we enter state C_AHEAD only if proto >= 96 */
1117 }
1118
1119 /* returns number of connections (== 1, for drbd 8.4)
1120  * expected to actually write this data,
1121  * which does NOT include those that we are L_AHEAD for. */
1122 static int drbd_process_write_request(struct drbd_request *req)
1123 {
1124         struct drbd_device *device = req->device;
1125         int remote, send_oos;
1126
1127         remote = drbd_should_do_remote(device->state);
1128         send_oos = drbd_should_send_out_of_sync(device->state);
1129
1130         /* Need to replicate writes.  Unless it is an empty flush,
1131          * which is better mapped to a DRBD P_BARRIER packet,
1132          * also for drbd wire protocol compatibility reasons.
1133          * If this was a flush, just start a new epoch.
1134          * Unless the current epoch was empty anyways, or we are not currently
1135          * replicating, in which case there is no point. */
1136         if (unlikely(req->i.size == 0)) {
1137                 /* The only size==0 bios we expect are empty flushes. */
1138                 D_ASSERT(device, req->master_bio->bi_opf & REQ_PREFLUSH);
1139                 if (remote)
1140                         _req_mod(req, QUEUE_AS_DRBD_BARRIER);
1141                 return remote;
1142         }
1143
1144         if (!remote && !send_oos)
1145                 return 0;
1146
1147         D_ASSERT(device, !(remote && send_oos));
1148
1149         if (remote) {
1150                 _req_mod(req, TO_BE_SENT);
1151                 _req_mod(req, QUEUE_FOR_NET_WRITE);
1152         } else if (drbd_set_out_of_sync(device, req->i.sector, req->i.size))
1153                 _req_mod(req, QUEUE_FOR_SEND_OOS);
1154
1155         return remote;
1156 }
1157
1158 static void drbd_process_discard_req(struct drbd_request *req)
1159 {
1160         struct block_device *bdev = req->device->ldev->backing_bdev;
1161
1162         if (blkdev_issue_zeroout(bdev, req->i.sector, req->i.size >> 9,
1163                         GFP_NOIO, 0))
1164                 req->private_bio->bi_status = BLK_STS_IOERR;
1165         bio_endio(req->private_bio);
1166 }
1167
1168 static void
1169 drbd_submit_req_private_bio(struct drbd_request *req)
1170 {
1171         struct drbd_device *device = req->device;
1172         struct bio *bio = req->private_bio;
1173         unsigned int type;
1174
1175         if (bio_op(bio) != REQ_OP_READ)
1176                 type = DRBD_FAULT_DT_WR;
1177         else if (bio->bi_opf & REQ_RAHEAD)
1178                 type = DRBD_FAULT_DT_RA;
1179         else
1180                 type = DRBD_FAULT_DT_RD;
1181
1182         bio_set_dev(bio, device->ldev->backing_bdev);
1183
1184         /* State may have changed since we grabbed our reference on the
1185          * ->ldev member. Double check, and short-circuit to endio.
1186          * In case the last activity log transaction failed to get on
1187          * stable storage, and this is a WRITE, we may not even submit
1188          * this bio. */
1189         if (get_ldev(device)) {
1190                 if (drbd_insert_fault(device, type))
1191                         bio_io_error(bio);
1192                 else if (bio_op(bio) == REQ_OP_WRITE_ZEROES ||
1193                          bio_op(bio) == REQ_OP_DISCARD)
1194                         drbd_process_discard_req(req);
1195                 else
1196                         generic_make_request(bio);
1197                 put_ldev(device);
1198         } else
1199                 bio_io_error(bio);
1200 }
1201
1202 static void drbd_queue_write(struct drbd_device *device, struct drbd_request *req)
1203 {
1204         spin_lock_irq(&device->resource->req_lock);
1205         list_add_tail(&req->tl_requests, &device->submit.writes);
1206         list_add_tail(&req->req_pending_master_completion,
1207                         &device->pending_master_completion[1 /* WRITE */]);
1208         spin_unlock_irq(&device->resource->req_lock);
1209         queue_work(device->submit.wq, &device->submit.worker);
1210         /* do_submit() may sleep internally on al_wait, too */
1211         wake_up(&device->al_wait);
1212 }
1213
1214 /* returns the new drbd_request pointer, if the caller is expected to
1215  * drbd_send_and_submit() it (to save latency), or NULL if we queued the
1216  * request on the submitter thread.
1217  * Returns ERR_PTR(-ENOMEM) if we cannot allocate a drbd_request.
1218  */
1219 static struct drbd_request *
1220 drbd_request_prepare(struct drbd_device *device, struct bio *bio, unsigned long start_jif)
1221 {
1222         const int rw = bio_data_dir(bio);
1223         struct drbd_request *req;
1224
1225         /* allocate outside of all locks; */
1226         req = drbd_req_new(device, bio);
1227         if (!req) {
1228                 dec_ap_bio(device);
1229                 /* only pass the error to the upper layers.
1230                  * if user cannot handle io errors, that's not our business. */
1231                 drbd_err(device, "could not kmalloc() req\n");
1232                 bio->bi_status = BLK_STS_RESOURCE;
1233                 bio_endio(bio);
1234                 return ERR_PTR(-ENOMEM);
1235         }
1236         req->start_jif = start_jif;
1237
1238         if (!get_ldev(device)) {
1239                 bio_put(req->private_bio);
1240                 req->private_bio = NULL;
1241         }
1242
1243         /* Update disk stats */
1244         _drbd_start_io_acct(device, req);
1245
1246         /* process discards always from our submitter thread */
1247         if (bio_op(bio) == REQ_OP_WRITE_ZEROES ||
1248             bio_op(bio) == REQ_OP_DISCARD)
1249                 goto queue_for_submitter_thread;
1250
1251         if (rw == WRITE && req->private_bio && req->i.size
1252         && !test_bit(AL_SUSPENDED, &device->flags)) {
1253                 if (!drbd_al_begin_io_fastpath(device, &req->i))
1254                         goto queue_for_submitter_thread;
1255                 req->rq_state |= RQ_IN_ACT_LOG;
1256                 req->in_actlog_jif = jiffies;
1257         }
1258         return req;
1259
1260  queue_for_submitter_thread:
1261         atomic_inc(&device->ap_actlog_cnt);
1262         drbd_queue_write(device, req);
1263         return NULL;
1264 }
1265
1266 /* Require at least one path to current data.
1267  * We don't want to allow writes on C_STANDALONE D_INCONSISTENT:
1268  * We would not allow to read what was written,
1269  * we would not have bumped the data generation uuids,
1270  * we would cause data divergence for all the wrong reasons.
1271  *
1272  * If we don't see at least one D_UP_TO_DATE, we will fail this request,
1273  * which either returns EIO, or, if OND_SUSPEND_IO is set, suspends IO,
1274  * and queues for retry later.
1275  */
1276 static bool may_do_writes(struct drbd_device *device)
1277 {
1278         const union drbd_dev_state s = device->state;
1279         return s.disk == D_UP_TO_DATE || s.pdsk == D_UP_TO_DATE;
1280 }
1281
1282 struct drbd_plug_cb {
1283         struct blk_plug_cb cb;
1284         struct drbd_request *most_recent_req;
1285         /* do we need more? */
1286 };
1287
1288 static void drbd_unplug(struct blk_plug_cb *cb, bool from_schedule)
1289 {
1290         struct drbd_plug_cb *plug = container_of(cb, struct drbd_plug_cb, cb);
1291         struct drbd_resource *resource = plug->cb.data;
1292         struct drbd_request *req = plug->most_recent_req;
1293
1294         kfree(cb);
1295         if (!req)
1296                 return;
1297
1298         spin_lock_irq(&resource->req_lock);
1299         /* In case the sender did not process it yet, raise the flag to
1300          * have it followed with P_UNPLUG_REMOTE just after. */
1301         req->rq_state |= RQ_UNPLUG;
1302         /* but also queue a generic unplug */
1303         drbd_queue_unplug(req->device);
1304         kref_put(&req->kref, drbd_req_destroy);
1305         spin_unlock_irq(&resource->req_lock);
1306 }
1307
1308 static struct drbd_plug_cb* drbd_check_plugged(struct drbd_resource *resource)
1309 {
1310         /* A lot of text to say
1311          * return (struct drbd_plug_cb*)blk_check_plugged(); */
1312         struct drbd_plug_cb *plug;
1313         struct blk_plug_cb *cb = blk_check_plugged(drbd_unplug, resource, sizeof(*plug));
1314
1315         if (cb)
1316                 plug = container_of(cb, struct drbd_plug_cb, cb);
1317         else
1318                 plug = NULL;
1319         return plug;
1320 }
1321
1322 static void drbd_update_plug(struct drbd_plug_cb *plug, struct drbd_request *req)
1323 {
1324         struct drbd_request *tmp = plug->most_recent_req;
1325         /* Will be sent to some peer.
1326          * Remember to tag it with UNPLUG_REMOTE on unplug */
1327         kref_get(&req->kref);
1328         plug->most_recent_req = req;
1329         if (tmp)
1330                 kref_put(&tmp->kref, drbd_req_destroy);
1331 }
1332
1333 static void drbd_send_and_submit(struct drbd_device *device, struct drbd_request *req)
1334 {
1335         struct drbd_resource *resource = device->resource;
1336         const int rw = bio_data_dir(req->master_bio);
1337         struct bio_and_error m = { NULL, };
1338         bool no_remote = false;
1339         bool submit_private_bio = false;
1340
1341         spin_lock_irq(&resource->req_lock);
1342         if (rw == WRITE) {
1343                 /* This may temporarily give up the req_lock,
1344                  * but will re-aquire it before it returns here.
1345                  * Needs to be before the check on drbd_suspended() */
1346                 complete_conflicting_writes(req);
1347                 /* no more giving up req_lock from now on! */
1348
1349                 /* check for congestion, and potentially stop sending
1350                  * full data updates, but start sending "dirty bits" only. */
1351                 maybe_pull_ahead(device);
1352         }
1353
1354
1355         if (drbd_suspended(device)) {
1356                 /* push back and retry: */
1357                 req->rq_state |= RQ_POSTPONED;
1358                 if (req->private_bio) {
1359                         bio_put(req->private_bio);
1360                         req->private_bio = NULL;
1361                         put_ldev(device);
1362                 }
1363                 goto out;
1364         }
1365
1366         /* We fail READ early, if we can not serve it.
1367          * We must do this before req is registered on any lists.
1368          * Otherwise, drbd_req_complete() will queue failed READ for retry. */
1369         if (rw != WRITE) {
1370                 if (!do_remote_read(req) && !req->private_bio)
1371                         goto nodata;
1372         }
1373
1374         /* which transfer log epoch does this belong to? */
1375         req->epoch = atomic_read(&first_peer_device(device)->connection->current_tle_nr);
1376
1377         /* no point in adding empty flushes to the transfer log,
1378          * they are mapped to drbd barriers already. */
1379         if (likely(req->i.size!=0)) {
1380                 if (rw == WRITE)
1381                         first_peer_device(device)->connection->current_tle_writes++;
1382
1383                 list_add_tail(&req->tl_requests, &first_peer_device(device)->connection->transfer_log);
1384         }
1385
1386         if (rw == WRITE) {
1387                 if (req->private_bio && !may_do_writes(device)) {
1388                         bio_put(req->private_bio);
1389                         req->private_bio = NULL;
1390                         put_ldev(device);
1391                         goto nodata;
1392                 }
1393                 if (!drbd_process_write_request(req))
1394                         no_remote = true;
1395         } else {
1396                 /* We either have a private_bio, or we can read from remote.
1397                  * Otherwise we had done the goto nodata above. */
1398                 if (req->private_bio == NULL) {
1399                         _req_mod(req, TO_BE_SENT);
1400                         _req_mod(req, QUEUE_FOR_NET_READ);
1401                 } else
1402                         no_remote = true;
1403         }
1404
1405         if (no_remote == false) {
1406                 struct drbd_plug_cb *plug = drbd_check_plugged(resource);
1407                 if (plug)
1408                         drbd_update_plug(plug, req);
1409         }
1410
1411         /* If it took the fast path in drbd_request_prepare, add it here.
1412          * The slow path has added it already. */
1413         if (list_empty(&req->req_pending_master_completion))
1414                 list_add_tail(&req->req_pending_master_completion,
1415                         &device->pending_master_completion[rw == WRITE]);
1416         if (req->private_bio) {
1417                 /* needs to be marked within the same spinlock */
1418                 req->pre_submit_jif = jiffies;
1419                 list_add_tail(&req->req_pending_local,
1420                         &device->pending_completion[rw == WRITE]);
1421                 _req_mod(req, TO_BE_SUBMITTED);
1422                 /* but we need to give up the spinlock to submit */
1423                 submit_private_bio = true;
1424         } else if (no_remote) {
1425 nodata:
1426                 if (__ratelimit(&drbd_ratelimit_state))
1427                         drbd_err(device, "IO ERROR: neither local nor remote data, sector %llu+%u\n",
1428                                         (unsigned long long)req->i.sector, req->i.size >> 9);
1429                 /* A write may have been queued for send_oos, however.
1430                  * So we can not simply free it, we must go through drbd_req_put_completion_ref() */
1431         }
1432
1433 out:
1434         drbd_req_put_completion_ref(req, &m, 1);
1435         spin_unlock_irq(&resource->req_lock);
1436
1437         /* Even though above is a kref_put(), this is safe.
1438          * As long as we still need to submit our private bio,
1439          * we hold a completion ref, and the request cannot disappear.
1440          * If however this request did not even have a private bio to submit
1441          * (e.g. remote read), req may already be invalid now.
1442          * That's why we cannot check on req->private_bio. */
1443         if (submit_private_bio)
1444                 drbd_submit_req_private_bio(req);
1445         if (m.bio)
1446                 complete_master_bio(device, &m);
1447 }
1448
1449 void __drbd_make_request(struct drbd_device *device, struct bio *bio, unsigned long start_jif)
1450 {
1451         struct drbd_request *req = drbd_request_prepare(device, bio, start_jif);
1452         if (IS_ERR_OR_NULL(req))
1453                 return;
1454         drbd_send_and_submit(device, req);
1455 }
1456
1457 static void submit_fast_path(struct drbd_device *device, struct list_head *incoming)
1458 {
1459         struct blk_plug plug;
1460         struct drbd_request *req, *tmp;
1461
1462         blk_start_plug(&plug);
1463         list_for_each_entry_safe(req, tmp, incoming, tl_requests) {
1464                 const int rw = bio_data_dir(req->master_bio);
1465
1466                 if (rw == WRITE /* rw != WRITE should not even end up here! */
1467                 && req->private_bio && req->i.size
1468                 && !test_bit(AL_SUSPENDED, &device->flags)) {
1469                         if (!drbd_al_begin_io_fastpath(device, &req->i))
1470                                 continue;
1471
1472                         req->rq_state |= RQ_IN_ACT_LOG;
1473                         req->in_actlog_jif = jiffies;
1474                         atomic_dec(&device->ap_actlog_cnt);
1475                 }
1476
1477                 list_del_init(&req->tl_requests);
1478                 drbd_send_and_submit(device, req);
1479         }
1480         blk_finish_plug(&plug);
1481 }
1482
1483 static bool prepare_al_transaction_nonblock(struct drbd_device *device,
1484                                             struct list_head *incoming,
1485                                             struct list_head *pending,
1486                                             struct list_head *later)
1487 {
1488         struct drbd_request *req;
1489         int wake = 0;
1490         int err;
1491
1492         spin_lock_irq(&device->al_lock);
1493         while ((req = list_first_entry_or_null(incoming, struct drbd_request, tl_requests))) {
1494                 err = drbd_al_begin_io_nonblock(device, &req->i);
1495                 if (err == -ENOBUFS)
1496                         break;
1497                 if (err == -EBUSY)
1498                         wake = 1;
1499                 if (err)
1500                         list_move_tail(&req->tl_requests, later);
1501                 else
1502                         list_move_tail(&req->tl_requests, pending);
1503         }
1504         spin_unlock_irq(&device->al_lock);
1505         if (wake)
1506                 wake_up(&device->al_wait);
1507         return !list_empty(pending);
1508 }
1509
1510 static void send_and_submit_pending(struct drbd_device *device, struct list_head *pending)
1511 {
1512         struct blk_plug plug;
1513         struct drbd_request *req;
1514
1515         blk_start_plug(&plug);
1516         while ((req = list_first_entry_or_null(pending, struct drbd_request, tl_requests))) {
1517                 req->rq_state |= RQ_IN_ACT_LOG;
1518                 req->in_actlog_jif = jiffies;
1519                 atomic_dec(&device->ap_actlog_cnt);
1520                 list_del_init(&req->tl_requests);
1521                 drbd_send_and_submit(device, req);
1522         }
1523         blk_finish_plug(&plug);
1524 }
1525
1526 void do_submit(struct work_struct *ws)
1527 {
1528         struct drbd_device *device = container_of(ws, struct drbd_device, submit.worker);
1529         LIST_HEAD(incoming);    /* from drbd_make_request() */
1530         LIST_HEAD(pending);     /* to be submitted after next AL-transaction commit */
1531         LIST_HEAD(busy);        /* blocked by resync requests */
1532
1533         /* grab new incoming requests */
1534         spin_lock_irq(&device->resource->req_lock);
1535         list_splice_tail_init(&device->submit.writes, &incoming);
1536         spin_unlock_irq(&device->resource->req_lock);
1537
1538         for (;;) {
1539                 DEFINE_WAIT(wait);
1540
1541                 /* move used-to-be-busy back to front of incoming */
1542                 list_splice_init(&busy, &incoming);
1543                 submit_fast_path(device, &incoming);
1544                 if (list_empty(&incoming))
1545                         break;
1546
1547                 for (;;) {
1548                         prepare_to_wait(&device->al_wait, &wait, TASK_UNINTERRUPTIBLE);
1549
1550                         list_splice_init(&busy, &incoming);
1551                         prepare_al_transaction_nonblock(device, &incoming, &pending, &busy);
1552                         if (!list_empty(&pending))
1553                                 break;
1554
1555                         schedule();
1556
1557                         /* If all currently "hot" activity log extents are kept busy by
1558                          * incoming requests, we still must not totally starve new
1559                          * requests to "cold" extents.
1560                          * Something left on &incoming means there had not been
1561                          * enough update slots available, and the activity log
1562                          * has been marked as "starving".
1563                          *
1564                          * Try again now, without looking for new requests,
1565                          * effectively blocking all new requests until we made
1566                          * at least _some_ progress with what we currently have.
1567                          */
1568                         if (!list_empty(&incoming))
1569                                 continue;
1570
1571                         /* Nothing moved to pending, but nothing left
1572                          * on incoming: all moved to busy!
1573                          * Grab new and iterate. */
1574                         spin_lock_irq(&device->resource->req_lock);
1575                         list_splice_tail_init(&device->submit.writes, &incoming);
1576                         spin_unlock_irq(&device->resource->req_lock);
1577                 }
1578                 finish_wait(&device->al_wait, &wait);
1579
1580                 /* If the transaction was full, before all incoming requests
1581                  * had been processed, skip ahead to commit, and iterate
1582                  * without splicing in more incoming requests from upper layers.
1583                  *
1584                  * Else, if all incoming have been processed,
1585                  * they have become either "pending" (to be submitted after
1586                  * next transaction commit) or "busy" (blocked by resync).
1587                  *
1588                  * Maybe more was queued, while we prepared the transaction?
1589                  * Try to stuff those into this transaction as well.
1590                  * Be strictly non-blocking here,
1591                  * we already have something to commit.
1592                  *
1593                  * Commit if we don't make any more progres.
1594                  */
1595
1596                 while (list_empty(&incoming)) {
1597                         LIST_HEAD(more_pending);
1598                         LIST_HEAD(more_incoming);
1599                         bool made_progress;
1600
1601                         /* It is ok to look outside the lock,
1602                          * it's only an optimization anyways */
1603                         if (list_empty(&device->submit.writes))
1604                                 break;
1605
1606                         spin_lock_irq(&device->resource->req_lock);
1607                         list_splice_tail_init(&device->submit.writes, &more_incoming);
1608                         spin_unlock_irq(&device->resource->req_lock);
1609
1610                         if (list_empty(&more_incoming))
1611                                 break;
1612
1613                         made_progress = prepare_al_transaction_nonblock(device, &more_incoming, &more_pending, &busy);
1614
1615                         list_splice_tail_init(&more_pending, &pending);
1616                         list_splice_tail_init(&more_incoming, &incoming);
1617                         if (!made_progress)
1618                                 break;
1619                 }
1620
1621                 drbd_al_begin_io_commit(device);
1622                 send_and_submit_pending(device, &pending);
1623         }
1624 }
1625
1626 blk_qc_t drbd_make_request(struct request_queue *q, struct bio *bio)
1627 {
1628         struct drbd_device *device = (struct drbd_device *) q->queuedata;
1629         unsigned long start_jif;
1630
1631         blk_queue_split(q, &bio);
1632
1633         start_jif = jiffies;
1634
1635         /*
1636          * what we "blindly" assume:
1637          */
1638         D_ASSERT(device, IS_ALIGNED(bio->bi_iter.bi_size, 512));
1639
1640         inc_ap_bio(device);
1641         __drbd_make_request(device, bio, start_jif);
1642         return BLK_QC_T_NONE;
1643 }
1644
1645 static bool net_timeout_reached(struct drbd_request *net_req,
1646                 struct drbd_connection *connection,
1647                 unsigned long now, unsigned long ent,
1648                 unsigned int ko_count, unsigned int timeout)
1649 {
1650         struct drbd_device *device = net_req->device;
1651
1652         if (!time_after(now, net_req->pre_send_jif + ent))
1653                 return false;
1654
1655         if (time_in_range(now, connection->last_reconnect_jif, connection->last_reconnect_jif + ent))
1656                 return false;
1657
1658         if (net_req->rq_state & RQ_NET_PENDING) {
1659                 drbd_warn(device, "Remote failed to finish a request within %ums > ko-count (%u) * timeout (%u * 0.1s)\n",
1660                         jiffies_to_msecs(now - net_req->pre_send_jif), ko_count, timeout);
1661                 return true;
1662         }
1663
1664         /* We received an ACK already (or are using protocol A),
1665          * but are waiting for the epoch closing barrier ack.
1666          * Check if we sent the barrier already.  We should not blame the peer
1667          * for being unresponsive, if we did not even ask it yet. */
1668         if (net_req->epoch == connection->send.current_epoch_nr) {
1669                 drbd_warn(device,
1670                         "We did not send a P_BARRIER for %ums > ko-count (%u) * timeout (%u * 0.1s); drbd kernel thread blocked?\n",
1671                         jiffies_to_msecs(now - net_req->pre_send_jif), ko_count, timeout);
1672                 return false;
1673         }
1674
1675         /* Worst case: we may have been blocked for whatever reason, then
1676          * suddenly are able to send a lot of requests (and epoch separating
1677          * barriers) in quick succession.
1678          * The timestamp of the net_req may be much too old and not correspond
1679          * to the sending time of the relevant unack'ed barrier packet, so
1680          * would trigger a spurious timeout.  The latest barrier packet may
1681          * have a too recent timestamp to trigger the timeout, potentially miss
1682          * a timeout.  Right now we don't have a place to conveniently store
1683          * these timestamps.
1684          * But in this particular situation, the application requests are still
1685          * completed to upper layers, DRBD should still "feel" responsive.
1686          * No need yet to kill this connection, it may still recover.
1687          * If not, eventually we will have queued enough into the network for
1688          * us to block. From that point of view, the timestamp of the last sent
1689          * barrier packet is relevant enough.
1690          */
1691         if (time_after(now, connection->send.last_sent_barrier_jif + ent)) {
1692                 drbd_warn(device, "Remote failed to answer a P_BARRIER (sent at %lu jif; now=%lu jif) within %ums > ko-count (%u) * timeout (%u * 0.1s)\n",
1693                         connection->send.last_sent_barrier_jif, now,
1694                         jiffies_to_msecs(now - connection->send.last_sent_barrier_jif), ko_count, timeout);
1695                 return true;
1696         }
1697         return false;
1698 }
1699
1700 /* A request is considered timed out, if
1701  * - we have some effective timeout from the configuration,
1702  *   with some state restrictions applied,
1703  * - the oldest request is waiting for a response from the network
1704  *   resp. the local disk,
1705  * - the oldest request is in fact older than the effective timeout,
1706  * - the connection was established (resp. disk was attached)
1707  *   for longer than the timeout already.
1708  * Note that for 32bit jiffies and very stable connections/disks,
1709  * we may have a wrap around, which is catched by
1710  *   !time_in_range(now, last_..._jif, last_..._jif + timeout).
1711  *
1712  * Side effect: once per 32bit wrap-around interval, which means every
1713  * ~198 days with 250 HZ, we have a window where the timeout would need
1714  * to expire twice (worst case) to become effective. Good enough.
1715  */
1716
1717 void request_timer_fn(struct timer_list *t)
1718 {
1719         struct drbd_device *device = from_timer(device, t, request_timer);
1720         struct drbd_connection *connection = first_peer_device(device)->connection;
1721         struct drbd_request *req_read, *req_write, *req_peer; /* oldest request */
1722         struct net_conf *nc;
1723         unsigned long oldest_submit_jif;
1724         unsigned long ent = 0, dt = 0, et, nt; /* effective timeout = ko_count * timeout */
1725         unsigned long now;
1726         unsigned int ko_count = 0, timeout = 0;
1727
1728         rcu_read_lock();
1729         nc = rcu_dereference(connection->net_conf);
1730         if (nc && device->state.conn >= C_WF_REPORT_PARAMS) {
1731                 ko_count = nc->ko_count;
1732                 timeout = nc->timeout;
1733         }
1734
1735         if (get_ldev(device)) { /* implicit state.disk >= D_INCONSISTENT */
1736                 dt = rcu_dereference(device->ldev->disk_conf)->disk_timeout * HZ / 10;
1737                 put_ldev(device);
1738         }
1739         rcu_read_unlock();
1740
1741
1742         ent = timeout * HZ/10 * ko_count;
1743         et = min_not_zero(dt, ent);
1744
1745         if (!et)
1746                 return; /* Recurring timer stopped */
1747
1748         now = jiffies;
1749         nt = now + et;
1750
1751         spin_lock_irq(&device->resource->req_lock);
1752         req_read = list_first_entry_or_null(&device->pending_completion[0], struct drbd_request, req_pending_local);
1753         req_write = list_first_entry_or_null(&device->pending_completion[1], struct drbd_request, req_pending_local);
1754
1755         /* maybe the oldest request waiting for the peer is in fact still
1756          * blocking in tcp sendmsg.  That's ok, though, that's handled via the
1757          * socket send timeout, requesting a ping, and bumping ko-count in
1758          * we_should_drop_the_connection().
1759          */
1760
1761         /* check the oldest request we did successfully sent,
1762          * but which is still waiting for an ACK. */
1763         req_peer = connection->req_ack_pending;
1764
1765         /* if we don't have such request (e.g. protocoll A)
1766          * check the oldest requests which is still waiting on its epoch
1767          * closing barrier ack. */
1768         if (!req_peer)
1769                 req_peer = connection->req_not_net_done;
1770
1771         /* evaluate the oldest peer request only in one timer! */
1772         if (req_peer && req_peer->device != device)
1773                 req_peer = NULL;
1774
1775         /* do we have something to evaluate? */
1776         if (req_peer == NULL && req_write == NULL && req_read == NULL)
1777                 goto out;
1778
1779         oldest_submit_jif =
1780                 (req_write && req_read)
1781                 ? ( time_before(req_write->pre_submit_jif, req_read->pre_submit_jif)
1782                   ? req_write->pre_submit_jif : req_read->pre_submit_jif )
1783                 : req_write ? req_write->pre_submit_jif
1784                 : req_read ? req_read->pre_submit_jif : now;
1785
1786         if (ent && req_peer && net_timeout_reached(req_peer, connection, now, ent, ko_count, timeout))
1787                 _conn_request_state(connection, NS(conn, C_TIMEOUT), CS_VERBOSE | CS_HARD);
1788
1789         if (dt && oldest_submit_jif != now &&
1790                  time_after(now, oldest_submit_jif + dt) &&
1791                 !time_in_range(now, device->last_reattach_jif, device->last_reattach_jif + dt)) {
1792                 drbd_warn(device, "Local backing device failed to meet the disk-timeout\n");
1793                 __drbd_chk_io_error(device, DRBD_FORCE_DETACH);
1794         }
1795
1796         /* Reschedule timer for the nearest not already expired timeout.
1797          * Fallback to now + min(effective network timeout, disk timeout). */
1798         ent = (ent && req_peer && time_before(now, req_peer->pre_send_jif + ent))
1799                 ? req_peer->pre_send_jif + ent : now + et;
1800         dt = (dt && oldest_submit_jif != now && time_before(now, oldest_submit_jif + dt))
1801                 ? oldest_submit_jif + dt : now + et;
1802         nt = time_before(ent, dt) ? ent : dt;
1803 out:
1804         spin_unlock_irq(&device->resource->req_lock);
1805         mod_timer(&device->request_timer, nt);
1806 }