OSCL-LXR linux-6.0.1/​drivers/​block/​drbd/​drbd_req.c	Source navigation Diff markup Identifier search General search
	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
    drbd_req.c
 
    This file is part of DRBD by Philipp Reisner and Lars Ellenberg.
 
    Copyright (C) 2001-2008, LINBIT Information Technologies GmbH.
    Copyright (C) 1999-2008, Philipp Reisner <philipp.reisner@linbit.com>.
    Copyright (C) 2002-2008, Lars Ellenberg <lars.ellenberg@linbit.com>.
 
 
  */
 
 #include <linux/module.h>
 
 #include <linux/slab.h>
 #include <linux/drbd.h>
 #include "drbd_int.h"
 #include "drbd_req.h"
 
 
 static bool drbd_may_do_local_read(struct drbd_device *device, sector_t sector, int size);
 
 static struct drbd_request *drbd_req_new(struct drbd_device *device, struct bio *bio_src)
 {
     struct drbd_request *req;
 
     req = mempool_alloc(&drbd_request_mempool, GFP_NOIO);
     if (!req)
         return NULL;
     memset(req, 0, sizeof(*req));
 
     req->private_bio = bio_alloc_clone(device->ldev->backing_bdev, bio_src,
                        GFP_NOIO, &drbd_io_bio_set);
     req->private_bio->bi_private = req;
     req->private_bio->bi_end_io = drbd_request_endio;
 
     req->rq_state = (bio_data_dir(bio_src) == WRITE ? RQ_WRITE : 0)
               | (bio_op(bio_src) == REQ_OP_WRITE_ZEROES ? RQ_ZEROES : 0)
               | (bio_op(bio_src) == REQ_OP_DISCARD ? RQ_UNMAP : 0);
     req->device = device;
     req->master_bio = bio_src;
     req->epoch = 0;
 
     drbd_clear_interval(&req->i);
     req->i.sector     = bio_src->bi_iter.bi_sector;
     req->i.size      = bio_src->bi_iter.bi_size;
     req->i.local = true;
     req->i.waiting = false;
 
     INIT_LIST_HEAD(&req->tl_requests);
     INIT_LIST_HEAD(&req->w.list);
     INIT_LIST_HEAD(&req->req_pending_master_completion);
     INIT_LIST_HEAD(&req->req_pending_local);
 
     /* one reference to be put by __drbd_make_request */
     atomic_set(&req->completion_ref, 1);
     /* one kref as long as completion_ref > 0 */
     kref_init(&req->kref);
     return req;
 }
 
 static void drbd_remove_request_interval(struct rb_root *root,
                      struct drbd_request *req)
 {
     struct drbd_device *device = req->device;
     struct drbd_interval *i = &req->i;
 
     drbd_remove_interval(root, i);
 
     /* Wake up any processes waiting for this request to complete.  */
     if (i->waiting)
         wake_up(&device->misc_wait);
 }
 
 void drbd_req_destroy(struct kref *kref)
 {
     struct drbd_request *req = container_of(kref, struct drbd_request, kref);
     struct drbd_device *device = req->device;
     const unsigned s = req->rq_state;
 
     if ((req->master_bio && !(s & RQ_POSTPONED)) ||
         atomic_read(&req->completion_ref) ||
         (s & RQ_LOCAL_PENDING) ||
         ((s & RQ_NET_MASK) && !(s & RQ_NET_DONE))) {
         drbd_err(device, "drbd_req_destroy: Logic BUG rq_state = 0x%x, completion_ref = %d\n",
                 s, atomic_read(&req->completion_ref));
         return;
     }
 
     /* If called from mod_rq_state (expected normal case) or
      * drbd_send_and_submit (the less likely normal path), this holds the
      * req_lock, and req->tl_requests will typicaly be on ->transfer_log,
      * though it may be still empty (never added to the transfer log).
      *
      * If called from do_retry(), we do NOT hold the req_lock, but we are
      * still allowed to unconditionally list_del(&req->tl_requests),
      * because it will be on a local on-stack list only. */
     list_del_init(&req->tl_requests);
 
     /* finally remove the request from the conflict detection
      * respective block_id verification interval tree. */
     if (!drbd_interval_empty(&req->i)) {
         struct rb_root *root;
 
         if (s & RQ_WRITE)
             root = &device->write_requests;
         else
             root = &device->read_requests;
         drbd_remove_request_interval(root, req);
     } else if (s & (RQ_NET_MASK & ~RQ_NET_DONE) && req->i.size != 0)
         drbd_err(device, "drbd_req_destroy: Logic BUG: interval empty, but: rq_state=0x%x, sect=%llu, size=%u\n",
             s, (unsigned long long)req->i.sector, req->i.size);
 
     /* if it was a write, we may have to set the corresponding
      * bit(s) out-of-sync first. If it had a local part, we need to
      * release the reference to the activity log. */
     if (s & RQ_WRITE) {
         /* Set out-of-sync unless both OK flags are set
          * (local only or remote failed).
          * Other places where we set out-of-sync:
          * READ with local io-error */
 
         /* There is a special case:
          * we may notice late that IO was suspended,
          * and postpone, or schedule for retry, a write,
          * before it even was submitted or sent.
          * In that case we do not want to touch the bitmap at all.
          */
         if ((s & (RQ_POSTPONED|RQ_LOCAL_MASK|RQ_NET_MASK)) != RQ_POSTPONED) {
             if (!(s & RQ_NET_OK) || !(s & RQ_LOCAL_OK))
                 drbd_set_out_of_sync(device, req->i.sector, req->i.size);
 
             if ((s & RQ_NET_OK) && (s & RQ_LOCAL_OK) && (s & RQ_NET_SIS))
                 drbd_set_in_sync(device, req->i.sector, req->i.size);
         }
 
         /* one might be tempted to move the drbd_al_complete_io
          * to the local io completion callback drbd_request_endio.
          * but, if this was a mirror write, we may only
          * drbd_al_complete_io after this is RQ_NET_DONE,
          * otherwise the extent could be dropped from the al
          * before it has actually been written on the peer.
          * if we crash before our peer knows about the request,
          * but after the extent has been dropped from the al,
          * we would forget to resync the corresponding extent.
          */
         if (s & RQ_IN_ACT_LOG) {
             if (get_ldev_if_state(device, D_FAILED)) {
                 drbd_al_complete_io(device, &req->i);
                 put_ldev(device);
             } else if (__ratelimit(&drbd_ratelimit_state)) {
                 drbd_warn(device, "Should have called drbd_al_complete_io(, %llu, %u), "
                      "but my Disk seems to have failed :(\n",
                      (unsigned long long) req->i.sector, req->i.size);
             }
         }
     }
 
     mempool_free(req, &drbd_request_mempool);
 }
 
 static void wake_all_senders(struct drbd_connection *connection)
 {
     wake_up(&connection->sender_work.q_wait);
 }
 
 /* must hold resource->req_lock */
 void start_new_tl_epoch(struct drbd_connection *connection)
 {
     /* no point closing an epoch, if it is empty, anyways. */
     if (connection->current_tle_writes == 0)
         return;
 
     connection->current_tle_writes = 0;
     atomic_inc(&connection->current_tle_nr);
     wake_all_senders(connection);
 }
 
 void complete_master_bio(struct drbd_device *device,
         struct bio_and_error *m)
 {
     if (unlikely(m->error))
         m->bio->bi_status = errno_to_blk_status(m->error);
     bio_endio(m->bio);
     dec_ap_bio(device);
 }
 
 
 /* Helper for __req_mod().
  * Set m->bio to the master bio, if it is fit to be completed,
  * or leave it alone (it is initialized to NULL in __req_mod),
  * if it has already been completed, or cannot be completed yet.
  * If m->bio is set, the error status to be returned is placed in m->error.
  */
 static
 void drbd_req_complete(struct drbd_request *req, struct bio_and_error *m)
 {
     const unsigned s = req->rq_state;
     struct drbd_device *device = req->device;
     int error, ok;
 
     /* we must not complete the master bio, while it is
      *  still being processed by _drbd_send_zc_bio (drbd_send_dblock)
      *  not yet acknowledged by the peer
      *  not yet completed by the local io subsystem
      * these flags may get cleared in any order by
      *  the worker,
      *  the receiver,
      *  the bio_endio completion callbacks.
      */
     if ((s & RQ_LOCAL_PENDING && !(s & RQ_LOCAL_ABORTED)) ||
         (s & RQ_NET_QUEUED) || (s & RQ_NET_PENDING) ||
         (s & RQ_COMPLETION_SUSP)) {
         drbd_err(device, "drbd_req_complete: Logic BUG rq_state = 0x%x\n", s);
         return;
     }
 
     if (!req->master_bio) {
         drbd_err(device, "drbd_req_complete: Logic BUG, master_bio == NULL!\n");
         return;
     }
 
     /*
      * figure out whether to report success or failure.
      *
      * report success when at least one of the operations succeeded.
      * or, to put the other way,
      * only report failure, when both operations failed.
      *
      * what to do about the failures is handled elsewhere.
      * what we need to do here is just: complete the master_bio.
      *
      * local completion error, if any, has been stored as ERR_PTR
      * in private_bio within drbd_request_endio.
      */
     ok = (s & RQ_LOCAL_OK) || (s & RQ_NET_OK);
     error = PTR_ERR(req->private_bio);
 
     /* Before we can signal completion to the upper layers,
      * we may need to close the current transfer log epoch.
      * We are within the request lock, so we can simply compare
      * the request epoch number with the current transfer log
      * epoch number.  If they match, increase the current_tle_nr,
      * and reset the transfer log epoch write_cnt.
      */
     if (op_is_write(bio_op(req->master_bio)) &&
         req->epoch == atomic_read(&first_peer_device(device)->connection->current_tle_nr))
         start_new_tl_epoch(first_peer_device(device)->connection);
 
     /* Update disk stats */
     bio_end_io_acct(req->master_bio, req->start_jif);
 
     /* If READ failed,
      * have it be pushed back to the retry work queue,
      * so it will re-enter __drbd_make_request(),
      * and be re-assigned to a suitable local or remote path,
      * or failed if we do not have access to good data anymore.
      *
      * Unless it was failed early by __drbd_make_request(),
      * because no path was available, in which case
      * it was not even added to the transfer_log.
      *
      * read-ahead may fail, and will not be retried.
      *
      * WRITE should have used all available paths already.
      */
     if (!ok &&
         bio_op(req->master_bio) == REQ_OP_READ &&
         !(req->master_bio->bi_opf & REQ_RAHEAD) &&
         !list_empty(&req->tl_requests))
         req->rq_state |= RQ_POSTPONED;
 
     if (!(req->rq_state & RQ_POSTPONED)) {
         m->error = ok ? 0 : (error ?: -EIO);
         m->bio = req->master_bio;
         req->master_bio = NULL;
         /* We leave it in the tree, to be able to verify later
          * write-acks in protocol != C during resync.
          * But we mark it as "complete", so it won't be counted as
          * conflict in a multi-primary setup. */
         req->i.completed = true;
     }
 
     if (req->i.waiting)
         wake_up(&device->misc_wait);
 
     /* Either we are about to complete to upper layers,
      * or we will restart this request.
      * In either case, the request object will be destroyed soon,
      * so better remove it from all lists. */
     list_del_init(&req->req_pending_master_completion);
 }
 
 /* still holds resource->req_lock */
 static void drbd_req_put_completion_ref(struct drbd_request *req, struct bio_and_error *m, int put)
 {
     struct drbd_device *device = req->device;
     D_ASSERT(device, m || (req->rq_state & RQ_POSTPONED));
 
     if (!put)
         return;
 
     if (!atomic_sub_and_test(put, &req->completion_ref))
         return;
 
     drbd_req_complete(req, m);
 
     /* local completion may still come in later,
      * we need to keep the req object around. */
     if (req->rq_state & RQ_LOCAL_ABORTED)
         return;
 
     if (req->rq_state & RQ_POSTPONED) {
         /* don't destroy the req object just yet,
          * but queue it for retry */
         drbd_restart_request(req);
         return;
     }
 
     kref_put(&req->kref, drbd_req_destroy);
 }
 
 static void set_if_null_req_next(struct drbd_peer_device *peer_device, struct drbd_request *req)
 {
     struct drbd_connection *connection = peer_device ? peer_device->connection : NULL;
     if (!connection)
         return;
     if (connection->req_next == NULL)
         connection->req_next = req;
 }
 
 static void advance_conn_req_next(struct drbd_peer_device *peer_device, struct drbd_request *req)
 {
     struct drbd_connection *connection = peer_device ? peer_device->connection : NULL;
     struct drbd_request *iter = req;
     if (!connection)
         return;
     if (connection->req_next != req)
         return;
 
     req = NULL;
     list_for_each_entry_continue(iter, &connection->transfer_log, tl_requests) {
         const unsigned int s = iter->rq_state;
 
         if (s & RQ_NET_QUEUED) {
             req = iter;
             break;
         }
     }
     connection->req_next = req;
 }
 
 static void set_if_null_req_ack_pending(struct drbd_peer_device *peer_device, struct drbd_request *req)
 {
     struct drbd_connection *connection = peer_device ? peer_device->connection : NULL;
     if (!connection)
         return;
     if (connection->req_ack_pending == NULL)
         connection->req_ack_pending = req;
 }
 
 static void advance_conn_req_ack_pending(struct drbd_peer_device *peer_device, struct drbd_request *req)
 {
     struct drbd_connection *connection = peer_device ? peer_device->connection : NULL;
     struct drbd_request *iter = req;
     if (!connection)
         return;
     if (connection->req_ack_pending != req)
         return;
 
     req = NULL;
     list_for_each_entry_continue(iter, &connection->transfer_log, tl_requests) {
         const unsigned int s = iter->rq_state;
 
         if ((s & RQ_NET_SENT) && (s & RQ_NET_PENDING)) {
             req = iter;
             break;
         }
     }
     connection->req_ack_pending = req;
 }
 
 static void set_if_null_req_not_net_done(struct drbd_peer_device *peer_device, struct drbd_request *req)
 {
     struct drbd_connection *connection = peer_device ? peer_device->connection : NULL;
     if (!connection)
         return;
     if (connection->req_not_net_done == NULL)
         connection->req_not_net_done = req;
 }
 
 static void advance_conn_req_not_net_done(struct drbd_peer_device *peer_device, struct drbd_request *req)
 {
     struct drbd_connection *connection = peer_device ? peer_device->connection : NULL;
     struct drbd_request *iter = req;
     if (!connection)
         return;
     if (connection->req_not_net_done != req)
         return;
 
     req = NULL;
     list_for_each_entry_continue(iter, &connection->transfer_log, tl_requests) {
         const unsigned int s = iter->rq_state;
 
         if ((s & RQ_NET_SENT) && !(s & RQ_NET_DONE)) {
             req = iter;
             break;
         }
     }
     connection->req_not_net_done = req;
 }
 
 /* I'd like this to be the only place that manipulates
  * req->completion_ref and req->kref. */
 static void mod_rq_state(struct drbd_request *req, struct bio_and_error *m,
         int clear, int set)
 {
     struct drbd_device *device = req->device;
     struct drbd_peer_device *peer_device = first_peer_device(device);
     unsigned s = req->rq_state;
     int c_put = 0;
 
     if (drbd_suspended(device) && !((s | clear) & RQ_COMPLETION_SUSP))
         set |= RQ_COMPLETION_SUSP;
 
     /* apply */
 
     req->rq_state &= ~clear;
     req->rq_state |= set;
 
     /* no change? */
     if (req->rq_state == s)
         return;
 
     /* intent: get references */
 
     kref_get(&req->kref);
 
     if (!(s & RQ_LOCAL_PENDING) && (set & RQ_LOCAL_PENDING))
         atomic_inc(&req->completion_ref);
 
     if (!(s & RQ_NET_PENDING) && (set & RQ_NET_PENDING)) {
         inc_ap_pending(device);
         atomic_inc(&req->completion_ref);
     }
 
     if (!(s & RQ_NET_QUEUED) && (set & RQ_NET_QUEUED)) {
         atomic_inc(&req->completion_ref);
         set_if_null_req_next(peer_device, req);
     }
 
     if (!(s & RQ_EXP_BARR_ACK) && (set & RQ_EXP_BARR_ACK))
         kref_get(&req->kref); /* wait for the DONE */
 
     if (!(s & RQ_NET_SENT) && (set & RQ_NET_SENT)) {
         /* potentially already completed in the ack_receiver thread */
         if (!(s & RQ_NET_DONE)) {
             atomic_add(req->i.size >> 9, &device->ap_in_flight);
             set_if_null_req_not_net_done(peer_device, req);
         }
         if (req->rq_state & RQ_NET_PENDING)
             set_if_null_req_ack_pending(peer_device, req);
     }
 
     if (!(s & RQ_COMPLETION_SUSP) && (set & RQ_COMPLETION_SUSP))
         atomic_inc(&req->completion_ref);
 
     /* progress: put references */
 
     if ((s & RQ_COMPLETION_SUSP) && (clear & RQ_COMPLETION_SUSP))
         ++c_put;
 
     if (!(s & RQ_LOCAL_ABORTED) && (set & RQ_LOCAL_ABORTED)) {
         D_ASSERT(device, req->rq_state & RQ_LOCAL_PENDING);
         ++c_put;
     }
 
     if ((s & RQ_LOCAL_PENDING) && (clear & RQ_LOCAL_PENDING)) {
         if (req->rq_state & RQ_LOCAL_ABORTED)
             kref_put(&req->kref, drbd_req_destroy);
         else
             ++c_put;
         list_del_init(&req->req_pending_local);
     }
 
     if ((s & RQ_NET_PENDING) && (clear & RQ_NET_PENDING)) {
         dec_ap_pending(device);
         ++c_put;
         req->acked_jif = jiffies;
         advance_conn_req_ack_pending(peer_device, req);
     }
 
     if ((s & RQ_NET_QUEUED) && (clear & RQ_NET_QUEUED)) {
         ++c_put;
         advance_conn_req_next(peer_device, req);
     }
 
     if (!(s & RQ_NET_DONE) && (set & RQ_NET_DONE)) {
         if (s & RQ_NET_SENT)
             atomic_sub(req->i.size >> 9, &device->ap_in_flight);
         if (s & RQ_EXP_BARR_ACK)
             kref_put(&req->kref, drbd_req_destroy);
         req->net_done_jif = jiffies;
 
         /* in ahead/behind mode, or just in case,
          * before we finally destroy this request,
          * the caching pointers must not reference it anymore */
         advance_conn_req_next(peer_device, req);
         advance_conn_req_ack_pending(peer_device, req);
         advance_conn_req_not_net_done(peer_device, req);
     }
 
     /* potentially complete and destroy */
 
     /* If we made progress, retry conflicting peer requests, if any. */
     if (req->i.waiting)
         wake_up(&device->misc_wait);
 
     drbd_req_put_completion_ref(req, m, c_put);
     kref_put(&req->kref, drbd_req_destroy);
 }
 
 static void drbd_report_io_error(struct drbd_device *device, struct drbd_request *req)
 {
     if (!__ratelimit(&drbd_ratelimit_state))
         return;
 
     drbd_warn(device, "local %s IO error sector %llu+%u on %pg\n",
             (req->rq_state & RQ_WRITE) ? "WRITE" : "READ",
             (unsigned long long)req->i.sector,
             req->i.size >> 9,
             device->ldev->backing_bdev);
 }
 
 /* Helper for HANDED_OVER_TO_NETWORK.
  * Is this a protocol A write (neither WRITE_ACK nor RECEIVE_ACK expected)?
  * Is it also still "PENDING"?
  * --> If so, clear PENDING and set NET_OK below.
  * If it is a protocol A write, but not RQ_PENDING anymore, neg-ack was faster
  * (and we must not set RQ_NET_OK) */
 static inline bool is_pending_write_protocol_A(struct drbd_request *req)
 {
     return (req->rq_state &
            (RQ_WRITE|RQ_NET_PENDING|RQ_EXP_WRITE_ACK|RQ_EXP_RECEIVE_ACK))
         == (RQ_WRITE|RQ_NET_PENDING);
 }
 
 /* obviously this could be coded as many single functions
  * instead of one huge switch,
  * or by putting the code directly in the respective locations
  * (as it has been before).
  *
  * but having it this way
  *  enforces that it is all in this one place, where it is easier to audit,
  *  it makes it obvious that whatever "event" "happens" to a request should
  *  happen "atomically" within the req_lock,
  *  and it enforces that we have to think in a very structured manner
  *  about the "events" that may happen to a request during its life time ...
  */
 int __req_mod(struct drbd_request *req, enum drbd_req_event what,
         struct bio_and_error *m)
 {
     struct drbd_device *const device = req->device;
     struct drbd_peer_device *const peer_device = first_peer_device(device);
     struct drbd_connection *const connection = peer_device ? peer_device->connection : NULL;
     struct net_conf *nc;
     int p, rv = 0;
 
     if (m)
         m->bio = NULL;
 
     switch (what) {
     default:
         drbd_err(device, "LOGIC BUG in %s:%u\n", __FILE__ , __LINE__);
         break;
 
     /* does not happen...
      * initialization done in drbd_req_new
     case CREATED:
         break;
         */
 
     case TO_BE_SENT: /* via network */
         /* reached via __drbd_make_request
          * and from w_read_retry_remote */
         D_ASSERT(device, !(req->rq_state & RQ_NET_MASK));
         rcu_read_lock();
         nc = rcu_dereference(connection->net_conf);
         p = nc->wire_protocol;
         rcu_read_unlock();
         req->rq_state |=
             p == DRBD_PROT_C ? RQ_EXP_WRITE_ACK :
             p == DRBD_PROT_B ? RQ_EXP_RECEIVE_ACK : 0;
         mod_rq_state(req, m, 0, RQ_NET_PENDING);
         break;
 
     case TO_BE_SUBMITTED: /* locally */
         /* reached via __drbd_make_request */
         D_ASSERT(device, !(req->rq_state & RQ_LOCAL_MASK));
         mod_rq_state(req, m, 0, RQ_LOCAL_PENDING);
         break;
 
     case COMPLETED_OK:
         if (req->rq_state & RQ_WRITE)
             device->writ_cnt += req->i.size >> 9;
         else
             device->read_cnt += req->i.size >> 9;
 
         mod_rq_state(req, m, RQ_LOCAL_PENDING,
                 RQ_LOCAL_COMPLETED|RQ_LOCAL_OK);
         break;
 
     case ABORT_DISK_IO:
         mod_rq_state(req, m, 0, RQ_LOCAL_ABORTED);
         break;
 
     case WRITE_COMPLETED_WITH_ERROR:
         drbd_report_io_error(device, req);
         __drbd_chk_io_error(device, DRBD_WRITE_ERROR);
         mod_rq_state(req, m, RQ_LOCAL_PENDING, RQ_LOCAL_COMPLETED);
         break;
 
     case READ_COMPLETED_WITH_ERROR:
         drbd_set_out_of_sync(device, req->i.sector, req->i.size);
         drbd_report_io_error(device, req);
         __drbd_chk_io_error(device, DRBD_READ_ERROR);
         fallthrough;
     case READ_AHEAD_COMPLETED_WITH_ERROR:
         /* it is legal to fail read-ahead, no __drbd_chk_io_error in that case. */
         mod_rq_state(req, m, RQ_LOCAL_PENDING, RQ_LOCAL_COMPLETED);
         break;
 
     case DISCARD_COMPLETED_NOTSUPP:
     case DISCARD_COMPLETED_WITH_ERROR:
         /* I'd rather not detach from local disk just because it
          * failed a REQ_OP_DISCARD. */
         mod_rq_state(req, m, RQ_LOCAL_PENDING, RQ_LOCAL_COMPLETED);
         break;
 
     case QUEUE_FOR_NET_READ:
         /* READ, and
          * no local disk,
          * or target area marked as invalid,
          * or just got an io-error. */
         /* from __drbd_make_request
          * or from bio_endio during read io-error recovery */
 
         /* So we can verify the handle in the answer packet.
          * Corresponding drbd_remove_request_interval is in
          * drbd_req_complete() */
         D_ASSERT(device, drbd_interval_empty(&req->i));
         drbd_insert_interval(&device->read_requests, &req->i);
 
         set_bit(UNPLUG_REMOTE, &device->flags);
 
         D_ASSERT(device, req->rq_state & RQ_NET_PENDING);
         D_ASSERT(device, (req->rq_state & RQ_LOCAL_MASK) == 0);
         mod_rq_state(req, m, 0, RQ_NET_QUEUED);
         req->w.cb = w_send_read_req;
         drbd_queue_work(&connection->sender_work,
                 &req->w);
         break;
 
     case QUEUE_FOR_NET_WRITE:
         /* assert something? */
         /* from __drbd_make_request only */
 
         /* Corresponding drbd_remove_request_interval is in
          * drbd_req_complete() */
         D_ASSERT(device, drbd_interval_empty(&req->i));
         drbd_insert_interval(&device->write_requests, &req->i);
 
         /* NOTE
          * In case the req ended up on the transfer log before being
          * queued on the worker, it could lead to this request being
          * missed during cleanup after connection loss.
          * So we have to do both operations here,
          * within the same lock that protects the transfer log.
          *
          * _req_add_to_epoch(req); this has to be after the
          * _maybe_start_new_epoch(req); which happened in
          * __drbd_make_request, because we now may set the bit
          * again ourselves to close the current epoch.
          *
          * Add req to the (now) current epoch (barrier). */
 
         /* otherwise we may lose an unplug, which may cause some remote
          * io-scheduler timeout to expire, increasing maximum latency,
          * hurting performance. */
         set_bit(UNPLUG_REMOTE, &device->flags);
 
         /* queue work item to send data */
         D_ASSERT(device, req->rq_state & RQ_NET_PENDING);
         mod_rq_state(req, m, 0, RQ_NET_QUEUED|RQ_EXP_BARR_ACK);
         req->w.cb =  w_send_dblock;
         drbd_queue_work(&connection->sender_work,
                 &req->w);
 
         /* close the epoch, in case it outgrew the limit */
         rcu_read_lock();
         nc = rcu_dereference(connection->net_conf);
         p = nc->max_epoch_size;
         rcu_read_unlock();
         if (connection->current_tle_writes >= p)
             start_new_tl_epoch(connection);
 
         break;
 
     case QUEUE_FOR_SEND_OOS:
         mod_rq_state(req, m, 0, RQ_NET_QUEUED);
         req->w.cb =  w_send_out_of_sync;
         drbd_queue_work(&connection->sender_work,
                 &req->w);
         break;
 
     case READ_RETRY_REMOTE_CANCELED:
     case SEND_CANCELED:
     case SEND_FAILED:
         /* real cleanup will be done from tl_clear.  just update flags
          * so it is no longer marked as on the worker queue */
         mod_rq_state(req, m, RQ_NET_QUEUED, 0);
         break;
 
     case HANDED_OVER_TO_NETWORK:
         /* assert something? */
         if (is_pending_write_protocol_A(req))
             /* this is what is dangerous about protocol A:
              * pretend it was successfully written on the peer. */
             mod_rq_state(req, m, RQ_NET_QUEUED|RQ_NET_PENDING,
                         RQ_NET_SENT|RQ_NET_OK);
         else
             mod_rq_state(req, m, RQ_NET_QUEUED, RQ_NET_SENT);
         /* It is still not yet RQ_NET_DONE until the
          * corresponding epoch barrier got acked as well,
          * so we know what to dirty on connection loss. */
         break;
 
     case OOS_HANDED_TO_NETWORK:
         /* Was not set PENDING, no longer QUEUED, so is now DONE
          * as far as this connection is concerned. */
         mod_rq_state(req, m, RQ_NET_QUEUED, RQ_NET_DONE);
         break;
 
     case CONNECTION_LOST_WHILE_PENDING:
         /* transfer log cleanup after connection loss */
         mod_rq_state(req, m,
                 RQ_NET_OK|RQ_NET_PENDING|RQ_COMPLETION_SUSP,
                 RQ_NET_DONE);
         break;
 
     case CONFLICT_RESOLVED:
         /* for superseded conflicting writes of multiple primaries,
          * there is no need to keep anything in the tl, potential
          * node crashes are covered by the activity log.
          *
          * If this request had been marked as RQ_POSTPONED before,
          * it will actually not be completed, but "restarted",
          * resubmitted from the retry worker context. */
         D_ASSERT(device, req->rq_state & RQ_NET_PENDING);
         D_ASSERT(device, req->rq_state & RQ_EXP_WRITE_ACK);
         mod_rq_state(req, m, RQ_NET_PENDING, RQ_NET_DONE|RQ_NET_OK);
         break;
 
     case WRITE_ACKED_BY_PEER_AND_SIS:
         req->rq_state |= RQ_NET_SIS;
         fallthrough;
     case WRITE_ACKED_BY_PEER:
         /* Normal operation protocol C: successfully written on peer.
          * During resync, even in protocol != C,
          * we requested an explicit write ack anyways.
          * Which means we cannot even assert anything here.
          * Nothing more to do here.
          * We want to keep the tl in place for all protocols, to cater
          * for volatile write-back caches on lower level devices. */
         goto ack_common;
     case RECV_ACKED_BY_PEER:
         D_ASSERT(device, req->rq_state & RQ_EXP_RECEIVE_ACK);
         /* protocol B; pretends to be successfully written on peer.
          * see also notes above in HANDED_OVER_TO_NETWORK about
          * protocol != C */
     ack_common:
         mod_rq_state(req, m, RQ_NET_PENDING, RQ_NET_OK);
         break;
 
     case POSTPONE_WRITE:
         D_ASSERT(device, req->rq_state & RQ_EXP_WRITE_ACK);
         /* If this node has already detected the write conflict, the
          * worker will be waiting on misc_wait.  Wake it up once this
          * request has completed locally.
          */
         D_ASSERT(device, req->rq_state & RQ_NET_PENDING);
         req->rq_state |= RQ_POSTPONED;
         if (req->i.waiting)
             wake_up(&device->misc_wait);
         /* Do not clear RQ_NET_PENDING. This request will make further
          * progress via restart_conflicting_writes() or
          * fail_postponed_requests(). Hopefully. */
         break;
 
     case NEG_ACKED:
         mod_rq_state(req, m, RQ_NET_OK|RQ_NET_PENDING, 0);
         break;
 
     case FAIL_FROZEN_DISK_IO:
         if (!(req->rq_state & RQ_LOCAL_COMPLETED))
             break;
         mod_rq_state(req, m, RQ_COMPLETION_SUSP, 0);
         break;
 
     case RESTART_FROZEN_DISK_IO:
         if (!(req->rq_state & RQ_LOCAL_COMPLETED))
             break;
 
         mod_rq_state(req, m,
                 RQ_COMPLETION_SUSP|RQ_LOCAL_COMPLETED,
                 RQ_LOCAL_PENDING);
 
         rv = MR_READ;
         if (bio_data_dir(req->master_bio) == WRITE)
             rv = MR_WRITE;
 
         get_ldev(device); /* always succeeds in this call path */
         req->w.cb = w_restart_disk_io;
         drbd_queue_work(&connection->sender_work,
                 &req->w);
         break;
 
     case RESEND:
         /* Simply complete (local only) READs. */
         if (!(req->rq_state & RQ_WRITE) && !req->w.cb) {
             mod_rq_state(req, m, RQ_COMPLETION_SUSP, 0);
             break;
         }
 
         /* If RQ_NET_OK is already set, we got a P_WRITE_ACK or P_RECV_ACK
            before the connection loss (B&C only); only P_BARRIER_ACK
            (or the local completion?) was missing when we suspended.
            Throwing them out of the TL here by pretending we got a BARRIER_ACK.
            During connection handshake, we ensure that the peer was not rebooted. */
         if (!(req->rq_state & RQ_NET_OK)) {
             /* FIXME could this possibly be a req->dw.cb == w_send_out_of_sync?
              * in that case we must not set RQ_NET_PENDING. */
 
             mod_rq_state(req, m, RQ_COMPLETION_SUSP, RQ_NET_QUEUED|RQ_NET_PENDING);
             if (req->w.cb) {
                 /* w.cb expected to be w_send_dblock, or w_send_read_req */
                 drbd_queue_work(&connection->sender_work,
                         &req->w);
                 rv = req->rq_state & RQ_WRITE ? MR_WRITE : MR_READ;
             } /* else: FIXME can this happen? */
             break;
         }
         fallthrough;    /* to BARRIER_ACKED */
 
     case BARRIER_ACKED:
         /* barrier ack for READ requests does not make sense */
         if (!(req->rq_state & RQ_WRITE))
             break;
 
         if (req->rq_state & RQ_NET_PENDING) {
             /* barrier came in before all requests were acked.
              * this is bad, because if the connection is lost now,
              * we won't be able to clean them up... */
             drbd_err(device, "FIXME (BARRIER_ACKED but pending)\n");
         }
         /* Allowed to complete requests, even while suspended.
          * As this is called for all requests within a matching epoch,
          * we need to filter, and only set RQ_NET_DONE for those that
          * have actually been on the wire. */
         mod_rq_state(req, m, RQ_COMPLETION_SUSP,
                 (req->rq_state & RQ_NET_MASK) ? RQ_NET_DONE : 0);
         break;
 
     case DATA_RECEIVED:
         D_ASSERT(device, req->rq_state & RQ_NET_PENDING);
         mod_rq_state(req, m, RQ_NET_PENDING, RQ_NET_OK|RQ_NET_DONE);
         break;
 
     case QUEUE_AS_DRBD_BARRIER:
         start_new_tl_epoch(connection);
         mod_rq_state(req, m, 0, RQ_NET_OK|RQ_NET_DONE);
         break;
     }
 
     return rv;
 }
 
 /* we may do a local read if:
  * - we are consistent (of course),
  * - or we are generally inconsistent,
  *   BUT we are still/already IN SYNC for this area.
  *   since size may be bigger than BM_BLOCK_SIZE,
  *   we may need to check several bits.
  */
 static bool drbd_may_do_local_read(struct drbd_device *device, sector_t sector, int size)
 {
     unsigned long sbnr, ebnr;
     sector_t esector, nr_sectors;
 
     if (device->state.disk == D_UP_TO_DATE)
         return true;
     if (device->state.disk != D_INCONSISTENT)
         return false;
     esector = sector + (size >> 9) - 1;
     nr_sectors = get_capacity(device->vdisk);
     D_ASSERT(device, sector  < nr_sectors);
     D_ASSERT(device, esector < nr_sectors);
 
     sbnr = BM_SECT_TO_BIT(sector);
     ebnr = BM_SECT_TO_BIT(esector);
 
     return drbd_bm_count_bits(device, sbnr, ebnr) == 0;
 }
 
 static bool remote_due_to_read_balancing(struct drbd_device *device, sector_t sector,
         enum drbd_read_balancing rbm)
 {
     int stripe_shift;
 
     switch (rbm) {
     case RB_CONGESTED_REMOTE:
         return false;
     case RB_LEAST_PENDING:
         return atomic_read(&device->local_cnt) >
             atomic_read(&device->ap_pending_cnt) + atomic_read(&device->rs_pending_cnt);
     case RB_32K_STRIPING:  /* stripe_shift = 15 */
     case RB_64K_STRIPING:
     case RB_128K_STRIPING:
     case RB_256K_STRIPING:
     case RB_512K_STRIPING:
     case RB_1M_STRIPING:   /* stripe_shift = 20 */
         stripe_shift = (rbm - RB_32K_STRIPING + 15);
         return (sector >> (stripe_shift - 9)) & 1;
     case RB_ROUND_ROBIN:
         return test_and_change_bit(READ_BALANCE_RR, &device->flags);
     case RB_PREFER_REMOTE:
         return true;
     case RB_PREFER_LOCAL:
     default:
         return false;
     }
 }
 
 /*
  * complete_conflicting_writes  -  wait for any conflicting write requests
  *
  * The write_requests tree contains all active write requests which we
  * currently know about.  Wait for any requests to complete which conflict with
  * the new one.
  *
  * Only way out: remove the conflicting intervals from the tree.
  */
 static void complete_conflicting_writes(struct drbd_request *req)
 {
     DEFINE_WAIT(wait);
     struct drbd_device *device = req->device;
     struct drbd_interval *i;
     sector_t sector = req->i.sector;
     int size = req->i.size;
 
     for (;;) {
         drbd_for_each_overlap(i, &device->write_requests, sector, size) {
             /* Ignore, if already completed to upper layers. */
             if (i->completed)
                 continue;
             /* Handle the first found overlap.  After the schedule
              * we have to restart the tree walk. */
             break;
         }
         if (!i) /* if any */
             break;
 
         /* Indicate to wake up device->misc_wait on progress.  */
         prepare_to_wait(&device->misc_wait, &wait, TASK_UNINTERRUPTIBLE);
         i->waiting = true;
         spin_unlock_irq(&device->resource->req_lock);
         schedule();
         spin_lock_irq(&device->resource->req_lock);
     }
     finish_wait(&device->misc_wait, &wait);
 }
 
 /* called within req_lock */
 static void maybe_pull_ahead(struct drbd_device *device)
 {
     struct drbd_connection *connection = first_peer_device(device)->connection;
     struct net_conf *nc;
     bool congested = false;
     enum drbd_on_congestion on_congestion;
 
     rcu_read_lock();
     nc = rcu_dereference(connection->net_conf);
     on_congestion = nc ? nc->on_congestion : OC_BLOCK;
     rcu_read_unlock();
     if (on_congestion == OC_BLOCK ||
         connection->agreed_pro_version < 96)
         return;
 
     if (on_congestion == OC_PULL_AHEAD && device->state.conn == C_AHEAD)
         return; /* nothing to do ... */
 
     /* If I don't even have good local storage, we can not reasonably try
      * to pull ahead of the peer. We also need the local reference to make
      * sure device->act_log is there.
      */
     if (!get_ldev_if_state(device, D_UP_TO_DATE))
         return;
 
     if (nc->cong_fill &&
         atomic_read(&device->ap_in_flight) >= nc->cong_fill) {
         drbd_info(device, "Congestion-fill threshold reached\n");
         congested = true;
     }
 
     if (device->act_log->used >= nc->cong_extents) {
         drbd_info(device, "Congestion-extents threshold reached\n");
         congested = true;
     }
 
     if (congested) {
         /* start a new epoch for non-mirrored writes */
         start_new_tl_epoch(first_peer_device(device)->connection);
 
         if (on_congestion == OC_PULL_AHEAD)
             _drbd_set_state(_NS(device, conn, C_AHEAD), 0, NULL);
         else  /*nc->on_congestion == OC_DISCONNECT */
             _drbd_set_state(_NS(device, conn, C_DISCONNECTING), 0, NULL);
     }
     put_ldev(device);
 }
 
 /* If this returns false, and req->private_bio is still set,
  * this should be submitted locally.
  *
  * If it returns false, but req->private_bio is not set,
  * we do not have access to good data :(
  *
  * Otherwise, this destroys req->private_bio, if any,
  * and returns true.
  */
 static bool do_remote_read(struct drbd_request *req)
 {
     struct drbd_device *device = req->device;
     enum drbd_read_balancing rbm;
 
     if (req->private_bio) {
         if (!drbd_may_do_local_read(device,
                     req->i.sector, req->i.size)) {
             bio_put(req->private_bio);
             req->private_bio = NULL;
             put_ldev(device);
         }
     }
 
     if (device->state.pdsk != D_UP_TO_DATE)
         return false;
 
     if (req->private_bio == NULL)
         return true;
 
     /* TODO: improve read balancing decisions, take into account drbd
      * protocol, pending requests etc. */
 
     rcu_read_lock();
     rbm = rcu_dereference(device->ldev->disk_conf)->read_balancing;
     rcu_read_unlock();
 
     if (rbm == RB_PREFER_LOCAL && req->private_bio)
         return false; /* submit locally */
 
     if (remote_due_to_read_balancing(device, req->i.sector, rbm)) {
         if (req->private_bio) {
             bio_put(req->private_bio);
             req->private_bio = NULL;
             put_ldev(device);
         }
         return true;
     }
 
     return false;
 }
 
 bool drbd_should_do_remote(union drbd_dev_state s)
 {
     return s.pdsk == D_UP_TO_DATE ||
         (s.pdsk >= D_INCONSISTENT &&
          s.conn >= C_WF_BITMAP_T &&
          s.conn < C_AHEAD);
     /* Before proto 96 that was >= CONNECTED instead of >= C_WF_BITMAP_T.
        That is equivalent since before 96 IO was frozen in the C_WF_BITMAP*
        states. */
 }
 
 static bool drbd_should_send_out_of_sync(union drbd_dev_state s)
 {
     return s.conn == C_AHEAD || s.conn == C_WF_BITMAP_S;
     /* pdsk = D_INCONSISTENT as a consequence. Protocol 96 check not necessary
        since we enter state C_AHEAD only if proto >= 96 */
 }
 
 /* returns number of connections (== 1, for drbd 8.4)
  * expected to actually write this data,
  * which does NOT include those that we are L_AHEAD for. */
 static int drbd_process_write_request(struct drbd_request *req)
 {
     struct drbd_device *device = req->device;
     int remote, send_oos;
 
     remote = drbd_should_do_remote(device->state);
     send_oos = drbd_should_send_out_of_sync(device->state);
 
     /* Need to replicate writes.  Unless it is an empty flush,
      * which is better mapped to a DRBD P_BARRIER packet,
      * also for drbd wire protocol compatibility reasons.
      * If this was a flush, just start a new epoch.
      * Unless the current epoch was empty anyways, or we are not currently
      * replicating, in which case there is no point. */
     if (unlikely(req->i.size == 0)) {
         /* The only size==0 bios we expect are empty flushes. */
         D_ASSERT(device, req->master_bio->bi_opf & REQ_PREFLUSH);
         if (remote)
             _req_mod(req, QUEUE_AS_DRBD_BARRIER);
         return remote;
     }
 
     if (!remote && !send_oos)
         return 0;
 
     D_ASSERT(device, !(remote && send_oos));
 
     if (remote) {
         _req_mod(req, TO_BE_SENT);
         _req_mod(req, QUEUE_FOR_NET_WRITE);
     } else if (drbd_set_out_of_sync(device, req->i.sector, req->i.size))
         _req_mod(req, QUEUE_FOR_SEND_OOS);
 
     return remote;
 }
 
 static void drbd_process_discard_or_zeroes_req(struct drbd_request *req, int flags)
 {
     int err = drbd_issue_discard_or_zero_out(req->device,
                 req->i.sector, req->i.size >> 9, flags);
     if (err)
         req->private_bio->bi_status = BLK_STS_IOERR;
     bio_endio(req->private_bio);
 }
 
 static void
 drbd_submit_req_private_bio(struct drbd_request *req)
 {
     struct drbd_device *device = req->device;
     struct bio *bio = req->private_bio;
     unsigned int type;
 
     if (bio_op(bio) != REQ_OP_READ)
         type = DRBD_FAULT_DT_WR;
     else if (bio->bi_opf & REQ_RAHEAD)
         type = DRBD_FAULT_DT_RA;
     else
         type = DRBD_FAULT_DT_RD;
 
     /* State may have changed since we grabbed our reference on the
      * ->ldev member. Double check, and short-circuit to endio.
      * In case the last activity log transaction failed to get on
      * stable storage, and this is a WRITE, we may not even submit
      * this bio. */
     if (get_ldev(device)) {
         if (drbd_insert_fault(device, type))
             bio_io_error(bio);
         else if (bio_op(bio) == REQ_OP_WRITE_ZEROES)
             drbd_process_discard_or_zeroes_req(req, EE_ZEROOUT |
                 ((bio->bi_opf & REQ_NOUNMAP) ? 0 : EE_TRIM));
         else if (bio_op(bio) == REQ_OP_DISCARD)
             drbd_process_discard_or_zeroes_req(req, EE_TRIM);
         else
             submit_bio_noacct(bio);
         put_ldev(device);
     } else
         bio_io_error(bio);
 }
 
 static void drbd_queue_write(struct drbd_device *device, struct drbd_request *req)
 {
     spin_lock_irq(&device->resource->req_lock);
     list_add_tail(&req->tl_requests, &device->submit.writes);
     list_add_tail(&req->req_pending_master_completion,
             &device->pending_master_completion[1 /* WRITE */]);
     spin_unlock_irq(&device->resource->req_lock);
     queue_work(device->submit.wq, &device->submit.worker);
     /* do_submit() may sleep internally on al_wait, too */
     wake_up(&device->al_wait);
 }
 
 /* returns the new drbd_request pointer, if the caller is expected to
  * drbd_send_and_submit() it (to save latency), or NULL if we queued the
  * request on the submitter thread.
  * Returns ERR_PTR(-ENOMEM) if we cannot allocate a drbd_request.
  */
 static struct drbd_request *
 drbd_request_prepare(struct drbd_device *device, struct bio *bio)
 {
     const int rw = bio_data_dir(bio);
     struct drbd_request *req;
 
     /* allocate outside of all locks; */
     req = drbd_req_new(device, bio);
     if (!req) {
         dec_ap_bio(device);
         /* only pass the error to the upper layers.
          * if user cannot handle io errors, that's not our business. */
         drbd_err(device, "could not kmalloc() req\n");
         bio->bi_status = BLK_STS_RESOURCE;
         bio_endio(bio);
         return ERR_PTR(-ENOMEM);
     }
 
     /* Update disk stats */
     req->start_jif = bio_start_io_acct(req->master_bio);
 
     if (!get_ldev(device)) {
         bio_put(req->private_bio);
         req->private_bio = NULL;
     }
 
     /* process discards always from our submitter thread */
     if (bio_op(bio) == REQ_OP_WRITE_ZEROES ||
         bio_op(bio) == REQ_OP_DISCARD)
         goto queue_for_submitter_thread;
 
     if (rw == WRITE && req->private_bio && req->i.size
     && !test_bit(AL_SUSPENDED, &device->flags)) {
         if (!drbd_al_begin_io_fastpath(device, &req->i))
             goto queue_for_submitter_thread;
         req->rq_state |= RQ_IN_ACT_LOG;
         req->in_actlog_jif = jiffies;
     }
     return req;
 
  queue_for_submitter_thread:
     atomic_inc(&device->ap_actlog_cnt);
     drbd_queue_write(device, req);
     return NULL;
 }
 
 /* Require at least one path to current data.
  * We don't want to allow writes on C_STANDALONE D_INCONSISTENT:
  * We would not allow to read what was written,
  * we would not have bumped the data generation uuids,
  * we would cause data divergence for all the wrong reasons.
  *
  * If we don't see at least one D_UP_TO_DATE, we will fail this request,
  * which either returns EIO, or, if OND_SUSPEND_IO is set, suspends IO,
  * and queues for retry later.
  */
 static bool may_do_writes(struct drbd_device *device)
 {
     const union drbd_dev_state s = device->state;
     return s.disk == D_UP_TO_DATE || s.pdsk == D_UP_TO_DATE;
 }
 
 struct drbd_plug_cb {
     struct blk_plug_cb cb;
     struct drbd_request *most_recent_req;
     /* do we need more? */
 };
 
 static void drbd_unplug(struct blk_plug_cb *cb, bool from_schedule)
 {
     struct drbd_plug_cb *plug = container_of(cb, struct drbd_plug_cb, cb);
     struct drbd_resource *resource = plug->cb.data;
     struct drbd_request *req = plug->most_recent_req;
 
     kfree(cb);
     if (!req)
         return;
 
     spin_lock_irq(&resource->req_lock);
     /* In case the sender did not process it yet, raise the flag to
      * have it followed with P_UNPLUG_REMOTE just after. */
     req->rq_state |= RQ_UNPLUG;
     /* but also queue a generic unplug */
     drbd_queue_unplug(req->device);
     kref_put(&req->kref, drbd_req_destroy);
     spin_unlock_irq(&resource->req_lock);
 }
 
 static struct drbd_plug_cb* drbd_check_plugged(struct drbd_resource *resource)
 {
     /* A lot of text to say
      * return (struct drbd_plug_cb*)blk_check_plugged(); */
     struct drbd_plug_cb *plug;
     struct blk_plug_cb *cb = blk_check_plugged(drbd_unplug, resource, sizeof(*plug));
 
     if (cb)
         plug = container_of(cb, struct drbd_plug_cb, cb);
     else
         plug = NULL;
     return plug;
 }
 
 static void drbd_update_plug(struct drbd_plug_cb *plug, struct drbd_request *req)
 {
     struct drbd_request *tmp = plug->most_recent_req;
     /* Will be sent to some peer.
      * Remember to tag it with UNPLUG_REMOTE on unplug */
     kref_get(&req->kref);
     plug->most_recent_req = req;
     if (tmp)
         kref_put(&tmp->kref, drbd_req_destroy);
 }
 
 static void drbd_send_and_submit(struct drbd_device *device, struct drbd_request *req)
 {
     struct drbd_resource *resource = device->resource;
     const int rw = bio_data_dir(req->master_bio);
     struct bio_and_error m = { NULL, };
     bool no_remote = false;
     bool submit_private_bio = false;
 
     spin_lock_irq(&resource->req_lock);
     if (rw == WRITE) {
         /* This may temporarily give up the req_lock,
          * but will re-aquire it before it returns here.
          * Needs to be before the check on drbd_suspended() */
         complete_conflicting_writes(req);
         /* no more giving up req_lock from now on! */
 
         /* check for congestion, and potentially stop sending
          * full data updates, but start sending "dirty bits" only. */
         maybe_pull_ahead(device);
     }
 
 
     if (drbd_suspended(device)) {
         /* push back and retry: */
         req->rq_state |= RQ_POSTPONED;
         if (req->private_bio) {
             bio_put(req->private_bio);
             req->private_bio = NULL;
             put_ldev(device);
         }
         goto out;
     }
 
     /* We fail READ early, if we can not serve it.
      * We must do this before req is registered on any lists.
      * Otherwise, drbd_req_complete() will queue failed READ for retry. */
     if (rw != WRITE) {
         if (!do_remote_read(req) && !req->private_bio)
             goto nodata;
     }
 
     /* which transfer log epoch does this belong to? */
     req->epoch = atomic_read(&first_peer_device(device)->connection->current_tle_nr);
 
     /* no point in adding empty flushes to the transfer log,
      * they are mapped to drbd barriers already. */
     if (likely(req->i.size!=0)) {
         if (rw == WRITE)
             first_peer_device(device)->connection->current_tle_writes++;
 
         list_add_tail(&req->tl_requests, &first_peer_device(device)->connection->transfer_log);
     }
 
     if (rw == WRITE) {
         if (req->private_bio && !may_do_writes(device)) {
             bio_put(req->private_bio);
             req->private_bio = NULL;
             put_ldev(device);
             goto nodata;
         }
         if (!drbd_process_write_request(req))
             no_remote = true;
     } else {
         /* We either have a private_bio, or we can read from remote.
          * Otherwise we had done the goto nodata above. */
         if (req->private_bio == NULL) {
             _req_mod(req, TO_BE_SENT);
             _req_mod(req, QUEUE_FOR_NET_READ);
         } else
             no_remote = true;
     }
 
     if (no_remote == false) {
         struct drbd_plug_cb *plug = drbd_check_plugged(resource);
         if (plug)
             drbd_update_plug(plug, req);
     }
 
     /* If it took the fast path in drbd_request_prepare, add it here.
      * The slow path has added it already. */
     if (list_empty(&req->req_pending_master_completion))
         list_add_tail(&req->req_pending_master_completion,
             &device->pending_master_completion[rw == WRITE]);
     if (req->private_bio) {
         /* needs to be marked within the same spinlock */
         req->pre_submit_jif = jiffies;
         list_add_tail(&req->req_pending_local,
             &device->pending_completion[rw == WRITE]);
         _req_mod(req, TO_BE_SUBMITTED);
         /* but we need to give up the spinlock to submit */
         submit_private_bio = true;
     } else if (no_remote) {
 nodata:
         if (__ratelimit(&drbd_ratelimit_state))
             drbd_err(device, "IO ERROR: neither local nor remote data, sector %llu+%u\n",
                     (unsigned long long)req->i.sector, req->i.size >> 9);
         /* A write may have been queued for send_oos, however.
          * So we can not simply free it, we must go through drbd_req_put_completion_ref() */
     }
 
 out:
     drbd_req_put_completion_ref(req, &m, 1);
     spin_unlock_irq(&resource->req_lock);
 
     /* Even though above is a kref_put(), this is safe.
      * As long as we still need to submit our private bio,
      * we hold a completion ref, and the request cannot disappear.
      * If however this request did not even have a private bio to submit
      * (e.g. remote read), req may already be invalid now.
      * That's why we cannot check on req->private_bio. */
     if (submit_private_bio)
         drbd_submit_req_private_bio(req);
     if (m.bio)
         complete_master_bio(device, &m);
 }
 
 void __drbd_make_request(struct drbd_device *device, struct bio *bio)
 {
     struct drbd_request *req = drbd_request_prepare(device, bio);
     if (IS_ERR_OR_NULL(req))
         return;
     drbd_send_and_submit(device, req);
 }
 
 static void submit_fast_path(struct drbd_device *device, struct list_head *incoming)
 {
     struct blk_plug plug;
     struct drbd_request *req, *tmp;
 
     blk_start_plug(&plug);
     list_for_each_entry_safe(req, tmp, incoming, tl_requests) {
         const int rw = bio_data_dir(req->master_bio);
 
         if (rw == WRITE /* rw != WRITE should not even end up here! */
         && req->private_bio && req->i.size
         && !test_bit(AL_SUSPENDED, &device->flags)) {
             if (!drbd_al_begin_io_fastpath(device, &req->i))
                 continue;
 
             req->rq_state |= RQ_IN_ACT_LOG;
             req->in_actlog_jif = jiffies;
             atomic_dec(&device->ap_actlog_cnt);
         }
 
         list_del_init(&req->tl_requests);
         drbd_send_and_submit(device, req);
     }
     blk_finish_plug(&plug);
 }
 
 static bool prepare_al_transaction_nonblock(struct drbd_device *device,
                         struct list_head *incoming,
                         struct list_head *pending,
                         struct list_head *later)
 {
     struct drbd_request *req;
     int wake = 0;
     int err;
 
     spin_lock_irq(&device->al_lock);
     while ((req = list_first_entry_or_null(incoming, struct drbd_request, tl_requests))) {
         err = drbd_al_begin_io_nonblock(device, &req->i);
         if (err == -ENOBUFS)
             break;
         if (err == -EBUSY)
             wake = 1;
         if (err)
             list_move_tail(&req->tl_requests, later);
         else
             list_move_tail(&req->tl_requests, pending);
     }
     spin_unlock_irq(&device->al_lock);
     if (wake)
         wake_up(&device->al_wait);
     return !list_empty(pending);
 }
 
 static void send_and_submit_pending(struct drbd_device *device, struct list_head *pending)
 {
     struct blk_plug plug;
     struct drbd_request *req;
 
     blk_start_plug(&plug);
     while ((req = list_first_entry_or_null(pending, struct drbd_request, tl_requests))) {
         req->rq_state |= RQ_IN_ACT_LOG;
         req->in_actlog_jif = jiffies;
         atomic_dec(&device->ap_actlog_cnt);
         list_del_init(&req->tl_requests);
         drbd_send_and_submit(device, req);
     }
     blk_finish_plug(&plug);
 }
 
 void do_submit(struct work_struct *ws)
 {
     struct drbd_device *device = container_of(ws, struct drbd_device, submit.worker);
     LIST_HEAD(incoming);    /* from drbd_make_request() */
     LIST_HEAD(pending); /* to be submitted after next AL-transaction commit */
     LIST_HEAD(busy);    /* blocked by resync requests */
 
     /* grab new incoming requests */
     spin_lock_irq(&device->resource->req_lock);
     list_splice_tail_init(&device->submit.writes, &incoming);
     spin_unlock_irq(&device->resource->req_lock);
 
     for (;;) {
         DEFINE_WAIT(wait);
 
         /* move used-to-be-busy back to front of incoming */
         list_splice_init(&busy, &incoming);
         submit_fast_path(device, &incoming);
         if (list_empty(&incoming))
             break;
 
         for (;;) {
             prepare_to_wait(&device->al_wait, &wait, TASK_UNINTERRUPTIBLE);
 
             list_splice_init(&busy, &incoming);
             prepare_al_transaction_nonblock(device, &incoming, &pending, &busy);
             if (!list_empty(&pending))
                 break;
 
             schedule();
 
             /* If all currently "hot" activity log extents are kept busy by
              * incoming requests, we still must not totally starve new
              * requests to "cold" extents.
              * Something left on &incoming means there had not been
              * enough update slots available, and the activity log
              * has been marked as "starving".
              *
              * Try again now, without looking for new requests,
              * effectively blocking all new requests until we made
              * at least _some_ progress with what we currently have.
              */
             if (!list_empty(&incoming))
                 continue;
 
             /* Nothing moved to pending, but nothing left
              * on incoming: all moved to busy!
              * Grab new and iterate. */
             spin_lock_irq(&device->resource->req_lock);
             list_splice_tail_init(&device->submit.writes, &incoming);
             spin_unlock_irq(&device->resource->req_lock);
         }
         finish_wait(&device->al_wait, &wait);
 
         /* If the transaction was full, before all incoming requests
          * had been processed, skip ahead to commit, and iterate
          * without splicing in more incoming requests from upper layers.
          *
          * Else, if all incoming have been processed,
          * they have become either "pending" (to be submitted after
          * next transaction commit) or "busy" (blocked by resync).
          *
          * Maybe more was queued, while we prepared the transaction?
          * Try to stuff those into this transaction as well.
          * Be strictly non-blocking here,
          * we already have something to commit.
          *
          * Commit if we don't make any more progres.
          */
 
         while (list_empty(&incoming)) {
             LIST_HEAD(more_pending);
             LIST_HEAD(more_incoming);
             bool made_progress;
 
             /* It is ok to look outside the lock,
              * it's only an optimization anyways */
             if (list_empty(&device->submit.writes))
                 break;
 
             spin_lock_irq(&device->resource->req_lock);
             list_splice_tail_init(&device->submit.writes, &more_incoming);
             spin_unlock_irq(&device->resource->req_lock);
 
             if (list_empty(&more_incoming))
                 break;
 
             made_progress = prepare_al_transaction_nonblock(device, &more_incoming, &more_pending, &busy);
 
             list_splice_tail_init(&more_pending, &pending);
             list_splice_tail_init(&more_incoming, &incoming);
             if (!made_progress)
                 break;
         }
 
         drbd_al_begin_io_commit(device);
         send_and_submit_pending(device, &pending);
     }
 }
 
 void drbd_submit_bio(struct bio *bio)
 {
     struct drbd_device *device = bio->bi_bdev->bd_disk->private_data;
 
     bio = bio_split_to_limits(bio);
 
     /*
      * what we "blindly" assume:
      */
     D_ASSERT(device, IS_ALIGNED(bio->bi_iter.bi_size, 512));
 
     inc_ap_bio(device);
     __drbd_make_request(device, bio);
 }
 
 static bool net_timeout_reached(struct drbd_request *net_req,
         struct drbd_connection *connection,
         unsigned long now, unsigned long ent,
         unsigned int ko_count, unsigned int timeout)
 {
     struct drbd_device *device = net_req->device;
 
     if (!time_after(now, net_req->pre_send_jif + ent))
         return false;
 
     if (time_in_range(now, connection->last_reconnect_jif, connection->last_reconnect_jif + ent))
         return false;
 
     if (net_req->rq_state & RQ_NET_PENDING) {
         drbd_warn(device, "Remote failed to finish a request within %ums > ko-count (%u) * timeout (%u * 0.1s)\n",
             jiffies_to_msecs(now - net_req->pre_send_jif), ko_count, timeout);
         return true;
     }
 
     /* We received an ACK already (or are using protocol A),
      * but are waiting for the epoch closing barrier ack.
      * Check if we sent the barrier already.  We should not blame the peer
      * for being unresponsive, if we did not even ask it yet. */
     if (net_req->epoch == connection->send.current_epoch_nr) {
         drbd_warn(device,
             "We did not send a P_BARRIER for %ums > ko-count (%u) * timeout (%u * 0.1s); drbd kernel thread blocked?\n",
             jiffies_to_msecs(now - net_req->pre_send_jif), ko_count, timeout);
         return false;
     }
 
     /* Worst case: we may have been blocked for whatever reason, then
      * suddenly are able to send a lot of requests (and epoch separating
      * barriers) in quick succession.
      * The timestamp of the net_req may be much too old and not correspond
      * to the sending time of the relevant unack'ed barrier packet, so
      * would trigger a spurious timeout.  The latest barrier packet may
      * have a too recent timestamp to trigger the timeout, potentially miss
      * a timeout.  Right now we don't have a place to conveniently store
      * these timestamps.
      * But in this particular situation, the application requests are still
      * completed to upper layers, DRBD should still "feel" responsive.
      * No need yet to kill this connection, it may still recover.
      * If not, eventually we will have queued enough into the network for
      * us to block. From that point of view, the timestamp of the last sent
      * barrier packet is relevant enough.
      */
     if (time_after(now, connection->send.last_sent_barrier_jif + ent)) {
         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",
             connection->send.last_sent_barrier_jif, now,
             jiffies_to_msecs(now - connection->send.last_sent_barrier_jif), ko_count, timeout);
         return true;
     }
     return false;
 }
 
 /* A request is considered timed out, if
  * - we have some effective timeout from the configuration,
  *   with some state restrictions applied,
  * - the oldest request is waiting for a response from the network
  *   resp. the local disk,
  * - the oldest request is in fact older than the effective timeout,
  * - the connection was established (resp. disk was attached)
  *   for longer than the timeout already.
  * Note that for 32bit jiffies and very stable connections/disks,
  * we may have a wrap around, which is catched by
  *   !time_in_range(now, last_..._jif, last_..._jif + timeout).
  *
  * Side effect: once per 32bit wrap-around interval, which means every
  * ~198 days with 250 HZ, we have a window where the timeout would need
  * to expire twice (worst case) to become effective. Good enough.
  */
 
 void request_timer_fn(struct timer_list *t)
 {
     struct drbd_device *device = from_timer(device, t, request_timer);
     struct drbd_connection *connection = first_peer_device(device)->connection;
     struct drbd_request *req_read, *req_write, *req_peer; /* oldest request */
     struct net_conf *nc;
     unsigned long oldest_submit_jif;
     unsigned long ent = 0, dt = 0, et, nt; /* effective timeout = ko_count * timeout */
     unsigned long now;
     unsigned int ko_count = 0, timeout = 0;
 
     rcu_read_lock();
     nc = rcu_dereference(connection->net_conf);
     if (nc && device->state.conn >= C_WF_REPORT_PARAMS) {
         ko_count = nc->ko_count;
         timeout = nc->timeout;
     }
 
     if (get_ldev(device)) { /* implicit state.disk >= D_INCONSISTENT */
         dt = rcu_dereference(device->ldev->disk_conf)->disk_timeout * HZ / 10;
         put_ldev(device);
     }
     rcu_read_unlock();
 
 
     ent = timeout * HZ/10 * ko_count;
     et = min_not_zero(dt, ent);
 
     if (!et)
         return; /* Recurring timer stopped */
 
     now = jiffies;
     nt = now + et;
 
     spin_lock_irq(&device->resource->req_lock);
     req_read = list_first_entry_or_null(&device->pending_completion[0], struct drbd_request, req_pending_local);
     req_write = list_first_entry_or_null(&device->pending_completion[1], struct drbd_request, req_pending_local);
 
     /* maybe the oldest request waiting for the peer is in fact still
      * blocking in tcp sendmsg.  That's ok, though, that's handled via the
      * socket send timeout, requesting a ping, and bumping ko-count in
      * we_should_drop_the_connection().
      */
 
     /* check the oldest request we did successfully sent,
      * but which is still waiting for an ACK. */
     req_peer = connection->req_ack_pending;
 
     /* if we don't have such request (e.g. protocoll A)
      * check the oldest requests which is still waiting on its epoch
      * closing barrier ack. */
     if (!req_peer)
         req_peer = connection->req_not_net_done;
 
     /* evaluate the oldest peer request only in one timer! */
     if (req_peer && req_peer->device != device)
         req_peer = NULL;
 
     /* do we have something to evaluate? */
     if (req_peer == NULL && req_write == NULL && req_read == NULL)
         goto out;
 
     oldest_submit_jif =
         (req_write && req_read)
         ? ( time_before(req_write->pre_submit_jif, req_read->pre_submit_jif)
           ? req_write->pre_submit_jif : req_read->pre_submit_jif )
         : req_write ? req_write->pre_submit_jif
         : req_read ? req_read->pre_submit_jif : now;
 
     if (ent && req_peer && net_timeout_reached(req_peer, connection, now, ent, ko_count, timeout))
         _conn_request_state(connection, NS(conn, C_TIMEOUT), CS_VERBOSE | CS_HARD);
 
     if (dt && oldest_submit_jif != now &&
          time_after(now, oldest_submit_jif + dt) &&
         !time_in_range(now, device->last_reattach_jif, device->last_reattach_jif + dt)) {
         drbd_warn(device, "Local backing device failed to meet the disk-timeout\n");
         __drbd_chk_io_error(device, DRBD_FORCE_DETACH);
     }
 
     /* Reschedule timer for the nearest not already expired timeout.
      * Fallback to now + min(effective network timeout, disk timeout). */
     ent = (ent && req_peer && time_before(now, req_peer->pre_send_jif + ent))
         ? req_peer->pre_send_jif + ent : now + et;
     dt = (dt && oldest_submit_jif != now && time_before(now, oldest_submit_jif + dt))
         ? oldest_submit_jif + dt : now + et;
     nt = time_before(ent, dt) ? ent : dt;
 out:
     spin_unlock_irq(&device->resource->req_lock);
     mod_timer(&device->request_timer, nt);
 }

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