drbd: Move the CREATE_BARRIER flag from connection to device

[mirror_ubuntu-zesty-kernel.git] / drivers / block / drbd / drbd_req.c

/*
   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>.

   drbd is free software; you can redistribute it and/or modify
   it under the terms of the GNU General Public License as published by
   the Free Software Foundation; either version 2, or (at your option)
   any later version.

   drbd is distributed in the hope that it will be useful,
   but WITHOUT ANY WARRANTY; without even the implied warranty of
   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   GNU General Public License for more details.

   You should have received a copy of the GNU General Public License
   along with drbd; see the file COPYING.  If not, write to
   the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.

 */

#include <linux/module.h>

#include <linux/slab.h>
#include <linux/drbd.h>
#include "drbd_int.h"
#include "drbd_req.h"


/* Update disk stats at start of I/O request */
static void _drbd_start_io_acct(struct drbd_conf *mdev, struct drbd_request *req, struct bio *bio)
{
        const int rw = bio_data_dir(bio);
        int cpu;
        cpu = part_stat_lock();
        part_stat_inc(cpu, &mdev->vdisk->part0, ios[rw]);
        part_stat_add(cpu, &mdev->vdisk->part0, sectors[rw], bio_sectors(bio));
        (void) cpu; /* The macro invocations above want the cpu argument, I do not like
                       the compiler warning about cpu only assigned but never used... */
        part_inc_in_flight(&mdev->vdisk->part0, rw);
        part_stat_unlock();
}

/* Update disk stats when completing request upwards */
static void _drbd_end_io_acct(struct drbd_conf *mdev, struct drbd_request *req)
{
        int rw = bio_data_dir(req->master_bio);
        unsigned long duration = jiffies - req->start_time;
        int cpu;
        cpu = part_stat_lock();
        part_stat_add(cpu, &mdev->vdisk->part0, ticks[rw], duration);
        part_round_stats(cpu, &mdev->vdisk->part0);
        part_dec_in_flight(&mdev->vdisk->part0, rw);
        part_stat_unlock();
}

static struct drbd_request *drbd_req_new(struct drbd_conf *mdev,
                                               struct bio *bio_src)
{
        struct drbd_request *req;

        req = mempool_alloc(drbd_request_mempool, GFP_NOIO);
        if (!req)
                return NULL;

        drbd_req_make_private_bio(req, bio_src);
        req->rq_state    = bio_data_dir(bio_src) == WRITE ? RQ_WRITE : 0;
        req->w.mdev      = mdev;
        req->master_bio  = bio_src;
        req->epoch       = 0;

        drbd_clear_interval(&req->i);
        req->i.sector     = bio_src->bi_sector;
        req->i.size      = bio_src->bi_size;
        req->i.local = true;
        req->i.waiting = false;

        INIT_LIST_HEAD(&req->tl_requests);
        INIT_LIST_HEAD(&req->w.list);

        return req;
}

static void drbd_req_free(struct drbd_request *req)
{
        mempool_free(req, drbd_request_mempool);
}

/* rw is bio_data_dir(), only READ or WRITE */
static void _req_is_done(struct drbd_conf *mdev, struct drbd_request *req, const int rw)
{
        const unsigned long s = req->rq_state;

        /* remove it from the transfer log.
         * well, only if it had been there in the first
         * place... if it had not (local only or conflicting
         * and never sent), it should still be "empty" as
         * initialized in drbd_req_new(), so we can list_del() it
         * here unconditionally */
        list_del(&req->tl_requests);

        /* 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 (rw == 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 */
                if (!(s & RQ_NET_OK) || !(s & RQ_LOCAL_OK))
                        drbd_set_out_of_sync(mdev, req->i.sector, req->i.size);

                if ((s & RQ_NET_OK) && (s & RQ_LOCAL_OK) && (s & RQ_NET_SIS))
                        drbd_set_in_sync(mdev, 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_LOCAL_MASK) {
                        if (get_ldev_if_state(mdev, D_FAILED)) {
                                if (s & RQ_IN_ACT_LOG)
                                        drbd_al_complete_io(mdev, &req->i);
                                put_ldev(mdev);
                        } else if (__ratelimit(&drbd_ratelimit_state)) {
                                dev_warn(DEV, "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);
                        }
                }
        }

        drbd_req_free(req);
}

static void queue_barrier(struct drbd_conf *mdev)
{
        struct drbd_tl_epoch *b;
        struct drbd_tconn *tconn = mdev->tconn;

        /* We are within the req_lock. Once we queued the barrier for sending,
         * we set the CREATE_BARRIER bit. It is cleared as soon as a new
         * barrier/epoch object is added. This is the only place this bit is
         * set. It indicates that the barrier for this epoch is already queued,
         * and no new epoch has been created yet. */
        if (test_bit(CREATE_BARRIER, &tconn->flags))
                return;

        b = tconn->newest_tle;
        b->w.cb = w_send_barrier;
        b->w.mdev = mdev;
        /* inc_ap_pending done here, so we won't
         * get imbalanced on connection loss.
         * dec_ap_pending will be done in got_BarrierAck
         * or (on connection loss) in tl_clear.  */
        inc_ap_pending(mdev);
        drbd_queue_work(&tconn->data.work, &b->w);
        set_bit(CREATE_BARRIER, &tconn->flags);
}

static void _about_to_complete_local_write(struct drbd_conf *mdev,
        struct drbd_request *req)
{
        const unsigned long s = req->rq_state;

        /* Before we can signal completion to the upper layers,
         * we may need to close the current epoch.
         * We can skip this, if this request has not even been sent, because we
         * did not have a fully established connection yet/anymore, during
         * bitmap exchange, or while we are C_AHEAD due to congestion policy.
         */
        if (mdev->state.conn >= C_CONNECTED &&
            (s & RQ_NET_SENT) != 0 &&
            req->epoch == mdev->tconn->newest_tle->br_number)
                queue_barrier(mdev);
}

void complete_master_bio(struct drbd_conf *mdev,
                struct bio_and_error *m)
{
        bio_endio(m->bio, m->error);
        dec_ap_bio(mdev);
}


static void drbd_remove_request_interval(struct rb_root *root,
                                         struct drbd_request *req)
{
        struct drbd_conf *mdev = req->w.mdev;
        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(&mdev->misc_wait);
}

/* 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.
 */
void _req_may_be_done(struct drbd_request *req, struct bio_and_error *m)
{
        const unsigned long s = req->rq_state;
        struct drbd_conf *mdev = req->w.mdev;
        int rw = req->rq_state & RQ_WRITE ? WRITE : READ;

        /* 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))
                return;
        if (req->i.waiting) {
                /* Retry all conflicting peer requests.  */
                wake_up(&mdev->misc_wait);
        }
        if (s & RQ_NET_QUEUED)
                return;
        if (s & RQ_NET_PENDING)
                return;

        if (req->master_bio) {
                /* this is DATA_RECEIVED (remote read)
                 * or protocol C P_WRITE_ACK
                 * or protocol B P_RECV_ACK
                 * or protocol A "HANDED_OVER_TO_NETWORK" (SendAck)
                 * or canceled or failed,
                 * or killed from the transfer log due to connection loss.
                 */

                /*
                 * 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.
                 */
                int ok = (s & RQ_LOCAL_OK) || (s & RQ_NET_OK);
                int error = PTR_ERR(req->private_bio);

                /* remove the request from the conflict detection
                 * respective block_id verification hash */
                if (!drbd_interval_empty(&req->i)) {
                        struct rb_root *root;

                        if (rw == WRITE)
                                root = &mdev->write_requests;
                        else
                                root = &mdev->read_requests;
                        drbd_remove_request_interval(root, req);
                } else if (!(s & RQ_POSTPONED))
                        D_ASSERT((s & (RQ_NET_MASK & ~RQ_NET_DONE)) == 0);

                /* for writes we need to do some extra housekeeping */
                if (rw == WRITE)
                        _about_to_complete_local_write(mdev, req);

                /* Update disk stats */
                _drbd_end_io_acct(mdev, req);

                if (!(s & RQ_POSTPONED)) {
                        m->error = ok ? 0 : (error ?: -EIO);
                        m->bio = req->master_bio;
                }
                req->master_bio = NULL;
        }

        if (s & RQ_LOCAL_PENDING)
                return;

        if ((s & RQ_NET_MASK) == 0 || (s & RQ_NET_DONE)) {
                /* this is disconnected (local only) operation,
                 * or protocol A, B, or C P_BARRIER_ACK,
                 * or killed from the transfer log due to connection loss. */
                _req_is_done(mdev, req, rw);
        }
        /* else: network part and not DONE yet. that is
         * protocol A, B, or C, barrier ack still pending... */
}

static void _req_may_be_done_not_susp(struct drbd_request *req, struct bio_and_error *m)
{
        struct drbd_conf *mdev = req->w.mdev;

        if (!drbd_suspended(mdev))
                _req_may_be_done(req, m);
}

/* 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_conf *mdev = req->w.mdev;
        struct net_conf *nc;
        int p, rv = 0;

        if (m)
                m->bio = NULL;

        switch (what) {
        default:
                dev_err(DEV, "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(!(req->rq_state & RQ_NET_MASK));
                req->rq_state |= RQ_NET_PENDING;
                rcu_read_lock();
                nc = rcu_dereference(mdev->tconn->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;
                inc_ap_pending(mdev);
                break;

        case TO_BE_SUBMITTED: /* locally */
                /* reached via __drbd_make_request */
                D_ASSERT(!(req->rq_state & RQ_LOCAL_MASK));
                req->rq_state |= RQ_LOCAL_PENDING;
                break;

        case COMPLETED_OK:
                if (req->rq_state & RQ_WRITE)
                        mdev->writ_cnt += req->i.size >> 9;
                else
                        mdev->read_cnt += req->i.size >> 9;

                req->rq_state |= (RQ_LOCAL_COMPLETED|RQ_LOCAL_OK);
                req->rq_state &= ~RQ_LOCAL_PENDING;

                _req_may_be_done_not_susp(req, m);
                put_ldev(mdev);
                break;

        case ABORT_DISK_IO:
                req->rq_state |= RQ_LOCAL_ABORTED;
                if (req->rq_state & RQ_WRITE)
                        _req_may_be_done_not_susp(req, m);
                else
                        goto goto_queue_for_net_read;
                break;

        case WRITE_COMPLETED_WITH_ERROR:
                req->rq_state |= RQ_LOCAL_COMPLETED;
                req->rq_state &= ~RQ_LOCAL_PENDING;

                __drbd_chk_io_error(mdev, false);
                _req_may_be_done_not_susp(req, m);
                put_ldev(mdev);
                break;

        case READ_AHEAD_COMPLETED_WITH_ERROR:
                /* it is legal to fail READA */
                req->rq_state |= RQ_LOCAL_COMPLETED;
                req->rq_state &= ~RQ_LOCAL_PENDING;
                _req_may_be_done_not_susp(req, m);
                put_ldev(mdev);
                break;

        case READ_COMPLETED_WITH_ERROR:
                drbd_set_out_of_sync(mdev, req->i.sector, req->i.size);

                req->rq_state |= RQ_LOCAL_COMPLETED;
                req->rq_state &= ~RQ_LOCAL_PENDING;

                D_ASSERT(!(req->rq_state & RQ_NET_MASK));

                __drbd_chk_io_error(mdev, false);
                put_ldev(mdev);

        goto_queue_for_net_read:

                /* no point in retrying if there is no good remote data,
                 * or we have no connection. */
                if (mdev->state.pdsk != D_UP_TO_DATE) {
                        _req_may_be_done_not_susp(req, m);
                        break;
                }

                /* _req_mod(req,TO_BE_SENT); oops, recursion... */
                req->rq_state |= RQ_NET_PENDING;
                inc_ap_pending(mdev);
                /* fall through: _req_mod(req,QUEUE_FOR_NET_READ); */

        case QUEUE_FOR_NET_READ:
                /* READ or READA, 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 hlist_del is in _req_may_be_done() */
                D_ASSERT(drbd_interval_empty(&req->i));
                drbd_insert_interval(&mdev->read_requests, &req->i);

                set_bit(UNPLUG_REMOTE, &mdev->flags);

                D_ASSERT(req->rq_state & RQ_NET_PENDING);
                req->rq_state |= RQ_NET_QUEUED;
                req->w.cb = (req->rq_state & RQ_LOCAL_MASK)
                        ? w_read_retry_remote
                        : w_send_read_req;
                drbd_queue_work(&mdev->tconn->data.work, &req->w);
                break;

        case QUEUE_FOR_NET_WRITE:
                /* assert something? */
                /* from __drbd_make_request only */

                /* corresponding hlist_del is in _req_may_be_done() */
                D_ASSERT(drbd_interval_empty(&req->i));
                drbd_insert_interval(&mdev->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, &mdev->flags);

                /* see __drbd_make_request,
                 * just after it grabs the req_lock */
                D_ASSERT(test_bit(CREATE_BARRIER, &mdev->tconn->flags) == 0);

                req->epoch = mdev->tconn->newest_tle->br_number;

                /* increment size of current epoch */
                mdev->tconn->newest_tle->n_writes++;

                /* queue work item to send data */
                D_ASSERT(req->rq_state & RQ_NET_PENDING);
                req->rq_state |= RQ_NET_QUEUED;
                req->w.cb =  w_send_dblock;
                drbd_queue_work(&mdev->tconn->data.work, &req->w);

                /* close the epoch, in case it outgrew the limit */
                rcu_read_lock();
                nc = rcu_dereference(mdev->tconn->net_conf);
                p = nc->max_epoch_size;
                rcu_read_unlock();
                if (mdev->tconn->newest_tle->n_writes >= p)
                        queue_barrier(mdev);

                break;

        case QUEUE_FOR_SEND_OOS:
                req->rq_state |= RQ_NET_QUEUED;
                req->w.cb =  w_send_out_of_sync;
                drbd_queue_work(&mdev->tconn->data.work, &req->w);
                break;

        case OOS_HANDED_TO_NETWORK:
                /* actually the same */
        case SEND_CANCELED:
                /* treat it the same */
        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 */
                req->rq_state &= ~RQ_NET_QUEUED;
                /* if we did it right, tl_clear should be scheduled only after
                 * this, so this should not be necessary! */
                _req_may_be_done_not_susp(req, m);
                break;

        case HANDED_OVER_TO_NETWORK:
                /* assert something? */
                if (bio_data_dir(req->master_bio) == WRITE)
                        atomic_add(req->i.size >> 9, &mdev->ap_in_flight);

                if (bio_data_dir(req->master_bio) == WRITE &&
                    !(req->rq_state & (RQ_EXP_RECEIVE_ACK | RQ_EXP_WRITE_ACK))) {
                        /* this is what is dangerous about protocol A:
                         * pretend it was successfully written on the peer. */
                        if (req->rq_state & RQ_NET_PENDING) {
                                dec_ap_pending(mdev);
                                req->rq_state &= ~RQ_NET_PENDING;
                                req->rq_state |= RQ_NET_OK;
                        } /* else: neg-ack was faster... */
                        /* 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 */
                }
                req->rq_state &= ~RQ_NET_QUEUED;
                req->rq_state |= RQ_NET_SENT;
                /* because _drbd_send_zc_bio could sleep, and may want to
                 * dereference the bio even after the "WRITE_ACKED_BY_PEER" and
                 * "COMPLETED_OK" events came in, once we return from
                 * _drbd_send_zc_bio (drbd_send_dblock), we have to check
                 * whether it is done already, and end it.  */
                _req_may_be_done_not_susp(req, m);
                break;

        case READ_RETRY_REMOTE_CANCELED:
                req->rq_state &= ~RQ_NET_QUEUED;
                /* fall through, in case we raced with drbd_disconnect */
        case CONNECTION_LOST_WHILE_PENDING:
                /* transfer log cleanup after connection loss */
                /* assert something? */
                if (req->rq_state & RQ_NET_PENDING)
                        dec_ap_pending(mdev);
                req->rq_state &= ~(RQ_NET_OK|RQ_NET_PENDING);
                req->rq_state |= RQ_NET_DONE;
                if (req->rq_state & RQ_NET_SENT && req->rq_state & RQ_WRITE)
                        atomic_sub(req->i.size >> 9, &mdev->ap_in_flight);

                /* if it is still queued, we may not complete it here.
                 * it will be canceled soon. */
                if (!(req->rq_state & RQ_NET_QUEUED))
                        _req_may_be_done(req, m); /* Allowed while state.susp */
                break;

        case WRITE_ACKED_BY_PEER_AND_SIS:
                req->rq_state |= RQ_NET_SIS;
        case DISCARD_WRITE:
                /* for discarded conflicting writes of multiple primaries,
                 * there is no need to keep anything in the tl, potential
                 * node crashes are covered by the activity log. */
                req->rq_state |= RQ_NET_DONE;
                /* fall through */
        case WRITE_ACKED_BY_PEER:
                D_ASSERT(req->rq_state & RQ_EXP_WRITE_ACK);
                /* protocol C; successfully written on peer.
                 * Nothing 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.
                 *
                 * A barrier request is expected to have forced all prior
                 * requests onto stable storage, so completion of a barrier
                 * request could set NET_DONE right here, and not wait for the
                 * P_BARRIER_ACK, but that is an unnecessary optimization. */

                goto ack_common;
                /* this makes it effectively the same as for: */
        case RECV_ACKED_BY_PEER:
                D_ASSERT(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:
                req->rq_state |= RQ_NET_OK;
                D_ASSERT(req->rq_state & RQ_NET_PENDING);
                dec_ap_pending(mdev);
                atomic_sub(req->i.size >> 9, &mdev->ap_in_flight);
                req->rq_state &= ~RQ_NET_PENDING;
                _req_may_be_done_not_susp(req, m);
                break;

        case POSTPONE_WRITE:
                D_ASSERT(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(req->rq_state & RQ_NET_PENDING);
                req->rq_state |= RQ_POSTPONED;
                _req_may_be_done_not_susp(req, m);
                break;

        case NEG_ACKED:
                /* assert something? */
                if (req->rq_state & RQ_NET_PENDING) {
                        dec_ap_pending(mdev);
                        atomic_sub(req->i.size >> 9, &mdev->ap_in_flight);
                }
                req->rq_state &= ~(RQ_NET_OK|RQ_NET_PENDING);

                req->rq_state |= RQ_NET_DONE;
                _req_may_be_done_not_susp(req, m);
                /* else: done by HANDED_OVER_TO_NETWORK */
                break;

        case FAIL_FROZEN_DISK_IO:
                if (!(req->rq_state & RQ_LOCAL_COMPLETED))
                        break;

                _req_may_be_done(req, m); /* Allowed while state.susp */
                break;

        case RESTART_FROZEN_DISK_IO:
                if (!(req->rq_state & RQ_LOCAL_COMPLETED))
                        break;

                req->rq_state &= ~RQ_LOCAL_COMPLETED;

                rv = MR_READ;
                if (bio_data_dir(req->master_bio) == WRITE)
                        rv = MR_WRITE;

                get_ldev(mdev);
                req->w.cb = w_restart_disk_io;
                drbd_queue_work(&mdev->tconn->data.work, &req->w);
                break;

        case RESEND:
                /* 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 was missing.
                   Trowing them out of the TL here by pretending we got a BARRIER_ACK
                   We ensure that the peer was not rebooted */
                if (!(req->rq_state & RQ_NET_OK)) {
                        if (req->w.cb) {
                                drbd_queue_work(&mdev->tconn->data.work, &req->w);
                                rv = req->rq_state & RQ_WRITE ? MR_WRITE : MR_READ;
                        }
                        break;
                }
                /* else, fall through to BARRIER_ACKED */

        case BARRIER_ACKED:
                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... */
                        dev_err(DEV, "FIXME (BARRIER_ACKED but pending)\n");
                        list_move(&req->tl_requests, &mdev->tconn->out_of_sequence_requests);
                }
                if ((req->rq_state & RQ_NET_MASK) != 0) {
                        req->rq_state |= RQ_NET_DONE;
                        if (!(req->rq_state & (RQ_EXP_RECEIVE_ACK | RQ_EXP_WRITE_ACK)))
                                atomic_sub(req->i.size>>9, &mdev->ap_in_flight);
                }
                _req_may_be_done(req, m); /* Allowed while state.susp */
                break;

        case DATA_RECEIVED:
                D_ASSERT(req->rq_state & RQ_NET_PENDING);
                dec_ap_pending(mdev);
                req->rq_state &= ~RQ_NET_PENDING;
                req->rq_state |= (RQ_NET_OK|RQ_NET_DONE);
                _req_may_be_done_not_susp(req, m);
                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_conf *mdev, sector_t sector, int size)
{
        unsigned long sbnr, ebnr;
        sector_t esector, nr_sectors;

        if (mdev->state.disk == D_UP_TO_DATE)
                return true;
        if (mdev->state.disk != D_INCONSISTENT)
                return false;
        esector = sector + (size >> 9) - 1;
        nr_sectors = drbd_get_capacity(mdev->this_bdev);
        D_ASSERT(sector  < nr_sectors);
        D_ASSERT(esector < nr_sectors);

        sbnr = BM_SECT_TO_BIT(sector);
        ebnr = BM_SECT_TO_BIT(esector);

        return drbd_bm_count_bits(mdev, sbnr, ebnr) == 0;
}

/*
 * 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.
 */
static int complete_conflicting_writes(struct drbd_conf *mdev,
                                       sector_t sector, int size)
{
        for(;;) {
                struct drbd_interval *i;
                int err;

                i = drbd_find_overlap(&mdev->write_requests, sector, size);
                if (!i)
                        return 0;
                err = drbd_wait_misc(mdev, i);
                if (err)
                        return err;
        }
}

int __drbd_make_request(struct drbd_conf *mdev, struct bio *bio, unsigned long start_time)
{
        const int rw = bio_rw(bio);
        const int size = bio->bi_size;
        const sector_t sector = bio->bi_sector;
        struct drbd_tl_epoch *b = NULL;
        struct drbd_request *req;
        struct net_conf *nc;
        int local, remote, send_oos = 0;
        int err;
        int ret = 0;

        /* allocate outside of all locks; */
        req = drbd_req_new(mdev, bio);
        if (!req) {
                dec_ap_bio(mdev);
                /* only pass the error to the upper layers.
                 * if user cannot handle io errors, that's not our business. */
                dev_err(DEV, "could not kmalloc() req\n");
                bio_endio(bio, -ENOMEM);
                return 0;
        }
        req->start_time = start_time;

        local = get_ldev(mdev);
        if (!local) {
                bio_put(req->private_bio); /* or we get a bio leak */
                req->private_bio = NULL;
        }
        if (rw == WRITE) {
                remote = 1;
        } else {
                /* READ || READA */
                if (local) {
                        if (!drbd_may_do_local_read(mdev, sector, size)) {
                                /* we could kick the syncer to
                                 * sync this extent asap, wait for
                                 * it, then continue locally.
                                 * Or just issue the request remotely.
                                 */
                                local = 0;
                                bio_put(req->private_bio);
                                req->private_bio = NULL;
                                put_ldev(mdev);
                        }
                }
                remote = !local && mdev->state.pdsk >= D_UP_TO_DATE;
        }

        /* If we have a disk, but a READA request is mapped to remote,
         * we are R_PRIMARY, D_INCONSISTENT, SyncTarget.
         * Just fail that READA request right here.
         *
         * THINK: maybe fail all READA when not local?
         *        or make this configurable...
         *        if network is slow, READA won't do any good.
         */
        if (rw == READA && mdev->state.disk >= D_INCONSISTENT && !local) {
                err = -EWOULDBLOCK;
                goto fail_and_free_req;
        }

        /* For WRITES going to the local disk, grab a reference on the target
         * extent.  This waits for any resync activity in the corresponding
         * resync extent to finish, and, if necessary, pulls in the target
         * extent into the activity log, which involves further disk io because
         * of transactional on-disk meta data updates. */
        if (rw == WRITE && local && !test_bit(AL_SUSPENDED, &mdev->flags)) {
                req->rq_state |= RQ_IN_ACT_LOG;
                drbd_al_begin_io(mdev, &req->i);
        }

        remote = remote && drbd_should_do_remote(mdev->state);
        send_oos = rw == WRITE && drbd_should_send_out_of_sync(mdev->state);
        D_ASSERT(!(remote && send_oos));

        if (!(local || remote) && !drbd_suspended(mdev)) {
                if (__ratelimit(&drbd_ratelimit_state))
                        dev_err(DEV, "IO ERROR: neither local nor remote disk\n");
                err = -EIO;
                goto fail_free_complete;
        }

        /* For WRITE request, we have to make sure that we have an
         * unused_spare_tle, in case we need to start a new epoch.
         * I try to be smart and avoid to pre-allocate always "just in case",
         * but there is a race between testing the bit and pointer outside the
         * spinlock, and grabbing the spinlock.
         * if we lost that race, we retry.  */
        if (rw == WRITE && (remote || send_oos) &&
            mdev->tconn->unused_spare_tle == NULL &&
            test_bit(CREATE_BARRIER, &mdev->tconn->flags)) {
allocate_barrier:
                b = kmalloc(sizeof(struct drbd_tl_epoch), GFP_NOIO);
                if (!b) {
                        dev_err(DEV, "Failed to alloc barrier.\n");
                        err = -ENOMEM;
                        goto fail_free_complete;
                }
        }

        /* GOOD, everything prepared, grab the spin_lock */
        spin_lock_irq(&mdev->tconn->req_lock);

        if (rw == WRITE) {
                err = complete_conflicting_writes(mdev, sector, size);
                if (err) {
                        if (err != -ERESTARTSYS)
                                _conn_request_state(mdev->tconn,
                                                    NS(conn, C_TIMEOUT),
                                                    CS_HARD);
                        spin_unlock_irq(&mdev->tconn->req_lock);
                        err = -EIO;
                        goto fail_free_complete;
                }
        }

        if (drbd_suspended(mdev)) {
                /* If we got suspended, use the retry mechanism of
                   generic_make_request() to restart processing of this
                   bio. In the next call to drbd_make_request
                   we sleep in inc_ap_bio() */
                ret = 1;
                spin_unlock_irq(&mdev->tconn->req_lock);
                goto fail_free_complete;
        }

        if (remote || send_oos) {
                remote = drbd_should_do_remote(mdev->state);
                send_oos = rw == WRITE && drbd_should_send_out_of_sync(mdev->state);
                D_ASSERT(!(remote && send_oos));

                if (!(remote || send_oos))
                        dev_warn(DEV, "lost connection while grabbing the req_lock!\n");
                if (!(local || remote)) {
                        dev_err(DEV, "IO ERROR: neither local nor remote disk\n");
                        spin_unlock_irq(&mdev->tconn->req_lock);
                        err = -EIO;
                        goto fail_free_complete;
                }
        }

        if (b && mdev->tconn->unused_spare_tle == NULL) {
                mdev->tconn->unused_spare_tle = b;
                b = NULL;
        }
        if (rw == WRITE && (remote || send_oos) &&
            mdev->tconn->unused_spare_tle == NULL &&
            test_bit(CREATE_BARRIER, &mdev->tconn->flags)) {
                /* someone closed the current epoch
                 * while we were grabbing the spinlock */
                spin_unlock_irq(&mdev->tconn->req_lock);
                goto allocate_barrier;
        }


        /* Update disk stats */
        _drbd_start_io_acct(mdev, req, bio);

        /* _maybe_start_new_epoch(mdev);
         * If we need to generate a write barrier packet, we have to add the
         * new epoch (barrier) object, and queue the barrier packet for sending,
         * and queue the req's data after it _within the same lock_, otherwise
         * we have race conditions were the reorder domains could be mixed up.
         *
         * Even read requests may start a new epoch and queue the corresponding
         * barrier packet.  To get the write ordering right, we only have to
         * make sure that, if this is a write request and it triggered a
         * barrier packet, this request is queued within the same spinlock. */
        if ((remote || send_oos) && mdev->tconn->unused_spare_tle &&
            test_and_clear_bit(CREATE_BARRIER, &mdev->tconn->flags)) {
                _tl_add_barrier(mdev->tconn, mdev->tconn->unused_spare_tle);
                mdev->tconn->unused_spare_tle = NULL;
        } else {
                D_ASSERT(!(remote && rw == WRITE &&
                           test_bit(CREATE_BARRIER, &mdev->tconn->flags)));
        }

        /* NOTE
         * Actually, 'local' may be wrong here already, since we may have failed
         * to write to the meta data, and may become wrong anytime because of
         * local io-error for some other request, which would lead to us
         * "detaching" the local disk.
         *
         * 'remote' may become wrong any time because the network could fail.
         *
         * This is a harmless race condition, though, since it is handled
         * correctly at the appropriate places; so it just defers the failure
         * of the respective operation.
         */

        /* mark them early for readability.
         * this just sets some state flags. */
        if (remote)
                _req_mod(req, TO_BE_SENT);
        if (local)
                _req_mod(req, TO_BE_SUBMITTED);

        list_add_tail(&req->tl_requests, &mdev->tconn->newest_tle->requests);

        /* NOTE remote first: to get the concurrent write detection right,
         * we must register the request before start of local IO.  */
        if (remote) {
                /* either WRITE and C_CONNECTED,
                 * or READ, and no local disk,
                 * or READ, but not in sync.
                 */
                _req_mod(req, (rw == WRITE)
                                ? QUEUE_FOR_NET_WRITE
                                : QUEUE_FOR_NET_READ);
        }
        if (send_oos && drbd_set_out_of_sync(mdev, sector, size))
                _req_mod(req, QUEUE_FOR_SEND_OOS);

        rcu_read_lock();
        nc = rcu_dereference(mdev->tconn->net_conf);
        if (remote &&
            nc->on_congestion != OC_BLOCK && mdev->tconn->agreed_pro_version >= 96) {
                int congested = 0;

                if (nc->cong_fill &&
                    atomic_read(&mdev->ap_in_flight) >= nc->cong_fill) {
                        dev_info(DEV, "Congestion-fill threshold reached\n");
                        congested = 1;
                }

                if (mdev->act_log->used >= nc->cong_extents) {
                        dev_info(DEV, "Congestion-extents threshold reached\n");
                        congested = 1;
                }

                if (congested) {
                        queue_barrier(mdev); /* last barrier, after mirrored writes */

                        if (nc->on_congestion == OC_PULL_AHEAD)
                                _drbd_set_state(_NS(mdev, conn, C_AHEAD), 0, NULL);
                        else  /*nc->on_congestion == OC_DISCONNECT */
                                _drbd_set_state(_NS(mdev, conn, C_DISCONNECTING), 0, NULL);
                }
        }
        rcu_read_unlock();

        spin_unlock_irq(&mdev->tconn->req_lock);
        kfree(b); /* if someone else has beaten us to it... */

        if (local) {
                req->private_bio->bi_bdev = mdev->ldev->backing_bdev;

                /* State may have changed since we grabbed our reference on the
                 * mdev->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(mdev)) {
                        if (drbd_insert_fault(mdev,   rw == WRITE ? DRBD_FAULT_DT_WR
                                                    : rw == READ  ? DRBD_FAULT_DT_RD
                                                    :               DRBD_FAULT_DT_RA))
                                bio_endio(req->private_bio, -EIO);
                        else
                                generic_make_request(req->private_bio);
                        put_ldev(mdev);
                } else
                        bio_endio(req->private_bio, -EIO);
        }

        return 0;

fail_free_complete:
        if (req->rq_state & RQ_IN_ACT_LOG)
                drbd_al_complete_io(mdev, &req->i);
fail_and_free_req:
        if (local) {
                bio_put(req->private_bio);
                req->private_bio = NULL;
                put_ldev(mdev);
        }
        if (!ret)
                bio_endio(bio, err);

        drbd_req_free(req);
        dec_ap_bio(mdev);
        kfree(b);

        return ret;
}

int drbd_make_request(struct request_queue *q, struct bio *bio)
{
        struct drbd_conf *mdev = (struct drbd_conf *) q->queuedata;
        unsigned long start_time;

        start_time = jiffies;

        /*
         * what we "blindly" assume:
         */
        D_ASSERT(bio->bi_size > 0);
        D_ASSERT(IS_ALIGNED(bio->bi_size, 512));

        inc_ap_bio(mdev);
        return __drbd_make_request(mdev, bio, start_time);
}

/* This is called by bio_add_page().
 *
 * q->max_hw_sectors and other global limits are already enforced there.
 *
 * We need to call down to our lower level device,
 * in case it has special restrictions.
 *
 * We also may need to enforce configured max-bio-bvecs limits.
 *
 * As long as the BIO is empty we have to allow at least one bvec,
 * regardless of size and offset, so no need to ask lower levels.
 */
int drbd_merge_bvec(struct request_queue *q, struct bvec_merge_data *bvm, struct bio_vec *bvec)
{
        struct drbd_conf *mdev = (struct drbd_conf *) q->queuedata;
        unsigned int bio_size = bvm->bi_size;
        int limit = DRBD_MAX_BIO_SIZE;
        int backing_limit;

        if (bio_size && get_ldev(mdev)) {
                struct request_queue * const b =
                        mdev->ldev->backing_bdev->bd_disk->queue;
                if (b->merge_bvec_fn) {
                        backing_limit = b->merge_bvec_fn(b, bvm, bvec);
                        limit = min(limit, backing_limit);
                }
                put_ldev(mdev);
        }
        return limit;
}

void request_timer_fn(unsigned long data)
{
        struct drbd_conf *mdev = (struct drbd_conf *) data;
        struct drbd_tconn *tconn = mdev->tconn;
        struct drbd_request *req; /* oldest request */
        struct list_head *le;
        struct net_conf *nc;
        unsigned long ent = 0, dt = 0, et, nt; /* effective timeout = ko_count * timeout */

        rcu_read_lock();
        nc = rcu_dereference(tconn->net_conf);
        ent = nc ? nc->timeout * HZ/10 * nc->ko_count : 0;

        if (get_ldev(mdev)) {
                dt = rcu_dereference(mdev->ldev->disk_conf)->disk_timeout * HZ / 10;
                put_ldev(mdev);
        }
        rcu_read_unlock();

        et = min_not_zero(dt, ent);

        if (!et || (mdev->state.conn < C_WF_REPORT_PARAMS && mdev->state.disk <= D_FAILED))
                return; /* Recurring timer stopped */

        spin_lock_irq(&tconn->req_lock);
        le = &tconn->oldest_tle->requests;
        if (list_empty(le)) {
                spin_unlock_irq(&tconn->req_lock);
                mod_timer(&mdev->request_timer, jiffies + et);
                return;
        }

        le = le->prev;
        req = list_entry(le, struct drbd_request, tl_requests);
        if (ent && req->rq_state & RQ_NET_PENDING) {
                if (time_is_before_eq_jiffies(req->start_time + ent)) {
                        dev_warn(DEV, "Remote failed to finish a request within ko-count * timeout\n");
                        _drbd_set_state(_NS(mdev, conn, C_TIMEOUT), CS_VERBOSE | CS_HARD, NULL);
                }
        }
        if (dt && req->rq_state & RQ_LOCAL_PENDING) {
                if (time_is_before_eq_jiffies(req->start_time + dt)) {
                        dev_warn(DEV, "Local backing device failed to meet the disk-timeout\n");
                        __drbd_chk_io_error(mdev, 1);
                }
        }
        nt = (time_is_before_eq_jiffies(req->start_time + et) ? jiffies : req->start_time) + et;
        spin_unlock_irq(&tconn->req_lock);
        mod_timer(&mdev->request_timer, nt);
}