// SPDX-License-Identifier: GPL-2.0-or-later
/*
   drbd_actlog.c

   This file is part of DRBD by Philipp Reisner and Lars Ellenberg.

   Copyright (C) 2003-2008, LINBIT Information Technologies GmbH.
   Copyright (C) 2003-2008, Philipp Reisner <philipp.reisner@linbit.com>.
   Copyright (C) 2003-2008, Lars Ellenberg <lars.ellenberg@linbit.com>.


 */

#include <linux/slab.h>
#include <linux/crc32c.h>
#include <linux/drbd.h>
#include <linux/drbd_limits.h>
#include "drbd_int.h"


enum al_transaction_types {
        AL_TR_UPDATE = 0,
        AL_TR_INITIALIZED = 0xffff
};
/* all fields on disc in big endian */
struct __packed al_transaction_on_disk {
        /* don't we all like magic */
        __be32  magic;

        /* to identify the most recent transaction block
         * in the on disk ring buffer */
        __be32  tr_number;

        /* checksum on the full 4k block, with this field set to 0. */
        __be32  crc32c;

        /* type of transaction, special transaction types like:
         * purge-all, set-all-idle, set-all-active, ... to-be-defined
         * see also enum al_transaction_types */
        __be16  transaction_type;

        /* we currently allow only a few thousand extents,
         * so 16bit will be enough for the slot number. */

        /* how many updates in this transaction */
        __be16  n_updates;

        /* maximum slot number, "al-extents" in drbd.conf speak.
         * Having this in each transaction should make reconfiguration
         * of that parameter easier. */
        __be16  context_size;

        /* slot number the context starts with */
        __be16  context_start_slot_nr;

        /* Some reserved bytes.  Expected usage is a 64bit counter of
         * sectors-written since device creation, and other data generation tag
         * supporting usage */
        __be32  __reserved[4];

        /* --- 36 byte used --- */

        /* Reserve space for up to AL_UPDATES_PER_TRANSACTION changes
         * in one transaction, then use the remaining byte in the 4k block for
         * context information.  "Flexible" number of updates per transaction
         * does not help, as we have to account for the case when all update
         * slots are used anyways, so it would only complicate code without
         * additional benefit.
         */
        __be16  update_slot_nr[AL_UPDATES_PER_TRANSACTION];

        /* but the extent number is 32bit, which at an extent size of 4 MiB
         * allows to cover device sizes of up to 2**54 Byte (16 PiB) */
        __be32  update_extent_nr[AL_UPDATES_PER_TRANSACTION];

        /* --- 420 bytes used (36 + 64*6) --- */

        /* 4096 - 420 = 3676 = 919 * 4 */
        __be32  context[AL_CONTEXT_PER_TRANSACTION];
};

void *drbd_md_get_buffer(struct drbd_device *device, const char *intent)
{
        int r;

        wait_event(device->misc_wait,
                   (r = atomic_cmpxchg(&device->md_io.in_use, 0, 1)) == 0 ||
                   device->state.disk <= D_FAILED);

        if (r)
                return NULL;

        device->md_io.current_use = intent;
        device->md_io.start_jif = jiffies;
        device->md_io.submit_jif = device->md_io.start_jif - 1;
        return page_address(device->md_io.page);
}

void drbd_md_put_buffer(struct drbd_device *device)
{
        if (atomic_dec_and_test(&device->md_io.in_use))
                wake_up(&device->misc_wait);
}

void wait_until_done_or_force_detached(struct drbd_device *device, struct drbd_backing_dev *bdev,
                                     unsigned int *done)
{
        long dt;

        rcu_read_lock();
        dt = rcu_dereference(bdev->disk_conf)->disk_timeout;
        rcu_read_unlock();
        dt = dt * HZ / 10;
        if (dt == 0)
                dt = MAX_SCHEDULE_TIMEOUT;

        dt = wait_event_timeout(device->misc_wait,
                        *done || test_bit(FORCE_DETACH, &device->flags), dt);
        if (dt == 0) {
                drbd_err(device, "meta-data IO operation timed out\n");
                drbd_chk_io_error(device, 1, DRBD_FORCE_DETACH);
        }
}

static int _drbd_md_sync_page_io(struct drbd_device *device,
                                 struct drbd_backing_dev *bdev,
                                 sector_t sector, int op)
{
        struct bio *bio;
        /* we do all our meta data IO in aligned 4k blocks. */
        const int size = 4096;
        int err, op_flags = 0;

        device->md_io.done = 0;
        device->md_io.error = -ENODEV;

        if ((op == REQ_OP_WRITE) && !test_bit(MD_NO_FUA, &device->flags))
                op_flags |= REQ_FUA | REQ_PREFLUSH;
        op_flags |= REQ_SYNC;

        bio = bio_alloc_bioset(bdev->md_bdev, 1, op | op_flags, GFP_NOIO,
                               &drbd_md_io_bio_set);
        bio->bi_iter.bi_sector = sector;
        err = -EIO;
        if (bio_add_page(bio, device->md_io.page, size, 0) != size)
                goto out;
        bio->bi_private = device;
        bio->bi_end_io = drbd_md_endio;

        if (op != REQ_OP_WRITE && device->state.disk == D_DISKLESS && device->ldev == NULL)
                /* special case, drbd_md_read() during drbd_adm_attach(): no get_ldev */
                ;
        else if (!get_ldev_if_state(device, D_ATTACHING)) {
                /* Corresponding put_ldev in drbd_md_endio() */
                drbd_err(device, "ASSERT FAILED: get_ldev_if_state() == 1 in _drbd_md_sync_page_io()\n");
                err = -ENODEV;
                goto out;
        }

        bio_get(bio); /* one bio_put() is in the completion handler */
        atomic_inc(&device->md_io.in_use); /* drbd_md_put_buffer() is in the completion handler */
        device->md_io.submit_jif = jiffies;
        if (drbd_insert_fault(device, (op == REQ_OP_WRITE) ? DRBD_FAULT_MD_WR : DRBD_FAULT_MD_RD))
                bio_io_error(bio);
        else
                submit_bio(bio);
        wait_until_done_or_force_detached(device, bdev, &device->md_io.done);
        if (!bio->bi_status)
                err = device->md_io.error;

 out:
        bio_put(bio);
        return err;
}

int drbd_md_sync_page_io(struct drbd_device *device, struct drbd_backing_dev *bdev,
                         sector_t sector, int op)
{
        int err;
        D_ASSERT(device, atomic_read(&device->md_io.in_use) == 1);

        BUG_ON(!bdev->md_bdev);

        dynamic_drbd_dbg(device, "meta_data io: %s [%d]:%s(,%llus,%s) %pS\n",
             current->comm, current->pid, __func__,
             (unsigned long long)sector, (op == REQ_OP_WRITE) ? "WRITE" : "READ",
             (void*)_RET_IP_ );

        if (sector < drbd_md_first_sector(bdev) ||
            sector + 7 > drbd_md_last_sector(bdev))
                drbd_alert(device, "%s [%d]:%s(,%llus,%s) out of range md access!\n",
                     current->comm, current->pid, __func__,
                     (unsigned long long)sector,
                     (op == REQ_OP_WRITE) ? "WRITE" : "READ");

        err = _drbd_md_sync_page_io(device, bdev, sector, op);
        if (err) {
                drbd_err(device, "drbd_md_sync_page_io(,%llus,%s) failed with error %d\n",
                    (unsigned long long)sector,
                    (op == REQ_OP_WRITE) ? "WRITE" : "READ", err);
        }
        return err;
}

static struct bm_extent *find_active_resync_extent(struct drbd_device *device, unsigned int enr)
{
        struct lc_element *tmp;
        tmp = lc_find(device->resync, enr/AL_EXT_PER_BM_SECT);
        if (unlikely(tmp != NULL)) {
                struct bm_extent  *bm_ext = lc_entry(tmp, struct bm_extent, lce);
                if (test_bit(BME_NO_WRITES, &bm_ext->flags))
                        return bm_ext;
        }
        return NULL;
}

static struct lc_element *_al_get(struct drbd_device *device, unsigned int enr, bool nonblock)
{
        struct lc_element *al_ext;
        struct bm_extent *bm_ext;
        int wake;

        spin_lock_irq(&device->al_lock);
        bm_ext = find_active_resync_extent(device, enr);
        if (bm_ext) {
                wake = !test_and_set_bit(BME_PRIORITY, &bm_ext->flags);
                spin_unlock_irq(&device->al_lock);
                if (wake)
                        wake_up(&device->al_wait);
                return NULL;
        }
        if (nonblock)
                al_ext = lc_try_get(device->act_log, enr);
        else
                al_ext = lc_get(device->act_log, enr);
        spin_unlock_irq(&device->al_lock);
        return al_ext;
}

bool drbd_al_begin_io_fastpath(struct drbd_device *device, struct drbd_interval *i)
{
        /* for bios crossing activity log extent boundaries,
         * we may need to activate two extents in one go */
        unsigned first = i->sector >> (AL_EXTENT_SHIFT-9);
        unsigned last = i->size == 0 ? first : (i->sector + (i->size >> 9) - 1) >> (AL_EXTENT_SHIFT-9);

        D_ASSERT(device, first <= last);
        D_ASSERT(device, atomic_read(&device->local_cnt) > 0);

        /* FIXME figure out a fast path for bios crossing AL extent boundaries */
        if (first != last)
                return false;

        return _al_get(device, first, true);
}

bool drbd_al_begin_io_prepare(struct drbd_device *device, struct drbd_interval *i)
{
        /* for bios crossing activity log extent boundaries,
         * we may need to activate two extents in one go */
        unsigned first = i->sector >> (AL_EXTENT_SHIFT-9);
        unsigned last = i->size == 0 ? first : (i->sector + (i->size >> 9) - 1) >> (AL_EXTENT_SHIFT-9);
        unsigned enr;
        bool need_transaction = false;

        D_ASSERT(device, first <= last);
        D_ASSERT(device, atomic_read(&device->local_cnt) > 0);

        for (enr = first; enr <= last; enr++) {
                struct lc_element *al_ext;
                wait_event(device->al_wait,
                                (al_ext = _al_get(device, enr, false)) != NULL);
                if (al_ext->lc_number != enr)
                        need_transaction = true;
        }
        return need_transaction;
}

#if (PAGE_SHIFT + 3) < (AL_EXTENT_SHIFT - BM_BLOCK_SHIFT)
/* Currently BM_BLOCK_SHIFT, BM_EXT_SHIFT and AL_EXTENT_SHIFT
 * are still coupled, or assume too much about their relation.
 * Code below will not work if this is violated.
 * Will be cleaned up with some followup patch.
 */
# error FIXME
#endif

static unsigned int al_extent_to_bm_page(unsigned int al_enr)
{
        return al_enr >>
                /* bit to page */
                ((PAGE_SHIFT + 3) -
                /* al extent number to bit */
                 (AL_EXTENT_SHIFT - BM_BLOCK_SHIFT));
}

static sector_t al_tr_number_to_on_disk_sector(struct drbd_device *device)
{
        const unsigned int stripes = device->ldev->md.al_stripes;
        const unsigned int stripe_size_4kB = device->ldev->md.al_stripe_size_4k;

        /* transaction number, modulo on-disk ring buffer wrap around */
        unsigned int t = device->al_tr_number % (device->ldev->md.al_size_4k);

        /* ... to aligned 4k on disk block */
        t = ((t % stripes) * stripe_size_4kB) + t/stripes;

        /* ... to 512 byte sector in activity log */
        t *= 8;

        /* ... plus offset to the on disk position */
        return device->ldev->md.md_offset + device->ldev->md.al_offset + t;
}

static int __al_write_transaction(struct drbd_device *device, struct al_transaction_on_disk *buffer)
{
        struct lc_element *e;
        sector_t sector;
        int i, mx;
        unsigned extent_nr;
        unsigned crc = 0;
        int err = 0;

        memset(buffer, 0, sizeof(*buffer));
        buffer->magic = cpu_to_be32(DRBD_AL_MAGIC);
        buffer->tr_number = cpu_to_be32(device->al_tr_number);

        i = 0;

        drbd_bm_reset_al_hints(device);

        /* Even though no one can start to change this list
         * once we set the LC_LOCKED -- from drbd_al_begin_io(),
         * lc_try_lock_for_transaction() --, someone may still
         * be in the process of changing it. */
        spin_lock_irq(&device->al_lock);
        list_for_each_entry(e, &device->act_log->to_be_changed, list) {
                if (i == AL_UPDATES_PER_TRANSACTION) {
                        i++;
                        break;
                }
                buffer->update_slot_nr[i] = cpu_to_be16(e->lc_index);
                buffer->update_extent_nr[i] = cpu_to_be32(e->lc_new_number);
                if (e->lc_number != LC_FREE)
                        drbd_bm_mark_for_writeout(device,
                                        al_extent_to_bm_page(e->lc_number));
                i++;
        }
        spin_unlock_irq(&device->al_lock);
        BUG_ON(i > AL_UPDATES_PER_TRANSACTION);

        buffer->n_updates = cpu_to_be16(i);
        for ( ; i < AL_UPDATES_PER_TRANSACTION; i++) {
                buffer->update_slot_nr[i] = cpu_to_be16(-1);
                buffer->update_extent_nr[i] = cpu_to_be32(LC_FREE);
        }

        buffer->context_size = cpu_to_be16(device->act_log->nr_elements);
        buffer->context_start_slot_nr = cpu_to_be16(device->al_tr_cycle);

        mx = min_t(int, AL_CONTEXT_PER_TRANSACTION,
                   device->act_log->nr_elements - device->al_tr_cycle);
        for (i = 0; i < mx; i++) {
                unsigned idx = device->al_tr_cycle + i;
                extent_nr = lc_element_by_index(device->act_log, idx)->lc_number;
                buffer->context[i] = cpu_to_be32(extent_nr);
        }
        for (; i < AL_CONTEXT_PER_TRANSACTION; i++)
                buffer->context[i] = cpu_to_be32(LC_FREE);

        device->al_tr_cycle += AL_CONTEXT_PER_TRANSACTION;
        if (device->al_tr_cycle >= device->act_log->nr_elements)
                device->al_tr_cycle = 0;

        sector = al_tr_number_to_on_disk_sector(device);

        crc = crc32c(0, buffer, 4096);
        buffer->crc32c = cpu_to_be32(crc);

        if (drbd_bm_write_hinted(device))
                err = -EIO;
        else {
                bool write_al_updates;
                rcu_read_lock();
                write_al_updates = rcu_dereference(device->ldev->disk_conf)->al_updates;
                rcu_read_unlock();
                if (write_al_updates) {
                        if (drbd_md_sync_page_io(device, device->ldev, sector, WRITE)) {
                                err = -EIO;
                                drbd_chk_io_error(device, 1, DRBD_META_IO_ERROR);
                        } else {
                                device->al_tr_number++;
                                device->al_writ_cnt++;
                        }
                }
        }

        return err;
}

static int al_write_transaction(struct drbd_device *device)
{
        struct al_transaction_on_disk *buffer;
        int err;

        if (!get_ldev(device)) {
                drbd_err(device, "disk is %s, cannot start al transaction\n",
                        drbd_disk_str(device->state.disk));
                return -EIO;
        }

        /* The bitmap write may have failed, causing a state change. */
        if (device->state.disk < D_INCONSISTENT) {
                drbd_err(device,
                        "disk is %s, cannot write al transaction\n",
                        drbd_disk_str(device->state.disk));
                put_ldev(device);
                return -EIO;
        }

        /* protects md_io_buffer, al_tr_cycle, ... */
        buffer = drbd_md_get_buffer(device, __func__);
        if (!buffer) {
                drbd_err(device, "disk failed while waiting for md_io buffer\n");
                put_ldev(device);
                return -ENODEV;
        }

        err = __al_write_transaction(device, buffer);

        drbd_md_put_buffer(device);
        put_ldev(device);

        return err;
}


void drbd_al_begin_io_commit(struct drbd_device *device)
{
        bool locked = false;

        /* Serialize multiple transactions.
         * This uses test_and_set_bit, memory barrier is implicit.
         */
        wait_event(device->al_wait,
                        device->act_log->pending_changes == 0 ||
                        (locked = lc_try_lock_for_transaction(device->act_log)));

        if (locked) {
                /* Double check: it may have been committed by someone else,
                 * while we have been waiting for the lock. */
                if (device->act_log->pending_changes) {
                        bool write_al_updates;

                        rcu_read_lock();
                        write_al_updates = rcu_dereference(device->ldev->disk_conf)->al_updates;
                        rcu_read_unlock();

                        if (write_al_updates)
                                al_write_transaction(device);
                        spin_lock_irq(&device->al_lock);
                        /* FIXME
                        if (err)
                                we need an "lc_cancel" here;
                        */
                        lc_committed(device->act_log);
                        spin_unlock_irq(&device->al_lock);
                }
                lc_unlock(device->act_log);
                wake_up(&device->al_wait);
        }
}

/*
 * @delegate:   delegate activity log I/O to the worker thread
 */
void drbd_al_begin_io(struct drbd_device *device, struct drbd_interval *i)
{
        if (drbd_al_begin_io_prepare(device, i))
                drbd_al_begin_io_commit(device);
}

int drbd_al_begin_io_nonblock(struct drbd_device *device, struct drbd_interval *i)
{
        struct lru_cache *al = device->act_log;
        /* for bios crossing activity log extent boundaries,
         * we may need to activate two extents in one go */
        unsigned first = i->sector >> (AL_EXTENT_SHIFT-9);
        unsigned last = i->size == 0 ? first : (i->sector + (i->size >> 9) - 1) >> (AL_EXTENT_SHIFT-9);
        unsigned nr_al_extents;
        unsigned available_update_slots;
        unsigned enr;

        D_ASSERT(device, first <= last);

        nr_al_extents = 1 + last - first; /* worst case: all touched extends are cold. */
        available_update_slots = min(al->nr_elements - al->used,
                                al->max_pending_changes - al->pending_changes);

        /* We want all necessary updates for a given request within the same transaction
         * We could first check how many updates are *actually* needed,
         * and use that instead of the worst-case nr_al_extents */
        if (available_update_slots < nr_al_extents) {
                /* Too many activity log extents are currently "hot".
                 *
                 * If we have accumulated pending changes already,
                 * we made progress.
                 *
                 * If we cannot get even a single pending change through,
                 * stop the fast path until we made some progress,
                 * or requests to "cold" extents could be starved. */
                if (!al->pending_changes)
                        __set_bit(__LC_STARVING, &device->act_log->flags);
                return -ENOBUFS;
        }

        /* Is resync active in this area? */
        for (enr = first; enr <= last; enr++) {
                struct lc_element *tmp;
                tmp = lc_find(device->resync, enr/AL_EXT_PER_BM_SECT);
                if (unlikely(tmp != NULL)) {
                        struct bm_extent  *bm_ext = lc_entry(tmp, struct bm_extent, lce);
                        if (test_bit(BME_NO_WRITES, &bm_ext->flags)) {
                                if (!test_and_set_bit(BME_PRIORITY, &bm_ext->flags))
                                        return -EBUSY;
                                return -EWOULDBLOCK;
                        }
                }
        }

        /* Checkout the refcounts.
         * Given that we checked for available elements and update slots above,
         * this has to be successful. */
        for (enr = first; enr <= last; enr++) {
                struct lc_element *al_ext;
                al_ext = lc_get_cumulative(device->act_log, enr);
                if (!al_ext)
                        drbd_info(device, "LOGIC BUG for enr=%u\n", enr);
        }
        return 0;
}

void drbd_al_complete_io(struct drbd_device *device, struct drbd_interval *i)
{
        /* for bios crossing activity log extent boundaries,
         * we may need to activate two extents in one go */
        unsigned first = i->sector >> (AL_EXTENT_SHIFT-9);
        unsigned last = i->size == 0 ? first : (i->sector + (i->size >> 9) - 1) >> (AL_EXTENT_SHIFT-9);
        unsigned enr;
        struct lc_element *extent;
        unsigned long flags;

        D_ASSERT(device, first <= last);
        spin_lock_irqsave(&device->al_lock, flags);

        for (enr = first; enr <= last; enr++) {
                extent = lc_find(device->act_log, enr);
                if (!extent) {
                        drbd_err(device, "al_complete_io() called on inactive extent %u\n", enr);
                        continue;
                }
                lc_put(device->act_log, extent);
        }
        spin_unlock_irqrestore(&device->al_lock, flags);
        wake_up(&device->al_wait);
}

static int _try_lc_del(struct drbd_device *device, struct lc_element *al_ext)
{
        int rv;

        spin_lock_irq(&device->al_lock);
        rv = (al_ext->refcnt == 0);
        if (likely(rv))
                lc_del(device->act_log, al_ext);
        spin_unlock_irq(&device->al_lock);

        return rv;
}

/**
 * drbd_al_shrink() - Removes all active extents form the activity log
 * @device:     DRBD device.
 *
 * Removes all active extents form the activity log, waiting until
 * the reference count of each entry dropped to 0 first, of course.
 *
 * You need to lock device->act_log with lc_try_lock() / lc_unlock()
 */
void drbd_al_shrink(struct drbd_device *device)
{
        struct lc_element *al_ext;
        int i;

        D_ASSERT(device, test_bit(__LC_LOCKED, &device->act_log->flags));

        for (i = 0; i < device->act_log->nr_elements; i++) {
                al_ext = lc_element_by_index(device->act_log, i);
                if (al_ext->lc_number == LC_FREE)
                        continue;
                wait_event(device->al_wait, _try_lc_del(device, al_ext));
        }

        wake_up(&device->al_wait);
}

int drbd_al_initialize(struct drbd_device *device, void *buffer)
{
        struct al_transaction_on_disk *al = buffer;
        struct drbd_md *md = &device->ldev->md;
        int al_size_4k = md->al_stripes * md->al_stripe_size_4k;
        int i;

        __al_write_transaction(device, al);
        /* There may or may not have been a pending transaction. */
        spin_lock_irq(&device->al_lock);
        lc_committed(device->act_log);
        spin_unlock_irq(&device->al_lock);

        /* The rest of the transactions will have an empty "updates" list, and
         * are written out only to provide the context, and to initialize the
         * on-disk ring buffer. */
        for (i = 1; i < al_size_4k; i++) {
                int err = __al_write_transaction(device, al);
                if (err)
                        return err;
        }
        return 0;
}

static const char *drbd_change_sync_fname[] = {
        [RECORD_RS_FAILED] = "drbd_rs_failed_io",
        [SET_IN_SYNC] = "drbd_set_in_sync",
        [SET_OUT_OF_SYNC] = "drbd_set_out_of_sync"
};

/* ATTENTION. The AL's extents are 4MB each, while the extents in the
 * resync LRU-cache are 16MB each.
 * The caller of this function has to hold an get_ldev() reference.
 *
 * Adjusts the caching members ->rs_left (success) or ->rs_failed (!success),
 * potentially pulling in (and recounting the corresponding bits)
 * this resync extent into the resync extent lru cache.
 *
 * Returns whether all bits have been cleared for this resync extent,
 * precisely: (rs_left <= rs_failed)
 *
 * TODO will be obsoleted once we have a caching lru of the on disk bitmap
 */
static bool update_rs_extent(struct drbd_device *device,
                unsigned int enr, int count,
                enum update_sync_bits_mode mode)
{
        struct lc_element *e;

        D_ASSERT(device, atomic_read(&device->local_cnt));

        /* When setting out-of-sync bits,
         * we don't need it cached (lc_find).
         * But if it is present in the cache,
         * we should update the cached bit count.
         * Otherwise, that extent should be in the resync extent lru cache
         * already -- or we want to pull it in if necessary -- (lc_get),
         * then update and check rs_left and rs_failed. */
        if (mode == SET_OUT_OF_SYNC)
                e = lc_find(device->resync, enr);
        else
                e = lc_get(device->resync, enr);
        if (e) {
                struct bm_extent *ext = lc_entry(e, struct bm_extent, lce);
                if (ext->lce.lc_number == enr) {
                        if (mode == SET_IN_SYNC)
                                ext->rs_left -= count;
                        else if (mode == SET_OUT_OF_SYNC)
                                ext->rs_left += count;
                        else
                                ext->rs_failed += count;
                        if (ext->rs_left < ext->rs_failed) {
                                drbd_warn(device, "BAD! enr=%u rs_left=%d "
                                    "rs_failed=%d count=%d cstate=%s\n",
                                     ext->lce.lc_number, ext->rs_left,
                                     ext->rs_failed, count,
                                     drbd_conn_str(device->state.conn));

                                /* We don't expect to be able to clear more bits
                                 * than have been set when we originally counted
                                 * the set bits to cache that value in ext->rs_left.
                                 * Whatever the reason (disconnect during resync,
                                 * delayed local completion of an application write),
                                 * try to fix it up by recounting here. */
                                ext->rs_left = drbd_bm_e_weight(device, enr);
                        }
                } else {
                        /* Normally this element should be in the cache,
                         * since drbd_rs_begin_io() pulled it already in.
                         *
                         * But maybe an application write finished, and we set
                         * something outside the resync lru_cache in sync.
                         */
                        int rs_left = drbd_bm_e_weight(device, enr);
                        if (ext->flags != 0) {
                                drbd_warn(device, "changing resync lce: %d[%u;%02lx]"
                                     " -> %d[%u;00]\n",
                                     ext->lce.lc_number, ext->rs_left,
                                     ext->flags, enr, rs_left);
                                ext->flags = 0;
                        }
                        if (ext->rs_failed) {
                                drbd_warn(device, "Kicking resync_lru element enr=%u "
                                     "out with rs_failed=%d\n",
                                     ext->lce.lc_number, ext->rs_failed);
                        }
                        ext->rs_left = rs_left;
                        ext->rs_failed = (mode == RECORD_RS_FAILED) ? count : 0;
                        /* we don't keep a persistent log of the resync lru,
                         * we can commit any change right away. */
                        lc_committed(device->resync);
                }
                if (mode != SET_OUT_OF_SYNC)
                        lc_put(device->resync, &ext->lce);
                /* no race, we are within the al_lock! */

                if (ext->rs_left <= ext->rs_failed) {
                        ext->rs_failed = 0;
                        return true;
                }
        } else if (mode != SET_OUT_OF_SYNC) {
                /* be quiet if lc_find() did not find it. */
                drbd_err(device, "lc_get() failed! locked=%d/%d flags=%lu\n",
                    device->resync_locked,
                    device->resync->nr_elements,
                    device->resync->flags);
        }
        return false;
}

void drbd_advance_rs_marks(struct drbd_device *device, unsigned long still_to_go)
{
        unsigned long now = jiffies;
        unsigned long last = device->rs_mark_time[device->rs_last_mark];
        int next = (device->rs_last_mark + 1) % DRBD_SYNC_MARKS;
        if (time_after_eq(now, last + DRBD_SYNC_MARK_STEP)) {
                if (device->rs_mark_left[device->rs_last_mark] != still_to_go &&
                    device->state.conn != C_PAUSED_SYNC_T &&
                    device->state.conn != C_PAUSED_SYNC_S) {
                        device->rs_mark_time[next] = now;
                        device->rs_mark_left[next] = still_to_go;
                        device->rs_last_mark = next;
                }
        }
}

/* It is called lazy update, so don't do write-out too often. */
static bool lazy_bitmap_update_due(struct drbd_device *device)
{
        return time_after(jiffies, device->rs_last_bcast + 2*HZ);
}

static void maybe_schedule_on_disk_bitmap_update(struct drbd_device *device, bool rs_done)
{
        if (rs_done) {
                struct drbd_connection *connection = first_peer_device(device)->connection;
                if (connection->agreed_pro_version <= 95 ||
                    is_sync_target_state(device->state.conn))
                        set_bit(RS_DONE, &device->flags);
                        /* and also set RS_PROGRESS below */

                /* Else: rather wait for explicit notification via receive_state,
                 * to avoid uuids-rotated-too-fast causing full resync
                 * in next handshake, in case the replication link breaks
                 * at the most unfortunate time... */
        } else if (!lazy_bitmap_update_due(device))
                return;

        drbd_device_post_work(device, RS_PROGRESS);
}

static int update_sync_bits(struct drbd_device *device,
                unsigned long sbnr, unsigned long ebnr,
                enum update_sync_bits_mode mode)
{
        /*
         * We keep a count of set bits per resync-extent in the ->rs_left
         * caching member, so we need to loop and work within the resync extent
         * alignment. Typically this loop will execute exactly once.
         */
        unsigned long flags;
        unsigned long count = 0;
        unsigned int cleared = 0;
        while (sbnr <= ebnr) {
                /* set temporary boundary bit number to last bit number within
                 * the resync extent of the current start bit number,
                 * but cap at provided end bit number */
                unsigned long tbnr = min(ebnr, sbnr | BM_BLOCKS_PER_BM_EXT_MASK);
                unsigned long c;

                if (mode == RECORD_RS_FAILED)
                        /* Only called from drbd_rs_failed_io(), bits
                         * supposedly still set.  Recount, maybe some
                         * of the bits have been successfully cleared
                         * by application IO meanwhile.
                         */
                        c = drbd_bm_count_bits(device, sbnr, tbnr);
                else if (mode == SET_IN_SYNC)
                        c = drbd_bm_clear_bits(device, sbnr, tbnr);
                else /* if (mode == SET_OUT_OF_SYNC) */
                        c = drbd_bm_set_bits(device, sbnr, tbnr);

                if (c) {
                        spin_lock_irqsave(&device->al_lock, flags);
                        cleared += update_rs_extent(device, BM_BIT_TO_EXT(sbnr), c, mode);
                        spin_unlock_irqrestore(&device->al_lock, flags);
                        count += c;
                }
                sbnr = tbnr + 1;
        }
        if (count) {
                if (mode == SET_IN_SYNC) {
                        unsigned long still_to_go = drbd_bm_total_weight(device);
                        bool rs_is_done = (still_to_go <= device->rs_failed);
                        drbd_advance_rs_marks(device, still_to_go);
                        if (cleared || rs_is_done)
                                maybe_schedule_on_disk_bitmap_update(device, rs_is_done);
                } else if (mode == RECORD_RS_FAILED)
                        device->rs_failed += count;
                wake_up(&device->al_wait);
        }
        return count;
}

static bool plausible_request_size(int size)
{
        return size > 0
                && size <= DRBD_MAX_BATCH_BIO_SIZE
                && IS_ALIGNED(size, 512);
}

/* clear the bit corresponding to the piece of storage in question:
 * size byte of data starting from sector.  Only clear a bits of the affected
 * one ore more _aligned_ BM_BLOCK_SIZE blocks.
 *
 * called by worker on C_SYNC_TARGET and receiver on SyncSource.
 *
 */
int __drbd_change_sync(struct drbd_device *device, sector_t sector, int size,
                enum update_sync_bits_mode mode)
{
        /* Is called from worker and receiver context _only_ */
        unsigned long sbnr, ebnr, lbnr;
        unsigned long count = 0;
        sector_t esector, nr_sectors;

        /* This would be an empty REQ_PREFLUSH, be silent. */
        if ((mode == SET_OUT_OF_SYNC) && size == 0)
                return 0;

        if (!plausible_request_size(size)) {
                drbd_err(device, "%s: sector=%llus size=%d nonsense!\n",
                                drbd_change_sync_fname[mode],
                                (unsigned long long)sector, size);
                return 0;
        }

        if (!get_ldev(device))
                return 0; /* no disk, no metadata, no bitmap to manipulate bits in */

        nr_sectors = get_capacity(device->vdisk);
        esector = sector + (size >> 9) - 1;

        if (!expect(sector < nr_sectors))
                goto out;
        if (!expect(esector < nr_sectors))
                esector = nr_sectors - 1;

        lbnr = BM_SECT_TO_BIT(nr_sectors-1);

        if (mode == SET_IN_SYNC) {
                /* Round up start sector, round down end sector.  We make sure
                 * we only clear full, aligned, BM_BLOCK_SIZE blocks. */
                if (unlikely(esector < BM_SECT_PER_BIT-1))
                        goto out;
                if (unlikely(esector == (nr_sectors-1)))
                        ebnr = lbnr;
                else
                        ebnr = BM_SECT_TO_BIT(esector - (BM_SECT_PER_BIT-1));
                sbnr = BM_SECT_TO_BIT(sector + BM_SECT_PER_BIT-1);
        } else {
                /* We set it out of sync, or record resync failure.
                 * Should not round anything here. */
                sbnr = BM_SECT_TO_BIT(sector);
                ebnr = BM_SECT_TO_BIT(esector);
        }

        count = update_sync_bits(device, sbnr, ebnr, mode);
out:
        put_ldev(device);
        return count;
}

static
struct bm_extent *_bme_get(struct drbd_device *device, unsigned int enr)
{
        struct lc_element *e;
        struct bm_extent *bm_ext;
        int wakeup = 0;
        unsigned long rs_flags;

        spin_lock_irq(&device->al_lock);
        if (device->resync_locked > device->resync->nr_elements/2) {
                spin_unlock_irq(&device->al_lock);
                return NULL;
        }
        e = lc_get(device->resync, enr);
        bm_ext = e ? lc_entry(e, struct bm_extent, lce) : NULL;
        if (bm_ext) {
                if (bm_ext->lce.lc_number != enr) {
                        bm_ext->rs_left = drbd_bm_e_weight(device, enr);
                        bm_ext->rs_failed = 0;
                        lc_committed(device->resync);
                        wakeup = 1;
                }
                if (bm_ext->lce.refcnt == 1)
                        device->resync_locked++;
                set_bit(BME_NO_WRITES, &bm_ext->flags);
        }
        rs_flags = device->resync->flags;
        spin_unlock_irq(&device->al_lock);
        if (wakeup)
                wake_up(&device->al_wait);

        if (!bm_ext) {
                if (rs_flags & LC_STARVING)
                        drbd_warn(device, "Have to wait for element"
                             " (resync LRU too small?)\n");
                BUG_ON(rs_flags & LC_LOCKED);
        }

        return bm_ext;
}

static int _is_in_al(struct drbd_device *device, unsigned int enr)
{
        int rv;

        spin_lock_irq(&device->al_lock);
        rv = lc_is_used(device->act_log, enr);
        spin_unlock_irq(&device->al_lock);

        return rv;
}

/**
 * drbd_rs_begin_io() - Gets an extent in the resync LRU cache and sets it to BME_LOCKED
 * @device:     DRBD device.
 * @sector:     The sector number.
 *
 * This functions sleeps on al_wait. Returns 0 on success, -EINTR if interrupted.
 */
int drbd_rs_begin_io(struct drbd_device *device, sector_t sector)
{
        unsigned int enr = BM_SECT_TO_EXT(sector);
        struct bm_extent *bm_ext;
        int i, sig;
        bool sa;

retry:
        sig = wait_event_interruptible(device->al_wait,
                        (bm_ext = _bme_get(device, enr)));
        if (sig)
                return -EINTR;

        if (test_bit(BME_LOCKED, &bm_ext->flags))
                return 0;

        /* step aside only while we are above c-min-rate; unless disabled. */
        sa = drbd_rs_c_min_rate_throttle(device);

        for (i = 0; i < AL_EXT_PER_BM_SECT; i++) {
                sig = wait_event_interruptible(device->al_wait,
                                               !_is_in_al(device, enr * AL_EXT_PER_BM_SECT + i) ||
                                               (sa && test_bit(BME_PRIORITY, &bm_ext->flags)));

                if (sig || (sa && test_bit(BME_PRIORITY, &bm_ext->flags))) {
                        spin_lock_irq(&device->al_lock);
                        if (lc_put(device->resync, &bm_ext->lce) == 0) {
                                bm_ext->flags = 0; /* clears BME_NO_WRITES and eventually BME_PRIORITY */
                                device->resync_locked--;
                                wake_up(&device->al_wait);
                        }
                        spin_unlock_irq(&device->al_lock);
                        if (sig)
                                return -EINTR;
                        if (schedule_timeout_interruptible(HZ/10))
                                return -EINTR;
                        goto retry;
                }
        }
        set_bit(BME_LOCKED, &bm_ext->flags);
        return 0;
}

/**
 * drbd_try_rs_begin_io() - Gets an extent in the resync LRU cache, does not sleep
 * @device:     DRBD device.
 * @sector:     The sector number.
 *
 * Gets an extent in the resync LRU cache, sets it to BME_NO_WRITES, then
 * tries to set it to BME_LOCKED. Returns 0 upon success, and -EAGAIN
 * if there is still application IO going on in this area.
 */
int drbd_try_rs_begin_io(struct drbd_device *device, sector_t sector)
{
        unsigned int enr = BM_SECT_TO_EXT(sector);
        const unsigned int al_enr = enr*AL_EXT_PER_BM_SECT;
        struct lc_element *e;
        struct bm_extent *bm_ext;
        int i;
        bool throttle = drbd_rs_should_slow_down(device, sector, true);

        /* If we need to throttle, a half-locked (only marked BME_NO_WRITES,
         * not yet BME_LOCKED) extent needs to be kicked out explicitly if we
         * need to throttle. There is at most one such half-locked extent,
         * which is remembered in resync_wenr. */

        if (throttle && device->resync_wenr != enr)
                return -EAGAIN;

        spin_lock_irq(&device->al_lock);
        if (device->resync_wenr != LC_FREE && device->resync_wenr != enr) {
                /* in case you have very heavy scattered io, it may
                 * stall the syncer undefined if we give up the ref count
                 * when we try again and requeue.
                 *
                 * if we don't give up the refcount, but the next time
                 * we are scheduled this extent has been "synced" by new
                 * application writes, we'd miss the lc_put on the
                 * extent we keep the refcount on.
                 * so we remembered which extent we had to try again, and
                 * if the next requested one is something else, we do
                 * the lc_put here...
                 * we also have to wake_up
                 */
                e = lc_find(device->resync, device->resync_wenr);
                bm_ext = e ? lc_entry(e, struct bm_extent, lce) : NULL;
                if (bm_ext) {
                        D_ASSERT(device, !test_bit(BME_LOCKED, &bm_ext->flags));
                        D_ASSERT(device, test_bit(BME_NO_WRITES, &bm_ext->flags));
                        clear_bit(BME_NO_WRITES, &bm_ext->flags);
                        device->resync_wenr = LC_FREE;
                        if (lc_put(device->resync, &bm_ext->lce) == 0) {
                                bm_ext->flags = 0;
                                device->resync_locked--;
                        }
                        wake_up(&device->al_wait);
                } else {
                        drbd_alert(device, "LOGIC BUG\n");
                }
        }
        /* TRY. */
        e = lc_try_get(device->resync, enr);
        bm_ext = e ? lc_entry(e, struct bm_extent, lce) : NULL;
        if (bm_ext) {
                if (test_bit(BME_LOCKED, &bm_ext->flags))
                        goto proceed;
                if (!test_and_set_bit(BME_NO_WRITES, &bm_ext->flags)) {
                        device->resync_locked++;
                } else {
                        /* we did set the BME_NO_WRITES,
                         * but then could not set BME_LOCKED,
                         * so we tried again.
                         * drop the extra reference. */
                        bm_ext->lce.refcnt--;
                        D_ASSERT(device, bm_ext->lce.refcnt > 0);
                }
                goto check_al;
        } else {
                /* do we rather want to try later? */
                if (device->resync_locked > device->resync->nr_elements-3)
                        goto try_again;
                /* Do or do not. There is no try. -- Yoda */
                e = lc_get(device->resync, enr);
                bm_ext = e ? lc_entry(e, struct bm_extent, lce) : NULL;
                if (!bm_ext) {
                        const unsigned long rs_flags = device->resync->flags;
                        if (rs_flags & LC_STARVING)
                                drbd_warn(device, "Have to wait for element"
                                     " (resync LRU too small?)\n");
                        BUG_ON(rs_flags & LC_LOCKED);
                        goto try_again;
                }
                if (bm_ext->lce.lc_number != enr) {
                        bm_ext->rs_left = drbd_bm_e_weight(device, enr);
                        bm_ext->rs_failed = 0;
                        lc_committed(device->resync);
                        wake_up(&device->al_wait);
                        D_ASSERT(device, test_bit(BME_LOCKED, &bm_ext->flags) == 0);
                }
                set_bit(BME_NO_WRITES, &bm_ext->flags);
                D_ASSERT(device, bm_ext->lce.refcnt == 1);
                device->resync_locked++;
                goto check_al;
        }
check_al:
        for (i = 0; i < AL_EXT_PER_BM_SECT; i++) {
                if (lc_is_used(device->act_log, al_enr+i))
                        goto try_again;
        }
        set_bit(BME_LOCKED, &bm_ext->flags);
proceed:
        device->resync_wenr = LC_FREE;
        spin_unlock_irq(&device->al_lock);
        return 0;

try_again:
        if (bm_ext) {
                if (throttle) {
                        D_ASSERT(device, !test_bit(BME_LOCKED, &bm_ext->flags));
                        D_ASSERT(device, test_bit(BME_NO_WRITES, &bm_ext->flags));
                        clear_bit(BME_NO_WRITES, &bm_ext->flags);
                        device->resync_wenr = LC_FREE;
                        if (lc_put(device->resync, &bm_ext->lce) == 0) {
                                bm_ext->flags = 0;
                                device->resync_locked--;
                        }
                        wake_up(&device->al_wait);
                } else
                        device->resync_wenr = enr;
        }
        spin_unlock_irq(&device->al_lock);
        return -EAGAIN;
}

void drbd_rs_complete_io(struct drbd_device *device, sector_t sector)
{
        unsigned int enr = BM_SECT_TO_EXT(sector);
        struct lc_element *e;
        struct bm_extent *bm_ext;
        unsigned long flags;

        spin_lock_irqsave(&device->al_lock, flags);
        e = lc_find(device->resync, enr);
        bm_ext = e ? lc_entry(e, struct bm_extent, lce) : NULL;
        if (!bm_ext) {
                spin_unlock_irqrestore(&device->al_lock, flags);
                if (__ratelimit(&drbd_ratelimit_state))
                        drbd_err(device, "drbd_rs_complete_io() called, but extent not found\n");
                return;
        }

        if (bm_ext->lce.refcnt == 0) {
                spin_unlock_irqrestore(&device->al_lock, flags);
                drbd_err(device, "drbd_rs_complete_io(,%llu [=%u]) called, "
                    "but refcnt is 0!?\n",
                    (unsigned long long)sector, enr);
                return;
        }

        if (lc_put(device->resync, &bm_ext->lce) == 0) {
                bm_ext->flags = 0; /* clear BME_LOCKED, BME_NO_WRITES and BME_PRIORITY */
                device->resync_locked--;
                wake_up(&device->al_wait);
        }

        spin_unlock_irqrestore(&device->al_lock, flags);
}

/**
 * drbd_rs_cancel_all() - Removes all extents from the resync LRU (even BME_LOCKED)
 * @device:     DRBD device.
 */
void drbd_rs_cancel_all(struct drbd_device *device)
{
        spin_lock_irq(&device->al_lock);

        if (get_ldev_if_state(device, D_FAILED)) { /* Makes sure ->resync is there. */
                lc_reset(device->resync);
                put_ldev(device);
        }
        device->resync_locked = 0;
        device->resync_wenr = LC_FREE;
        spin_unlock_irq(&device->al_lock);
        wake_up(&device->al_wait);
}

/**
 * drbd_rs_del_all() - Gracefully remove all extents from the resync LRU
 * @device:     DRBD device.
 *
 * Returns 0 upon success, -EAGAIN if at least one reference count was
 * not zero.
 */
int drbd_rs_del_all(struct drbd_device *device)
{
        struct lc_element *e;
        struct bm_extent *bm_ext;
        int i;

        spin_lock_irq(&device->al_lock);

        if (get_ldev_if_state(device, D_FAILED)) {
                /* ok, ->resync is there. */
                for (i = 0; i < device->resync->nr_elements; i++) {
                        e = lc_element_by_index(device->resync, i);
                        bm_ext = lc_entry(e, struct bm_extent, lce);
                        if (bm_ext->lce.lc_number == LC_FREE)
                                continue;
                        if (bm_ext->lce.lc_number == device->resync_wenr) {
                                drbd_info(device, "dropping %u in drbd_rs_del_all, apparently"
                                     " got 'synced' by application io\n",
                                     device->resync_wenr);
                                D_ASSERT(device, !test_bit(BME_LOCKED, &bm_ext->flags));
                                D_ASSERT(device, test_bit(BME_NO_WRITES, &bm_ext->flags));
                                clear_bit(BME_NO_WRITES, &bm_ext->flags);
                                device->resync_wenr = LC_FREE;
                                lc_put(device->resync, &bm_ext->lce);
                        }
                        if (bm_ext->lce.refcnt != 0) {
                                drbd_info(device, "Retrying drbd_rs_del_all() later. "
                                     "refcnt=%d\n", bm_ext->lce.refcnt);
                                put_ldev(device);
                                spin_unlock_irq(&device->al_lock);
                                return -EAGAIN;
                        }
                        D_ASSERT(device, !test_bit(BME_LOCKED, &bm_ext->flags));
                        D_ASSERT(device, !test_bit(BME_NO_WRITES, &bm_ext->flags));
                        lc_del(device->resync, &bm_ext->lce);
                }
                D_ASSERT(device, device->resync->used == 0);
                put_ldev(device);
        }
        spin_unlock_irq(&device->al_lock);
        wake_up(&device->al_wait);

        return 0;
}