drbd: Hold a reference to ldev while doing meta-data IO

[deliverable/linux.git] / drivers / block / drbd / drbd_actlog.c

/*
   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>.

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

/* We maintain a trivial checksum in our on disk activity log.
 * With that we can ensure correct operation even when the storage
 * device might do a partial (last) sector write while losing power.
 */
struct __packed al_transaction {
        u32       magic;
        u32       tr_number;
        struct __packed {
                u32 pos;
                u32 extent; } updates[1 + AL_EXTENTS_PT];
        u32       xor_sum;
};

struct update_odbm_work {
        struct drbd_work w;
        unsigned int enr;
};

struct update_al_work {
        struct drbd_work w;
        struct lc_element *al_ext;
        struct completion event;
        unsigned int enr;
        /* if old_enr != LC_FREE, write corresponding bitmap sector, too */
        unsigned int old_enr;
};

struct drbd_atodb_wait {
        atomic_t           count;
        struct completion  io_done;
        struct drbd_conf   *mdev;
        int                error;
};


int w_al_write_transaction(struct drbd_conf *, struct drbd_work *, int);

void *drbd_md_get_buffer(struct drbd_conf *mdev)
{
        int r;

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

        return r ? NULL : page_address(mdev->md_io_page);
}

void drbd_md_put_buffer(struct drbd_conf *mdev)
{
        if (atomic_dec_and_test(&mdev->md_io_in_use))
                wake_up(&mdev->misc_wait);
}

static bool md_io_allowed(struct drbd_conf *mdev)
{
        enum drbd_disk_state ds = mdev->state.disk;
        return ds >= D_NEGOTIATING || ds == D_ATTACHING;
}

void wait_until_done_or_disk_failure(struct drbd_conf *mdev, unsigned int *done)
{
        wait_event(mdev->misc_wait, *done || !md_io_allowed(mdev));
}

static int _drbd_md_sync_page_io(struct drbd_conf *mdev,
                                 struct drbd_backing_dev *bdev,
                                 struct page *page, sector_t sector,
                                 int rw, int size)
{
        struct bio *bio;
        int ok;

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

        if ((rw & WRITE) && !test_bit(MD_NO_FUA, &mdev->flags))
                rw |= REQ_FUA | REQ_FLUSH;
        rw |= REQ_SYNC;

        bio = bio_alloc(GFP_NOIO, 1);
        bio->bi_bdev = bdev->md_bdev;
        bio->bi_sector = sector;
        ok = (bio_add_page(bio, page, size, 0) == size);
        if (!ok)
                goto out;
        bio->bi_private = &mdev->md_io;
        bio->bi_end_io = drbd_md_io_complete;
        bio->bi_rw = rw;

        if (!get_ldev_if_state(mdev, D_ATTACHING)) {  /* Corresponding put_ldev in drbd_md_io_complete() */
                dev_err(DEV, "ASSERT FAILED: get_ldev_if_state() == 1 in _drbd_md_sync_page_io()\n");
                ok = 0;
                goto out;
        }

        bio_get(bio); /* one bio_put() is in the completion handler */
        atomic_inc(&mdev->md_io_in_use); /* drbd_md_put_buffer() is in the completion handler */
        if (drbd_insert_fault(mdev, (rw & WRITE) ? DRBD_FAULT_MD_WR : DRBD_FAULT_MD_RD))
                bio_endio(bio, -EIO);
        else
                submit_bio(rw, bio);
        wait_until_done_or_disk_failure(mdev, &mdev->md_io.done);
        ok = bio_flagged(bio, BIO_UPTODATE) && mdev->md_io.error == 0;

 out:
        bio_put(bio);
        return ok;
}

int drbd_md_sync_page_io(struct drbd_conf *mdev, struct drbd_backing_dev *bdev,
                         sector_t sector, int rw)
{
        int logical_block_size, mask, ok;
        int offset = 0;
        struct page *iop = mdev->md_io_page;

        D_ASSERT(atomic_read(&mdev->md_io_in_use) == 1);

        BUG_ON(!bdev->md_bdev);

        logical_block_size = bdev_logical_block_size(bdev->md_bdev);
        if (logical_block_size == 0)
                logical_block_size = MD_SECTOR_SIZE;

        /* in case logical_block_size != 512 [ s390 only? ] */
        if (logical_block_size != MD_SECTOR_SIZE) {
                mask = (logical_block_size / MD_SECTOR_SIZE) - 1;
                D_ASSERT(mask == 1 || mask == 3 || mask == 7);
                D_ASSERT(logical_block_size == (mask+1) * MD_SECTOR_SIZE);
                offset = sector & mask;
                sector = sector & ~mask;
                iop = mdev->md_io_tmpp;

                if (rw & WRITE) {
                        /* these are GFP_KERNEL pages, pre-allocated
                         * on device initialization */
                        void *p = page_address(mdev->md_io_page);
                        void *hp = page_address(mdev->md_io_tmpp);

                        ok = _drbd_md_sync_page_io(mdev, bdev, iop, sector,
                                        READ, logical_block_size);

                        if (unlikely(!ok)) {
                                dev_err(DEV, "drbd_md_sync_page_io(,%llus,"
                                    "READ [logical_block_size!=512]) failed!\n",
                                    (unsigned long long)sector);
                                return 0;
                        }

                        memcpy(hp + offset*MD_SECTOR_SIZE, p, MD_SECTOR_SIZE);
                }
        }

        if (sector < drbd_md_first_sector(bdev) ||
            sector > drbd_md_last_sector(bdev))
                dev_alert(DEV, "%s [%d]:%s(,%llus,%s) out of range md access!\n",
                     current->comm, current->pid, __func__,
                     (unsigned long long)sector, (rw & WRITE) ? "WRITE" : "READ");

        ok = _drbd_md_sync_page_io(mdev, bdev, iop, sector, rw, logical_block_size);
        if (unlikely(!ok)) {
                dev_err(DEV, "drbd_md_sync_page_io(,%llus,%s) failed!\n",
                    (unsigned long long)sector, (rw & WRITE) ? "WRITE" : "READ");
                return 0;
        }

        if (logical_block_size != MD_SECTOR_SIZE && !(rw & WRITE)) {
                void *p = page_address(mdev->md_io_page);
                void *hp = page_address(mdev->md_io_tmpp);

                memcpy(p, hp + offset*MD_SECTOR_SIZE, MD_SECTOR_SIZE);
        }

        return ok;
}

static struct lc_element *_al_get(struct drbd_conf *mdev, unsigned int enr)
{
        struct lc_element *al_ext;
        struct lc_element *tmp;
        unsigned long     al_flags = 0;
        int wake;

        spin_lock_irq(&mdev->al_lock);
        tmp = lc_find(mdev->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)) {
                        wake = !test_and_set_bit(BME_PRIORITY, &bm_ext->flags);
                        spin_unlock_irq(&mdev->al_lock);
                        if (wake)
                                wake_up(&mdev->al_wait);
                        return NULL;
                }
        }
        al_ext   = lc_get(mdev->act_log, enr);
        al_flags = mdev->act_log->flags;
        spin_unlock_irq(&mdev->al_lock);

        /*
        if (!al_ext) {
                if (al_flags & LC_STARVING)
                        dev_warn(DEV, "Have to wait for LRU element (AL too small?)\n");
                if (al_flags & LC_DIRTY)
                        dev_warn(DEV, "Ongoing AL update (AL device too slow?)\n");
        }
        */

        return al_ext;
}

void drbd_al_begin_io(struct drbd_conf *mdev, sector_t sector)
{
        unsigned int enr = (sector >> (AL_EXTENT_SHIFT-9));
        struct lc_element *al_ext;
        struct update_al_work al_work;

        D_ASSERT(atomic_read(&mdev->local_cnt) > 0);

        wait_event(mdev->al_wait, (al_ext = _al_get(mdev, enr)));

        if (al_ext->lc_number != enr) {
                /* drbd_al_write_transaction(mdev,al_ext,enr);
                 * recurses into generic_make_request(), which
                 * disallows recursion, bios being serialized on the
                 * current->bio_tail list now.
                 * we have to delegate updates to the activity log
                 * to the worker thread. */
                init_completion(&al_work.event);
                al_work.al_ext = al_ext;
                al_work.enr = enr;
                al_work.old_enr = al_ext->lc_number;
                al_work.w.cb = w_al_write_transaction;
                drbd_queue_work_front(&mdev->data.work, &al_work.w);
                wait_for_completion(&al_work.event);

                mdev->al_writ_cnt++;

                spin_lock_irq(&mdev->al_lock);
                lc_changed(mdev->act_log, al_ext);
                spin_unlock_irq(&mdev->al_lock);
                wake_up(&mdev->al_wait);
        }
}

void drbd_al_complete_io(struct drbd_conf *mdev, sector_t sector)
{
        unsigned int enr = (sector >> (AL_EXTENT_SHIFT-9));
        struct lc_element *extent;
        unsigned long flags;

        spin_lock_irqsave(&mdev->al_lock, flags);

        extent = lc_find(mdev->act_log, enr);

        if (!extent) {
                spin_unlock_irqrestore(&mdev->al_lock, flags);
                dev_err(DEV, "al_complete_io() called on inactive extent %u\n", enr);
                return;
        }

        if (lc_put(mdev->act_log, extent) == 0)
                wake_up(&mdev->al_wait);

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

#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 unsigned int rs_extent_to_bm_page(unsigned int rs_enr)
{
        return rs_enr >>
                /* bit to page */
                ((PAGE_SHIFT + 3) -
                /* al extent number to bit */
                 (BM_EXT_SHIFT - BM_BLOCK_SHIFT));
}

int
w_al_write_transaction(struct drbd_conf *mdev, struct drbd_work *w, int unused)
{
        struct update_al_work *aw = container_of(w, struct update_al_work, w);
        struct lc_element *updated = aw->al_ext;
        const unsigned int new_enr = aw->enr;
        const unsigned int evicted = aw->old_enr;
        struct al_transaction *buffer;
        sector_t sector;
        int i, n, mx;
        unsigned int extent_nr;
        u32 xor_sum = 0;

        if (!get_ldev(mdev)) {
                dev_err(DEV,
                        "disk is %s, cannot start al transaction (-%d +%d)\n",
                        drbd_disk_str(mdev->state.disk), evicted, new_enr);
                complete(&((struct update_al_work *)w)->event);
                return 1;
        }
        /* do we have to do a bitmap write, first?
         * TODO reduce maximum latency:
         * submit both bios, then wait for both,
         * instead of doing two synchronous sector writes.
         * For now, we must not write the transaction,
         * if we cannot write out the bitmap of the evicted extent. */
        if (mdev->state.conn < C_CONNECTED && evicted != LC_FREE)
                drbd_bm_write_page(mdev, al_extent_to_bm_page(evicted));

        /* The bitmap write may have failed, causing a state change. */
        if (mdev->state.disk < D_INCONSISTENT) {
                dev_err(DEV,
                        "disk is %s, cannot write al transaction (-%d +%d)\n",
                        drbd_disk_str(mdev->state.disk), evicted, new_enr);
                complete(&((struct update_al_work *)w)->event);
                put_ldev(mdev);
                return 1;
        }

        buffer = drbd_md_get_buffer(mdev); /* protects md_io_buffer, al_tr_cycle, ... */
        if (!buffer) {
                dev_err(DEV, "disk failed while waiting for md_io buffer\n");
                complete(&((struct update_al_work *)w)->event);
                put_ldev(mdev);
                return 1;
        }

        buffer->magic = __constant_cpu_to_be32(DRBD_MAGIC);
        buffer->tr_number = cpu_to_be32(mdev->al_tr_number);

        n = lc_index_of(mdev->act_log, updated);

        buffer->updates[0].pos = cpu_to_be32(n);
        buffer->updates[0].extent = cpu_to_be32(new_enr);

        xor_sum ^= new_enr;

        mx = min_t(int, AL_EXTENTS_PT,
                   mdev->act_log->nr_elements - mdev->al_tr_cycle);
        for (i = 0; i < mx; i++) {
                unsigned idx = mdev->al_tr_cycle + i;
                extent_nr = lc_element_by_index(mdev->act_log, idx)->lc_number;
                buffer->updates[i+1].pos = cpu_to_be32(idx);
                buffer->updates[i+1].extent = cpu_to_be32(extent_nr);
                xor_sum ^= extent_nr;
        }
        for (; i < AL_EXTENTS_PT; i++) {
                buffer->updates[i+1].pos = __constant_cpu_to_be32(-1);
                buffer->updates[i+1].extent = __constant_cpu_to_be32(LC_FREE);
                xor_sum ^= LC_FREE;
        }
        mdev->al_tr_cycle += AL_EXTENTS_PT;
        if (mdev->al_tr_cycle >= mdev->act_log->nr_elements)
                mdev->al_tr_cycle = 0;

        buffer->xor_sum = cpu_to_be32(xor_sum);

        sector =  mdev->ldev->md.md_offset
                + mdev->ldev->md.al_offset + mdev->al_tr_pos;

        if (!drbd_md_sync_page_io(mdev, mdev->ldev, sector, WRITE))
                drbd_chk_io_error(mdev, 1, true);

        if (++mdev->al_tr_pos >
            div_ceil(mdev->act_log->nr_elements, AL_EXTENTS_PT))
                mdev->al_tr_pos = 0;

        D_ASSERT(mdev->al_tr_pos < MD_AL_MAX_SIZE);
        mdev->al_tr_number++;

        drbd_md_put_buffer(mdev);

        complete(&((struct update_al_work *)w)->event);
        put_ldev(mdev);

        return 1;
}

/**
 * drbd_al_read_tr() - Read a single transaction from the on disk activity log
 * @mdev:       DRBD device.
 * @bdev:       Block device to read form.
 * @b:          pointer to an al_transaction.
 * @index:      On disk slot of the transaction to read.
 *
 * Returns -1 on IO error, 0 on checksum error and 1 upon success.
 */
static int drbd_al_read_tr(struct drbd_conf *mdev,
                           struct drbd_backing_dev *bdev,
                           struct al_transaction *b,
                           int index)
{
        sector_t sector;
        int rv, i;
        u32 xor_sum = 0;

        sector = bdev->md.md_offset + bdev->md.al_offset + index;

        /* Dont process error normally,
         * as this is done before disk is attached! */
        if (!drbd_md_sync_page_io(mdev, bdev, sector, READ))
                return -1;

        rv = (be32_to_cpu(b->magic) == DRBD_MAGIC);

        for (i = 0; i < AL_EXTENTS_PT + 1; i++)
                xor_sum ^= be32_to_cpu(b->updates[i].extent);
        rv &= (xor_sum == be32_to_cpu(b->xor_sum));

        return rv;
}

/**
 * drbd_al_read_log() - Restores the activity log from its on disk representation.
 * @mdev:       DRBD device.
 * @bdev:       Block device to read form.
 *
 * Returns 1 on success, returns 0 when reading the log failed due to IO errors.
 */
int drbd_al_read_log(struct drbd_conf *mdev, struct drbd_backing_dev *bdev)
{
        struct al_transaction *buffer;
        int i;
        int rv;
        int mx;
        int active_extents = 0;
        int transactions = 0;
        int found_valid = 0;
        int from = 0;
        int to = 0;
        u32 from_tnr = 0;
        u32 to_tnr = 0;
        u32 cnr;

        mx = div_ceil(mdev->act_log->nr_elements, AL_EXTENTS_PT);

        /* lock out all other meta data io for now,
         * and make sure the page is mapped.
         */
        buffer = drbd_md_get_buffer(mdev);
        if (!buffer)
                return 0;

        /* Find the valid transaction in the log */
        for (i = 0; i <= mx; i++) {
                rv = drbd_al_read_tr(mdev, bdev, buffer, i);
                if (rv == 0)
                        continue;
                if (rv == -1) {
                        drbd_md_put_buffer(mdev);
                        return 0;
                }
                cnr = be32_to_cpu(buffer->tr_number);

                if (++found_valid == 1) {
                        from = i;
                        to = i;
                        from_tnr = cnr;
                        to_tnr = cnr;
                        continue;
                }
                if ((int)cnr - (int)from_tnr < 0) {
                        D_ASSERT(from_tnr - cnr + i - from == mx+1);
                        from = i;
                        from_tnr = cnr;
                }
                if ((int)cnr - (int)to_tnr > 0) {
                        D_ASSERT(cnr - to_tnr == i - to);
                        to = i;
                        to_tnr = cnr;
                }
        }

        if (!found_valid) {
                dev_warn(DEV, "No usable activity log found.\n");
                drbd_md_put_buffer(mdev);
                return 1;
        }

        /* Read the valid transactions.
         * dev_info(DEV, "Reading from %d to %d.\n",from,to); */
        i = from;
        while (1) {
                int j, pos;
                unsigned int extent_nr;
                unsigned int trn;

                rv = drbd_al_read_tr(mdev, bdev, buffer, i);
                ERR_IF(rv == 0) goto cancel;
                if (rv == -1) {
                        drbd_md_put_buffer(mdev);
                        return 0;
                }

                trn = be32_to_cpu(buffer->tr_number);

                spin_lock_irq(&mdev->al_lock);

                /* This loop runs backwards because in the cyclic
                   elements there might be an old version of the
                   updated element (in slot 0). So the element in slot 0
                   can overwrite old versions. */
                for (j = AL_EXTENTS_PT; j >= 0; j--) {
                        pos = be32_to_cpu(buffer->updates[j].pos);
                        extent_nr = be32_to_cpu(buffer->updates[j].extent);

                        if (extent_nr == LC_FREE)
                                continue;

                        lc_set(mdev->act_log, extent_nr, pos);
                        active_extents++;
                }
                spin_unlock_irq(&mdev->al_lock);

                transactions++;

cancel:
                if (i == to)
                        break;
                i++;
                if (i > mx)
                        i = 0;
        }

        mdev->al_tr_number = to_tnr+1;
        mdev->al_tr_pos = to;
        if (++mdev->al_tr_pos >
            div_ceil(mdev->act_log->nr_elements, AL_EXTENTS_PT))
                mdev->al_tr_pos = 0;

        /* ok, we are done with it */
        drbd_md_put_buffer(mdev);

        dev_info(DEV, "Found %d transactions (%d active extents) in activity log.\n",
             transactions, active_extents);

        return 1;
}

/**
 * drbd_al_apply_to_bm() - Sets the bitmap to diry(1) where covered ba active AL extents
 * @mdev:       DRBD device.
 */
void drbd_al_apply_to_bm(struct drbd_conf *mdev)
{
        unsigned int enr;
        unsigned long add = 0;
        char ppb[10];
        int i, tmp;

        wait_event(mdev->al_wait, lc_try_lock(mdev->act_log));

        for (i = 0; i < mdev->act_log->nr_elements; i++) {
                enr = lc_element_by_index(mdev->act_log, i)->lc_number;
                if (enr == LC_FREE)
                        continue;
                tmp = drbd_bm_ALe_set_all(mdev, enr);
                dynamic_dev_dbg(DEV, "AL: set %d bits in extent %u\n", tmp, enr);
                add += tmp;
        }

        lc_unlock(mdev->act_log);
        wake_up(&mdev->al_wait);

        dev_info(DEV, "Marked additional %s as out-of-sync based on AL.\n",
             ppsize(ppb, Bit2KB(add)));
}

static int _try_lc_del(struct drbd_conf *mdev, struct lc_element *al_ext)
{
        int rv;

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

        return rv;
}

/**
 * drbd_al_shrink() - Removes all active extents form the activity log
 * @mdev:       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 mdev->act_log with lc_try_lock() / lc_unlock()
 */
void drbd_al_shrink(struct drbd_conf *mdev)
{
        struct lc_element *al_ext;
        int i;

        D_ASSERT(test_bit(__LC_DIRTY, &mdev->act_log->flags));

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

        wake_up(&mdev->al_wait);
}

static int w_update_odbm(struct drbd_conf *mdev, struct drbd_work *w, int unused)
{
        struct update_odbm_work *udw = container_of(w, struct update_odbm_work, w);

        if (!get_ldev(mdev)) {
                if (__ratelimit(&drbd_ratelimit_state))
                        dev_warn(DEV, "Can not update on disk bitmap, local IO disabled.\n");
                kfree(udw);
                return 1;
        }

        drbd_bm_write_page(mdev, rs_extent_to_bm_page(udw->enr));
        put_ldev(mdev);

        kfree(udw);

        if (drbd_bm_total_weight(mdev) <= mdev->rs_failed) {
                switch (mdev->state.conn) {
                case C_SYNC_SOURCE:  case C_SYNC_TARGET:
                case C_PAUSED_SYNC_S: case C_PAUSED_SYNC_T:
                        drbd_resync_finished(mdev);
                default:
                        /* nothing to do */
                        break;
                }
        }
        drbd_bcast_sync_progress(mdev);

        return 1;
}


/* 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.
 *
 * TODO will be obsoleted once we have a caching lru of the on disk bitmap
 */
static void drbd_try_clear_on_disk_bm(struct drbd_conf *mdev, sector_t sector,
                                      int count, int success)
{
        struct lc_element *e;
        struct update_odbm_work *udw;

        unsigned int enr;

        D_ASSERT(atomic_read(&mdev->local_cnt));

        /* I simply assume that a sector/size pair never crosses
         * a 16 MB extent border. (Currently this is true...) */
        enr = BM_SECT_TO_EXT(sector);

        e = lc_get(mdev->resync, enr);
        if (e) {
                struct bm_extent *ext = lc_entry(e, struct bm_extent, lce);
                if (ext->lce.lc_number == enr) {
                        if (success)
                                ext->rs_left -= count;
                        else
                                ext->rs_failed += count;
                        if (ext->rs_left < ext->rs_failed) {
                                dev_err(DEV, "BAD! sector=%llus enr=%u rs_left=%d "
                                    "rs_failed=%d count=%d\n",
                                     (unsigned long long)sector,
                                     ext->lce.lc_number, ext->rs_left,
                                     ext->rs_failed, count);
                                dump_stack();

                                lc_put(mdev->resync, &ext->lce);
                                drbd_force_state(mdev, NS(conn, C_DISCONNECTING));
                                return;
                        }
                } 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(mdev, enr);
                        if (ext->flags != 0) {
                                dev_warn(DEV, "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) {
                                dev_warn(DEV, "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 = success ? 0 : count;
                        lc_changed(mdev->resync, &ext->lce);
                }
                lc_put(mdev->resync, &ext->lce);
                /* no race, we are within the al_lock! */

                if (ext->rs_left == ext->rs_failed) {
                        ext->rs_failed = 0;

                        udw = kmalloc(sizeof(*udw), GFP_ATOMIC);
                        if (udw) {
                                udw->enr = ext->lce.lc_number;
                                udw->w.cb = w_update_odbm;
                                drbd_queue_work_front(&mdev->data.work, &udw->w);
                        } else {
                                dev_warn(DEV, "Could not kmalloc an udw\n");
                        }
                }
        } else {
                dev_err(DEV, "lc_get() failed! locked=%d/%d flags=%lu\n",
                    mdev->resync_locked,
                    mdev->resync->nr_elements,
                    mdev->resync->flags);
        }
}

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

/* 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.
 *
 */
void __drbd_set_in_sync(struct drbd_conf *mdev, sector_t sector, int size,
                       const char *file, const unsigned int line)
{
        /* Is called from worker and receiver context _only_ */
        unsigned long sbnr, ebnr, lbnr;
        unsigned long count = 0;
        sector_t esector, nr_sectors;
        int wake_up = 0;
        unsigned long flags;

        if (size <= 0 || (size & 0x1ff) != 0 || size > DRBD_MAX_BIO_SIZE) {
                dev_err(DEV, "drbd_set_in_sync: sector=%llus size=%d nonsense!\n",
                                (unsigned long long)sector, size);
                return;
        }
        nr_sectors = drbd_get_capacity(mdev->this_bdev);
        esector = sector + (size >> 9) - 1;

        ERR_IF(sector >= nr_sectors) return;
        ERR_IF(esector >= nr_sectors) esector = (nr_sectors-1);

        lbnr = BM_SECT_TO_BIT(nr_sectors-1);

        /* we clear it (in sync).
         * round up start sector, round down end sector.  we make sure we only
         * clear full, aligned, BM_BLOCK_SIZE (4K) blocks */
        if (unlikely(esector < BM_SECT_PER_BIT-1))
                return;
        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);

        if (sbnr > ebnr)
                return;

        /*
         * ok, (capacity & 7) != 0 sometimes, but who cares...
         * we count rs_{total,left} in bits, not sectors.
         */
        count = drbd_bm_clear_bits(mdev, sbnr, ebnr);
        if (count && get_ldev(mdev)) {
                drbd_advance_rs_marks(mdev, drbd_bm_total_weight(mdev));
                spin_lock_irqsave(&mdev->al_lock, flags);
                drbd_try_clear_on_disk_bm(mdev, sector, count, true);
                spin_unlock_irqrestore(&mdev->al_lock, flags);

                /* just wake_up unconditional now, various lc_chaged(),
                 * lc_put() in drbd_try_clear_on_disk_bm(). */
                wake_up = 1;
                put_ldev(mdev);
        }
        if (wake_up)
                wake_up(&mdev->al_wait);
}

/*
 * this is intended to set one request worth of data out of sync.
 * affects at least 1 bit,
 * and at most 1+DRBD_MAX_BIO_SIZE/BM_BLOCK_SIZE bits.
 *
 * called by tl_clear and drbd_send_dblock (==drbd_make_request).
 * so this can be _any_ process.
 */
int __drbd_set_out_of_sync(struct drbd_conf *mdev, sector_t sector, int size,
                            const char *file, const unsigned int line)
{
        unsigned long sbnr, ebnr, lbnr, flags;
        sector_t esector, nr_sectors;
        unsigned int enr, count = 0;
        struct lc_element *e;

        if (size <= 0 || (size & 0x1ff) != 0 || size > DRBD_MAX_BIO_SIZE) {
                dev_err(DEV, "sector: %llus, size: %d\n",
                        (unsigned long long)sector, size);
                return 0;
        }

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

        nr_sectors = drbd_get_capacity(mdev->this_bdev);
        esector = sector + (size >> 9) - 1;

        ERR_IF(sector >= nr_sectors)
                goto out;
        ERR_IF(esector >= nr_sectors)
                esector = (nr_sectors-1);

        lbnr = BM_SECT_TO_BIT(nr_sectors-1);

        /* we set it out of sync,
         * we do not need to round anything here */
        sbnr = BM_SECT_TO_BIT(sector);
        ebnr = BM_SECT_TO_BIT(esector);

        /* ok, (capacity & 7) != 0 sometimes, but who cares...
         * we count rs_{total,left} in bits, not sectors.  */
        spin_lock_irqsave(&mdev->al_lock, flags);
        count = drbd_bm_set_bits(mdev, sbnr, ebnr);

        enr = BM_SECT_TO_EXT(sector);
        e = lc_find(mdev->resync, enr);
        if (e)
                lc_entry(e, struct bm_extent, lce)->rs_left += count;
        spin_unlock_irqrestore(&mdev->al_lock, flags);

out:
        put_ldev(mdev);

        return count;
}

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

        spin_lock_irq(&mdev->al_lock);
        if (mdev->resync_locked > mdev->resync->nr_elements/2) {
                spin_unlock_irq(&mdev->al_lock);
                return NULL;
        }
        e = lc_get(mdev->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(mdev, enr);
                        bm_ext->rs_failed = 0;
                        lc_changed(mdev->resync, &bm_ext->lce);
                        wakeup = 1;
                }
                if (bm_ext->lce.refcnt == 1)
                        mdev->resync_locked++;
                set_bit(BME_NO_WRITES, &bm_ext->flags);
        }
        rs_flags = mdev->resync->flags;
        spin_unlock_irq(&mdev->al_lock);
        if (wakeup)
                wake_up(&mdev->al_wait);

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

        return bm_ext;
}

static int _is_in_al(struct drbd_conf *mdev, unsigned int enr)
{
        struct lc_element *al_ext;
        int rv = 0;

        spin_lock_irq(&mdev->al_lock);
        if (unlikely(enr == mdev->act_log->new_number))
                rv = 1;
        else {
                al_ext = lc_find(mdev->act_log, enr);
                if (al_ext) {
                        if (al_ext->refcnt)
                                rv = 1;
                }
        }
        spin_unlock_irq(&mdev->al_lock);

        /*
        if (unlikely(rv)) {
                dev_info(DEV, "Delaying sync read until app's write is done\n");
        }
        */
        return rv;
}

/**
 * drbd_rs_begin_io() - Gets an extent in the resync LRU cache and sets it to BME_LOCKED
 * @mdev:       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_conf *mdev, sector_t sector)
{
        unsigned int enr = BM_SECT_TO_EXT(sector);
        struct bm_extent *bm_ext;
        int i, sig;
        int sa = 200; /* Step aside 200 times, then grab the extent and let app-IO wait.
                         200 times -> 20 seconds. */

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

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

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

                if (sig || (test_bit(BME_PRIORITY, &bm_ext->flags) && sa)) {
                        spin_lock_irq(&mdev->al_lock);
                        if (lc_put(mdev->resync, &bm_ext->lce) == 0) {
                                bm_ext->flags = 0; /* clears BME_NO_WRITES and eventually BME_PRIORITY */
                                mdev->resync_locked--;
                                wake_up(&mdev->al_wait);
                        }
                        spin_unlock_irq(&mdev->al_lock);
                        if (sig)
                                return -EINTR;
                        if (schedule_timeout_interruptible(HZ/10))
                                return -EINTR;
                        if (sa && --sa == 0)
                                dev_warn(DEV,"drbd_rs_begin_io() stepped aside for 20sec."
                                         "Resync stalled?\n");
                        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
 * @mdev:       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_conf *mdev, 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;

        spin_lock_irq(&mdev->al_lock);
        if (mdev->resync_wenr != LC_FREE && mdev->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(mdev->resync, mdev->resync_wenr);
                bm_ext = e ? lc_entry(e, struct bm_extent, lce) : NULL;
                if (bm_ext) {
                        D_ASSERT(!test_bit(BME_LOCKED, &bm_ext->flags));
                        D_ASSERT(test_bit(BME_NO_WRITES, &bm_ext->flags));
                        clear_bit(BME_NO_WRITES, &bm_ext->flags);
                        mdev->resync_wenr = LC_FREE;
                        if (lc_put(mdev->resync, &bm_ext->lce) == 0)
                                mdev->resync_locked--;
                        wake_up(&mdev->al_wait);
                } else {
                        dev_alert(DEV, "LOGIC BUG\n");
                }
        }
        /* TRY. */
        e = lc_try_get(mdev->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)) {
                        mdev->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(bm_ext->lce.refcnt > 0);
                }
                goto check_al;
        } else {
                /* do we rather want to try later? */
                if (mdev->resync_locked > mdev->resync->nr_elements-3)
                        goto try_again;
                /* Do or do not. There is no try. -- Yoda */
                e = lc_get(mdev->resync, enr);
                bm_ext = e ? lc_entry(e, struct bm_extent, lce) : NULL;
                if (!bm_ext) {
                        const unsigned long rs_flags = mdev->resync->flags;
                        if (rs_flags & LC_STARVING)
                                dev_warn(DEV, "Have to wait for element"
                                     " (resync LRU too small?)\n");
                        BUG_ON(rs_flags & LC_DIRTY);
                        goto try_again;
                }
                if (bm_ext->lce.lc_number != enr) {
                        bm_ext->rs_left = drbd_bm_e_weight(mdev, enr);
                        bm_ext->rs_failed = 0;
                        lc_changed(mdev->resync, &bm_ext->lce);
                        wake_up(&mdev->al_wait);
                        D_ASSERT(test_bit(BME_LOCKED, &bm_ext->flags) == 0);
                }
                set_bit(BME_NO_WRITES, &bm_ext->flags);
                D_ASSERT(bm_ext->lce.refcnt == 1);
                mdev->resync_locked++;
                goto check_al;
        }
check_al:
        for (i = 0; i < AL_EXT_PER_BM_SECT; i++) {
                if (unlikely(al_enr+i == mdev->act_log->new_number))
                        goto try_again;
                if (lc_is_used(mdev->act_log, al_enr+i))
                        goto try_again;
        }
        set_bit(BME_LOCKED, &bm_ext->flags);
proceed:
        mdev->resync_wenr = LC_FREE;
        spin_unlock_irq(&mdev->al_lock);
        return 0;

try_again:
        if (bm_ext)
                mdev->resync_wenr = enr;
        spin_unlock_irq(&mdev->al_lock);
        return -EAGAIN;
}

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

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

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

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

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

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

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

        spin_lock_irq(&mdev->al_lock);

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

        return 0;
}

/**
 * drbd_rs_failed_io() - Record information on a failure to resync the specified blocks
 * @mdev:       DRBD device.
 * @sector:     The sector number.
 * @size:       Size of failed IO operation, in byte.
 */
void drbd_rs_failed_io(struct drbd_conf *mdev, sector_t sector, int size)
{
        /* Is called from worker and receiver context _only_ */
        unsigned long sbnr, ebnr, lbnr;
        unsigned long count;
        sector_t esector, nr_sectors;
        int wake_up = 0;

        if (size <= 0 || (size & 0x1ff) != 0 || size > DRBD_MAX_BIO_SIZE) {
                dev_err(DEV, "drbd_rs_failed_io: sector=%llus size=%d nonsense!\n",
                                (unsigned long long)sector, size);
                return;
        }
        nr_sectors = drbd_get_capacity(mdev->this_bdev);
        esector = sector + (size >> 9) - 1;

        ERR_IF(sector >= nr_sectors) return;
        ERR_IF(esector >= nr_sectors) esector = (nr_sectors-1);

        lbnr = BM_SECT_TO_BIT(nr_sectors-1);

        /*
         * round up start sector, round down end sector.  we make sure we only
         * handle full, aligned, BM_BLOCK_SIZE (4K) blocks */
        if (unlikely(esector < BM_SECT_PER_BIT-1))
                return;
        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);

        if (sbnr > ebnr)
                return;

        /*
         * ok, (capacity & 7) != 0 sometimes, but who cares...
         * we count rs_{total,left} in bits, not sectors.
         */
        spin_lock_irq(&mdev->al_lock);
        count = drbd_bm_count_bits(mdev, sbnr, ebnr);
        if (count) {
                mdev->rs_failed += count;

                if (get_ldev(mdev)) {
                        drbd_try_clear_on_disk_bm(mdev, sector, count, false);
                        put_ldev(mdev);
                }

                /* just wake_up unconditional now, various lc_chaged(),
                 * lc_put() in drbd_try_clear_on_disk_bm(). */
                wake_up = 1;
        }
        spin_unlock_irq(&mdev->al_lock);
        if (wake_up)
                wake_up(&mdev->al_wait);
}