Rebase master to b117

[mirror_zfs-debian.git] / module / zfs / dnode_sync.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */

#include <sys/zfs_context.h>
#include <sys/dbuf.h>
#include <sys/dnode.h>
#include <sys/dmu.h>
#include <sys/dmu_tx.h>
#include <sys/dmu_objset.h>
#include <sys/dsl_dataset.h>
#include <sys/spa.h>

static void
dnode_increase_indirection(dnode_t *dn, dmu_tx_t *tx)
{
        dmu_buf_impl_t *db;
        int txgoff = tx->tx_txg & TXG_MASK;
        int nblkptr = dn->dn_phys->dn_nblkptr;
        int old_toplvl = dn->dn_phys->dn_nlevels - 1;
        int new_level = dn->dn_next_nlevels[txgoff];
        int i;

        rw_enter(&dn->dn_struct_rwlock, RW_WRITER);

        /* this dnode can't be paged out because it's dirty */
        ASSERT(dn->dn_phys->dn_type != DMU_OT_NONE);
        ASSERT(RW_WRITE_HELD(&dn->dn_struct_rwlock));
        ASSERT(new_level > 1 && dn->dn_phys->dn_nlevels > 0);

        db = dbuf_hold_level(dn, dn->dn_phys->dn_nlevels, 0, FTAG);
        ASSERT(db != NULL);

        dn->dn_phys->dn_nlevels = new_level;
        dprintf("os=%p obj=%llu, increase to %d\n", dn->dn_objset,
            dn->dn_object, dn->dn_phys->dn_nlevels);

        /* check for existing blkptrs in the dnode */
        for (i = 0; i < nblkptr; i++)
                if (!BP_IS_HOLE(&dn->dn_phys->dn_blkptr[i]))
                        break;
        if (i != nblkptr) {
                /* transfer dnode's block pointers to new indirect block */
                (void) dbuf_read(db, NULL, DB_RF_MUST_SUCCEED|DB_RF_HAVESTRUCT);
                ASSERT(db->db.db_data);
                ASSERT(arc_released(db->db_buf));
                ASSERT3U(sizeof (blkptr_t) * nblkptr, <=, db->db.db_size);
                bcopy(dn->dn_phys->dn_blkptr, db->db.db_data,
                    sizeof (blkptr_t) * nblkptr);
                arc_buf_freeze(db->db_buf);
        }

        /* set dbuf's parent pointers to new indirect buf */
        for (i = 0; i < nblkptr; i++) {
                dmu_buf_impl_t *child = dbuf_find(dn, old_toplvl, i);

                if (child == NULL)
                        continue;
                ASSERT3P(child->db_dnode, ==, dn);
                if (child->db_parent && child->db_parent != dn->dn_dbuf) {
                        ASSERT(child->db_parent->db_level == db->db_level);
                        ASSERT(child->db_blkptr !=
                            &dn->dn_phys->dn_blkptr[child->db_blkid]);
                        mutex_exit(&child->db_mtx);
                        continue;
                }
                ASSERT(child->db_parent == NULL ||
                    child->db_parent == dn->dn_dbuf);

                child->db_parent = db;
                dbuf_add_ref(db, child);
                if (db->db.db_data)
                        child->db_blkptr = (blkptr_t *)db->db.db_data + i;
                else
                        child->db_blkptr = NULL;
                dprintf_dbuf_bp(child, child->db_blkptr,
                    "changed db_blkptr to new indirect %s", "");

                mutex_exit(&child->db_mtx);
        }

        bzero(dn->dn_phys->dn_blkptr, sizeof (blkptr_t) * nblkptr);

        dbuf_rele(db, FTAG);

        rw_exit(&dn->dn_struct_rwlock);
}

static int
free_blocks(dnode_t *dn, blkptr_t *bp, int num, dmu_tx_t *tx)
{
        dsl_dataset_t *ds = dn->dn_objset->os_dsl_dataset;
        uint64_t bytesfreed = 0;
        int i, blocks_freed = 0;

        dprintf("ds=%p obj=%llx num=%d\n", ds, dn->dn_object, num);

        for (i = 0; i < num; i++, bp++) {
                if (BP_IS_HOLE(bp))
                        continue;

                bytesfreed += dsl_dataset_block_kill(ds, bp, dn->dn_zio, tx);
                ASSERT3U(bytesfreed, <=, DN_USED_BYTES(dn->dn_phys));
                bzero(bp, sizeof (blkptr_t));
                blocks_freed += 1;
        }
        dnode_diduse_space(dn, -bytesfreed);
        return (blocks_freed);
}

#ifdef ZFS_DEBUG
static void
free_verify(dmu_buf_impl_t *db, uint64_t start, uint64_t end, dmu_tx_t *tx)
{
        int off, num;
        int i, err, epbs;
        uint64_t txg = tx->tx_txg;

        epbs = db->db_dnode->dn_phys->dn_indblkshift - SPA_BLKPTRSHIFT;
        off = start - (db->db_blkid * 1<<epbs);
        num = end - start + 1;

        ASSERT3U(off, >=, 0);
        ASSERT3U(num, >=, 0);
        ASSERT3U(db->db_level, >, 0);
        ASSERT3U(db->db.db_size, ==, 1<<db->db_dnode->dn_phys->dn_indblkshift);
        ASSERT3U(off+num, <=, db->db.db_size >> SPA_BLKPTRSHIFT);
        ASSERT(db->db_blkptr != NULL);

        for (i = off; i < off+num; i++) {
                uint64_t *buf;
                dmu_buf_impl_t *child;
                dbuf_dirty_record_t *dr;
                int j;

                ASSERT(db->db_level == 1);

                rw_enter(&db->db_dnode->dn_struct_rwlock, RW_READER);
                err = dbuf_hold_impl(db->db_dnode, db->db_level-1,
                    (db->db_blkid << epbs) + i, TRUE, FTAG, &child);
                rw_exit(&db->db_dnode->dn_struct_rwlock);
                if (err == ENOENT)
                        continue;
                ASSERT(err == 0);
                ASSERT(child->db_level == 0);
                dr = child->db_last_dirty;
                while (dr && dr->dr_txg > txg)
                        dr = dr->dr_next;
                ASSERT(dr == NULL || dr->dr_txg == txg);

                /* data_old better be zeroed */
                if (dr) {
                        buf = dr->dt.dl.dr_data->b_data;
                        for (j = 0; j < child->db.db_size >> 3; j++) {
                                if (buf[j] != 0) {
                                        panic("freed data not zero: "
                                            "child=%p i=%d off=%d num=%d\n",
                                            (void *)child, i, off, num);
                                }
                        }
                }

                /*
                 * db_data better be zeroed unless it's dirty in a
                 * future txg.
                 */
                mutex_enter(&child->db_mtx);
                buf = child->db.db_data;
                if (buf != NULL && child->db_state != DB_FILL &&
                    child->db_last_dirty == NULL) {
                        for (j = 0; j < child->db.db_size >> 3; j++) {
                                if (buf[j] != 0) {
                                        panic("freed data not zero: "
                                            "child=%p i=%d off=%d num=%d\n",
                                            (void *)child, i, off, num);
                                }
                        }
                }
                mutex_exit(&child->db_mtx);

                dbuf_rele(child, FTAG);
        }
}
#endif

#define ALL -1

static int
free_children(dmu_buf_impl_t *db, uint64_t blkid, uint64_t nblks, int trunc,
    dmu_tx_t *tx)
{
        dnode_t *dn = db->db_dnode;
        blkptr_t *bp;
        dmu_buf_impl_t *subdb;
        uint64_t start, end, dbstart, dbend, i;
        int epbs, shift, err;
        int all = TRUE;
        int blocks_freed = 0;

        /*
         * There is a small possibility that this block will not be cached:
         *   1 - if level > 1 and there are no children with level <= 1
         *   2 - if we didn't get a dirty hold (because this block had just
         *       finished being written -- and so had no holds), and then this
         *       block got evicted before we got here.
         */
        if (db->db_state != DB_CACHED)
                (void) dbuf_read(db, NULL, DB_RF_MUST_SUCCEED);

        arc_release(db->db_buf, db);
        bp = (blkptr_t *)db->db.db_data;

        epbs = db->db_dnode->dn_phys->dn_indblkshift - SPA_BLKPTRSHIFT;
        shift = (db->db_level - 1) * epbs;
        dbstart = db->db_blkid << epbs;
        start = blkid >> shift;
        if (dbstart < start) {
                bp += start - dbstart;
                all = FALSE;
        } else {
                start = dbstart;
        }
        dbend = ((db->db_blkid + 1) << epbs) - 1;
        end = (blkid + nblks - 1) >> shift;
        if (dbend <= end)
                end = dbend;
        else if (all)
                all = trunc;
        ASSERT3U(start, <=, end);

        if (db->db_level == 1) {
                FREE_VERIFY(db, start, end, tx);
                blocks_freed = free_blocks(dn, bp, end-start+1, tx);
                arc_buf_freeze(db->db_buf);
                ASSERT(all || blocks_freed == 0 || db->db_last_dirty);
                return (all ? ALL : blocks_freed);
        }

        for (i = start; i <= end; i++, bp++) {
                if (BP_IS_HOLE(bp))
                        continue;
                rw_enter(&dn->dn_struct_rwlock, RW_READER);
                err = dbuf_hold_impl(dn, db->db_level-1, i, TRUE, FTAG, &subdb);
                ASSERT3U(err, ==, 0);
                rw_exit(&dn->dn_struct_rwlock);

                if (free_children(subdb, blkid, nblks, trunc, tx) == ALL) {
                        ASSERT3P(subdb->db_blkptr, ==, bp);
                        blocks_freed += free_blocks(dn, bp, 1, tx);
                } else {
                        all = FALSE;
                }
                dbuf_rele(subdb, FTAG);
        }
        arc_buf_freeze(db->db_buf);
#ifdef ZFS_DEBUG
        bp -= (end-start)+1;
        for (i = start; i <= end; i++, bp++) {
                if (i == start && blkid != 0)
                        continue;
                else if (i == end && !trunc)
                        continue;
                ASSERT3U(bp->blk_birth, ==, 0);
        }
#endif
        ASSERT(all || blocks_freed == 0 || db->db_last_dirty);
        return (all ? ALL : blocks_freed);
}

/*
 * free_range: Traverse the indicated range of the provided file
 * and "free" all the blocks contained there.
 */
static void
dnode_sync_free_range(dnode_t *dn, uint64_t blkid, uint64_t nblks, dmu_tx_t *tx)
{
        blkptr_t *bp = dn->dn_phys->dn_blkptr;
        dmu_buf_impl_t *db;
        int trunc, start, end, shift, i, err;
        int dnlevel = dn->dn_phys->dn_nlevels;

        if (blkid > dn->dn_phys->dn_maxblkid)
                return;

        ASSERT(dn->dn_phys->dn_maxblkid < UINT64_MAX);
        trunc = blkid + nblks > dn->dn_phys->dn_maxblkid;
        if (trunc)
                nblks = dn->dn_phys->dn_maxblkid - blkid + 1;

        /* There are no indirect blocks in the object */
        if (dnlevel == 1) {
                if (blkid >= dn->dn_phys->dn_nblkptr) {
                        /* this range was never made persistent */
                        return;
                }
                ASSERT3U(blkid + nblks, <=, dn->dn_phys->dn_nblkptr);
                (void) free_blocks(dn, bp + blkid, nblks, tx);
                if (trunc) {
                        uint64_t off = (dn->dn_phys->dn_maxblkid + 1) *
                            (dn->dn_phys->dn_datablkszsec << SPA_MINBLOCKSHIFT);
                        dn->dn_phys->dn_maxblkid = (blkid ? blkid - 1 : 0);
                        ASSERT(off < dn->dn_phys->dn_maxblkid ||
                            dn->dn_phys->dn_maxblkid == 0 ||
                            dnode_next_offset(dn, 0, &off, 1, 1, 0) != 0);
                }
                return;
        }

        shift = (dnlevel - 1) * (dn->dn_phys->dn_indblkshift - SPA_BLKPTRSHIFT);
        start = blkid >> shift;
        ASSERT(start < dn->dn_phys->dn_nblkptr);
        end = (blkid + nblks - 1) >> shift;
        bp += start;
        for (i = start; i <= end; i++, bp++) {
                if (BP_IS_HOLE(bp))
                        continue;
                rw_enter(&dn->dn_struct_rwlock, RW_READER);
                err = dbuf_hold_impl(dn, dnlevel-1, i, TRUE, FTAG, &db);
                ASSERT3U(err, ==, 0);
                rw_exit(&dn->dn_struct_rwlock);

                if (free_children(db, blkid, nblks, trunc, tx) == ALL) {
                        ASSERT3P(db->db_blkptr, ==, bp);
                        (void) free_blocks(dn, bp, 1, tx);
                }
                dbuf_rele(db, FTAG);
        }
        if (trunc) {
                uint64_t off = (dn->dn_phys->dn_maxblkid + 1) *
                    (dn->dn_phys->dn_datablkszsec << SPA_MINBLOCKSHIFT);
                dn->dn_phys->dn_maxblkid = (blkid ? blkid - 1 : 0);
                ASSERT(off < dn->dn_phys->dn_maxblkid ||
                    dn->dn_phys->dn_maxblkid == 0 ||
                    dnode_next_offset(dn, 0, &off, 1, 1, 0) != 0);
        }
}

/*
 * Try to kick all the dnodes dbufs out of the cache...
 */
void
dnode_evict_dbufs(dnode_t *dn)
{
        int progress;
        int pass = 0;

        do {
                dmu_buf_impl_t *db, marker;
                int evicting = FALSE;

                progress = FALSE;
                mutex_enter(&dn->dn_dbufs_mtx);
                list_insert_tail(&dn->dn_dbufs, &marker);
                db = list_head(&dn->dn_dbufs);
                for (; db != &marker; db = list_head(&dn->dn_dbufs)) {
                        list_remove(&dn->dn_dbufs, db);
                        list_insert_tail(&dn->dn_dbufs, db);
                        ASSERT3P(db->db_dnode, ==, dn);

                        mutex_enter(&db->db_mtx);
                        if (db->db_state == DB_EVICTING) {
                                progress = TRUE;
                                evicting = TRUE;
                                mutex_exit(&db->db_mtx);
                        } else if (refcount_is_zero(&db->db_holds)) {
                                progress = TRUE;
                                dbuf_clear(db); /* exits db_mtx for us */
                        } else {
                                mutex_exit(&db->db_mtx);
                        }

                }
                list_remove(&dn->dn_dbufs, &marker);
                /*
                 * NB: we need to drop dn_dbufs_mtx between passes so
                 * that any DB_EVICTING dbufs can make progress.
                 * Ideally, we would have some cv we could wait on, but
                 * since we don't, just wait a bit to give the other
                 * thread a chance to run.
                 */
                mutex_exit(&dn->dn_dbufs_mtx);
                if (evicting)
                        delay(1);
                pass++;
                ASSERT(pass < 100); /* sanity check */
        } while (progress);

        rw_enter(&dn->dn_struct_rwlock, RW_WRITER);
        if (dn->dn_bonus && refcount_is_zero(&dn->dn_bonus->db_holds)) {
                mutex_enter(&dn->dn_bonus->db_mtx);
                dbuf_evict(dn->dn_bonus);
                dn->dn_bonus = NULL;
        }
        rw_exit(&dn->dn_struct_rwlock);
}

static void
dnode_undirty_dbufs(list_t *list)
{
        dbuf_dirty_record_t *dr;

        while (dr = list_head(list)) {
                dmu_buf_impl_t *db = dr->dr_dbuf;
                uint64_t txg = dr->dr_txg;

                mutex_enter(&db->db_mtx);
                /* XXX - use dbuf_undirty()? */
                list_remove(list, dr);
                ASSERT(db->db_last_dirty == dr);
                db->db_last_dirty = NULL;
                db->db_dirtycnt -= 1;
                if (db->db_level == 0) {
                        ASSERT(db->db_blkid == DB_BONUS_BLKID ||
                            dr->dt.dl.dr_data == db->db_buf);
                        dbuf_unoverride(dr);
                        mutex_exit(&db->db_mtx);
                } else {
                        mutex_exit(&db->db_mtx);
                        dnode_undirty_dbufs(&dr->dt.di.dr_children);
                }
                kmem_free(dr, sizeof (dbuf_dirty_record_t));
                dbuf_rele(db, (void *)(uintptr_t)txg);
        }
}

static void
dnode_sync_free(dnode_t *dn, dmu_tx_t *tx)
{
        int txgoff = tx->tx_txg & TXG_MASK;

        ASSERT(dmu_tx_is_syncing(tx));

        /*
         * Our contents should have been freed in dnode_sync() by the
         * free range record inserted by the caller of dnode_free().
         */
        ASSERT3U(DN_USED_BYTES(dn->dn_phys), ==, 0);
        ASSERT(BP_IS_HOLE(dn->dn_phys->dn_blkptr));

        dnode_undirty_dbufs(&dn->dn_dirty_records[txgoff]);
        dnode_evict_dbufs(dn);
        ASSERT3P(list_head(&dn->dn_dbufs), ==, NULL);

        /*
         * XXX - It would be nice to assert this, but we may still
         * have residual holds from async evictions from the arc...
         *
         * zfs_obj_to_path() also depends on this being
         * commented out.
         *
         * ASSERT3U(refcount_count(&dn->dn_holds), ==, 1);
         */

        /* Undirty next bits */
        dn->dn_next_nlevels[txgoff] = 0;
        dn->dn_next_indblkshift[txgoff] = 0;
        dn->dn_next_blksz[txgoff] = 0;

        /* ASSERT(blkptrs are zero); */
        ASSERT(dn->dn_phys->dn_type != DMU_OT_NONE);
        ASSERT(dn->dn_type != DMU_OT_NONE);

        ASSERT(dn->dn_free_txg > 0);
        if (dn->dn_allocated_txg != dn->dn_free_txg)
                dbuf_will_dirty(dn->dn_dbuf, tx);
        bzero(dn->dn_phys, sizeof (dnode_phys_t));

        mutex_enter(&dn->dn_mtx);
        dn->dn_type = DMU_OT_NONE;
        dn->dn_maxblkid = 0;
        dn->dn_allocated_txg = 0;
        dn->dn_free_txg = 0;
        mutex_exit(&dn->dn_mtx);

        ASSERT(dn->dn_object != DMU_META_DNODE_OBJECT);

        dnode_rele(dn, (void *)(uintptr_t)tx->tx_txg);
        /*
         * Now that we've released our hold, the dnode may
         * be evicted, so we musn't access it.
         */
}

/*
 * Write out the dnode's dirty buffers.
 */
void
dnode_sync(dnode_t *dn, dmu_tx_t *tx)
{
        free_range_t *rp;
        dnode_phys_t *dnp = dn->dn_phys;
        int txgoff = tx->tx_txg & TXG_MASK;
        list_t *list = &dn->dn_dirty_records[txgoff];
        static const dnode_phys_t zerodn = { 0 };

        ASSERT(dmu_tx_is_syncing(tx));
        ASSERT(dnp->dn_type != DMU_OT_NONE || dn->dn_allocated_txg);
        ASSERT(dnp->dn_type != DMU_OT_NONE ||
            bcmp(dnp, &zerodn, DNODE_SIZE) == 0);
        DNODE_VERIFY(dn);

        ASSERT(dn->dn_dbuf == NULL || arc_released(dn->dn_dbuf->db_buf));

        if (dmu_objset_userused_enabled(dn->dn_objset) &&
            !DMU_OBJECT_IS_SPECIAL(dn->dn_object)) {
                ASSERT(dn->dn_oldphys == NULL);
                dn->dn_oldphys = zio_buf_alloc(sizeof (dnode_phys_t));
                *dn->dn_oldphys = *dn->dn_phys; /* struct assignment */
                dn->dn_phys->dn_flags |= DNODE_FLAG_USERUSED_ACCOUNTED;
        } else {
                /* Once we account for it, we should always account for it. */
                ASSERT(!(dn->dn_phys->dn_flags &
                    DNODE_FLAG_USERUSED_ACCOUNTED));
        }

        mutex_enter(&dn->dn_mtx);
        if (dn->dn_allocated_txg == tx->tx_txg) {
                /* The dnode is newly allocated or reallocated */
                if (dnp->dn_type == DMU_OT_NONE) {
                        /* this is a first alloc, not a realloc */
                        dnp->dn_nlevels = 1;
                        dnp->dn_nblkptr = dn->dn_nblkptr;
                }

                dnp->dn_type = dn->dn_type;
                dnp->dn_bonustype = dn->dn_bonustype;
                dnp->dn_bonuslen = dn->dn_bonuslen;
        }

        ASSERT(dnp->dn_nlevels > 1 ||
            BP_IS_HOLE(&dnp->dn_blkptr[0]) ||
            BP_GET_LSIZE(&dnp->dn_blkptr[0]) ==
            dnp->dn_datablkszsec << SPA_MINBLOCKSHIFT);

        if (dn->dn_next_blksz[txgoff]) {
                ASSERT(P2PHASE(dn->dn_next_blksz[txgoff],
                    SPA_MINBLOCKSIZE) == 0);
                ASSERT(BP_IS_HOLE(&dnp->dn_blkptr[0]) ||
                    dn->dn_maxblkid == 0 || list_head(list) != NULL ||
                    dn->dn_next_blksz[txgoff] >> SPA_MINBLOCKSHIFT ==
                    dnp->dn_datablkszsec);
                dnp->dn_datablkszsec =
                    dn->dn_next_blksz[txgoff] >> SPA_MINBLOCKSHIFT;
                dn->dn_next_blksz[txgoff] = 0;
        }

        if (dn->dn_next_bonuslen[txgoff]) {
                if (dn->dn_next_bonuslen[txgoff] == DN_ZERO_BONUSLEN)
                        dnp->dn_bonuslen = 0;
                else
                        dnp->dn_bonuslen = dn->dn_next_bonuslen[txgoff];
                ASSERT(dnp->dn_bonuslen <= DN_MAX_BONUSLEN);
                dn->dn_next_bonuslen[txgoff] = 0;
        }

        if (dn->dn_next_indblkshift[txgoff]) {
                ASSERT(dnp->dn_nlevels == 1);
                dnp->dn_indblkshift = dn->dn_next_indblkshift[txgoff];
                dn->dn_next_indblkshift[txgoff] = 0;
        }

        /*
         * Just take the live (open-context) values for checksum and compress.
         * Strictly speaking it's a future leak, but nothing bad happens if we
         * start using the new checksum or compress algorithm a little early.
         */
        dnp->dn_checksum = dn->dn_checksum;
        dnp->dn_compress = dn->dn_compress;

        mutex_exit(&dn->dn_mtx);

        /* process all the "freed" ranges in the file */
        while (rp = avl_last(&dn->dn_ranges[txgoff])) {
                dnode_sync_free_range(dn, rp->fr_blkid, rp->fr_nblks, tx);
                /* grab the mutex so we don't race with dnode_block_freed() */
                mutex_enter(&dn->dn_mtx);
                avl_remove(&dn->dn_ranges[txgoff], rp);
                mutex_exit(&dn->dn_mtx);
                kmem_free(rp, sizeof (free_range_t));
        }

        if (dn->dn_free_txg > 0 && dn->dn_free_txg <= tx->tx_txg) {
                dnode_sync_free(dn, tx);
                return;
        }

        if (dn->dn_next_nblkptr[txgoff]) {
                /* this should only happen on a realloc */
                ASSERT(dn->dn_allocated_txg == tx->tx_txg);
                if (dn->dn_next_nblkptr[txgoff] > dnp->dn_nblkptr) {
                        /* zero the new blkptrs we are gaining */
                        bzero(dnp->dn_blkptr + dnp->dn_nblkptr,
                            sizeof (blkptr_t) *
                            (dn->dn_next_nblkptr[txgoff] - dnp->dn_nblkptr));
#ifdef ZFS_DEBUG
                } else {
                        int i;
                        ASSERT(dn->dn_next_nblkptr[txgoff] < dnp->dn_nblkptr);
                        /* the blkptrs we are losing better be unallocated */
                        for (i = dn->dn_next_nblkptr[txgoff];
                            i < dnp->dn_nblkptr; i++)
                                ASSERT(BP_IS_HOLE(&dnp->dn_blkptr[i]));
#endif
                }
                mutex_enter(&dn->dn_mtx);
                dnp->dn_nblkptr = dn->dn_next_nblkptr[txgoff];
                dn->dn_next_nblkptr[txgoff] = 0;
                mutex_exit(&dn->dn_mtx);
        }

        if (dn->dn_next_nlevels[txgoff]) {
                dnode_increase_indirection(dn, tx);
                dn->dn_next_nlevels[txgoff] = 0;
        }

        dbuf_sync_list(list, tx);

        if (!DMU_OBJECT_IS_SPECIAL(dn->dn_object)) {
                ASSERT3P(list_head(list), ==, NULL);
                dnode_rele(dn, (void *)(uintptr_t)tx->tx_txg);
        }

        /*
         * Although we have dropped our reference to the dnode, it
         * can't be evicted until its written, and we haven't yet
         * initiated the IO for the dnode's dbuf.
         */
}