Merge commit '7e3488dc6cdcb0c04e1ce167a1a3bfef83b5f2e0'

[unleashed.git] / kernel / fs / zfs / vdev_initialize.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 (c) 2016 by Delphix. All rights reserved.
 */

#include <sys/spa.h>
#include <sys/spa_impl.h>
#include <sys/txg.h>
#include <sys/vdev_impl.h>
#include <sys/refcount.h>
#include <sys/metaslab_impl.h>
#include <sys/dsl_synctask.h>
#include <sys/zap.h>
#include <sys/dmu_tx.h>

/*
 * Maximum number of metaslabs per group that can be initialized
 * simultaneously.
 */
int max_initialize_ms = 3;

/*
 * Value that is written to disk during initialization.
 */
uint64_t zfs_initialize_value = 0xdeadbeefdeadbeefULL;

/* maximum number of I/Os outstanding per leaf vdev */
int zfs_initialize_limit = 1;

/* size of initializing writes; default 1MiB, see zfs_remove_max_segment */
uint64_t zfs_initialize_chunk_size = 1024 * 1024;

static boolean_t
vdev_initialize_should_stop(vdev_t *vd)
{
        return (vd->vdev_initialize_exit_wanted || !vdev_writeable(vd) ||
            vd->vdev_detached || vd->vdev_top->vdev_removing);
}

static void
vdev_initialize_zap_update_sync(void *arg, dmu_tx_t *tx)
{
        /*
         * We pass in the guid instead of the vdev_t since the vdev may
         * have been freed prior to the sync task being processed. This
         * happens when a vdev is detached as we call spa_config_vdev_exit(),
         * stop the intializing thread, schedule the sync task, and free
         * the vdev. Later when the scheduled sync task is invoked, it would
         * find that the vdev has been freed.
         */
        uint64_t guid = *(uint64_t *)arg;
        uint64_t txg = dmu_tx_get_txg(tx);
        kmem_free(arg, sizeof (uint64_t));

        vdev_t *vd = spa_lookup_by_guid(tx->tx_pool->dp_spa, guid, B_FALSE);
        if (vd == NULL || vd->vdev_top->vdev_removing || !vdev_is_concrete(vd))
                return;

        uint64_t last_offset = vd->vdev_initialize_offset[txg & TXG_MASK];
        vd->vdev_initialize_offset[txg & TXG_MASK] = 0;

        VERIFY(vd->vdev_leaf_zap != 0);

        objset_t *mos = vd->vdev_spa->spa_meta_objset;

        if (last_offset > 0) {
                vd->vdev_initialize_last_offset = last_offset;
                VERIFY0(zap_update(mos, vd->vdev_leaf_zap,
                    VDEV_LEAF_ZAP_INITIALIZE_LAST_OFFSET,
                    sizeof (last_offset), 1, &last_offset, tx));
        }
        if (vd->vdev_initialize_action_time > 0) {
                uint64_t val = (uint64_t)vd->vdev_initialize_action_time;
                VERIFY0(zap_update(mos, vd->vdev_leaf_zap,
                    VDEV_LEAF_ZAP_INITIALIZE_ACTION_TIME, sizeof (val),
                    1, &val, tx));
        }

        uint64_t initialize_state = vd->vdev_initialize_state;
        VERIFY0(zap_update(mos, vd->vdev_leaf_zap,
            VDEV_LEAF_ZAP_INITIALIZE_STATE, sizeof (initialize_state), 1,
            &initialize_state, tx));
}

static void
vdev_initialize_change_state(vdev_t *vd, vdev_initializing_state_t new_state)
{
        ASSERT(MUTEX_HELD(&vd->vdev_initialize_lock));
        spa_t *spa = vd->vdev_spa;

        if (new_state == vd->vdev_initialize_state)
                return;

        /*
         * Copy the vd's guid, this will be freed by the sync task.
         */
        uint64_t *guid = kmem_zalloc(sizeof (uint64_t), KM_SLEEP);
        *guid = vd->vdev_guid;

        /*
         * If we're suspending, then preserving the original start time.
         */
        if (vd->vdev_initialize_state != VDEV_INITIALIZE_SUSPENDED) {
                vd->vdev_initialize_action_time = gethrestime_sec();
        }
        vd->vdev_initialize_state = new_state;

        dmu_tx_t *tx = dmu_tx_create_dd(spa_get_dsl(spa)->dp_mos_dir);
        VERIFY0(dmu_tx_assign(tx, TXG_WAIT));
        dsl_sync_task_nowait(spa_get_dsl(spa), vdev_initialize_zap_update_sync,
            guid, 2, ZFS_SPACE_CHECK_RESERVED, tx);

        switch (new_state) {
        case VDEV_INITIALIZE_ACTIVE:
                spa_history_log_internal(spa, "initialize", tx,
                    "vdev=%s activated", vd->vdev_path);
                break;
        case VDEV_INITIALIZE_SUSPENDED:
                spa_history_log_internal(spa, "initialize", tx,
                    "vdev=%s suspended", vd->vdev_path);
                break;
        case VDEV_INITIALIZE_CANCELED:
                spa_history_log_internal(spa, "initialize", tx,
                    "vdev=%s canceled", vd->vdev_path);
                break;
        case VDEV_INITIALIZE_COMPLETE:
                spa_history_log_internal(spa, "initialize", tx,
                    "vdev=%s complete", vd->vdev_path);
                break;
        default:
                panic("invalid state %llu", (unsigned long long)new_state);
        }

        dmu_tx_commit(tx);
}

static void
vdev_initialize_cb(zio_t *zio)
{
        vdev_t *vd = zio->io_vd;
        mutex_enter(&vd->vdev_initialize_io_lock);
        if (zio->io_error == ENXIO && !vdev_writeable(vd)) {
                /*
                 * The I/O failed because the vdev was unavailable; roll the
                 * last offset back. (This works because spa_sync waits on
                 * spa_txg_zio before it runs sync tasks.)
                 */
                uint64_t *off =
                    &vd->vdev_initialize_offset[zio->io_txg & TXG_MASK];
                *off = MIN(*off, zio->io_offset);
        } else {
                /*
                 * Since initializing is best-effort, we ignore I/O errors and
                 * rely on vdev_probe to determine if the errors are more
                 * critical.
                 */
                if (zio->io_error != 0)
                        vd->vdev_stat.vs_initialize_errors++;

                vd->vdev_initialize_bytes_done += zio->io_orig_size;
        }
        ASSERT3U(vd->vdev_initialize_inflight, >, 0);
        vd->vdev_initialize_inflight--;
        cv_broadcast(&vd->vdev_initialize_io_cv);
        mutex_exit(&vd->vdev_initialize_io_lock);

        spa_config_exit(vd->vdev_spa, SCL_STATE_ALL, vd);
}

/* Takes care of physical writing and limiting # of concurrent ZIOs. */
static int
vdev_initialize_write(vdev_t *vd, uint64_t start, uint64_t size, abd_t *data)
{
        spa_t *spa = vd->vdev_spa;

        /* Limit inflight initializing I/Os */
        mutex_enter(&vd->vdev_initialize_io_lock);
        while (vd->vdev_initialize_inflight >= zfs_initialize_limit) {
                cv_wait(&vd->vdev_initialize_io_cv,
                    &vd->vdev_initialize_io_lock);
        }
        vd->vdev_initialize_inflight++;
        mutex_exit(&vd->vdev_initialize_io_lock);

        dmu_tx_t *tx = dmu_tx_create_dd(spa_get_dsl(spa)->dp_mos_dir);
        VERIFY0(dmu_tx_assign(tx, TXG_WAIT));
        uint64_t txg = dmu_tx_get_txg(tx);

        spa_config_enter(spa, SCL_STATE_ALL, vd, RW_READER);
        mutex_enter(&vd->vdev_initialize_lock);

        if (vd->vdev_initialize_offset[txg & TXG_MASK] == 0) {
                uint64_t *guid = kmem_zalloc(sizeof (uint64_t), KM_SLEEP);
                *guid = vd->vdev_guid;

                /* This is the first write of this txg. */
                dsl_sync_task_nowait(spa_get_dsl(spa),
                    vdev_initialize_zap_update_sync, guid, 2,
                    ZFS_SPACE_CHECK_RESERVED, tx);
        }

        /*
         * We know the vdev struct will still be around since all
         * consumers of vdev_free must stop the initialization first.
         */
        if (vdev_initialize_should_stop(vd)) {
                mutex_enter(&vd->vdev_initialize_io_lock);
                ASSERT3U(vd->vdev_initialize_inflight, >, 0);
                vd->vdev_initialize_inflight--;
                mutex_exit(&vd->vdev_initialize_io_lock);
                spa_config_exit(vd->vdev_spa, SCL_STATE_ALL, vd);
                mutex_exit(&vd->vdev_initialize_lock);
                dmu_tx_commit(tx);
                return (SET_ERROR(EINTR));
        }
        mutex_exit(&vd->vdev_initialize_lock);

        vd->vdev_initialize_offset[txg & TXG_MASK] = start + size;
        zio_nowait(zio_write_phys(spa->spa_txg_zio[txg & TXG_MASK], vd, start,
            size, data, ZIO_CHECKSUM_OFF, vdev_initialize_cb, NULL,
            ZIO_PRIORITY_INITIALIZING, ZIO_FLAG_CANFAIL, B_FALSE));
        /* vdev_initialize_cb releases SCL_STATE_ALL */

        dmu_tx_commit(tx);

        return (0);
}

/*
 * Translate a logical range to the physical range for the specified vdev_t.
 * This function is initially called with a leaf vdev and will walk each
 * parent vdev until it reaches a top-level vdev. Once the top-level is
 * reached the physical range is initialized and the recursive function
 * begins to unwind. As it unwinds it calls the parent's vdev specific
 * translation function to do the real conversion.
 */
void
vdev_xlate(vdev_t *vd, const range_seg_t *logical_rs, range_seg_t *physical_rs)
{
        /*
         * Walk up the vdev tree
         */
        if (vd != vd->vdev_top) {
                vdev_xlate(vd->vdev_parent, logical_rs, physical_rs);
        } else {
                /*
                 * We've reached the top-level vdev, initialize the
                 * physical range to the logical range and start to
                 * unwind.
                 */
                physical_rs->rs_start = logical_rs->rs_start;
                physical_rs->rs_end = logical_rs->rs_end;
                return;
        }

        vdev_t *pvd = vd->vdev_parent;
        ASSERT3P(pvd, !=, NULL);
        ASSERT3P(pvd->vdev_ops->vdev_op_xlate, !=, NULL);

        /*
         * As this recursive function unwinds, translate the logical
         * range into its physical components by calling the
         * vdev specific translate function.
         */
        range_seg_t intermediate = { 0 };
        pvd->vdev_ops->vdev_op_xlate(vd, physical_rs, &intermediate);

        physical_rs->rs_start = intermediate.rs_start;
        physical_rs->rs_end = intermediate.rs_end;
}

/*
 * Callback to fill each ABD chunk with zfs_initialize_value. len must be
 * divisible by sizeof (uint64_t), and buf must be 8-byte aligned. The ABD
 * allocation will guarantee these for us.
 */
/* ARGSUSED */
static int
vdev_initialize_block_fill(void *buf, size_t len, void *unused)
{
        ASSERT0(len % sizeof (uint64_t));
        for (uint64_t i = 0; i < len; i += sizeof (uint64_t)) {
                *(uint64_t *)((char *)(buf) + i) = zfs_initialize_value;
        }
        return (0);
}

static abd_t *
vdev_initialize_block_alloc()
{
        /* Allocate ABD for filler data */
        abd_t *data = abd_alloc_for_io(zfs_initialize_chunk_size, B_FALSE);

        ASSERT0(zfs_initialize_chunk_size % sizeof (uint64_t));
        (void) abd_iterate_func(data, 0, zfs_initialize_chunk_size,
            vdev_initialize_block_fill, NULL);

        return (data);
}

static void
vdev_initialize_block_free(abd_t *data)
{
        abd_free(data);
}

static int
vdev_initialize_ranges(vdev_t *vd, abd_t *data)
{
        avl_tree_t *rt = &vd->vdev_initialize_tree->rt_root;

        for (range_seg_t *rs = avl_first(rt); rs != NULL;
            rs = AVL_NEXT(rt, rs)) {
                uint64_t size = rs->rs_end - rs->rs_start;

                /* Split range into legally-sized physical chunks */
                uint64_t writes_required =
                    ((size - 1) / zfs_initialize_chunk_size) + 1;

                for (uint64_t w = 0; w < writes_required; w++) {
                        int error;

                        error = vdev_initialize_write(vd,
                            VDEV_LABEL_START_SIZE + rs->rs_start +
                            (w * zfs_initialize_chunk_size),
                            MIN(size - (w * zfs_initialize_chunk_size),
                            zfs_initialize_chunk_size), data);
                        if (error != 0)
                                return (error);
                }
        }
        return (0);
}

static void
vdev_initialize_ms_load(metaslab_t *msp)
{
        ASSERT(MUTEX_HELD(&msp->ms_lock));

        metaslab_load_wait(msp);
        if (!msp->ms_loaded)
                VERIFY0(metaslab_load(msp));
}

static void
vdev_initialize_mg_wait(metaslab_group_t *mg)
{
        ASSERT(MUTEX_HELD(&mg->mg_ms_initialize_lock));
        while (mg->mg_initialize_updating) {
                cv_wait(&mg->mg_ms_initialize_cv, &mg->mg_ms_initialize_lock);
        }
}

static void
vdev_initialize_mg_mark(metaslab_group_t *mg)
{
        ASSERT(MUTEX_HELD(&mg->mg_ms_initialize_lock));
        ASSERT(mg->mg_initialize_updating);

        while (mg->mg_ms_initializing >= max_initialize_ms) {
                cv_wait(&mg->mg_ms_initialize_cv, &mg->mg_ms_initialize_lock);
        }
        mg->mg_ms_initializing++;
        ASSERT3U(mg->mg_ms_initializing, <=, max_initialize_ms);
}

/*
 * Mark the metaslab as being initialized to prevent any allocations
 * on this metaslab. We must also track how many metaslabs are currently
 * being initialized within a metaslab group and limit them to prevent
 * allocation failures from occurring because all metaslabs are being
 * initialized.
 */
static void
vdev_initialize_ms_mark(metaslab_t *msp)
{
        ASSERT(!MUTEX_HELD(&msp->ms_lock));
        metaslab_group_t *mg = msp->ms_group;

        mutex_enter(&mg->mg_ms_initialize_lock);

        /*
         * To keep an accurate count of how many threads are initializing
         * a specific metaslab group, we only allow one thread to mark
         * the metaslab group at a time. This ensures that the value of
         * ms_initializing will be accurate when we decide to mark a metaslab
         * group as being initialized. To do this we force all other threads
         * to wait till the metaslab's mg_initialize_updating flag is no
         * longer set.
         */
        vdev_initialize_mg_wait(mg);
        mg->mg_initialize_updating = B_TRUE;
        if (msp->ms_initializing == 0) {
                vdev_initialize_mg_mark(mg);
        }
        mutex_enter(&msp->ms_lock);
        msp->ms_initializing++;
        mutex_exit(&msp->ms_lock);

        mg->mg_initialize_updating = B_FALSE;
        cv_broadcast(&mg->mg_ms_initialize_cv);
        mutex_exit(&mg->mg_ms_initialize_lock);
}

static void
vdev_initialize_ms_unmark(metaslab_t *msp)
{
        ASSERT(!MUTEX_HELD(&msp->ms_lock));
        metaslab_group_t *mg = msp->ms_group;
        mutex_enter(&mg->mg_ms_initialize_lock);
        mutex_enter(&msp->ms_lock);
        if (--msp->ms_initializing == 0) {
                mg->mg_ms_initializing--;
                cv_broadcast(&mg->mg_ms_initialize_cv);
        }
        mutex_exit(&msp->ms_lock);
        mutex_exit(&mg->mg_ms_initialize_lock);
}

static void
vdev_initialize_calculate_progress(vdev_t *vd)
{
        ASSERT(spa_config_held(vd->vdev_spa, SCL_CONFIG, RW_READER) ||
            spa_config_held(vd->vdev_spa, SCL_CONFIG, RW_WRITER));
        ASSERT(vd->vdev_leaf_zap != 0);

        vd->vdev_initialize_bytes_est = 0;
        vd->vdev_initialize_bytes_done = 0;

        for (uint64_t i = 0; i < vd->vdev_top->vdev_ms_count; i++) {
                metaslab_t *msp = vd->vdev_top->vdev_ms[i];
                mutex_enter(&msp->ms_lock);

                uint64_t ms_free = msp->ms_size -
                    space_map_allocated(msp->ms_sm);

                if (vd->vdev_top->vdev_ops == &vdev_raidz_ops)
                        ms_free /= vd->vdev_top->vdev_children;

                /*
                 * Convert the metaslab range to a physical range
                 * on our vdev. We use this to determine if we are
                 * in the middle of this metaslab range.
                 */
                range_seg_t logical_rs, physical_rs;
                logical_rs.rs_start = msp->ms_start;
                logical_rs.rs_end = msp->ms_start + msp->ms_size;
                vdev_xlate(vd, &logical_rs, &physical_rs);

                if (vd->vdev_initialize_last_offset <= physical_rs.rs_start) {
                        vd->vdev_initialize_bytes_est += ms_free;
                        mutex_exit(&msp->ms_lock);
                        continue;
                } else if (vd->vdev_initialize_last_offset >
                    physical_rs.rs_end) {
                        vd->vdev_initialize_bytes_done += ms_free;
                        vd->vdev_initialize_bytes_est += ms_free;
                        mutex_exit(&msp->ms_lock);
                        continue;
                }

                /*
                 * If we get here, we're in the middle of initializing this
                 * metaslab. Load it and walk the free tree for more accurate
                 * progress estimation.
                 */
                vdev_initialize_ms_load(msp);

                for (range_seg_t *rs = avl_first(&msp->ms_allocatable->rt_root); rs;
                    rs = AVL_NEXT(&msp->ms_allocatable->rt_root, rs)) {
                        logical_rs.rs_start = rs->rs_start;
                        logical_rs.rs_end = rs->rs_end;
                        vdev_xlate(vd, &logical_rs, &physical_rs);

                        uint64_t size = physical_rs.rs_end -
                            physical_rs.rs_start;
                        vd->vdev_initialize_bytes_est += size;
                        if (vd->vdev_initialize_last_offset >
                            physical_rs.rs_end) {
                                vd->vdev_initialize_bytes_done += size;
                        } else if (vd->vdev_initialize_last_offset >
                            physical_rs.rs_start &&
                            vd->vdev_initialize_last_offset <
                            physical_rs.rs_end) {
                                vd->vdev_initialize_bytes_done +=
                                    vd->vdev_initialize_last_offset -
                                    physical_rs.rs_start;
                        }
                }
                mutex_exit(&msp->ms_lock);
        }
}

static void
vdev_initialize_load(vdev_t *vd)
{
        ASSERT(spa_config_held(vd->vdev_spa, SCL_CONFIG, RW_READER) ||
            spa_config_held(vd->vdev_spa, SCL_CONFIG, RW_WRITER));
        ASSERT(vd->vdev_leaf_zap != 0);

        if (vd->vdev_initialize_state == VDEV_INITIALIZE_ACTIVE ||
            vd->vdev_initialize_state == VDEV_INITIALIZE_SUSPENDED) {
                int err = zap_lookup(vd->vdev_spa->spa_meta_objset,
                    vd->vdev_leaf_zap, VDEV_LEAF_ZAP_INITIALIZE_LAST_OFFSET,
                    sizeof (vd->vdev_initialize_last_offset), 1,
                    &vd->vdev_initialize_last_offset);
                ASSERT(err == 0 || err == ENOENT);
        }

        vdev_initialize_calculate_progress(vd);
}


/*
 * Convert the logical range into a physcial range and add it to our
 * avl tree.
 */
void
vdev_initialize_range_add(void *arg, uint64_t start, uint64_t size)
{
        vdev_t *vd = arg;
        range_seg_t logical_rs, physical_rs;
        logical_rs.rs_start = start;
        logical_rs.rs_end = start + size;

        ASSERT(vd->vdev_ops->vdev_op_leaf);
        vdev_xlate(vd, &logical_rs, &physical_rs);

        IMPLY(vd->vdev_top == vd,
            logical_rs.rs_start == physical_rs.rs_start);
        IMPLY(vd->vdev_top == vd,
            logical_rs.rs_end == physical_rs.rs_end);

        /* Only add segments that we have not visited yet */
        if (physical_rs.rs_end <= vd->vdev_initialize_last_offset)
                return;

        /* Pick up where we left off mid-range. */
        if (vd->vdev_initialize_last_offset > physical_rs.rs_start) {
                zfs_dbgmsg("range write: vd %s changed (%llu, %llu) to "
                    "(%llu, %llu)", vd->vdev_path,
                    (u_longlong_t)physical_rs.rs_start,
                    (u_longlong_t)physical_rs.rs_end,
                    (u_longlong_t)vd->vdev_initialize_last_offset,
                    (u_longlong_t)physical_rs.rs_end);
                ASSERT3U(physical_rs.rs_end, >,
                    vd->vdev_initialize_last_offset);
                physical_rs.rs_start = vd->vdev_initialize_last_offset;
        }
        ASSERT3U(physical_rs.rs_end, >=, physical_rs.rs_start);

        /*
         * With raidz, it's possible that the logical range does not live on
         * this leaf vdev. We only add the physical range to this vdev's if it
         * has a length greater than 0.
         */
        if (physical_rs.rs_end > physical_rs.rs_start) {
                range_tree_add(vd->vdev_initialize_tree, physical_rs.rs_start,
                    physical_rs.rs_end - physical_rs.rs_start);
        } else {
                ASSERT3U(physical_rs.rs_end, ==, physical_rs.rs_start);
        }
}

static void
vdev_initialize_thread(void *arg)
{
        vdev_t *vd = arg;
        spa_t *spa = vd->vdev_spa;
        int error = 0;
        uint64_t ms_count = 0;

        ASSERT(vdev_is_concrete(vd));
        spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER);

        vd->vdev_initialize_last_offset = 0;
        vdev_initialize_load(vd);

        abd_t *deadbeef = vdev_initialize_block_alloc();

        vd->vdev_initialize_tree = range_tree_create(NULL, NULL);

        for (uint64_t i = 0; !vd->vdev_detached &&
            i < vd->vdev_top->vdev_ms_count; i++) {
                metaslab_t *msp = vd->vdev_top->vdev_ms[i];

                /*
                 * If we've expanded the top-level vdev or it's our
                 * first pass, calculate our progress.
                 */
                if (vd->vdev_top->vdev_ms_count != ms_count) {
                        vdev_initialize_calculate_progress(vd);
                        ms_count = vd->vdev_top->vdev_ms_count;
                }

                vdev_initialize_ms_mark(msp);
                mutex_enter(&msp->ms_lock);
                vdev_initialize_ms_load(msp);

                range_tree_walk(msp->ms_allocatable, vdev_initialize_range_add,
                    vd);
                mutex_exit(&msp->ms_lock);

                spa_config_exit(spa, SCL_CONFIG, FTAG);
                error = vdev_initialize_ranges(vd, deadbeef);
                vdev_initialize_ms_unmark(msp);
                spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER);

                range_tree_vacate(vd->vdev_initialize_tree, NULL, NULL);
                if (error != 0)
                        break;
        }

        spa_config_exit(spa, SCL_CONFIG, FTAG);
        mutex_enter(&vd->vdev_initialize_io_lock);
        while (vd->vdev_initialize_inflight > 0) {
                cv_wait(&vd->vdev_initialize_io_cv,
                    &vd->vdev_initialize_io_lock);
        }
        mutex_exit(&vd->vdev_initialize_io_lock);

        range_tree_destroy(vd->vdev_initialize_tree);
        vdev_initialize_block_free(deadbeef);
        vd->vdev_initialize_tree = NULL;

        mutex_enter(&vd->vdev_initialize_lock);
        if (!vd->vdev_initialize_exit_wanted && vdev_writeable(vd)) {
                vdev_initialize_change_state(vd, VDEV_INITIALIZE_COMPLETE);
        }
        ASSERT(vd->vdev_initialize_thread != NULL ||
            vd->vdev_initialize_inflight == 0);

        /*
         * Drop the vdev_initialize_lock while we sync out the
         * txg since it's possible that a device might be trying to
         * come online and must check to see if it needs to restart an
         * initialization. That thread will be holding the spa_config_lock
         * which would prevent the txg_wait_synced from completing.
         */
        mutex_exit(&vd->vdev_initialize_lock);
        txg_wait_synced(spa_get_dsl(spa), 0);
        mutex_enter(&vd->vdev_initialize_lock);

        vd->vdev_initialize_thread = NULL;
        cv_broadcast(&vd->vdev_initialize_cv);
        mutex_exit(&vd->vdev_initialize_lock);
}

/*
 * Initiates a device. Caller must hold vdev_initialize_lock.
 * Device must be a leaf and not already be initializing.
 */
void
vdev_initialize(vdev_t *vd)
{
        ASSERT(MUTEX_HELD(&vd->vdev_initialize_lock));
        ASSERT(vd->vdev_ops->vdev_op_leaf);
        ASSERT(vdev_is_concrete(vd));
        ASSERT3P(vd->vdev_initialize_thread, ==, NULL);
        ASSERT(!vd->vdev_detached);
        ASSERT(!vd->vdev_initialize_exit_wanted);
        ASSERT(!vd->vdev_top->vdev_removing);

        vdev_initialize_change_state(vd, VDEV_INITIALIZE_ACTIVE);
        vd->vdev_initialize_thread = thread_create(NULL, 0,
            vdev_initialize_thread, vd, 0, &p0, TS_RUN, maxclsyspri);
}

/*
 * Stop initializng a device, with the resultant initialing state being
 * tgt_state. Blocks until the initializing thread has exited.
 * Caller must hold vdev_initialize_lock and must not be writing to the spa
 * config, as the initializing thread may try to enter the config as a reader
 * before exiting.
 */
void
vdev_initialize_stop(vdev_t *vd, vdev_initializing_state_t tgt_state)
{
        spa_t *spa = vd->vdev_spa;
        ASSERT(!spa_config_held(spa, SCL_CONFIG | SCL_STATE, RW_WRITER));

        ASSERT(MUTEX_HELD(&vd->vdev_initialize_lock));
        ASSERT(vd->vdev_ops->vdev_op_leaf);
        ASSERT(vdev_is_concrete(vd));

        /*
         * Allow cancel requests to proceed even if the initialize thread
         * has stopped.
         */
        if (vd->vdev_initialize_thread == NULL &&
            tgt_state != VDEV_INITIALIZE_CANCELED) {
                return;
        }

        vdev_initialize_change_state(vd, tgt_state);
        vd->vdev_initialize_exit_wanted = B_TRUE;
        while (vd->vdev_initialize_thread != NULL)
                cv_wait(&vd->vdev_initialize_cv, &vd->vdev_initialize_lock);

        ASSERT3P(vd->vdev_initialize_thread, ==, NULL);
        vd->vdev_initialize_exit_wanted = B_FALSE;
}

static void
vdev_initialize_stop_all_impl(vdev_t *vd, vdev_initializing_state_t tgt_state)
{
        if (vd->vdev_ops->vdev_op_leaf && vdev_is_concrete(vd)) {
                mutex_enter(&vd->vdev_initialize_lock);
                vdev_initialize_stop(vd, tgt_state);
                mutex_exit(&vd->vdev_initialize_lock);
                return;
        }

        for (uint64_t i = 0; i < vd->vdev_children; i++) {
                vdev_initialize_stop_all_impl(vd->vdev_child[i], tgt_state);
        }
}

/*
 * Convenience function to stop initializing of a vdev tree and set all
 * initialize thread pointers to NULL.
 */
void
vdev_initialize_stop_all(vdev_t *vd, vdev_initializing_state_t tgt_state)
{
        vdev_initialize_stop_all_impl(vd, tgt_state);

        if (vd->vdev_spa->spa_sync_on) {
                /* Make sure that our state has been synced to disk */
                txg_wait_synced(spa_get_dsl(vd->vdev_spa), 0);
        }
}

void
vdev_initialize_restart(vdev_t *vd)
{
        ASSERT(MUTEX_HELD(&spa_namespace_lock));
        ASSERT(!spa_config_held(vd->vdev_spa, SCL_ALL, RW_WRITER));

        if (vd->vdev_leaf_zap != 0) {
                mutex_enter(&vd->vdev_initialize_lock);
                uint64_t initialize_state = VDEV_INITIALIZE_NONE;
                int err = zap_lookup(vd->vdev_spa->spa_meta_objset,
                    vd->vdev_leaf_zap, VDEV_LEAF_ZAP_INITIALIZE_STATE,
                    sizeof (initialize_state), 1, &initialize_state);
                ASSERT(err == 0 || err == ENOENT);
                vd->vdev_initialize_state = initialize_state;

                uint64_t timestamp = 0;
                err = zap_lookup(vd->vdev_spa->spa_meta_objset,
                    vd->vdev_leaf_zap, VDEV_LEAF_ZAP_INITIALIZE_ACTION_TIME,
                    sizeof (timestamp), 1, &timestamp);
                ASSERT(err == 0 || err == ENOENT);
                vd->vdev_initialize_action_time = (time_t)timestamp;

                if (vd->vdev_initialize_state == VDEV_INITIALIZE_SUSPENDED ||
                    vd->vdev_offline) {
                        /* load progress for reporting, but don't resume */
                        vdev_initialize_load(vd);
                } else if (vd->vdev_initialize_state ==
                    VDEV_INITIALIZE_ACTIVE && vdev_writeable(vd)) {
                        vdev_initialize(vd);
                }

                mutex_exit(&vd->vdev_initialize_lock);
        }

        for (uint64_t i = 0; i < vd->vdev_children; i++) {
                vdev_initialize_restart(vd->vdev_child[i]);
        }
}