/*
 * raid5.c : Multiple Devices driver for Linux
 *         Copyright (C) 1996, 1997 Ingo Molnar, Miguel de Icaza, Gadi Oxman
 *         Copyright (C) 1999, 2000 Ingo Molnar
 *         Copyright (C) 2002, 2003 H. Peter Anvin
 *
 * RAID-4/5/6 management functions.
 * Thanks to Penguin Computing for making the RAID-6 development possible
 * by donating a test server!
 *
 * This program 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.
 *
 * You should have received a copy of the GNU General Public License
 * (for example /usr/src/linux/COPYING); if not, write to the Free
 * Software Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
 */

/*
 * BITMAP UNPLUGGING:
 *
 * The sequencing for updating the bitmap reliably is a little
 * subtle (and I got it wrong the first time) so it deserves some
 * explanation.
 *
 * We group bitmap updates into batches.  Each batch has a number.
 * We may write out several batches at once, but that isn't very important.
 * conf->seq_write is the number of the last batch successfully written.
 * conf->seq_flush is the number of the last batch that was closed to
 *    new additions.
 * When we discover that we will need to write to any block in a stripe
 * (in add_stripe_bio) we update the in-memory bitmap and record in sh->bm_seq
 * the number of the batch it will be in. This is seq_flush+1.
 * When we are ready to do a write, if that batch hasn't been written yet,
 *   we plug the array and queue the stripe for later.
 * When an unplug happens, we increment bm_flush, thus closing the current
 *   batch.
 * When we notice that bm_flush > bm_write, we write out all pending updates
 * to the bitmap, and advance bm_write to where bm_flush was.
 * This may occasionally write a bit out twice, but is sure never to
 * miss any bits.
 */

#include <linux/blkdev.h>
#include <linux/kthread.h>
#include <linux/raid/pq.h>
#include <linux/async_tx.h>
#include <linux/async.h>
#include <linux/seq_file.h>
#include <linux/cpu.h>
#include <linux/slab.h>
#include <linux/ratelimit.h>
#include "md.h"
#include "raid5.h"
#include "raid0.h"
#include "bitmap.h"

/*
 * Stripe cache
 */

#define NR_STRIPES              256
#define STRIPE_SIZE             PAGE_SIZE
#define STRIPE_SHIFT            (PAGE_SHIFT - 9)
#define STRIPE_SECTORS          (STRIPE_SIZE>>9)
#define IO_THRESHOLD            1
#define BYPASS_THRESHOLD        1
#define NR_HASH                 (PAGE_SIZE / sizeof(struct hlist_head))
#define HASH_MASK               (NR_HASH - 1)

#define stripe_hash(conf, sect) (&((conf)->stripe_hashtbl[((sect) >> STRIPE_SHIFT) & HASH_MASK]))

/* bio's attached to a stripe+device for I/O are linked together in bi_sector
 * order without overlap.  There may be several bio's per stripe+device, and
 * a bio could span several devices.
 * When walking this list for a particular stripe+device, we must never proceed
 * beyond a bio that extends past this device, as the next bio might no longer
 * be valid.
 * This macro is used to determine the 'next' bio in the list, given the sector
 * of the current stripe+device
 */
#define r5_next_bio(bio, sect) ( ( (bio)->bi_sector + ((bio)->bi_size>>9) < sect + STRIPE_SECTORS) ? (bio)->bi_next : NULL)
/*
 * The following can be used to debug the driver
 */
#define RAID5_PARANOIA  1
#if RAID5_PARANOIA && defined(CONFIG_SMP)
# define CHECK_DEVLOCK() assert_spin_locked(&conf->device_lock)
#else
# define CHECK_DEVLOCK()
#endif

#ifdef DEBUG
#define inline
#define __inline__
#endif

/*
 * We maintain a biased count of active stripes in the bottom 16 bits of
 * bi_phys_segments, and a count of processed stripes in the upper 16 bits
 */
static inline int raid5_bi_phys_segments(struct bio *bio)
{
        return bio->bi_phys_segments & 0xffff;
}

static inline int raid5_bi_hw_segments(struct bio *bio)
{
        return (bio->bi_phys_segments >> 16) & 0xffff;
}

static inline int raid5_dec_bi_phys_segments(struct bio *bio)
{
        --bio->bi_phys_segments;
        return raid5_bi_phys_segments(bio);
}

static inline int raid5_dec_bi_hw_segments(struct bio *bio)
{
        unsigned short val = raid5_bi_hw_segments(bio);

        --val;
        bio->bi_phys_segments = (val << 16) | raid5_bi_phys_segments(bio);
        return val;
}

static inline void raid5_set_bi_hw_segments(struct bio *bio, unsigned int cnt)
{
        bio->bi_phys_segments = raid5_bi_phys_segments(bio) | (cnt << 16);
}

/* Find first data disk in a raid6 stripe */
static inline int raid6_d0(struct stripe_head *sh)
{
        if (sh->ddf_layout)
                /* ddf always start from first device */
                return 0;
        /* md starts just after Q block */
        if (sh->qd_idx == sh->disks - 1)
                return 0;
        else
                return sh->qd_idx + 1;
}
static inline int raid6_next_disk(int disk, int raid_disks)
{
        disk++;
        return (disk < raid_disks) ? disk : 0;
}

/* When walking through the disks in a raid5, starting at raid6_d0,
 * We need to map each disk to a 'slot', where the data disks are slot
 * 0 .. raid_disks-3, the parity disk is raid_disks-2 and the Q disk
 * is raid_disks-1.  This help does that mapping.
 */
static int raid6_idx_to_slot(int idx, struct stripe_head *sh,
                             int *count, int syndrome_disks)
{
        int slot = *count;

        if (sh->ddf_layout)
                (*count)++;
        if (idx == sh->pd_idx)
                return syndrome_disks;
        if (idx == sh->qd_idx)
                return syndrome_disks + 1;
        if (!sh->ddf_layout)
                (*count)++;
        return slot;
}

static void return_io(struct bio *return_bi)
{
        struct bio *bi = return_bi;
        while (bi) {

                return_bi = bi->bi_next;
                bi->bi_next = NULL;
                bi->bi_size = 0;
                bio_endio(bi, 0);
                bi = return_bi;
        }
}

static void print_raid5_conf (raid5_conf_t *conf);

static int stripe_operations_active(struct stripe_head *sh)
{
        return sh->check_state || sh->reconstruct_state ||
               test_bit(STRIPE_BIOFILL_RUN, &sh->state) ||
               test_bit(STRIPE_COMPUTE_RUN, &sh->state);
}

static void __release_stripe(raid5_conf_t *conf, struct stripe_head *sh)
{
        if (atomic_dec_and_test(&sh->count)) {
                BUG_ON(!list_empty(&sh->lru));
                BUG_ON(atomic_read(&conf->active_stripes)==0);
                if (test_bit(STRIPE_HANDLE, &sh->state)) {
                        if (test_bit(STRIPE_DELAYED, &sh->state))
                                list_add_tail(&sh->lru, &conf->delayed_list);
                        else if (test_bit(STRIPE_BIT_DELAY, &sh->state) &&
                                   sh->bm_seq - conf->seq_write > 0)
                                list_add_tail(&sh->lru, &conf->bitmap_list);
                        else {
                                clear_bit(STRIPE_BIT_DELAY, &sh->state);
                                list_add_tail(&sh->lru, &conf->handle_list);
                        }
                        md_wakeup_thread(conf->mddev->thread);
                } else {
                        BUG_ON(stripe_operations_active(sh));
                        if (test_and_clear_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
                                atomic_dec(&conf->preread_active_stripes);
                                if (atomic_read(&conf->preread_active_stripes) < IO_THRESHOLD)
                                        md_wakeup_thread(conf->mddev->thread);
                        }
                        atomic_dec(&conf->active_stripes);
                        if (!test_bit(STRIPE_EXPANDING, &sh->state)) {
                                list_add_tail(&sh->lru, &conf->inactive_list);
                                wake_up(&conf->wait_for_stripe);
                                if (conf->retry_read_aligned)
                                        md_wakeup_thread(conf->mddev->thread);
                        }
                }
        }
}

static void release_stripe(struct stripe_head *sh)
{
        raid5_conf_t *conf = sh->raid_conf;
        unsigned long flags;

        spin_lock_irqsave(&conf->device_lock, flags);
        __release_stripe(conf, sh);
        spin_unlock_irqrestore(&conf->device_lock, flags);
}

static inline void remove_hash(struct stripe_head *sh)
{
        pr_debug("remove_hash(), stripe %llu\n",
                (unsigned long long)sh->sector);

        hlist_del_init(&sh->hash);
}

static inline void insert_hash(raid5_conf_t *conf, struct stripe_head *sh)
{
        struct hlist_head *hp = stripe_hash(conf, sh->sector);

        pr_debug("insert_hash(), stripe %llu\n",
                (unsigned long long)sh->sector);

        CHECK_DEVLOCK();
        hlist_add_head(&sh->hash, hp);
}


/* find an idle stripe, make sure it is unhashed, and return it. */
static struct stripe_head *get_free_stripe(raid5_conf_t *conf)
{
        struct stripe_head *sh = NULL;
        struct list_head *first;

        CHECK_DEVLOCK();
        if (list_empty(&conf->inactive_list))
                goto out;
        first = conf->inactive_list.next;
        sh = list_entry(first, struct stripe_head, lru);
        list_del_init(first);
        remove_hash(sh);
        atomic_inc(&conf->active_stripes);
out:
        return sh;
}

static void shrink_buffers(struct stripe_head *sh)
{
        struct page *p;
        int i;
        int num = sh->raid_conf->pool_size;

        for (i = 0; i < num ; i++) {
                p = sh->dev[i].page;
                if (!p)
                        continue;
                sh->dev[i].page = NULL;
                put_page(p);
        }
}

static int grow_buffers(struct stripe_head *sh)
{
        int i;
        int num = sh->raid_conf->pool_size;

        for (i = 0; i < num; i++) {
                struct page *page;

                if (!(page = alloc_page(GFP_KERNEL))) {
                        return 1;
                }
                sh->dev[i].page = page;
        }
        return 0;
}

static void raid5_build_block(struct stripe_head *sh, int i, int previous);
static void stripe_set_idx(sector_t stripe, raid5_conf_t *conf, int previous,
                            struct stripe_head *sh);

static void init_stripe(struct stripe_head *sh, sector_t sector, int previous)
{
        raid5_conf_t *conf = sh->raid_conf;
        int i;

        BUG_ON(atomic_read(&sh->count) != 0);
        BUG_ON(test_bit(STRIPE_HANDLE, &sh->state));
        BUG_ON(stripe_operations_active(sh));

        CHECK_DEVLOCK();
        pr_debug("init_stripe called, stripe %llu\n",
                (unsigned long long)sh->sector);

        remove_hash(sh);

        sh->generation = conf->generation - previous;
        sh->disks = previous ? conf->previous_raid_disks : conf->raid_disks;
        sh->sector = sector;
        stripe_set_idx(sector, conf, previous, sh);
        sh->state = 0;


        for (i = sh->disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];

                if (dev->toread || dev->read || dev->towrite || dev->written ||
                    test_bit(R5_LOCKED, &dev->flags)) {
                        printk(KERN_ERR "sector=%llx i=%d %p %p %p %p %d\n",
                               (unsigned long long)sh->sector, i, dev->toread,
                               dev->read, dev->towrite, dev->written,
                               test_bit(R5_LOCKED, &dev->flags));
                        WARN_ON(1);
                }
                dev->flags = 0;
                raid5_build_block(sh, i, previous);
        }
        insert_hash(conf, sh);
}

static struct stripe_head *__find_stripe(raid5_conf_t *conf, sector_t sector,
                                         short generation)
{
        struct stripe_head *sh;
        struct hlist_node *hn;

        CHECK_DEVLOCK();
        pr_debug("__find_stripe, sector %llu\n", (unsigned long long)sector);
        hlist_for_each_entry(sh, hn, stripe_hash(conf, sector), hash)
                if (sh->sector == sector && sh->generation == generation)
                        return sh;
        pr_debug("__stripe %llu not in cache\n", (unsigned long long)sector);
        return NULL;
}

/*
 * Need to check if array has failed when deciding whether to:
 *  - start an array
 *  - remove non-faulty devices
 *  - add a spare
 *  - allow a reshape
 * This determination is simple when no reshape is happening.
 * However if there is a reshape, we need to carefully check
 * both the before and after sections.
 * This is because some failed devices may only affect one
 * of the two sections, and some non-in_sync devices may
 * be insync in the section most affected by failed devices.
 */
static int has_failed(raid5_conf_t *conf)
{
        int degraded;
        int i;
        if (conf->mddev->reshape_position == MaxSector)
                return conf->mddev->degraded > conf->max_degraded;

        rcu_read_lock();
        degraded = 0;
        for (i = 0; i < conf->previous_raid_disks; i++) {
                mdk_rdev_t *rdev = rcu_dereference(conf->disks[i].rdev);
                if (!rdev || test_bit(Faulty, &rdev->flags))
                        degraded++;
                else if (test_bit(In_sync, &rdev->flags))
                        ;
                else
                        /* not in-sync or faulty.
                         * If the reshape increases the number of devices,
                         * this is being recovered by the reshape, so
                         * this 'previous' section is not in_sync.
                         * If the number of devices is being reduced however,
                         * the device can only be part of the array if
                         * we are reverting a reshape, so this section will
                         * be in-sync.
                         */
                        if (conf->raid_disks >= conf->previous_raid_disks)
                                degraded++;
        }
        rcu_read_unlock();
        if (degraded > conf->max_degraded)
                return 1;
        rcu_read_lock();
        degraded = 0;
        for (i = 0; i < conf->raid_disks; i++) {
                mdk_rdev_t *rdev = rcu_dereference(conf->disks[i].rdev);
                if (!rdev || test_bit(Faulty, &rdev->flags))
                        degraded++;
                else if (test_bit(In_sync, &rdev->flags))
                        ;
                else
                        /* not in-sync or faulty.
                         * If reshape increases the number of devices, this
                         * section has already been recovered, else it
                         * almost certainly hasn't.
                         */
                        if (conf->raid_disks <= conf->previous_raid_disks)
                                degraded++;
        }
        rcu_read_unlock();
        if (degraded > conf->max_degraded)
                return 1;
        return 0;
}

static struct stripe_head *
get_active_stripe(raid5_conf_t *conf, sector_t sector,
                  int previous, int noblock, int noquiesce)
{
        struct stripe_head *sh;

        pr_debug("get_stripe, sector %llu\n", (unsigned long long)sector);

        spin_lock_irq(&conf->device_lock);

        do {
                wait_event_lock_irq(conf->wait_for_stripe,
                                    conf->quiesce == 0 || noquiesce,
                                    conf->device_lock, /* nothing */);
                sh = __find_stripe(conf, sector, conf->generation - previous);
                if (!sh) {
                        if (!conf->inactive_blocked)
                                sh = get_free_stripe(conf);
                        if (noblock && sh == NULL)
                                break;
                        if (!sh) {
                                conf->inactive_blocked = 1;
                                wait_event_lock_irq(conf->wait_for_stripe,
                                                    !list_empty(&conf->inactive_list) &&
                                                    (atomic_read(&conf->active_stripes)
                                                     < (conf->max_nr_stripes *3/4)
                                                     || !conf->inactive_blocked),
                                                    conf->device_lock,
                                                    );
                                conf->inactive_blocked = 0;
                        } else
                                init_stripe(sh, sector, previous);
                } else {
                        if (atomic_read(&sh->count)) {
                                BUG_ON(!list_empty(&sh->lru)
                                    && !test_bit(STRIPE_EXPANDING, &sh->state));
                        } else {
                                if (!test_bit(STRIPE_HANDLE, &sh->state))
                                        atomic_inc(&conf->active_stripes);
                                if (list_empty(&sh->lru) &&
                                    !test_bit(STRIPE_EXPANDING, &sh->state))
                                        BUG();
                                list_del_init(&sh->lru);
                        }
                }
        } while (sh == NULL);

        if (sh)
                atomic_inc(&sh->count);

        spin_unlock_irq(&conf->device_lock);
        return sh;
}

static void
raid5_end_read_request(struct bio *bi, int error);
static void
raid5_end_write_request(struct bio *bi, int error);

static void ops_run_io(struct stripe_head *sh, struct stripe_head_state *s)
{
        raid5_conf_t *conf = sh->raid_conf;
        int i, disks = sh->disks;

        might_sleep();

        for (i = disks; i--; ) {
                int rw;
                struct bio *bi;
                mdk_rdev_t *rdev;
                if (test_and_clear_bit(R5_Wantwrite, &sh->dev[i].flags)) {
                        if (test_and_clear_bit(R5_WantFUA, &sh->dev[i].flags))
                                rw = WRITE_FUA;
                        else
                                rw = WRITE;
                } else if (test_and_clear_bit(R5_Wantread, &sh->dev[i].flags))
                        rw = READ;
                else
                        continue;

                bi = &sh->dev[i].req;

                bi->bi_rw = rw;
                if (rw & WRITE)
                        bi->bi_end_io = raid5_end_write_request;
                else
                        bi->bi_end_io = raid5_end_read_request;

                rcu_read_lock();
                rdev = rcu_dereference(conf->disks[i].rdev);
                if (rdev && test_bit(Faulty, &rdev->flags))
                        rdev = NULL;
                if (rdev)
                        atomic_inc(&rdev->nr_pending);
                rcu_read_unlock();

                /* We have already checked bad blocks for reads.  Now
                 * need to check for writes.
                 */
                while ((rw & WRITE) && rdev &&
                       test_bit(WriteErrorSeen, &rdev->flags)) {
                        sector_t first_bad;
                        int bad_sectors;
                        int bad = is_badblock(rdev, sh->sector, STRIPE_SECTORS,
                                              &first_bad, &bad_sectors);
                        if (!bad)
                                break;

                        if (bad < 0) {
                                set_bit(BlockedBadBlocks, &rdev->flags);
                                if (!conf->mddev->external &&
                                    conf->mddev->flags) {
                                        /* It is very unlikely, but we might
                                         * still need to write out the
                                         * bad block log - better give it
                                         * a chance*/
                                        md_check_recovery(conf->mddev);
                                }
                                md_wait_for_blocked_rdev(rdev, conf->mddev);
                        } else {
                                /* Acknowledged bad block - skip the write */
                                rdev_dec_pending(rdev, conf->mddev);
                                rdev = NULL;
                        }
                }

                if (rdev) {
                        if (s->syncing || s->expanding || s->expanded)
                                md_sync_acct(rdev->bdev, STRIPE_SECTORS);

                        set_bit(STRIPE_IO_STARTED, &sh->state);

                        bi->bi_bdev = rdev->bdev;
                        pr_debug("%s: for %llu schedule op %ld on disc %d\n",
                                __func__, (unsigned long long)sh->sector,
                                bi->bi_rw, i);
                        atomic_inc(&sh->count);
                        bi->bi_sector = sh->sector + rdev->data_offset;
                        bi->bi_flags = 1 << BIO_UPTODATE;
                        bi->bi_vcnt = 1;
                        bi->bi_max_vecs = 1;
                        bi->bi_idx = 0;
                        bi->bi_io_vec = &sh->dev[i].vec;
                        bi->bi_io_vec[0].bv_len = STRIPE_SIZE;
                        bi->bi_io_vec[0].bv_offset = 0;
                        bi->bi_size = STRIPE_SIZE;
                        bi->bi_next = NULL;
                        generic_make_request(bi);
                } else {
                        if (rw & WRITE)
                                set_bit(STRIPE_DEGRADED, &sh->state);
                        pr_debug("skip op %ld on disc %d for sector %llu\n",
                                bi->bi_rw, i, (unsigned long long)sh->sector);
                        clear_bit(R5_LOCKED, &sh->dev[i].flags);
                        set_bit(STRIPE_HANDLE, &sh->state);
                }
        }
}

static struct dma_async_tx_descriptor *
async_copy_data(int frombio, struct bio *bio, struct page *page,
        sector_t sector, struct dma_async_tx_descriptor *tx)
{
        struct bio_vec *bvl;
        struct page *bio_page;
        int i;
        int page_offset;
        struct async_submit_ctl submit;
        enum async_tx_flags flags = 0;

        if (bio->bi_sector >= sector)
                page_offset = (signed)(bio->bi_sector - sector) * 512;
        else
                page_offset = (signed)(sector - bio->bi_sector) * -512;

        if (frombio)
                flags |= ASYNC_TX_FENCE;
        init_async_submit(&submit, flags, tx, NULL, NULL, NULL);

        bio_for_each_segment(bvl, bio, i) {
                int len = bvl->bv_len;
                int clen;
                int b_offset = 0;

                if (page_offset < 0) {
                        b_offset = -page_offset;
                        page_offset += b_offset;
                        len -= b_offset;
                }

                if (len > 0 && page_offset + len > STRIPE_SIZE)
                        clen = STRIPE_SIZE - page_offset;
                else
                        clen = len;

                if (clen > 0) {
                        b_offset += bvl->bv_offset;
                        bio_page = bvl->bv_page;
                        if (frombio)
                                tx = async_memcpy(page, bio_page, page_offset,
                                                  b_offset, clen, &submit);
                        else
                                tx = async_memcpy(bio_page, page, b_offset,
                                                  page_offset, clen, &submit);
                }
                /* chain the operations */
                submit.depend_tx = tx;

                if (clen < len) /* hit end of page */
                        break;
                page_offset +=  len;
        }

        return tx;
}

static void ops_complete_biofill(void *stripe_head_ref)
{
        struct stripe_head *sh = stripe_head_ref;
        struct bio *return_bi = NULL;
        raid5_conf_t *conf = sh->raid_conf;
        int i;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        /* clear completed biofills */
        spin_lock_irq(&conf->device_lock);
        for (i = sh->disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];

                /* acknowledge completion of a biofill operation */
                /* and check if we need to reply to a read request,
                 * new R5_Wantfill requests are held off until
                 * !STRIPE_BIOFILL_RUN
                 */
                if (test_and_clear_bit(R5_Wantfill, &dev->flags)) {
                        struct bio *rbi, *rbi2;

                        BUG_ON(!dev->read);
                        rbi = dev->read;
                        dev->read = NULL;
                        while (rbi && rbi->bi_sector <
                                dev->sector + STRIPE_SECTORS) {
                                rbi2 = r5_next_bio(rbi, dev->sector);
                                if (!raid5_dec_bi_phys_segments(rbi)) {
                                        rbi->bi_next = return_bi;
                                        return_bi = rbi;
                                }
                                rbi = rbi2;
                        }
                }
        }
        spin_unlock_irq(&conf->device_lock);
        clear_bit(STRIPE_BIOFILL_RUN, &sh->state);

        return_io(return_bi);

        set_bit(STRIPE_HANDLE, &sh->state);
        release_stripe(sh);
}

static void ops_run_biofill(struct stripe_head *sh)
{
        struct dma_async_tx_descriptor *tx = NULL;
        raid5_conf_t *conf = sh->raid_conf;
        struct async_submit_ctl submit;
        int i;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        for (i = sh->disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];
                if (test_bit(R5_Wantfill, &dev->flags)) {
                        struct bio *rbi;
                        spin_lock_irq(&conf->device_lock);
                        dev->read = rbi = dev->toread;
                        dev->toread = NULL;
                        spin_unlock_irq(&conf->device_lock);
                        while (rbi && rbi->bi_sector <
                                dev->sector + STRIPE_SECTORS) {
                                tx = async_copy_data(0, rbi, dev->page,
                                        dev->sector, tx);
                                rbi = r5_next_bio(rbi, dev->sector);
                        }
                }
        }

        atomic_inc(&sh->count);
        init_async_submit(&submit, ASYNC_TX_ACK, tx, ops_complete_biofill, sh, NULL);
        async_trigger_callback(&submit);
}

static void mark_target_uptodate(struct stripe_head *sh, int target)
{
        struct r5dev *tgt;

        if (target < 0)
                return;

        tgt = &sh->dev[target];
        set_bit(R5_UPTODATE, &tgt->flags);
        BUG_ON(!test_bit(R5_Wantcompute, &tgt->flags));
        clear_bit(R5_Wantcompute, &tgt->flags);
}

static void ops_complete_compute(void *stripe_head_ref)
{
        struct stripe_head *sh = stripe_head_ref;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        /* mark the computed target(s) as uptodate */
        mark_target_uptodate(sh, sh->ops.target);
        mark_target_uptodate(sh, sh->ops.target2);

        clear_bit(STRIPE_COMPUTE_RUN, &sh->state);
        if (sh->check_state == check_state_compute_run)
                sh->check_state = check_state_compute_result;
        set_bit(STRIPE_HANDLE, &sh->state);
        release_stripe(sh);
}

/* return a pointer to the address conversion region of the scribble buffer */
static addr_conv_t *to_addr_conv(struct stripe_head *sh,
                                 struct raid5_percpu *percpu)
{
        return percpu->scribble + sizeof(struct page *) * (sh->disks + 2);
}

static struct dma_async_tx_descriptor *
ops_run_compute5(struct stripe_head *sh, struct raid5_percpu *percpu)
{
        int disks = sh->disks;
        struct page **xor_srcs = percpu->scribble;
        int target = sh->ops.target;
        struct r5dev *tgt = &sh->dev[target];
        struct page *xor_dest = tgt->page;
        int count = 0;
        struct dma_async_tx_descriptor *tx;
        struct async_submit_ctl submit;
        int i;

        pr_debug("%s: stripe %llu block: %d\n",
                __func__, (unsigned long long)sh->sector, target);
        BUG_ON(!test_bit(R5_Wantcompute, &tgt->flags));

        for (i = disks; i--; )
                if (i != target)
                        xor_srcs[count++] = sh->dev[i].page;

        atomic_inc(&sh->count);

        init_async_submit(&submit, ASYNC_TX_FENCE|ASYNC_TX_XOR_ZERO_DST, NULL,
                          ops_complete_compute, sh, to_addr_conv(sh, percpu));
        if (unlikely(count == 1))
                tx = async_memcpy(xor_dest, xor_srcs[0], 0, 0, STRIPE_SIZE, &submit);
        else
                tx = async_xor(xor_dest, xor_srcs, 0, count, STRIPE_SIZE, &submit);

        return tx;
}

/* set_syndrome_sources - populate source buffers for gen_syndrome
 * @srcs - (struct page *) array of size sh->disks
 * @sh - stripe_head to parse
 *
 * Populates srcs in proper layout order for the stripe and returns the
 * 'count' of sources to be used in a call to async_gen_syndrome.  The P
 * destination buffer is recorded in srcs[count] and the Q destination
 * is recorded in srcs[count+1]].
 */
static int set_syndrome_sources(struct page **srcs, struct stripe_head *sh)
{
        int disks = sh->disks;
        int syndrome_disks = sh->ddf_layout ? disks : (disks - 2);
        int d0_idx = raid6_d0(sh);
        int count;
        int i;

        for (i = 0; i < disks; i++)
                srcs[i] = NULL;

        count = 0;
        i = d0_idx;
        do {
                int slot = raid6_idx_to_slot(i, sh, &count, syndrome_disks);

                srcs[slot] = sh->dev[i].page;
                i = raid6_next_disk(i, disks);
        } while (i != d0_idx);

        return syndrome_disks;
}

static struct dma_async_tx_descriptor *
ops_run_compute6_1(struct stripe_head *sh, struct raid5_percpu *percpu)
{
        int disks = sh->disks;
        struct page **blocks = percpu->scribble;
        int target;
        int qd_idx = sh->qd_idx;
        struct dma_async_tx_descriptor *tx;
        struct async_submit_ctl submit;
        struct r5dev *tgt;
        struct page *dest;
        int i;
        int count;

        if (sh->ops.target < 0)
                target = sh->ops.target2;
        else if (sh->ops.target2 < 0)
                target = sh->ops.target;
        else
                /* we should only have one valid target */
                BUG();
        BUG_ON(target < 0);
        pr_debug("%s: stripe %llu block: %d\n",
                __func__, (unsigned long long)sh->sector, target);

        tgt = &sh->dev[target];
        BUG_ON(!test_bit(R5_Wantcompute, &tgt->flags));
        dest = tgt->page;

        atomic_inc(&sh->count);

        if (target == qd_idx) {
                count = set_syndrome_sources(blocks, sh);
                blocks[count] = NULL; /* regenerating p is not necessary */
                BUG_ON(blocks[count+1] != dest); /* q should already be set */
                init_async_submit(&submit, ASYNC_TX_FENCE, NULL,
                                  ops_complete_compute, sh,
                                  to_addr_conv(sh, percpu));
                tx = async_gen_syndrome(blocks, 0, count+2, STRIPE_SIZE, &submit);
        } else {
                /* Compute any data- or p-drive using XOR */
                count = 0;
                for (i = disks; i-- ; ) {
                        if (i == target || i == qd_idx)
                                continue;
                        blocks[count++] = sh->dev[i].page;
                }

                init_async_submit(&submit, ASYNC_TX_FENCE|ASYNC_TX_XOR_ZERO_DST,
                                  NULL, ops_complete_compute, sh,
                                  to_addr_conv(sh, percpu));
                tx = async_xor(dest, blocks, 0, count, STRIPE_SIZE, &submit);
        }

        return tx;
}

static struct dma_async_tx_descriptor *
ops_run_compute6_2(struct stripe_head *sh, struct raid5_percpu *percpu)
{
        int i, count, disks = sh->disks;
        int syndrome_disks = sh->ddf_layout ? disks : disks-2;
        int d0_idx = raid6_d0(sh);
        int faila = -1, failb = -1;
        int target = sh->ops.target;
        int target2 = sh->ops.target2;
        struct r5dev *tgt = &sh->dev[target];
        struct r5dev *tgt2 = &sh->dev[target2];
        struct dma_async_tx_descriptor *tx;
        struct page **blocks = percpu->scribble;
        struct async_submit_ctl submit;

        pr_debug("%s: stripe %llu block1: %d block2: %d\n",
                 __func__, (unsigned long long)sh->sector, target, target2);
        BUG_ON(target < 0 || target2 < 0);
        BUG_ON(!test_bit(R5_Wantcompute, &tgt->flags));
        BUG_ON(!test_bit(R5_Wantcompute, &tgt2->flags));

        /* we need to open-code set_syndrome_sources to handle the
         * slot number conversion for 'faila' and 'failb'
         */
        for (i = 0; i < disks ; i++)
                blocks[i] = NULL;
        count = 0;
        i = d0_idx;
        do {
                int slot = raid6_idx_to_slot(i, sh, &count, syndrome_disks);

                blocks[slot] = sh->dev[i].page;

                if (i == target)
                        faila = slot;
                if (i == target2)
                        failb = slot;
                i = raid6_next_disk(i, disks);
        } while (i != d0_idx);

        BUG_ON(faila == failb);
        if (failb < faila)
                swap(faila, failb);
        pr_debug("%s: stripe: %llu faila: %d failb: %d\n",
                 __func__, (unsigned long long)sh->sector, faila, failb);

        atomic_inc(&sh->count);

        if (failb == syndrome_disks+1) {
                /* Q disk is one of the missing disks */
                if (faila == syndrome_disks) {
                        /* Missing P+Q, just recompute */
                        init_async_submit(&submit, ASYNC_TX_FENCE, NULL,
                                          ops_complete_compute, sh,
                                          to_addr_conv(sh, percpu));
                        return async_gen_syndrome(blocks, 0, syndrome_disks+2,
                                                  STRIPE_SIZE, &submit);
                } else {
                        struct page *dest;
                        int data_target;
                        int qd_idx = sh->qd_idx;

                        /* Missing D+Q: recompute D from P, then recompute Q */
                        if (target == qd_idx)
                                data_target = target2;
                        else
                                data_target = target;

                        count = 0;
                        for (i = disks; i-- ; ) {
                                if (i == data_target || i == qd_idx)
                                        continue;
                                blocks[count++] = sh->dev[i].page;
                        }
                        dest = sh->dev[data_target].page;
                        init_async_submit(&submit,
                                          ASYNC_TX_FENCE|ASYNC_TX_XOR_ZERO_DST,
                                          NULL, NULL, NULL,
                                          to_addr_conv(sh, percpu));
                        tx = async_xor(dest, blocks, 0, count, STRIPE_SIZE,
                                       &submit);

                        count = set_syndrome_sources(blocks, sh);
                        init_async_submit(&submit, ASYNC_TX_FENCE, tx,
                                          ops_complete_compute, sh,
                                          to_addr_conv(sh, percpu));
                        return async_gen_syndrome(blocks, 0, count+2,
                                                  STRIPE_SIZE, &submit);
                }
        } else {
                init_async_submit(&submit, ASYNC_TX_FENCE, NULL,
                                  ops_complete_compute, sh,
                                  to_addr_conv(sh, percpu));
                if (failb == syndrome_disks) {
                        /* We're missing D+P. */
                        return async_raid6_datap_recov(syndrome_disks+2,
                                                       STRIPE_SIZE, faila,
                                                       blocks, &submit);
                } else {
                        /* We're missing D+D. */
                        return async_raid6_2data_recov(syndrome_disks+2,
                                                       STRIPE_SIZE, faila, failb,
                                                       blocks, &submit);
                }
        }
}


static void ops_complete_prexor(void *stripe_head_ref)
{
        struct stripe_head *sh = stripe_head_ref;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

}

static struct dma_async_tx_descriptor *
ops_run_prexor(struct stripe_head *sh, struct raid5_percpu *percpu,
               struct dma_async_tx_descriptor *tx)
{
        int disks = sh->disks;
        struct page **xor_srcs = percpu->scribble;
        int count = 0, pd_idx = sh->pd_idx, i;
        struct async_submit_ctl submit;

        /* existing parity data subtracted */
        struct page *xor_dest = xor_srcs[count++] = sh->dev[pd_idx].page;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        for (i = disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];
                /* Only process blocks that are known to be uptodate */
                if (test_bit(R5_Wantdrain, &dev->flags))
                        xor_srcs[count++] = dev->page;
        }

        init_async_submit(&submit, ASYNC_TX_FENCE|ASYNC_TX_XOR_DROP_DST, tx,
                          ops_complete_prexor, sh, to_addr_conv(sh, percpu));
        tx = async_xor(xor_dest, xor_srcs, 0, count, STRIPE_SIZE, &submit);

        return tx;
}

static struct dma_async_tx_descriptor *
ops_run_biodrain(struct stripe_head *sh, struct dma_async_tx_descriptor *tx)
{
        int disks = sh->disks;
        int i;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        for (i = disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];
                struct bio *chosen;

                if (test_and_clear_bit(R5_Wantdrain, &dev->flags)) {
                        struct bio *wbi;

                        spin_lock_irq(&sh->raid_conf->device_lock);
                        chosen = dev->towrite;
                        dev->towrite = NULL;
                        BUG_ON(dev->written);
                        wbi = dev->written = chosen;
                        spin_unlock_irq(&sh->raid_conf->device_lock);

                        while (wbi && wbi->bi_sector <
                                dev->sector + STRIPE_SECTORS) {
                                if (wbi->bi_rw & REQ_FUA)
                                        set_bit(R5_WantFUA, &dev->flags);
                                tx = async_copy_data(1, wbi, dev->page,
                                        dev->sector, tx);
                                wbi = r5_next_bio(wbi, dev->sector);
                        }
                }
        }

        return tx;
}

static void ops_complete_reconstruct(void *stripe_head_ref)
{
        struct stripe_head *sh = stripe_head_ref;
        int disks = sh->disks;
        int pd_idx = sh->pd_idx;
        int qd_idx = sh->qd_idx;
        int i;
        bool fua = false;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        for (i = disks; i--; )
                fua |= test_bit(R5_WantFUA, &sh->dev[i].flags);

        for (i = disks; i--; ) {
                struct r5dev *dev = &sh->dev[i];

                if (dev->written || i == pd_idx || i == qd_idx) {
                        set_bit(R5_UPTODATE, &dev->flags);
                        if (fua)
                                set_bit(R5_WantFUA, &dev->flags);
                }
        }

        if (sh->reconstruct_state == reconstruct_state_drain_run)
                sh->reconstruct_state = reconstruct_state_drain_result;
        else if (sh->reconstruct_state == reconstruct_state_prexor_drain_run)
                sh->reconstruct_state = reconstruct_state_prexor_drain_result;
        else {
                BUG_ON(sh->reconstruct_state != reconstruct_state_run);
                sh->reconstruct_state = reconstruct_state_result;
        }

        set_bit(STRIPE_HANDLE, &sh->state);
        release_stripe(sh);
}

static void
ops_run_reconstruct5(struct stripe_head *sh, struct raid5_percpu *percpu,
                     struct dma_async_tx_descriptor *tx)
{
        int disks = sh->disks;
        struct page **xor_srcs = percpu->scribble;
        struct async_submit_ctl submit;
        int count = 0, pd_idx = sh->pd_idx, i;
        struct page *xor_dest;
        int prexor = 0;
        unsigned long flags;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        /* check if prexor is active which means only process blocks
         * that are part of a read-modify-write (written)
         */
        if (sh->reconstruct_state == reconstruct_state_prexor_drain_run) {
                prexor = 1;
                xor_dest = xor_srcs[count++] = sh->dev[pd_idx].page;
                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if (dev->written)
                                xor_srcs[count++] = dev->page;
                }
        } else {
                xor_dest = sh->dev[pd_idx].page;
                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if (i != pd_idx)
                                xor_srcs[count++] = dev->page;
                }
        }

        /* 1/ if we prexor'd then the dest is reused as a source
         * 2/ if we did not prexor then we are redoing the parity
         * set ASYNC_TX_XOR_DROP_DST and ASYNC_TX_XOR_ZERO_DST
         * for the synchronous xor case
         */
        flags = ASYNC_TX_ACK |
                (prexor ? ASYNC_TX_XOR_DROP_DST : ASYNC_TX_XOR_ZERO_DST);

        atomic_inc(&sh->count);

        init_async_submit(&submit, flags, tx, ops_complete_reconstruct, sh,
                          to_addr_conv(sh, percpu));
        if (unlikely(count == 1))
                tx = async_memcpy(xor_dest, xor_srcs[0], 0, 0, STRIPE_SIZE, &submit);
        else
                tx = async_xor(xor_dest, xor_srcs, 0, count, STRIPE_SIZE, &submit);
}

static void
ops_run_reconstruct6(struct stripe_head *sh, struct raid5_percpu *percpu,
                     struct dma_async_tx_descriptor *tx)
{
        struct async_submit_ctl submit;
        struct page **blocks = percpu->scribble;
        int count;

        pr_debug("%s: stripe %llu\n", __func__, (unsigned long long)sh->sector);

        count = set_syndrome_sources(blocks, sh);

        atomic_inc(&sh->count);

        init_async_submit(&submit, ASYNC_TX_ACK, tx, ops_complete_reconstruct,
                          sh, to_addr_conv(sh, percpu));
        async_gen_syndrome(blocks, 0, count+2, STRIPE_SIZE,  &submit);
}

static void ops_complete_check(void *stripe_head_ref)
{
        struct stripe_head *sh = stripe_head_ref;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        sh->check_state = check_state_check_result;
        set_bit(STRIPE_HANDLE, &sh->state);
        release_stripe(sh);
}

static void ops_run_check_p(struct stripe_head *sh, struct raid5_percpu *percpu)
{
        int disks = sh->disks;
        int pd_idx = sh->pd_idx;
        int qd_idx = sh->qd_idx;
        struct page *xor_dest;
        struct page **xor_srcs = percpu->scribble;
        struct dma_async_tx_descriptor *tx;
        struct async_submit_ctl submit;
        int count;
        int i;

        pr_debug("%s: stripe %llu\n", __func__,
                (unsigned long long)sh->sector);

        count = 0;
        xor_dest = sh->dev[pd_idx].page;
        xor_srcs[count++] = xor_dest;
        for (i = disks; i--; ) {
                if (i == pd_idx || i == qd_idx)
                        continue;
                xor_srcs[count++] = sh->dev[i].page;
        }

        init_async_submit(&submit, 0, NULL, NULL, NULL,
                          to_addr_conv(sh, percpu));
        tx = async_xor_val(xor_dest, xor_srcs, 0, count, STRIPE_SIZE,
                           &sh->ops.zero_sum_result, &submit);

        atomic_inc(&sh->count);
        init_async_submit(&submit, ASYNC_TX_ACK, tx, ops_complete_check, sh, NULL);
        tx = async_trigger_callback(&submit);
}

static void ops_run_check_pq(struct stripe_head *sh, struct raid5_percpu *percpu, int checkp)
{
        struct page **srcs = percpu->scribble;
        struct async_submit_ctl submit;
        int count;

        pr_debug("%s: stripe %llu checkp: %d\n", __func__,
                (unsigned long long)sh->sector, checkp);

        count = set_syndrome_sources(srcs, sh);
        if (!checkp)
                srcs[count] = NULL;

        atomic_inc(&sh->count);
        init_async_submit(&submit, ASYNC_TX_ACK, NULL, ops_complete_check,
                          sh, to_addr_conv(sh, percpu));
        async_syndrome_val(srcs, 0, count+2, STRIPE_SIZE,
                           &sh->ops.zero_sum_result, percpu->spare_page, &submit);
}

static void __raid_run_ops(struct stripe_head *sh, unsigned long ops_request)
{
        int overlap_clear = 0, i, disks = sh->disks;
        struct dma_async_tx_descriptor *tx = NULL;
        raid5_conf_t *conf = sh->raid_conf;
        int level = conf->level;
        struct raid5_percpu *percpu;
        unsigned long cpu;

        cpu = get_cpu();
        percpu = per_cpu_ptr(conf->percpu, cpu);
        if (test_bit(STRIPE_OP_BIOFILL, &ops_request)) {
                ops_run_biofill(sh);
                overlap_clear++;
        }

        if (test_bit(STRIPE_OP_COMPUTE_BLK, &ops_request)) {
                if (level < 6)
                        tx = ops_run_compute5(sh, percpu);
                else {
                        if (sh->ops.target2 < 0 || sh->ops.target < 0)
                                tx = ops_run_compute6_1(sh, percpu);
                        else
                                tx = ops_run_compute6_2(sh, percpu);
                }
                /* terminate the chain if reconstruct is not set to be run */
                if (tx && !test_bit(STRIPE_OP_RECONSTRUCT, &ops_request))
                        async_tx_ack(tx);
        }

        if (test_bit(STRIPE_OP_PREXOR, &ops_request))
                tx = ops_run_prexor(sh, percpu, tx);

        if (test_bit(STRIPE_OP_BIODRAIN, &ops_request)) {
                tx = ops_run_biodrain(sh, tx);
                overlap_clear++;
        }

        if (test_bit(STRIPE_OP_RECONSTRUCT, &ops_request)) {
                if (level < 6)
                        ops_run_reconstruct5(sh, percpu, tx);
                else
                        ops_run_reconstruct6(sh, percpu, tx);
        }

        if (test_bit(STRIPE_OP_CHECK, &ops_request)) {
                if (sh->check_state == check_state_run)
                        ops_run_check_p(sh, percpu);
                else if (sh->check_state == check_state_run_q)
                        ops_run_check_pq(sh, percpu, 0);
                else if (sh->check_state == check_state_run_pq)
                        ops_run_check_pq(sh, percpu, 1);
                else
                        BUG();
        }

        if (overlap_clear)
                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if (test_and_clear_bit(R5_Overlap, &dev->flags))
                                wake_up(&sh->raid_conf->wait_for_overlap);
                }
        put_cpu();
}

#ifdef CONFIG_MULTICORE_RAID456
static void async_run_ops(void *param, async_cookie_t cookie)
{
        struct stripe_head *sh = param;
        unsigned long ops_request = sh->ops.request;

        clear_bit_unlock(STRIPE_OPS_REQ_PENDING, &sh->state);
        wake_up(&sh->ops.wait_for_ops);

        __raid_run_ops(sh, ops_request);
        release_stripe(sh);
}

static void raid_run_ops(struct stripe_head *sh, unsigned long ops_request)
{
        /* since handle_stripe can be called outside of raid5d context
         * we need to ensure sh->ops.request is de-staged before another
         * request arrives
         */
        wait_event(sh->ops.wait_for_ops,
                   !test_and_set_bit_lock(STRIPE_OPS_REQ_PENDING, &sh->state));
        sh->ops.request = ops_request;

        atomic_inc(&sh->count);
        async_schedule(async_run_ops, sh);
}
#else
#define raid_run_ops __raid_run_ops
#endif

static int grow_one_stripe(raid5_conf_t *conf)
{
        struct stripe_head *sh;
        sh = kmem_cache_zalloc(conf->slab_cache, GFP_KERNEL);
        if (!sh)
                return 0;

        sh->raid_conf = conf;
        #ifdef CONFIG_MULTICORE_RAID456
        init_waitqueue_head(&sh->ops.wait_for_ops);
        #endif

        if (grow_buffers(sh)) {
                shrink_buffers(sh);
                kmem_cache_free(conf->slab_cache, sh);
                return 0;
        }
        /* we just created an active stripe so... */
        atomic_set(&sh->count, 1);
        atomic_inc(&conf->active_stripes);
        INIT_LIST_HEAD(&sh->lru);
        release_stripe(sh);
        return 1;
}

static int grow_stripes(raid5_conf_t *conf, int num)
{
        struct kmem_cache *sc;
        int devs = max(conf->raid_disks, conf->previous_raid_disks);

        if (conf->mddev->gendisk)
                sprintf(conf->cache_name[0],
                        "raid%d-%s", conf->level, mdname(conf->mddev));
        else
                sprintf(conf->cache_name[0],
                        "raid%d-%p", conf->level, conf->mddev);
        sprintf(conf->cache_name[1], "%s-alt", conf->cache_name[0]);

        conf->active_name = 0;
        sc = kmem_cache_create(conf->cache_name[conf->active_name],
                               sizeof(struct stripe_head)+(devs-1)*sizeof(struct r5dev),
                               0, 0, NULL);
        if (!sc)
                return 1;
        conf->slab_cache = sc;
        conf->pool_size = devs;
        while (num--)
                if (!grow_one_stripe(conf))
                        return 1;
        return 0;
}

/**
 * scribble_len - return the required size of the scribble region
 * @num - total number of disks in the array
 *
 * The size must be enough to contain:
 * 1/ a struct page pointer for each device in the array +2
 * 2/ room to convert each entry in (1) to its corresponding dma
 *    (dma_map_page()) or page (page_address()) address.
 *
 * Note: the +2 is for the destination buffers of the ddf/raid6 case where we
 * calculate over all devices (not just the data blocks), using zeros in place
 * of the P and Q blocks.
 */
static size_t scribble_len(int num)
{
        size_t len;

        len = sizeof(struct page *) * (num+2) + sizeof(addr_conv_t) * (num+2);

        return len;
}

static int resize_stripes(raid5_conf_t *conf, int newsize)
{
        /* Make all the stripes able to hold 'newsize' devices.
         * New slots in each stripe get 'page' set to a new page.
         *
         * This happens in stages:
         * 1/ create a new kmem_cache and allocate the required number of
         *    stripe_heads.
         * 2/ gather all the old stripe_heads and tranfer the pages across
         *    to the new stripe_heads.  This will have the side effect of
         *    freezing the array as once all stripe_heads have been collected,
         *    no IO will be possible.  Old stripe heads are freed once their
         *    pages have been transferred over, and the old kmem_cache is
         *    freed when all stripes are done.
         * 3/ reallocate conf->disks to be suitable bigger.  If this fails,
         *    we simple return a failre status - no need to clean anything up.
         * 4/ allocate new pages for the new slots in the new stripe_heads.
         *    If this fails, we don't bother trying the shrink the
         *    stripe_heads down again, we just leave them as they are.
         *    As each stripe_head is processed the new one is released into
         *    active service.
         *
         * Once step2 is started, we cannot afford to wait for a write,
         * so we use GFP_NOIO allocations.
         */
        struct stripe_head *osh, *nsh;
        LIST_HEAD(newstripes);
        struct disk_info *ndisks;
        unsigned long cpu;
        int err;
        struct kmem_cache *sc;
        int i;

        if (newsize <= conf->pool_size)
                return 0; /* never bother to shrink */

        err = md_allow_write(conf->mddev);
        if (err)
                return err;

        /* Step 1 */
        sc = kmem_cache_create(conf->cache_name[1-conf->active_name],
                               sizeof(struct stripe_head)+(newsize-1)*sizeof(struct r5dev),
                               0, 0, NULL);
        if (!sc)
                return -ENOMEM;

        for (i = conf->max_nr_stripes; i; i--) {
                nsh = kmem_cache_zalloc(sc, GFP_KERNEL);
                if (!nsh)
                        break;

                nsh->raid_conf = conf;
                #ifdef CONFIG_MULTICORE_RAID456
                init_waitqueue_head(&nsh->ops.wait_for_ops);
                #endif

                list_add(&nsh->lru, &newstripes);
        }
        if (i) {
                /* didn't get enough, give up */
                while (!list_empty(&newstripes)) {
                        nsh = list_entry(newstripes.next, struct stripe_head, lru);
                        list_del(&nsh->lru);
                        kmem_cache_free(sc, nsh);
                }
                kmem_cache_destroy(sc);
                return -ENOMEM;
        }
        /* Step 2 - Must use GFP_NOIO now.
         * OK, we have enough stripes, start collecting inactive
         * stripes and copying them over
         */
        list_for_each_entry(nsh, &newstripes, lru) {
                spin_lock_irq(&conf->device_lock);
                wait_event_lock_irq(conf->wait_for_stripe,
                                    !list_empty(&conf->inactive_list),
                                    conf->device_lock,
                                    );
                osh = get_free_stripe(conf);
                spin_unlock_irq(&conf->device_lock);
                atomic_set(&nsh->count, 1);
                for(i=0; i<conf->pool_size; i++)
                        nsh->dev[i].page = osh->dev[i].page;
                for( ; i<newsize; i++)
                        nsh->dev[i].page = NULL;
                kmem_cache_free(conf->slab_cache, osh);
        }
        kmem_cache_destroy(conf->slab_cache);

        /* Step 3.
         * At this point, we are holding all the stripes so the array
         * is completely stalled, so now is a good time to resize
         * conf->disks and the scribble region
         */
        ndisks = kzalloc(newsize * sizeof(struct disk_info), GFP_NOIO);
        if (ndisks) {
                for (i=0; i<conf->raid_disks; i++)
                        ndisks[i] = conf->disks[i];
                kfree(conf->disks);
                conf->disks = ndisks;
        } else
                err = -ENOMEM;

        get_online_cpus();
        conf->scribble_len = scribble_len(newsize);
        for_each_present_cpu(cpu) {
                struct raid5_percpu *percpu;
                void *scribble;

                percpu = per_cpu_ptr(conf->percpu, cpu);
                scribble = kmalloc(conf->scribble_len, GFP_NOIO);

                if (scribble) {
                        kfree(percpu->scribble);
                        percpu->scribble = scribble;
                } else {
                        err = -ENOMEM;
                        break;
                }
        }
        put_online_cpus();

        /* Step 4, return new stripes to service */
        while(!list_empty(&newstripes)) {
                nsh = list_entry(newstripes.next, struct stripe_head, lru);
                list_del_init(&nsh->lru);

                for (i=conf->raid_disks; i < newsize; i++)
                        if (nsh->dev[i].page == NULL) {
                                struct page *p = alloc_page(GFP_NOIO);
                                nsh->dev[i].page = p;
                                if (!p)
                                        err = -ENOMEM;
                        }
                release_stripe(nsh);
        }
        /* critical section pass, GFP_NOIO no longer needed */

        conf->slab_cache = sc;
        conf->active_name = 1-conf->active_name;
        conf->pool_size = newsize;
        return err;
}

static int drop_one_stripe(raid5_conf_t *conf)
{
        struct stripe_head *sh;

        spin_lock_irq(&conf->device_lock);
        sh = get_free_stripe(conf);
        spin_unlock_irq(&conf->device_lock);
        if (!sh)
                return 0;
        BUG_ON(atomic_read(&sh->count));
        shrink_buffers(sh);
        kmem_cache_free(conf->slab_cache, sh);
        atomic_dec(&conf->active_stripes);
        return 1;
}

static void shrink_stripes(raid5_conf_t *conf)
{
        while (drop_one_stripe(conf))
                ;

        if (conf->slab_cache)
                kmem_cache_destroy(conf->slab_cache);
        conf->slab_cache = NULL;
}

static void raid5_end_read_request(struct bio * bi, int error)
{
        struct stripe_head *sh = bi->bi_private;
        raid5_conf_t *conf = sh->raid_conf;
        int disks = sh->disks, i;
        int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);
        char b[BDEVNAME_SIZE];
        mdk_rdev_t *rdev;


        for (i=0 ; i<disks; i++)
                if (bi == &sh->dev[i].req)
                        break;

        pr_debug("end_read_request %llu/%d, count: %d, uptodate %d.\n",
                (unsigned long long)sh->sector, i, atomic_read(&sh->count),
                uptodate);
        if (i == disks) {
                BUG();
                return;
        }

        if (uptodate) {
                set_bit(R5_UPTODATE, &sh->dev[i].flags);
                if (test_bit(R5_ReadError, &sh->dev[i].flags)) {
                        rdev = conf->disks[i].rdev;
                        printk_ratelimited(
                                KERN_INFO
                                "md/raid:%s: read error corrected"
                                " (%lu sectors at %llu on %s)\n",
                                mdname(conf->mddev), STRIPE_SECTORS,
                                (unsigned long long)(sh->sector
                                                     + rdev->data_offset),
                                bdevname(rdev->bdev, b));
                        atomic_add(STRIPE_SECTORS, &rdev->corrected_errors);
                        clear_bit(R5_ReadError, &sh->dev[i].flags);
                        clear_bit(R5_ReWrite, &sh->dev[i].flags);
                }
                if (atomic_read(&conf->disks[i].rdev->read_errors))
                        atomic_set(&conf->disks[i].rdev->read_errors, 0);
        } else {
                const char *bdn = bdevname(conf->disks[i].rdev->bdev, b);
                int retry = 0;
                rdev = conf->disks[i].rdev;

                clear_bit(R5_UPTODATE, &sh->dev[i].flags);
                atomic_inc(&rdev->read_errors);
                if (conf->mddev->degraded >= conf->max_degraded)
                        printk_ratelimited(
                                KERN_WARNING
                                "md/raid:%s: read error not correctable "
                                "(sector %llu on %s).\n",
                                mdname(conf->mddev),
                                (unsigned long long)(sh->sector
                                                     + rdev->data_offset),
                                bdn);
                else if (test_bit(R5_ReWrite, &sh->dev[i].flags))
                        /* Oh, no!!! */
                        printk_ratelimited(
                                KERN_WARNING
                                "md/raid:%s: read error NOT corrected!! "
                                "(sector %llu on %s).\n",
                                mdname(conf->mddev),
                                (unsigned long long)(sh->sector
                                                     + rdev->data_offset),
                                bdn);
                else if (atomic_read(&rdev->read_errors)
                         > conf->max_nr_stripes)
                        printk(KERN_WARNING
                               "md/raid:%s: Too many read errors, failing device %s.\n",
                               mdname(conf->mddev), bdn);
                else
                        retry = 1;
                if (retry)
                        set_bit(R5_ReadError, &sh->dev[i].flags);
                else {
                        clear_bit(R5_ReadError, &sh->dev[i].flags);
                        clear_bit(R5_ReWrite, &sh->dev[i].flags);
                        md_error(conf->mddev, rdev);
                }
        }
        rdev_dec_pending(conf->disks[i].rdev, conf->mddev);
        clear_bit(R5_LOCKED, &sh->dev[i].flags);
        set_bit(STRIPE_HANDLE, &sh->state);
        release_stripe(sh);
}

static void raid5_end_write_request(struct bio *bi, int error)
{
        struct stripe_head *sh = bi->bi_private;
        raid5_conf_t *conf = sh->raid_conf;
        int disks = sh->disks, i;
        int uptodate = test_bit(BIO_UPTODATE, &bi->bi_flags);
        sector_t first_bad;
        int bad_sectors;

        for (i=0 ; i<disks; i++)
                if (bi == &sh->dev[i].req)
                        break;

        pr_debug("end_write_request %llu/%d, count %d, uptodate: %d.\n",
                (unsigned long long)sh->sector, i, atomic_read(&sh->count),
                uptodate);
        if (i == disks) {
                BUG();
                return;
        }

        if (!uptodate) {
                set_bit(WriteErrorSeen, &conf->disks[i].rdev->flags);
                set_bit(R5_WriteError, &sh->dev[i].flags);
        } else if (is_badblock(conf->disks[i].rdev, sh->sector, STRIPE_SECTORS,
                               &first_bad, &bad_sectors))
                set_bit(R5_MadeGood, &sh->dev[i].flags);

        rdev_dec_pending(conf->disks[i].rdev, conf->mddev);
        
        clear_bit(R5_LOCKED, &sh->dev[i].flags);
        set_bit(STRIPE_HANDLE, &sh->state);
        release_stripe(sh);
}


static sector_t compute_blocknr(struct stripe_head *sh, int i, int previous);
        
static void raid5_build_block(struct stripe_head *sh, int i, int previous)
{
        struct r5dev *dev = &sh->dev[i];

        bio_init(&dev->req);
        dev->req.bi_io_vec = &dev->vec;
        dev->req.bi_vcnt++;
        dev->req.bi_max_vecs++;
        dev->vec.bv_page = dev->page;
        dev->vec.bv_len = STRIPE_SIZE;
        dev->vec.bv_offset = 0;

        dev->req.bi_sector = sh->sector;
        dev->req.bi_private = sh;

        dev->flags = 0;
        dev->sector = compute_blocknr(sh, i, previous);
}

static void error(mddev_t *mddev, mdk_rdev_t *rdev)
{
        char b[BDEVNAME_SIZE];
        raid5_conf_t *conf = mddev->private;
        pr_debug("raid456: error called\n");

        if (test_and_clear_bit(In_sync, &rdev->flags)) {
                unsigned long flags;
                spin_lock_irqsave(&conf->device_lock, flags);
                mddev->degraded++;
                spin_unlock_irqrestore(&conf->device_lock, flags);
                /*
                 * if recovery was running, make sure it aborts.
                 */
                set_bit(MD_RECOVERY_INTR, &mddev->recovery);
        }
        set_bit(Blocked, &rdev->flags);
        set_bit(Faulty, &rdev->flags);
        set_bit(MD_CHANGE_DEVS, &mddev->flags);
        printk(KERN_ALERT
               "md/raid:%s: Disk failure on %s, disabling device.\n"
               "md/raid:%s: Operation continuing on %d devices.\n",
               mdname(mddev),
               bdevname(rdev->bdev, b),
               mdname(mddev),
               conf->raid_disks - mddev->degraded);
}

/*
 * Input: a 'big' sector number,
 * Output: index of the data and parity disk, and the sector # in them.
 */
static sector_t raid5_compute_sector(raid5_conf_t *conf, sector_t r_sector,
                                     int previous, int *dd_idx,
                                     struct stripe_head *sh)
{
        sector_t stripe, stripe2;
        sector_t chunk_number;
        unsigned int chunk_offset;
        int pd_idx, qd_idx;
        int ddf_layout = 0;
        sector_t new_sector;
        int algorithm = previous ? conf->prev_algo
                                 : conf->algorithm;
        int sectors_per_chunk = previous ? conf->prev_chunk_sectors
                                         : conf->chunk_sectors;
        int raid_disks = previous ? conf->previous_raid_disks
                                  : conf->raid_disks;
        int data_disks = raid_disks - conf->max_degraded;

        /* First compute the information on this sector */

        /*
         * Compute the chunk number and the sector offset inside the chunk
         */
        chunk_offset = sector_div(r_sector, sectors_per_chunk);
        chunk_number = r_sector;

        /*
         * Compute the stripe number
         */
        stripe = chunk_number;
        *dd_idx = sector_div(stripe, data_disks);
        stripe2 = stripe;
        /*
         * Select the parity disk based on the user selected algorithm.
         */
        pd_idx = qd_idx = -1;
        switch(conf->level) {
        case 4:
                pd_idx = data_disks;
                break;
        case 5:
                switch (algorithm) {
                case ALGORITHM_LEFT_ASYMMETRIC:
                        pd_idx = data_disks - sector_div(stripe2, raid_disks);
                        if (*dd_idx >= pd_idx)
                                (*dd_idx)++;
                        break;
                case ALGORITHM_RIGHT_ASYMMETRIC:
                        pd_idx = sector_div(stripe2, raid_disks);
                        if (*dd_idx >= pd_idx)
                                (*dd_idx)++;
                        break;
                case ALGORITHM_LEFT_SYMMETRIC:
                        pd_idx = data_disks - sector_div(stripe2, raid_disks);
                        *dd_idx = (pd_idx + 1 + *dd_idx) % raid_disks;
                        break;
                case ALGORITHM_RIGHT_SYMMETRIC:
                        pd_idx = sector_div(stripe2, raid_disks);
                        *dd_idx = (pd_idx + 1 + *dd_idx) % raid_disks;
                        break;
                case ALGORITHM_PARITY_0:
                        pd_idx = 0;
                        (*dd_idx)++;
                        break;
                case ALGORITHM_PARITY_N:
                        pd_idx = data_disks;
                        break;
                default:
                        BUG();
                }
                break;
        case 6:

                switch (algorithm) {
                case ALGORITHM_LEFT_ASYMMETRIC:
                        pd_idx = raid_disks - 1 - sector_div(stripe2, raid_disks);
                        qd_idx = pd_idx + 1;
                        if (pd_idx == raid_disks-1) {
                                (*dd_idx)++;    /* Q D D D P */
                                qd_idx = 0;
                        } else if (*dd_idx >= pd_idx)
                                (*dd_idx) += 2; /* D D P Q D */
                        break;
                case ALGORITHM_RIGHT_ASYMMETRIC:
                        pd_idx = sector_div(stripe2, raid_disks);
                        qd_idx = pd_idx + 1;
                        if (pd_idx == raid_disks-1) {
                                (*dd_idx)++;    /* Q D D D P */
                                qd_idx = 0;
                        } else if (*dd_idx >= pd_idx)
                                (*dd_idx) += 2; /* D D P Q D */
                        break;
                case ALGORITHM_LEFT_SYMMETRIC:
                        pd_idx = raid_disks - 1 - sector_div(stripe2, raid_disks);
                        qd_idx = (pd_idx + 1) % raid_disks;
                        *dd_idx = (pd_idx + 2 + *dd_idx) % raid_disks;
                        break;
                case ALGORITHM_RIGHT_SYMMETRIC:
                        pd_idx = sector_div(stripe2, raid_disks);
                        qd_idx = (pd_idx + 1) % raid_disks;
                        *dd_idx = (pd_idx + 2 + *dd_idx) % raid_disks;
                        break;

                case ALGORITHM_PARITY_0:
                        pd_idx = 0;
                        qd_idx = 1;
                        (*dd_idx) += 2;
                        break;
                case ALGORITHM_PARITY_N:
                        pd_idx = data_disks;
                        qd_idx = data_disks + 1;
                        break;

                case ALGORITHM_ROTATING_ZERO_RESTART:
                        /* Exactly the same as RIGHT_ASYMMETRIC, but or
                         * of blocks for computing Q is different.
                         */
                        pd_idx = sector_div(stripe2, raid_disks);
                        qd_idx = pd_idx + 1;
                        if (pd_idx == raid_disks-1) {
                                (*dd_idx)++;    /* Q D D D P */
                                qd_idx = 0;
                        } else if (*dd_idx >= pd_idx)
                                (*dd_idx) += 2; /* D D P Q D */
                        ddf_layout = 1;
                        break;

                case ALGORITHM_ROTATING_N_RESTART:
                        /* Same a left_asymmetric, by first stripe is
                         * D D D P Q  rather than
                         * Q D D D P
                         */
                        stripe2 += 1;
                        pd_idx = raid_disks - 1 - sector_div(stripe2, raid_disks);
                        qd_idx = pd_idx + 1;
                        if (pd_idx == raid_disks-1) {
                                (*dd_idx)++;    /* Q D D D P */
                                qd_idx = 0;
                        } else if (*dd_idx >= pd_idx)
                                (*dd_idx) += 2; /* D D P Q D */
                        ddf_layout = 1;
                        break;

                case ALGORITHM_ROTATING_N_CONTINUE:
                        /* Same as left_symmetric but Q is before P */
                        pd_idx = raid_disks - 1 - sector_div(stripe2, raid_disks);
                        qd_idx = (pd_idx + raid_disks - 1) % raid_disks;
                        *dd_idx = (pd_idx + 1 + *dd_idx) % raid_disks;
                        ddf_layout = 1;
                        break;

                case ALGORITHM_LEFT_ASYMMETRIC_6:
                        /* RAID5 left_asymmetric, with Q on last device */
                        pd_idx = data_disks - sector_div(stripe2, raid_disks-1);
                        if (*dd_idx >= pd_idx)
                                (*dd_idx)++;
                        qd_idx = raid_disks - 1;
                        break;

                case ALGORITHM_RIGHT_ASYMMETRIC_6:
                        pd_idx = sector_div(stripe2, raid_disks-1);
                        if (*dd_idx >= pd_idx)
                                (*dd_idx)++;
                        qd_idx = raid_disks - 1;
                        break;

                case ALGORITHM_LEFT_SYMMETRIC_6:
                        pd_idx = data_disks - sector_div(stripe2, raid_disks-1);
                        *dd_idx = (pd_idx + 1 + *dd_idx) % (raid_disks-1);
                        qd_idx = raid_disks - 1;
                        break;

                case ALGORITHM_RIGHT_SYMMETRIC_6:
                        pd_idx = sector_div(stripe2, raid_disks-1);
                        *dd_idx = (pd_idx + 1 + *dd_idx) % (raid_disks-1);
                        qd_idx = raid_disks - 1;
                        break;

                case ALGORITHM_PARITY_0_6:
                        pd_idx = 0;
                        (*dd_idx)++;
                        qd_idx = raid_disks - 1;
                        break;

                default:
                        BUG();
                }
                break;
        }

        if (sh) {
                sh->pd_idx = pd_idx;
                sh->qd_idx = qd_idx;
                sh->ddf_layout = ddf_layout;
        }
        /*
         * Finally, compute the new sector number
         */
        new_sector = (sector_t)stripe * sectors_per_chunk + chunk_offset;
        return new_sector;
}


static sector_t compute_blocknr(struct stripe_head *sh, int i, int previous)
{
        raid5_conf_t *conf = sh->raid_conf;
        int raid_disks = sh->disks;
        int data_disks = raid_disks - conf->max_degraded;
        sector_t new_sector = sh->sector, check;
        int sectors_per_chunk = previous ? conf->prev_chunk_sectors
                                         : conf->chunk_sectors;
        int algorithm = previous ? conf->prev_algo
                                 : conf->algorithm;
        sector_t stripe;
        int chunk_offset;
        sector_t chunk_number;
        int dummy1, dd_idx = i;
        sector_t r_sector;
        struct stripe_head sh2;


        chunk_offset = sector_div(new_sector, sectors_per_chunk);
        stripe = new_sector;

        if (i == sh->pd_idx)
                return 0;
        switch(conf->level) {
        case 4: break;
        case 5:
                switch (algorithm) {
                case ALGORITHM_LEFT_ASYMMETRIC:
                case ALGORITHM_RIGHT_ASYMMETRIC:
                        if (i > sh->pd_idx)
                                i--;
                        break;
                case ALGORITHM_LEFT_SYMMETRIC:
                case ALGORITHM_RIGHT_SYMMETRIC:
                        if (i < sh->pd_idx)
                                i += raid_disks;
                        i -= (sh->pd_idx + 1);

                        break;
                case ALGORITHM_PARITY_0:
                        i -= 1;
                        break;
                case ALGORITHM_PARITY_N:
                        break;
                default:
                        BUG();
                }
                break;
        case 6:
                if (i == sh->qd_idx)
                        return 0; /* It is the Q disk */
                switch (algorithm) {
                case ALGORITHM_LEFT_ASYMMETRIC:
                case ALGORITHM_RIGHT_ASYMMETRIC:
                case ALGORITHM_ROTATING_ZERO_RESTART:
                case ALGORITHM_ROTATING_N_RESTART:
                        if (sh->pd_idx == raid_disks-1)
                                i--;    /* Q D D D P */
                        else if (i > sh->pd_idx)
                                i -= 2; /* D D P Q D */
                        break;
                case ALGORITHM_LEFT_SYMMETRIC:
                case ALGORITHM_RIGHT_SYMMETRIC:
                        if (sh->pd_idx == raid_disks-1)
                                i--; /* Q D D D P */
                        else {
                                /* D D P Q D */
                                if (i < sh->pd_idx)
                                        i += raid_disks;
                                i -= (sh->pd_idx + 2);
                        }
                        break;
                case ALGORITHM_PARITY_0:
                        i -= 2;
                        break;
                case ALGORITHM_PARITY_N:
                        break;
                case ALGORITHM_ROTATING_N_CONTINUE:
                        /* Like left_symmetric, but P is before Q */
                        if (sh->pd_idx == 0)
                                i--;    /* P D D D Q */
                        else {
                                /* D D Q P D */
                                if (i < sh->pd_idx)
                                        i += raid_disks;
                                i -= (sh->pd_idx + 1);
                        }
                        break;
                case ALGORITHM_LEFT_ASYMMETRIC_6:
                case ALGORITHM_RIGHT_ASYMMETRIC_6:
                        if (i > sh->pd_idx)
                                i--;
                        break;
                case ALGORITHM_LEFT_SYMMETRIC_6:
                case ALGORITHM_RIGHT_SYMMETRIC_6:
                        if (i < sh->pd_idx)
                                i += data_disks + 1;
                        i -= (sh->pd_idx + 1);
                        break;
                case ALGORITHM_PARITY_0_6:
                        i -= 1;
                        break;
                default:
                        BUG();
                }
                break;
        }

        chunk_number = stripe * data_disks + i;
        r_sector = chunk_number * sectors_per_chunk + chunk_offset;

        check = raid5_compute_sector(conf, r_sector,
                                     previous, &dummy1, &sh2);
        if (check != sh->sector || dummy1 != dd_idx || sh2.pd_idx != sh->pd_idx
                || sh2.qd_idx != sh->qd_idx) {
                printk(KERN_ERR "md/raid:%s: compute_blocknr: map not correct\n",
                       mdname(conf->mddev));
                return 0;
        }
        return r_sector;
}


static void
schedule_reconstruction(struct stripe_head *sh, struct stripe_head_state *s,
                         int rcw, int expand)
{
        int i, pd_idx = sh->pd_idx, disks = sh->disks;
        raid5_conf_t *conf = sh->raid_conf;
        int level = conf->level;

        if (rcw) {
                /* if we are not expanding this is a proper write request, and
                 * there will be bios with new data to be drained into the
                 * stripe cache
                 */
                if (!expand) {
                        sh->reconstruct_state = reconstruct_state_drain_run;
                        set_bit(STRIPE_OP_BIODRAIN, &s->ops_request);
                } else
                        sh->reconstruct_state = reconstruct_state_run;

                set_bit(STRIPE_OP_RECONSTRUCT, &s->ops_request);

                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];

                        if (dev->towrite) {
                                set_bit(R5_LOCKED, &dev->flags);
                                set_bit(R5_Wantdrain, &dev->flags);
                                if (!expand)
                                        clear_bit(R5_UPTODATE, &dev->flags);
                                s->locked++;
                        }
                }
                if (s->locked + conf->max_degraded == disks)
                        if (!test_and_set_bit(STRIPE_FULL_WRITE, &sh->state))
                                atomic_inc(&conf->pending_full_writes);
        } else {
                BUG_ON(level == 6);
                BUG_ON(!(test_bit(R5_UPTODATE, &sh->dev[pd_idx].flags) ||
                        test_bit(R5_Wantcompute, &sh->dev[pd_idx].flags)));

                sh->reconstruct_state = reconstruct_state_prexor_drain_run;
                set_bit(STRIPE_OP_PREXOR, &s->ops_request);
                set_bit(STRIPE_OP_BIODRAIN, &s->ops_request);
                set_bit(STRIPE_OP_RECONSTRUCT, &s->ops_request);

                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if (i == pd_idx)
                                continue;

                        if (dev->towrite &&
                            (test_bit(R5_UPTODATE, &dev->flags) ||
                             test_bit(R5_Wantcompute, &dev->flags))) {
                                set_bit(R5_Wantdrain, &dev->flags);
                                set_bit(R5_LOCKED, &dev->flags);
                                clear_bit(R5_UPTODATE, &dev->flags);
                                s->locked++;
                        }
                }
        }

        /* keep the parity disk(s) locked while asynchronous operations
         * are in flight
         */
        set_bit(R5_LOCKED, &sh->dev[pd_idx].flags);
        clear_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
        s->locked++;

        if (level == 6) {
                int qd_idx = sh->qd_idx;
                struct r5dev *dev = &sh->dev[qd_idx];

                set_bit(R5_LOCKED, &dev->flags);
                clear_bit(R5_UPTODATE, &dev->flags);
                s->locked++;
        }

        pr_debug("%s: stripe %llu locked: %d ops_request: %lx\n",
                __func__, (unsigned long long)sh->sector,
                s->locked, s->ops_request);
}

/*
 * Each stripe/dev can have one or more bion attached.
 * toread/towrite point to the first in a chain.
 * The bi_next chain must be in order.
 */
static int add_stripe_bio(struct stripe_head *sh, struct bio *bi, int dd_idx, int forwrite)
{
        struct bio **bip;
        raid5_conf_t *conf = sh->raid_conf;
        int firstwrite=0;

        pr_debug("adding bi b#%llu to stripe s#%llu\n",
                (unsigned long long)bi->bi_sector,
                (unsigned long long)sh->sector);


        spin_lock_irq(&conf->device_lock);
        if (forwrite) {
                bip = &sh->dev[dd_idx].towrite;
                if (*bip == NULL && sh->dev[dd_idx].written == NULL)
                        firstwrite = 1;
        } else
                bip = &sh->dev[dd_idx].toread;
        while (*bip && (*bip)->bi_sector < bi->bi_sector) {
                if ((*bip)->bi_sector + ((*bip)->bi_size >> 9) > bi->bi_sector)
                        goto overlap;
                bip = & (*bip)->bi_next;
        }
        if (*bip && (*bip)->bi_sector < bi->bi_sector + ((bi->bi_size)>>9))
                goto overlap;

        BUG_ON(*bip && bi->bi_next && (*bip) != bi->bi_next);
        if (*bip)
                bi->bi_next = *bip;
        *bip = bi;
        bi->bi_phys_segments++;

        if (forwrite) {
                /* check if page is covered */
                sector_t sector = sh->dev[dd_idx].sector;
                for (bi=sh->dev[dd_idx].towrite;
                     sector < sh->dev[dd_idx].sector + STRIPE_SECTORS &&
                             bi && bi->bi_sector <= sector;
                     bi = r5_next_bio(bi, sh->dev[dd_idx].sector)) {
                        if (bi->bi_sector + (bi->bi_size>>9) >= sector)
                                sector = bi->bi_sector + (bi->bi_size>>9);
                }
                if (sector >= sh->dev[dd_idx].sector + STRIPE_SECTORS)
                        set_bit(R5_OVERWRITE, &sh->dev[dd_idx].flags);
        }
        spin_unlock_irq(&conf->device_lock);

        pr_debug("added bi b#%llu to stripe s#%llu, disk %d.\n",
                (unsigned long long)(*bip)->bi_sector,
                (unsigned long long)sh->sector, dd_idx);

        if (conf->mddev->bitmap && firstwrite) {
                bitmap_startwrite(conf->mddev->bitmap, sh->sector,
                                  STRIPE_SECTORS, 0);
                sh->bm_seq = conf->seq_flush+1;
                set_bit(STRIPE_BIT_DELAY, &sh->state);
        }
        return 1;

 overlap:
        set_bit(R5_Overlap, &sh->dev[dd_idx].flags);
        spin_unlock_irq(&conf->device_lock);
        return 0;
}

static void end_reshape(raid5_conf_t *conf);

static void stripe_set_idx(sector_t stripe, raid5_conf_t *conf, int previous,
                            struct stripe_head *sh)
{
        int sectors_per_chunk =
                previous ? conf->prev_chunk_sectors : conf->chunk_sectors;
        int dd_idx;
        int chunk_offset = sector_div(stripe, sectors_per_chunk);
        int disks = previous ? conf->previous_raid_disks : conf->raid_disks;

        raid5_compute_sector(conf,
                             stripe * (disks - conf->max_degraded)
                             *sectors_per_chunk + chunk_offset,
                             previous,
                             &dd_idx, sh);
}

static void
handle_failed_stripe(raid5_conf_t *conf, struct stripe_head *sh,
                                struct stripe_head_state *s, int disks,
                                struct bio **return_bi)
{
        int i;
        for (i = disks; i--; ) {
                struct bio *bi;
                int bitmap_end = 0;

                if (test_bit(R5_ReadError, &sh->dev[i].flags)) {
                        mdk_rdev_t *rdev;
                        rcu_read_lock();
                        rdev = rcu_dereference(conf->disks[i].rdev);
                        if (rdev && test_bit(In_sync, &rdev->flags))
                                atomic_inc(&rdev->nr_pending);
                        else
                                rdev = NULL;
                        rcu_read_unlock();
                        if (rdev) {
                                if (!rdev_set_badblocks(
                                            rdev,
                                            sh->sector,
                                            STRIPE_SECTORS, 0))
                                        md_error(conf->mddev, rdev);
                                rdev_dec_pending(rdev, conf->mddev);
                        }
                }
                spin_lock_irq(&conf->device_lock);
                /* fail all writes first */
                bi = sh->dev[i].towrite;
                sh->dev[i].towrite = NULL;
                if (bi) {
                        s->to_write--;
                        bitmap_end = 1;
                }

                if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
                        wake_up(&conf->wait_for_overlap);

                while (bi && bi->bi_sector <
                        sh->dev[i].sector + STRIPE_SECTORS) {
                        struct bio *nextbi = r5_next_bio(bi, sh->dev[i].sector);
                        clear_bit(BIO_UPTODATE, &bi->bi_flags);
                        if (!raid5_dec_bi_phys_segments(bi)) {
                                md_write_end(conf->mddev);
                                bi->bi_next = *return_bi;
                                *return_bi = bi;
                        }
                        bi = nextbi;
                }
                /* and fail all 'written' */
                bi = sh->dev[i].written;
                sh->dev[i].written = NULL;
                if (bi) bitmap_end = 1;
                while (bi && bi->bi_sector <
                       sh->dev[i].sector + STRIPE_SECTORS) {
                        struct bio *bi2 = r5_next_bio(bi, sh->dev[i].sector);
                        clear_bit(BIO_UPTODATE, &bi->bi_flags);
                        if (!raid5_dec_bi_phys_segments(bi)) {
                                md_write_end(conf->mddev);
                                bi->bi_next = *return_bi;
                                *return_bi = bi;
                        }
                        bi = bi2;
                }

                /* fail any reads if this device is non-operational and
                 * the data has not reached the cache yet.
                 */
                if (!test_bit(R5_Wantfill, &sh->dev[i].flags) &&
                    (!test_bit(R5_Insync, &sh->dev[i].flags) ||
                      test_bit(R5_ReadError, &sh->dev[i].flags))) {
                        bi = sh->dev[i].toread;
                        sh->dev[i].toread = NULL;
                        if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
                                wake_up(&conf->wait_for_overlap);
                        if (bi) s->to_read--;
                        while (bi && bi->bi_sector <
                               sh->dev[i].sector + STRIPE_SECTORS) {
                                struct bio *nextbi =
                                        r5_next_bio(bi, sh->dev[i].sector);
                                clear_bit(BIO_UPTODATE, &bi->bi_flags);
                                if (!raid5_dec_bi_phys_segments(bi)) {
                                        bi->bi_next = *return_bi;
                                        *return_bi = bi;
                                }
                                bi = nextbi;
                        }
                }
                spin_unlock_irq(&conf->device_lock);
                if (bitmap_end)
                        bitmap_endwrite(conf->mddev->bitmap, sh->sector,
                                        STRIPE_SECTORS, 0, 0);
                /* If we were in the middle of a write the parity block might
                 * still be locked - so just clear all R5_LOCKED flags
                 */
                clear_bit(R5_LOCKED, &sh->dev[i].flags);
        }

        if (test_and_clear_bit(STRIPE_FULL_WRITE, &sh->state))
                if (atomic_dec_and_test(&conf->pending_full_writes))
                        md_wakeup_thread(conf->mddev->thread);
}

static void
handle_failed_sync(raid5_conf_t *conf, struct stripe_head *sh,
                   struct stripe_head_state *s)
{
        int abort = 0;
        int i;

        md_done_sync(conf->mddev, STRIPE_SECTORS, 0);
        clear_bit(STRIPE_SYNCING, &sh->state);
        s->syncing = 0;
        /* There is nothing more to do for sync/check/repair.
         * For recover we need to record a bad block on all
         * non-sync devices, or abort the recovery
         */
        if (!test_bit(MD_RECOVERY_RECOVER, &conf->mddev->recovery))
                return;
        /* During recovery devices cannot be removed, so locking and
         * refcounting of rdevs is not needed
         */
        for (i = 0; i < conf->raid_disks; i++) {
                mdk_rdev_t *rdev = conf->disks[i].rdev;
                if (!rdev
                    || test_bit(Faulty, &rdev->flags)
                    || test_bit(In_sync, &rdev->flags))
                        continue;
                if (!rdev_set_badblocks(rdev, sh->sector,
                                        STRIPE_SECTORS, 0))
                        abort = 1;
        }
        if (abort) {
                conf->recovery_disabled = conf->mddev->recovery_disabled;
                set_bit(MD_RECOVERY_INTR, &conf->mddev->recovery);
        }
}

/* fetch_block - checks the given member device to see if its data needs
 * to be read or computed to satisfy a request.
 *
 * Returns 1 when no more member devices need to be checked, otherwise returns
 * 0 to tell the loop in handle_stripe_fill to continue
 */
static int fetch_block(struct stripe_head *sh, struct stripe_head_state *s,
                       int disk_idx, int disks)
{
        struct r5dev *dev = &sh->dev[disk_idx];
        struct r5dev *fdev[2] = { &sh->dev[s->failed_num[0]],
                                  &sh->dev[s->failed_num[1]] };

        /* is the data in this block needed, and can we get it? */
        if (!test_bit(R5_LOCKED, &dev->flags) &&
            !test_bit(R5_UPTODATE, &dev->flags) &&
            (dev->toread ||
             (dev->towrite && !test_bit(R5_OVERWRITE, &dev->flags)) ||
             s->syncing || s->expanding ||
             (s->failed >= 1 && fdev[0]->toread) ||
             (s->failed >= 2 && fdev[1]->toread) ||
             (sh->raid_conf->level <= 5 && s->failed && fdev[0]->towrite &&
              !test_bit(R5_OVERWRITE, &fdev[0]->flags)) ||
             (sh->raid_conf->level == 6 && s->failed && s->to_write))) {
                /* we would like to get this block, possibly by computing it,
                 * otherwise read it if the backing disk is insync
                 */
                BUG_ON(test_bit(R5_Wantcompute, &dev->flags));
                BUG_ON(test_bit(R5_Wantread, &dev->flags));
                if ((s->uptodate == disks - 1) &&
                    (s->failed && (disk_idx == s->failed_num[0] ||
                                   disk_idx == s->failed_num[1]))) {
                        /* have disk failed, and we're requested to fetch it;
                         * do compute it
                         */
                        pr_debug("Computing stripe %llu block %d\n",
                               (unsigned long long)sh->sector, disk_idx);
                        set_bit(STRIPE_COMPUTE_RUN, &sh->state);
                        set_bit(STRIPE_OP_COMPUTE_BLK, &s->ops_request);
                        set_bit(R5_Wantcompute, &dev->flags);
                        sh->ops.target = disk_idx;
                        sh->ops.target2 = -1; /* no 2nd target */
                        s->req_compute = 1;
                        /* Careful: from this point on 'uptodate' is in the eye
                         * of raid_run_ops which services 'compute' operations
                         * before writes. R5_Wantcompute flags a block that will
                         * be R5_UPTODATE by the time it is needed for a
                         * subsequent operation.
                         */
                        s->uptodate++;
                        return 1;
                } else if (s->uptodate == disks-2 && s->failed >= 2) {
                        /* Computing 2-failure is *very* expensive; only
                         * do it if failed >= 2
                         */
                        int other;
                        for (other = disks; other--; ) {
                                if (other == disk_idx)
                                        continue;
                                if (!test_bit(R5_UPTODATE,
                                      &sh->dev[other].flags))
                                        break;
                        }
                        BUG_ON(other < 0);
                        pr_debug("Computing stripe %llu blocks %d,%d\n",
                               (unsigned long long)sh->sector,
                               disk_idx, other);
                        set_bit(STRIPE_COMPUTE_RUN, &sh->state);
                        set_bit(STRIPE_OP_COMPUTE_BLK, &s->ops_request);
                        set_bit(R5_Wantcompute, &sh->dev[disk_idx].flags);
                        set_bit(R5_Wantcompute, &sh->dev[other].flags);
                        sh->ops.target = disk_idx;
                        sh->ops.target2 = other;
                        s->uptodate += 2;
                        s->req_compute = 1;
                        return 1;
                } else if (test_bit(R5_Insync, &dev->flags)) {
                        set_bit(R5_LOCKED, &dev->flags);
                        set_bit(R5_Wantread, &dev->flags);
                        s->locked++;
                        pr_debug("Reading block %d (sync=%d)\n",
                                disk_idx, s->syncing);
                }
        }

        return 0;
}

/**
 * handle_stripe_fill - read or compute data to satisfy pending requests.
 */
static void handle_stripe_fill(struct stripe_head *sh,
                               struct stripe_head_state *s,
                               int disks)
{
        int i;

        /* look for blocks to read/compute, skip this if a compute
         * is already in flight, or if the stripe contents are in the
         * midst of changing due to a write
         */
        if (!test_bit(STRIPE_COMPUTE_RUN, &sh->state) && !sh->check_state &&
            !sh->reconstruct_state)
                for (i = disks; i--; )
                        if (fetch_block(sh, s, i, disks))
                                break;
        set_bit(STRIPE_HANDLE, &sh->state);
}


/* handle_stripe_clean_event
 * any written block on an uptodate or failed drive can be returned.
 * Note that if we 'wrote' to a failed drive, it will be UPTODATE, but
 * never LOCKED, so we don't need to test 'failed' directly.
 */
static void handle_stripe_clean_event(raid5_conf_t *conf,
        struct stripe_head *sh, int disks, struct bio **return_bi)
{
        int i;
        struct r5dev *dev;

        for (i = disks; i--; )
                if (sh->dev[i].written) {
                        dev = &sh->dev[i];
                        if (!test_bit(R5_LOCKED, &dev->flags) &&
                                test_bit(R5_UPTODATE, &dev->flags)) {
                                /* We can return any write requests */
                                struct bio *wbi, *wbi2;
                                int bitmap_end = 0;
                                pr_debug("Return write for disc %d\n", i);
                                spin_lock_irq(&conf->device_lock);
                                wbi = dev->written;
                                dev->written = NULL;
                                while (wbi && wbi->bi_sector <
                                        dev->sector + STRIPE_SECTORS) {
                                        wbi2 = r5_next_bio(wbi, dev->sector);
                                        if (!raid5_dec_bi_phys_segments(wbi)) {
                                                md_write_end(conf->mddev);
                                                wbi->bi_next = *return_bi;
                                                *return_bi = wbi;
                                        }
                                        wbi = wbi2;
                                }
                                if (dev->towrite == NULL)
                                        bitmap_end = 1;
                                spin_unlock_irq(&conf->device_lock);
                                if (bitmap_end)
                                        bitmap_endwrite(conf->mddev->bitmap,
                                                        sh->sector,
                                                        STRIPE_SECTORS,
                                         !test_bit(STRIPE_DEGRADED, &sh->state),
                                                        0);
                        }
                }

        if (test_and_clear_bit(STRIPE_FULL_WRITE, &sh->state))
                if (atomic_dec_and_test(&conf->pending_full_writes))
                        md_wakeup_thread(conf->mddev->thread);
}

static void handle_stripe_dirtying(raid5_conf_t *conf,
                                   struct stripe_head *sh,
                                   struct stripe_head_state *s,
                                   int disks)
{
        int rmw = 0, rcw = 0, i;
        if (conf->max_degraded == 2) {
                /* RAID6 requires 'rcw' in current implementation
                 * Calculate the real rcw later - for now fake it
                 * look like rcw is cheaper
                 */
                rcw = 1; rmw = 2;
        } else for (i = disks; i--; ) {
                /* would I have to read this buffer for read_modify_write */
                struct r5dev *dev = &sh->dev[i];
                if ((dev->towrite || i == sh->pd_idx) &&
                    !test_bit(R5_LOCKED, &dev->flags) &&
                    !(test_bit(R5_UPTODATE, &dev->flags) ||
                      test_bit(R5_Wantcompute, &dev->flags))) {
                        if (test_bit(R5_Insync, &dev->flags))
                                rmw++;
                        else
                                rmw += 2*disks;  /* cannot read it */
                }
                /* Would I have to read this buffer for reconstruct_write */
                if (!test_bit(R5_OVERWRITE, &dev->flags) && i != sh->pd_idx &&
                    !test_bit(R5_LOCKED, &dev->flags) &&
                    !(test_bit(R5_UPTODATE, &dev->flags) ||
                    test_bit(R5_Wantcompute, &dev->flags))) {
                        if (test_bit(R5_Insync, &dev->flags)) rcw++;
                        else
                                rcw += 2*disks;
                }
        }
        pr_debug("for sector %llu, rmw=%d rcw=%d\n",
                (unsigned long long)sh->sector, rmw, rcw);
        set_bit(STRIPE_HANDLE, &sh->state);
        if (rmw < rcw && rmw > 0)
                /* prefer read-modify-write, but need to get some data */
                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if ((dev->towrite || i == sh->pd_idx) &&
                            !test_bit(R5_LOCKED, &dev->flags) &&
                            !(test_bit(R5_UPTODATE, &dev->flags) ||
                            test_bit(R5_Wantcompute, &dev->flags)) &&
                            test_bit(R5_Insync, &dev->flags)) {
                                if (
                                  test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
                                        pr_debug("Read_old block "
                                                "%d for r-m-w\n", i);
                                        set_bit(R5_LOCKED, &dev->flags);
                                        set_bit(R5_Wantread, &dev->flags);
                                        s->locked++;
                                } else {
                                        set_bit(STRIPE_DELAYED, &sh->state);
                                        set_bit(STRIPE_HANDLE, &sh->state);
                                }
                        }
                }
        if (rcw <= rmw && rcw > 0) {
                /* want reconstruct write, but need to get some data */
                rcw = 0;
                for (i = disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        if (!test_bit(R5_OVERWRITE, &dev->flags) &&
                            i != sh->pd_idx && i != sh->qd_idx &&
                            !test_bit(R5_LOCKED, &dev->flags) &&
                            !(test_bit(R5_UPTODATE, &dev->flags) ||
                              test_bit(R5_Wantcompute, &dev->flags))) {
                                rcw++;
                                if (!test_bit(R5_Insync, &dev->flags))
                                        continue; /* it's a failed drive */
                                if (
                                  test_bit(STRIPE_PREREAD_ACTIVE, &sh->state)) {
                                        pr_debug("Read_old block "
                                                "%d for Reconstruct\n", i);
                                        set_bit(R5_LOCKED, &dev->flags);
                                        set_bit(R5_Wantread, &dev->flags);
                                        s->locked++;
                                } else {
                                        set_bit(STRIPE_DELAYED, &sh->state);
                                        set_bit(STRIPE_HANDLE, &sh->state);
                                }
                        }
                }
        }
        /* now if nothing is locked, and if we have enough data,
         * we can start a write request
         */
        /* since handle_stripe can be called at any time we need to handle the
         * case where a compute block operation has been submitted and then a
         * subsequent call wants to start a write request.  raid_run_ops only
         * handles the case where compute block and reconstruct are requested
         * simultaneously.  If this is not the case then new writes need to be
         * held off until the compute completes.
         */
        if ((s->req_compute || !test_bit(STRIPE_COMPUTE_RUN, &sh->state)) &&
            (s->locked == 0 && (rcw == 0 || rmw == 0) &&
            !test_bit(STRIPE_BIT_DELAY, &sh->state)))
                schedule_reconstruction(sh, s, rcw == 0, 0);
}

static void handle_parity_checks5(raid5_conf_t *conf, struct stripe_head *sh,
                                struct stripe_head_state *s, int disks)
{
        struct r5dev *dev = NULL;

        set_bit(STRIPE_HANDLE, &sh->state);

        switch (sh->check_state) {
        case check_state_idle:
                /* start a new check operation if there are no failures */
                if (s->failed == 0) {
                        BUG_ON(s->uptodate != disks);
                        sh->check_state = check_state_run;
                        set_bit(STRIPE_OP_CHECK, &s->ops_request);
                        clear_bit(R5_UPTODATE, &sh->dev[sh->pd_idx].flags);
                        s->uptodate--;
                        break;
                }
                dev = &sh->dev[s->failed_num[0]];
                /* fall through */
        case check_state_compute_result:
                sh->check_state = check_state_idle;
                if (!dev)
                        dev = &sh->dev[sh->pd_idx];

                /* check that a write has not made the stripe insync */
                if (test_bit(STRIPE_INSYNC, &sh->state))
                        break;

                /* either failed parity check, or recovery is happening */
                BUG_ON(!test_bit(R5_UPTODATE, &dev->flags));
                BUG_ON(s->uptodate != disks);

                set_bit(R5_LOCKED, &dev->flags);
                s->locked++;
                set_bit(R5_Wantwrite, &dev->flags);

                clear_bit(STRIPE_DEGRADED, &sh->state);
                set_bit(STRIPE_INSYNC, &sh->state);
                break;
        case check_state_run:
                break; /* we will be called again upon completion */
        case check_state_check_result:
                sh->check_state = check_state_idle;

                /* if a failure occurred during the check operation, leave
                 * STRIPE_INSYNC not set and let the stripe be handled again
                 */
                if (s->failed)
                        break;

                /* handle a successful check operation, if parity is correct
                 * we are done.  Otherwise update the mismatch count and repair
                 * parity if !MD_RECOVERY_CHECK
                 */
                if ((sh->ops.zero_sum_result & SUM_CHECK_P_RESULT) == 0)
                        /* parity is correct (on disc,
                         * not in buffer any more)
                         */
                        set_bit(STRIPE_INSYNC, &sh->state);
                else {
                        conf->mddev->resync_mismatches += STRIPE_SECTORS;
                        if (test_bit(MD_RECOVERY_CHECK, &conf->mddev->recovery))
                                /* don't try to repair!! */
                                set_bit(STRIPE_INSYNC, &sh->state);
                        else {
                                sh->check_state = check_state_compute_run;
                                set_bit(STRIPE_COMPUTE_RUN, &sh->state);
                                set_bit(STRIPE_OP_COMPUTE_BLK, &s->ops_request);
                                set_bit(R5_Wantcompute,
                                        &sh->dev[sh->pd_idx].flags);
                                sh->ops.target = sh->pd_idx;
                                sh->ops.target2 = -1;
                                s->uptodate++;
                        }
                }
                break;
        case check_state_compute_run:
                break;
        default:
                printk(KERN_ERR "%s: unknown check_state: %d sector: %llu\n",
                       __func__, sh->check_state,
                       (unsigned long long) sh->sector);
                BUG();
        }
}


static void handle_parity_checks6(raid5_conf_t *conf, struct stripe_head *sh,
                                  struct stripe_head_state *s,
                                  int disks)
{
        int pd_idx = sh->pd_idx;
        int qd_idx = sh->qd_idx;
        struct r5dev *dev;

        set_bit(STRIPE_HANDLE, &sh->state);

        BUG_ON(s->failed > 2);

        /* Want to check and possibly repair P and Q.
         * However there could be one 'failed' device, in which
         * case we can only check one of them, possibly using the
         * other to generate missing data
         */

        switch (sh->check_state) {
        case check_state_idle:
                /* start a new check operation if there are < 2 failures */
                if (s->failed == s->q_failed) {
                        /* The only possible failed device holds Q, so it
                         * makes sense to check P (If anything else were failed,
                         * we would have used P to recreate it).
                         */
                        sh->check_state = check_state_run;
                }
                if (!s->q_failed && s->failed < 2) {
                        /* Q is not failed, and we didn't use it to generate
                         * anything, so it makes sense to check it
                         */
                        if (sh->check_state == check_state_run)
                                sh->check_state = check_state_run_pq;
                        else
                                sh->check_state = check_state_run_q;
                }

                /* discard potentially stale zero_sum_result */
                sh->ops.zero_sum_result = 0;

                if (sh->check_state == check_state_run) {
                        /* async_xor_zero_sum destroys the contents of P */
                        clear_bit(R5_UPTODATE, &sh->dev[pd_idx].flags);
                        s->uptodate--;
                }
                if (sh->check_state >= check_state_run &&
                    sh->check_state <= check_state_run_pq) {
                        /* async_syndrome_zero_sum preserves P and Q, so
                         * no need to mark them !uptodate here
                         */
                        set_bit(STRIPE_OP_CHECK, &s->ops_request);
                        break;
                }

                /* we have 2-disk failure */
                BUG_ON(s->failed != 2);
                /* fall through */
        case check_state_compute_result:
                sh->check_state = check_state_idle;

                /* check that a write has not made the stripe insync */
                if (test_bit(STRIPE_INSYNC, &sh->state))
                        break;

                /* now write out any block on a failed drive,
                 * or P or Q if they were recomputed
                 */
                BUG_ON(s->uptodate < disks - 1); /* We don't need Q to recover */
                if (s->failed == 2) {
                        dev = &sh->dev[s->failed_num[1]];
                        s->locked++;
                        set_bit(R5_LOCKED, &dev->flags);
                        set_bit(R5_Wantwrite, &dev->flags);
                }
                if (s->failed >= 1) {
                        dev = &sh->dev[s->failed_num[0]];
                        s->locked++;
                        set_bit(R5_LOCKED, &dev->flags);
                        set_bit(R5_Wantwrite, &dev->flags);
                }
                if (sh->ops.zero_sum_result & SUM_CHECK_P_RESULT) {
                        dev = &sh->dev[pd_idx];
                        s->locked++;
                        set_bit(R5_LOCKED, &dev->flags);
                        set_bit(R5_Wantwrite, &dev->flags);
                }
                if (sh->ops.zero_sum_result & SUM_CHECK_Q_RESULT) {
                        dev = &sh->dev[qd_idx];
                        s->locked++;
                        set_bit(R5_LOCKED, &dev->flags);
                        set_bit(R5_Wantwrite, &dev->flags);
                }
                clear_bit(STRIPE_DEGRADED, &sh->state);

                set_bit(STRIPE_INSYNC, &sh->state);
                break;
        case check_state_run:
        case check_state_run_q:
        case check_state_run_pq:
                break; /* we will be called again upon completion */
        case check_state_check_result:
                sh->check_state = check_state_idle;

                /* handle a successful check operation, if parity is correct
                 * we are done.  Otherwise update the mismatch count and repair
                 * parity if !MD_RECOVERY_CHECK
                 */
                if (sh->ops.zero_sum_result == 0) {
                        /* both parities are correct */
                        if (!s->failed)
                                set_bit(STRIPE_INSYNC, &sh->state);
                        else {
                                /* in contrast to the raid5 case we can validate
                                 * parity, but still have a failure to write
                                 * back
                                 */
                                sh->check_state = check_state_compute_result;
                                /* Returning at this point means that we may go
                                 * off and bring p and/or q uptodate again so
                                 * we make sure to check zero_sum_result again
                                 * to verify if p or q need writeback
                                 */
                        }
                } else {
                        conf->mddev->resync_mismatches += STRIPE_SECTORS;
                        if (test_bit(MD_RECOVERY_CHECK, &conf->mddev->recovery))
                                /* don't try to repair!! */
                                set_bit(STRIPE_INSYNC, &sh->state);
                        else {
                                int *target = &sh->ops.target;

                                sh->ops.target = -1;
                                sh->ops.target2 = -1;
                                sh->check_state = check_state_compute_run;
                                set_bit(STRIPE_COMPUTE_RUN, &sh->state);
                                set_bit(STRIPE_OP_COMPUTE_BLK, &s->ops_request);
                                if (sh->ops.zero_sum_result & SUM_CHECK_P_RESULT) {
                                        set_bit(R5_Wantcompute,
                                                &sh->dev[pd_idx].flags);
                                        *target = pd_idx;
                                        target = &sh->ops.target2;
                                        s->uptodate++;
                                }
                                if (sh->ops.zero_sum_result & SUM_CHECK_Q_RESULT) {
                                        set_bit(R5_Wantcompute,
                                                &sh->dev[qd_idx].flags);
                                        *target = qd_idx;
                                        s->uptodate++;
                                }
                        }
                }
                break;
        case check_state_compute_run:
                break;
        default:
                printk(KERN_ERR "%s: unknown check_state: %d sector: %llu\n",
                       __func__, sh->check_state,
                       (unsigned long long) sh->sector);
                BUG();
        }
}

static void handle_stripe_expansion(raid5_conf_t *conf, struct stripe_head *sh)
{
        int i;

        /* We have read all the blocks in this stripe and now we need to
         * copy some of them into a target stripe for expand.
         */
        struct dma_async_tx_descriptor *tx = NULL;
        clear_bit(STRIPE_EXPAND_SOURCE, &sh->state);
        for (i = 0; i < sh->disks; i++)
                if (i != sh->pd_idx && i != sh->qd_idx) {
                        int dd_idx, j;
                        struct stripe_head *sh2;
                        struct async_submit_ctl submit;

                        sector_t bn = compute_blocknr(sh, i, 1);
                        sector_t s = raid5_compute_sector(conf, bn, 0,
                                                          &dd_idx, NULL);
                        sh2 = get_active_stripe(conf, s, 0, 1, 1);
                        if (sh2 == NULL)
                                /* so far only the early blocks of this stripe
                                 * have been requested.  When later blocks
                                 * get requested, we will try again
                                 */
                                continue;
                        if (!test_bit(STRIPE_EXPANDING, &sh2->state) ||
                           test_bit(R5_Expanded, &sh2->dev[dd_idx].flags)) {
                                /* must have already done this block */
                                release_stripe(sh2);
                                continue;
                        }

                        /* place all the copies on one channel */
                        init_async_submit(&submit, 0, tx, NULL, NULL, NULL);
                        tx = async_memcpy(sh2->dev[dd_idx].page,
                                          sh->dev[i].page, 0, 0, STRIPE_SIZE,
                                          &submit);

                        set_bit(R5_Expanded, &sh2->dev[dd_idx].flags);
                        set_bit(R5_UPTODATE, &sh2->dev[dd_idx].flags);
                        for (j = 0; j < conf->raid_disks; j++)
                                if (j != sh2->pd_idx &&
                                    j != sh2->qd_idx &&
                                    !test_bit(R5_Expanded, &sh2->dev[j].flags))
                                        break;
                        if (j == conf->raid_disks) {
                                set_bit(STRIPE_EXPAND_READY, &sh2->state);
                                set_bit(STRIPE_HANDLE, &sh2->state);
                        }
                        release_stripe(sh2);

                }
        /* done submitting copies, wait for them to complete */
        if (tx) {
                async_tx_ack(tx);
                dma_wait_for_async_tx(tx);
        }
}


/*
 * handle_stripe - do things to a stripe.
 *
 * We lock the stripe and then examine the state of various bits
 * to see what needs to be done.
 * Possible results:
 *    return some read request which now have data
 *    return some write requests which are safely on disc
 *    schedule a read on some buffers
 *    schedule a write of some buffers
 *    return confirmation of parity correctness
 *
 * buffers are taken off read_list or write_list, and bh_cache buffers
 * get BH_Lock set before the stripe lock is released.
 *
 */

static void analyse_stripe(struct stripe_head *sh, struct stripe_head_state *s)
{
        raid5_conf_t *conf = sh->raid_conf;
        int disks = sh->disks;
        struct r5dev *dev;
        int i;

        memset(s, 0, sizeof(*s));

        s->syncing = test_bit(STRIPE_SYNCING, &sh->state);
        s->expanding = test_bit(STRIPE_EXPAND_SOURCE, &sh->state);
        s->expanded = test_bit(STRIPE_EXPAND_READY, &sh->state);
        s->failed_num[0] = -1;
        s->failed_num[1] = -1;