/*
 * raid1.c : Multiple Devices driver for Linux
 *
 * Copyright (C) 1999, 2000, 2001 Ingo Molnar, Red Hat
 *
 * Copyright (C) 1996, 1997, 1998 Ingo Molnar, Miguel de Icaza, Gadi Oxman
 *
 * RAID-1 management functions.
 *
 * Better read-balancing code written by Mika Kuoppala <miku@iki.fi>, 2000
 *
 * Fixes to reconstruction by Jakob Østergaard" <jakob@ostenfeld.dk>
 * Various fixes by Neil Brown <neilb@cse.unsw.edu.au>
 *
 * Changes by Peter T. Breuer <ptb@it.uc3m.es> 31/1/2003 to support
 * bitmapped intelligence in resync:
 *
 *      - bitmap marked during normal i/o
 *      - bitmap used to skip nondirty blocks during sync
 *
 * Additions to bitmap code, (C) 2003-2004 Paul Clements, SteelEye Technology:
 * - persistent bitmap code
 *
 * 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.
 */

#include <linux/slab.h>
#include <linux/delay.h>
#include <linux/blkdev.h>
#include <linux/module.h>
#include <linux/seq_file.h>
#include <linux/ratelimit.h>
#include <linux/sched/signal.h>

#include <trace/events/block.h>

#include "md.h"
#include "raid1.h"
#include "bitmap.h"

#define UNSUPPORTED_MDDEV_FLAGS         \
        ((1L << MD_HAS_JOURNAL) |       \
         (1L << MD_JOURNAL_CLEAN))

/*
 * Number of guaranteed r1bios in case of extreme VM load:
 */
#define NR_RAID1_BIOS 256

/* when we get a read error on a read-only array, we redirect to another
 * device without failing the first device, or trying to over-write to
 * correct the read error.  To keep track of bad blocks on a per-bio
 * level, we store IO_BLOCKED in the appropriate 'bios' pointer
 */
#define IO_BLOCKED ((struct bio *)1)
/* When we successfully write to a known bad-block, we need to remove the
 * bad-block marking which must be done from process context.  So we record
 * the success by setting devs[n].bio to IO_MADE_GOOD
 */
#define IO_MADE_GOOD ((struct bio *)2)

#define BIO_SPECIAL(bio) ((unsigned long)bio <= 2)

/* When there are this many requests queue to be written by
 * the raid1 thread, we become 'congested' to provide back-pressure
 * for writeback.
 */
static int max_queued_requests = 1024;

static void allow_barrier(struct r1conf *conf, sector_t sector_nr);
static void lower_barrier(struct r1conf *conf, sector_t sector_nr);

#define raid1_log(md, fmt, args...)                             \
        do { if ((md)->queue) blk_add_trace_msg((md)->queue, "raid1 " fmt, ##args); } while (0)

static void * r1bio_pool_alloc(gfp_t gfp_flags, void *data)
{
        struct pool_info *pi = data;
        int size = offsetof(struct r1bio, bios[pi->raid_disks]);

        /* allocate a r1bio with room for raid_disks entries in the bios array */
        return kzalloc(size, gfp_flags);
}

static void r1bio_pool_free(void *r1_bio, void *data)
{
        kfree(r1_bio);
}

#define RESYNC_BLOCK_SIZE (64*1024)
#define RESYNC_DEPTH 32
#define RESYNC_SECTORS (RESYNC_BLOCK_SIZE >> 9)
#define RESYNC_PAGES ((RESYNC_BLOCK_SIZE + PAGE_SIZE-1) / PAGE_SIZE)
#define RESYNC_WINDOW (RESYNC_BLOCK_SIZE * RESYNC_DEPTH)
#define RESYNC_WINDOW_SECTORS (RESYNC_WINDOW >> 9)
#define CLUSTER_RESYNC_WINDOW (16 * RESYNC_WINDOW)
#define CLUSTER_RESYNC_WINDOW_SECTORS (CLUSTER_RESYNC_WINDOW >> 9)

static void * r1buf_pool_alloc(gfp_t gfp_flags, void *data)
{
        struct pool_info *pi = data;
        struct r1bio *r1_bio;
        struct bio *bio;
        int need_pages;
        int i, j;

        r1_bio = r1bio_pool_alloc(gfp_flags, pi);
        if (!r1_bio)
                return NULL;

        /*
         * Allocate bios : 1 for reading, n-1 for writing
         */
        for (j = pi->raid_disks ; j-- ; ) {
                bio = bio_kmalloc(gfp_flags, RESYNC_PAGES);
                if (!bio)
                        goto out_free_bio;
                r1_bio->bios[j] = bio;
        }
        /*
         * Allocate RESYNC_PAGES data pages and attach them to
         * the first bio.
         * If this is a user-requested check/repair, allocate
         * RESYNC_PAGES for each bio.
         */
        if (test_bit(MD_RECOVERY_REQUESTED, &pi->mddev->recovery))
                need_pages = pi->raid_disks;
        else
                need_pages = 1;
        for (j = 0; j < need_pages; j++) {
                bio = r1_bio->bios[j];
                bio->bi_vcnt = RESYNC_PAGES;

                if (bio_alloc_pages(bio, gfp_flags))
                        goto out_free_pages;
        }
        /* If not user-requests, copy the page pointers to all bios */
        if (!test_bit(MD_RECOVERY_REQUESTED, &pi->mddev->recovery)) {
                for (i=0; i<RESYNC_PAGES ; i++)
                        for (j=1; j<pi->raid_disks; j++)
                                r1_bio->bios[j]->bi_io_vec[i].bv_page =
                                        r1_bio->bios[0]->bi_io_vec[i].bv_page;
        }

        r1_bio->master_bio = NULL;

        return r1_bio;

out_free_pages:
        while (--j >= 0)
                bio_free_pages(r1_bio->bios[j]);

out_free_bio:
        while (++j < pi->raid_disks)
                bio_put(r1_bio->bios[j]);
        r1bio_pool_free(r1_bio, data);
        return NULL;
}

static void r1buf_pool_free(void *__r1_bio, void *data)
{
        struct pool_info *pi = data;
        int i,j;
        struct r1bio *r1bio = __r1_bio;

        for (i = 0; i < RESYNC_PAGES; i++)
                for (j = pi->raid_disks; j-- ;) {
                        if (j == 0 ||
                            r1bio->bios[j]->bi_io_vec[i].bv_page !=
                            r1bio->bios[0]->bi_io_vec[i].bv_page)
                                safe_put_page(r1bio->bios[j]->bi_io_vec[i].bv_page);
                }
        for (i=0 ; i < pi->raid_disks; i++)
                bio_put(r1bio->bios[i]);

        r1bio_pool_free(r1bio, data);
}

static void put_all_bios(struct r1conf *conf, struct r1bio *r1_bio)
{
        int i;

        for (i = 0; i < conf->raid_disks * 2; i++) {
                struct bio **bio = r1_bio->bios + i;
                if (!BIO_SPECIAL(*bio))
                        bio_put(*bio);
                *bio = NULL;
        }
}

static void free_r1bio(struct r1bio *r1_bio)
{
        struct r1conf *conf = r1_bio->mddev->private;

        put_all_bios(conf, r1_bio);
        mempool_free(r1_bio, conf->r1bio_pool);
}

static void put_buf(struct r1bio *r1_bio)
{
        struct r1conf *conf = r1_bio->mddev->private;
        sector_t sect = r1_bio->sector;
        int i;

        for (i = 0; i < conf->raid_disks * 2; i++) {
                struct bio *bio = r1_bio->bios[i];
                if (bio->bi_end_io)
                        rdev_dec_pending(conf->mirrors[i].rdev, r1_bio->mddev);
        }

        mempool_free(r1_bio, conf->r1buf_pool);

        lower_barrier(conf, sect);
}

static void reschedule_retry(struct r1bio *r1_bio)
{
        unsigned long flags;
        struct mddev *mddev = r1_bio->mddev;
        struct r1conf *conf = mddev->private;
        int idx;

        idx = sector_to_idx(r1_bio->sector);
        spin_lock_irqsave(&conf->device_lock, flags);
        list_add(&r1_bio->retry_list, &conf->retry_list);
        atomic_inc(&conf->nr_queued[idx]);
        spin_unlock_irqrestore(&conf->device_lock, flags);

        wake_up(&conf->wait_barrier);
        md_wakeup_thread(mddev->thread);
}

/*
 * raid_end_bio_io() is called when we have finished servicing a mirrored
 * operation and are ready to return a success/failure code to the buffer
 * cache layer.
 */
static void call_bio_endio(struct r1bio *r1_bio)
{
        struct bio *bio = r1_bio->master_bio;
        int done;
        struct r1conf *conf = r1_bio->mddev->private;
        sector_t bi_sector = bio->bi_iter.bi_sector;

        if (bio->bi_phys_segments) {
                unsigned long flags;
                spin_lock_irqsave(&conf->device_lock, flags);
                bio->bi_phys_segments--;
                done = (bio->bi_phys_segments == 0);
                spin_unlock_irqrestore(&conf->device_lock, flags);
                /*
                 * make_request() might be waiting for
                 * bi_phys_segments to decrease
                 */
                wake_up(&conf->wait_barrier);
        } else
                done = 1;

        if (!test_bit(R1BIO_Uptodate, &r1_bio->state))
                bio->bi_error = -EIO;

        if (done) {
                bio_endio(bio);
                /*
                 * Wake up any possible resync thread that waits for the device
                 * to go idle.
                 */
                allow_barrier(conf, bi_sector);
        }
}

static void raid_end_bio_io(struct r1bio *r1_bio)
{
        struct bio *bio = r1_bio->master_bio;

        /* if nobody has done the final endio yet, do it now */
        if (!test_and_set_bit(R1BIO_Returned, &r1_bio->state)) {
                pr_debug("raid1: sync end %s on sectors %llu-%llu\n",
                         (bio_data_dir(bio) == WRITE) ? "write" : "read",
                         (unsigned long long) bio->bi_iter.bi_sector,
                         (unsigned long long) bio_end_sector(bio) - 1);

                call_bio_endio(r1_bio);
        }
        free_r1bio(r1_bio);
}

/*
 * Update disk head position estimator based on IRQ completion info.
 */
static inline void update_head_pos(int disk, struct r1bio *r1_bio)
{
        struct r1conf *conf = r1_bio->mddev->private;

        conf->mirrors[disk].head_position =
                r1_bio->sector + (r1_bio->sectors);
}

/*
 * Find the disk number which triggered given bio
 */
static int find_bio_disk(struct r1bio *r1_bio, struct bio *bio)
{
        int mirror;
        struct r1conf *conf = r1_bio->mddev->private;
        int raid_disks = conf->raid_disks;

        for (mirror = 0; mirror < raid_disks * 2; mirror++)
                if (r1_bio->bios[mirror] == bio)
                        break;

        BUG_ON(mirror == raid_disks * 2);
        update_head_pos(mirror, r1_bio);

        return mirror;
}

static void raid1_end_read_request(struct bio *bio)
{
        int uptodate = !bio->bi_error;
        struct r1bio *r1_bio = bio->bi_private;
        struct r1conf *conf = r1_bio->mddev->private;
        struct md_rdev *rdev = conf->mirrors[r1_bio->read_disk].rdev;

        /*
         * this branch is our 'one mirror IO has finished' event handler:
         */
        update_head_pos(r1_bio->read_disk, r1_bio);

        if (uptodate)
                set_bit(R1BIO_Uptodate, &r1_bio->state);
        else if (test_bit(FailFast, &rdev->flags) &&
                 test_bit(R1BIO_FailFast, &r1_bio->state))
                /* This was a fail-fast read so we definitely
                 * want to retry */
                ;
        else {
                /* If all other devices have failed, we want to return
                 * the error upwards rather than fail the last device.
                 * Here we redefine "uptodate" to mean "Don't want to retry"
                 */
                unsigned long flags;
                spin_lock_irqsave(&conf->device_lock, flags);
                if (r1_bio->mddev->degraded == conf->raid_disks ||
                    (r1_bio->mddev->degraded == conf->raid_disks-1 &&
                     test_bit(In_sync, &rdev->flags)))
                        uptodate = 1;
                spin_unlock_irqrestore(&conf->device_lock, flags);
        }

        if (uptodate) {
                raid_end_bio_io(r1_bio);
                rdev_dec_pending(rdev, conf->mddev);
        } else {
                /*
                 * oops, read error:
                 */
                char b[BDEVNAME_SIZE];
                pr_err_ratelimited("md/raid1:%s: %s: rescheduling sector %llu\n",
                                   mdname(conf->mddev),
                                   bdevname(rdev->bdev, b),
                                   (unsigned long long)r1_bio->sector);
                set_bit(R1BIO_ReadError, &r1_bio->state);
                reschedule_retry(r1_bio);
                /* don't drop the reference on read_disk yet */
        }
}

static void close_write(struct r1bio *r1_bio)
{
        /* it really is the end of this request */
        if (test_bit(R1BIO_BehindIO, &r1_bio->state)) {
                /* free extra copy of the data pages */
                int i = r1_bio->behind_page_count;
                while (i--)
                        safe_put_page(r1_bio->behind_bvecs[i].bv_page);
                kfree(r1_bio->behind_bvecs);
                r1_bio->behind_bvecs = NULL;
        }
        /* clear the bitmap if all writes complete successfully */
        bitmap_endwrite(r1_bio->mddev->bitmap, r1_bio->sector,
                        r1_bio->sectors,
                        !test_bit(R1BIO_Degraded, &r1_bio->state),
                        test_bit(R1BIO_BehindIO, &r1_bio->state));
        md_write_end(r1_bio->mddev);
}

static void r1_bio_write_done(struct r1bio *r1_bio)
{
        if (!atomic_dec_and_test(&r1_bio->remaining))
                return;

        if (test_bit(R1BIO_WriteError, &r1_bio->state))
                reschedule_retry(r1_bio);
        else {
                close_write(r1_bio);
                if (test_bit(R1BIO_MadeGood, &r1_bio->state))
                        reschedule_retry(r1_bio);
                else
                        raid_end_bio_io(r1_bio);
        }
}

static void raid1_end_write_request(struct bio *bio)
{
        struct r1bio *r1_bio = bio->bi_private;
        int behind = test_bit(R1BIO_BehindIO, &r1_bio->state);
        struct r1conf *conf = r1_bio->mddev->private;
        struct bio *to_put = NULL;
        int mirror = find_bio_disk(r1_bio, bio);
        struct md_rdev *rdev = conf->mirrors[mirror].rdev;
        bool discard_error;

        discard_error = bio->bi_error && bio_op(bio) == REQ_OP_DISCARD;

        /*
         * 'one mirror IO has finished' event handler:
         */
        if (bio->bi_error && !discard_error) {
                set_bit(WriteErrorSeen, &rdev->flags);
                if (!test_and_set_bit(WantReplacement, &rdev->flags))
                        set_bit(MD_RECOVERY_NEEDED, &
                                conf->mddev->recovery);

                if (test_bit(FailFast, &rdev->flags) &&
                    (bio->bi_opf & MD_FAILFAST) &&
                    /* We never try FailFast to WriteMostly devices */
                    !test_bit(WriteMostly, &rdev->flags)) {
                        md_error(r1_bio->mddev, rdev);
                        if (!test_bit(Faulty, &rdev->flags))
                                /* This is the only remaining device,
                                 * We need to retry the write without
                                 * FailFast
                                 */
                                set_bit(R1BIO_WriteError, &r1_bio->state);
                        else {
                                /* Finished with this branch */
                                r1_bio->bios[mirror] = NULL;
                                to_put = bio;
                        }
                } else
                        set_bit(R1BIO_WriteError, &r1_bio->state);
        } else {
                /*
                 * Set R1BIO_Uptodate in our master bio, so that we
                 * will return a good error code for to the higher
                 * levels even if IO on some other mirrored buffer
                 * fails.
                 *
                 * The 'master' represents the composite IO operation
                 * to user-side. So if something waits for IO, then it
                 * will wait for the 'master' bio.
                 */
                sector_t first_bad;
                int bad_sectors;

                r1_bio->bios[mirror] = NULL;
                to_put = bio;
                /*
                 * Do not set R1BIO_Uptodate if the current device is
                 * rebuilding or Faulty. This is because we cannot use
                 * such device for properly reading the data back (we could
                 * potentially use it, if the current write would have felt
                 * before rdev->recovery_offset, but for simplicity we don't
                 * check this here.
                 */
                if (test_bit(In_sync, &rdev->flags) &&
                    !test_bit(Faulty, &rdev->flags))
                        set_bit(R1BIO_Uptodate, &r1_bio->state);

                /* Maybe we can clear some bad blocks. */
                if (is_badblock(rdev, r1_bio->sector, r1_bio->sectors,
                                &first_bad, &bad_sectors) && !discard_error) {
                        r1_bio->bios[mirror] = IO_MADE_GOOD;
                        set_bit(R1BIO_MadeGood, &r1_bio->state);
                }
        }

        if (behind) {
                if (test_bit(WriteMostly, &rdev->flags))
                        atomic_dec(&r1_bio->behind_remaining);

                /*
                 * In behind mode, we ACK the master bio once the I/O
                 * has safely reached all non-writemostly
                 * disks. Setting the Returned bit ensures that this
                 * gets done only once -- we don't ever want to return
                 * -EIO here, instead we'll wait
                 */
                if (atomic_read(&r1_bio->behind_remaining) >= (atomic_read(&r1_bio->remaining)-1) &&
                    test_bit(R1BIO_Uptodate, &r1_bio->state)) {
                        /* Maybe we can return now */
                        if (!test_and_set_bit(R1BIO_Returned, &r1_bio->state)) {
                                struct bio *mbio = r1_bio->master_bio;
                                pr_debug("raid1: behind end write sectors"
                                         " %llu-%llu\n",
                                         (unsigned long long) mbio->bi_iter.bi_sector,
                                         (unsigned long long) bio_end_sector(mbio) - 1);
                                call_bio_endio(r1_bio);
                        }
                }
        }
        if (r1_bio->bios[mirror] == NULL)
                rdev_dec_pending(rdev, conf->mddev);

        /*
         * Let's see if all mirrored write operations have finished
         * already.
         */
        r1_bio_write_done(r1_bio);

        if (to_put)
                bio_put(to_put);
}

static sector_t align_to_barrier_unit_end(sector_t start_sector,
                                          sector_t sectors)
{
        sector_t len;

        WARN_ON(sectors == 0);
        /*
         * len is the number of sectors from start_sector to end of the
         * barrier unit which start_sector belongs to.
         */
        len = round_up(start_sector + 1, BARRIER_UNIT_SECTOR_SIZE) -
              start_sector;

        if (len > sectors)
                len = sectors;

        return len;
}

/*
 * This routine returns the disk from which the requested read should
 * be done. There is a per-array 'next expected sequential IO' sector
 * number - if this matches on the next IO then we use the last disk.
 * There is also a per-disk 'last know head position' sector that is
 * maintained from IRQ contexts, both the normal and the resync IO
 * completion handlers update this position correctly. If there is no
 * perfect sequential match then we pick the disk whose head is closest.
 *
 * If there are 2 mirrors in the same 2 devices, performance degrades
 * because position is mirror, not device based.
 *
 * The rdev for the device selected will have nr_pending incremented.
 */
static int read_balance(struct r1conf *conf, struct r1bio *r1_bio, int *max_sectors)
{
        const sector_t this_sector = r1_bio->sector;
        int sectors;
        int best_good_sectors;
        int best_disk, best_dist_disk, best_pending_disk;
        int has_nonrot_disk;
        int disk;
        sector_t best_dist;
        unsigned int min_pending;
        struct md_rdev *rdev;
        int choose_first;
        int choose_next_idle;

        rcu_read_lock();
        /*
         * Check if we can balance. We can balance on the whole
         * device if no resync is going on, or below the resync window.
         * We take the first readable disk when above the resync window.
         */
 retry:
        sectors = r1_bio->sectors;
        best_disk = -1;
        best_dist_disk = -1;
        best_dist = MaxSector;
        best_pending_disk = -1;
        min_pending = UINT_MAX;
        best_good_sectors = 0;
        has_nonrot_disk = 0;
        choose_next_idle = 0;
        clear_bit(R1BIO_FailFast, &r1_bio->state);

        if ((conf->mddev->recovery_cp < this_sector + sectors) ||
            (mddev_is_clustered(conf->mddev) &&
            md_cluster_ops->area_resyncing(conf->mddev, READ, this_sector,
                    this_sector + sectors)))
                choose_first = 1;
        else
                choose_first = 0;

        for (disk = 0 ; disk < conf->raid_disks * 2 ; disk++) {
                sector_t dist;
                sector_t first_bad;
                int bad_sectors;
                unsigned int pending;
                bool nonrot;

                rdev = rcu_dereference(conf->mirrors[disk].rdev);
                if (r1_bio->bios[disk] == IO_BLOCKED
                    || rdev == NULL
                    || test_bit(Faulty, &rdev->flags))
                        continue;
                if (!test_bit(In_sync, &rdev->flags) &&
                    rdev->recovery_offset < this_sector + sectors)
                        continue;
                if (test_bit(WriteMostly, &rdev->flags)) {
                        /* Don't balance among write-mostly, just
                         * use the first as a last resort */
                        if (best_dist_disk < 0) {
                                if (is_badblock(rdev, this_sector, sectors,
                                                &first_bad, &bad_sectors)) {
                                        if (first_bad <= this_sector)
                                                /* Cannot use this */
                                                continue;
                                        best_good_sectors = first_bad - this_sector;
                                } else
                                        best_good_sectors = sectors;
                                best_dist_disk = disk;
                                best_pending_disk = disk;
                        }
                        continue;
                }
                /* This is a reasonable device to use.  It might
                 * even be best.
                 */
                if (is_badblock(rdev, this_sector, sectors,
                                &first_bad, &bad_sectors)) {
                        if (best_dist < MaxSector)
                                /* already have a better device */
                                continue;
                        if (first_bad <= this_sector) {
                                /* cannot read here. If this is the 'primary'
                                 * device, then we must not read beyond
                                 * bad_sectors from another device..
                                 */
                                bad_sectors -= (this_sector - first_bad);
                                if (choose_first && sectors > bad_sectors)
                                        sectors = bad_sectors;
                                if (best_good_sectors > sectors)
                                        best_good_sectors = sectors;

                        } else {
                                sector_t good_sectors = first_bad - this_sector;
                                if (good_sectors > best_good_sectors) {
                                        best_good_sectors = good_sectors;
                                        best_disk = disk;
                                }
                                if (choose_first)
                                        break;
                        }
                        continue;
                } else
                        best_good_sectors = sectors;

                if (best_disk >= 0)
                        /* At least two disks to choose from so failfast is OK */
                        set_bit(R1BIO_FailFast, &r1_bio->state);

                nonrot = blk_queue_nonrot(bdev_get_queue(rdev->bdev));
                has_nonrot_disk |= nonrot;
                pending = atomic_read(&rdev->nr_pending);
                dist = abs(this_sector - conf->mirrors[disk].head_position);
                if (choose_first) {
                        best_disk = disk;
                        break;
                }
                /* Don't change to another disk for sequential reads */
                if (conf->mirrors[disk].next_seq_sect == this_sector
                    || dist == 0) {
                        int opt_iosize = bdev_io_opt(rdev->bdev) >> 9;
                        struct raid1_info *mirror = &conf->mirrors[disk];

                        best_disk = disk;
                        /*
                         * If buffered sequential IO size exceeds optimal
                         * iosize, check if there is idle disk. If yes, choose
                         * the idle disk. read_balance could already choose an
                         * idle disk before noticing it's a sequential IO in
                         * this disk. This doesn't matter because this disk
                         * will idle, next time it will be utilized after the
                         * first disk has IO size exceeds optimal iosize. In
                         * this way, iosize of the first disk will be optimal
                         * iosize at least. iosize of the second disk might be
                         * small, but not a big deal since when the second disk
                         * starts IO, the first disk is likely still busy.
                         */
                        if (nonrot && opt_iosize > 0 &&
                            mirror->seq_start != MaxSector &&
                            mirror->next_seq_sect > opt_iosize &&
                            mirror->next_seq_sect - opt_iosize >=
                            mirror->seq_start) {
                                choose_next_idle = 1;
                                continue;
                        }
                        break;
                }

                if (choose_next_idle)
                        continue;

                if (min_pending > pending) {
                        min_pending = pending;
                        best_pending_disk = disk;
                }

                if (dist < best_dist) {
                        best_dist = dist;
                        best_dist_disk = disk;
                }
        }

        /*
         * If all disks are rotational, choose the closest disk. If any disk is
         * non-rotational, choose the disk with less pending request even the
         * disk is rotational, which might/might not be optimal for raids with
         * mixed ratation/non-rotational disks depending on workload.
         */
        if (best_disk == -1) {
                if (has_nonrot_disk || min_pending == 0)
                        best_disk = best_pending_disk;
                else
                        best_disk = best_dist_disk;
        }

        if (best_disk >= 0) {
                rdev = rcu_dereference(conf->mirrors[best_disk].rdev);
                if (!rdev)
                        goto retry;
                atomic_inc(&rdev->nr_pending);
                sectors = best_good_sectors;

                if (conf->mirrors[best_disk].next_seq_sect != this_sector)
                        conf->mirrors[best_disk].seq_start = this_sector;

                conf->mirrors[best_disk].next_seq_sect = this_sector + sectors;
        }
        rcu_read_unlock();
        *max_sectors = sectors;

        return best_disk;
}

static int raid1_congested(struct mddev *mddev, int bits)
{
        struct r1conf *conf = mddev->private;
        int i, ret = 0;

        if ((bits & (1 << WB_async_congested)) &&
            conf->pending_count >= max_queued_requests)
                return 1;

        rcu_read_lock();
        for (i = 0; i < conf->raid_disks * 2; i++) {
                struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev);
                if (rdev && !test_bit(Faulty, &rdev->flags)) {
                        struct request_queue *q = bdev_get_queue(rdev->bdev);

                        BUG_ON(!q);

                        /* Note the '|| 1' - when read_balance prefers
                         * non-congested targets, it can be removed
                         */
                        if ((bits & (1 << WB_async_congested)) || 1)
                                ret |= bdi_congested(q->backing_dev_info, bits);
                        else
                                ret &= bdi_congested(q->backing_dev_info, bits);
                }
        }
        rcu_read_unlock();
        return ret;
}

static void flush_pending_writes(struct r1conf *conf)
{
        /* Any writes that have been queued but are awaiting
         * bitmap updates get flushed here.
         */
        spin_lock_irq(&conf->device_lock);

        if (conf->pending_bio_list.head) {
                struct bio *bio;
                bio = bio_list_get(&conf->pending_bio_list);
                conf->pending_count = 0;
                spin_unlock_irq(&conf->device_lock);
                /* flush any pending bitmap writes to
                 * disk before proceeding w/ I/O */
                bitmap_unplug(conf->mddev->bitmap);
                wake_up(&conf->wait_barrier);

                while (bio) { /* submit pending writes */
                        struct bio *next = bio->bi_next;
                        struct md_rdev *rdev = (void*)bio->bi_bdev;
                        bio->bi_next = NULL;
                        bio->bi_bdev = rdev->bdev;
                        if (test_bit(Faulty, &rdev->flags)) {
                                bio->bi_error = -EIO;
                                bio_endio(bio);
                        } else if (unlikely((bio_op(bio) == REQ_OP_DISCARD) &&
                                            !blk_queue_discard(bdev_get_queue(bio->bi_bdev))))
                                /* Just ignore it */
                                bio_endio(bio);
                        else
                                generic_make_request(bio);
                        bio = next;
                }
        } else
                spin_unlock_irq(&conf->device_lock);
}

/* Barriers....
 * Sometimes we need to suspend IO while we do something else,
 * either some resync/recovery, or reconfigure the array.
 * To do this we raise a 'barrier'.
 * The 'barrier' is a counter that can be raised multiple times
 * to count how many activities are happening which preclude
 * normal IO.
 * We can only raise the barrier if there is no pending IO.
 * i.e. if nr_pending == 0.
 * We choose only to raise the barrier if no-one is waiting for the
 * barrier to go down.  This means that as soon as an IO request
 * is ready, no other operations which require a barrier will start
 * until the IO request has had a chance.
 *
 * So: regular IO calls 'wait_barrier'.  When that returns there
 *    is no backgroup IO happening,  It must arrange to call
 *    allow_barrier when it has finished its IO.
 * backgroup IO calls must call raise_barrier.  Once that returns
 *    there is no normal IO happeing.  It must arrange to call
 *    lower_barrier when the particular background IO completes.
 */
static void raise_barrier(struct r1conf *conf, sector_t sector_nr)
{
        int idx = sector_to_idx(sector_nr);

        spin_lock_irq(&conf->resync_lock);

        /* Wait until no block IO is waiting */
        wait_event_lock_irq(conf->wait_barrier,
                            !atomic_read(&conf->nr_waiting[idx]),
                            conf->resync_lock);

        /* block any new IO from starting */
        atomic_inc(&conf->barrier[idx]);
        /*
         * In raise_barrier() we firstly increase conf->barrier[idx] then
         * check conf->nr_pending[idx]. In _wait_barrier() we firstly
         * increase conf->nr_pending[idx] then check conf->barrier[idx].
         * A memory barrier here to make sure conf->nr_pending[idx] won't
         * be fetched before conf->barrier[idx] is increased. Otherwise
         * there will be a race between raise_barrier() and _wait_barrier().
         */
        smp_mb__after_atomic();

        /* For these conditions we must wait:
         * A: while the array is in frozen state
         * B: while conf->nr_pending[idx] is not 0, meaning regular I/O
         *    existing in corresponding I/O barrier bucket.
         * C: while conf->barrier[idx] >= RESYNC_DEPTH, meaning reaches
         *    max resync count which allowed on current I/O barrier bucket.
         */
        wait_event_lock_irq(conf->wait_barrier,
                            !conf->array_frozen &&
                             !atomic_read(&conf->nr_pending[idx]) &&
                             atomic_read(&conf->barrier[idx]) < RESYNC_DEPTH,
                            conf->resync_lock);

        atomic_inc(&conf->nr_pending[idx]);
        spin_unlock_irq(&conf->resync_lock);
}

static void lower_barrier(struct r1conf *conf, sector_t sector_nr)
{
        int idx = sector_to_idx(sector_nr);

        BUG_ON(atomic_read(&conf->barrier[idx]) <= 0);

        atomic_dec(&conf->barrier[idx]);
        atomic_dec(&conf->nr_pending[idx]);
        wake_up(&conf->wait_barrier);
}

static void _wait_barrier(struct r1conf *conf, int idx)
{
        /*
         * We need to increase conf->nr_pending[idx] very early here,
         * then raise_barrier() can be blocked when it waits for
         * conf->nr_pending[idx] to be 0. Then we can avoid holding
         * conf->resync_lock when there is no barrier raised in same
         * barrier unit bucket. Also if the array is frozen, I/O
         * should be blocked until array is unfrozen.
         */
        atomic_inc(&conf->nr_pending[idx]);
        /*
         * In _wait_barrier() we firstly increase conf->nr_pending[idx], then
         * check conf->barrier[idx]. In raise_barrier() we firstly increase
         * conf->barrier[idx], then check conf->nr_pending[idx]. A memory
         * barrier is necessary here to make sure conf->barrier[idx] won't be
         * fetched before conf->nr_pending[idx] is increased. Otherwise there
         * will be a race between _wait_barrier() and raise_barrier().
         */
        smp_mb__after_atomic();

        /*
         * Don't worry about checking two atomic_t variables at same time
         * here. If during we check conf->barrier[idx], the array is
         * frozen (conf->array_frozen is 1), and chonf->barrier[idx] is
         * 0, it is safe to return and make the I/O continue. Because the
         * array is frozen, all I/O returned here will eventually complete
         * or be queued, no race will happen. See code comment in
         * frozen_array().
         */
        if (!READ_ONCE(conf->array_frozen) &&
            !atomic_read(&conf->barrier[idx]))
                return;

        /*
         * After holding conf->resync_lock, conf->nr_pending[idx]
         * should be decreased before waiting for barrier to drop.
         * Otherwise, we may encounter a race condition because
         * raise_barrer() might be waiting for conf->nr_pending[idx]
         * to be 0 at same time.
         */
        spin_lock_irq(&conf->resync_lock);
        atomic_inc(&conf->nr_waiting[idx]);
        atomic_dec(&conf->nr_pending[idx]);
        /*
         * In case freeze_array() is waiting for
         * get_unqueued_pending() == extra
         */
        wake_up(&conf->wait_barrier);
        /* Wait for the barrier in same barrier unit bucket to drop. */
        wait_event_lock_irq(conf->wait_barrier,
                            !conf->array_frozen &&
                             !atomic_read(&conf->barrier[idx]),
                            conf->resync_lock);
        atomic_inc(&conf->nr_pending[idx]);
        atomic_dec(&conf->nr_waiting[idx]);
        spin_unlock_irq(&conf->resync_lock);
}

static void wait_read_barrier(struct r1conf *conf, sector_t sector_nr)
{
        int idx = sector_to_idx(sector_nr);

        /*
         * Very similar to _wait_barrier(). The difference is, for read
         * I/O we don't need wait for sync I/O, but if the whole array
         * is frozen, the read I/O still has to wait until the array is
         * unfrozen. Since there is no ordering requirement with
         * conf->barrier[idx] here, memory barrier is unnecessary as well.
         */
        atomic_inc(&conf->nr_pending[idx]);

        if (!READ_ONCE(conf->array_frozen))
                return;

        spin_lock_irq(&conf->resync_lock);
        atomic_inc(&conf->nr_waiting[idx]);
        atomic_dec(&conf->nr_pending[idx]);
        /*
         * In case freeze_array() is waiting for
         * get_unqueued_pending() == extra
         */
        wake_up(&conf->wait_barrier);
        /* Wait for array to be unfrozen */
        wait_event_lock_irq(conf->wait_barrier,
                            !conf->array_frozen,
                            conf->resync_lock);
        atomic_inc(&conf->nr_pending[idx]);
        atomic_dec(&conf->nr_waiting[idx]);
        spin_unlock_irq(&conf->resync_lock);
}

static void wait_barrier(struct r1conf *conf, sector_t sector_nr)
{
        int idx = sector_to_idx(sector_nr);

        _wait_barrier(conf, idx);
}

static void wait_all_barriers(struct r1conf *conf)
{
        int idx;

        for (idx = 0; idx < BARRIER_BUCKETS_NR; idx++)
                _wait_barrier(conf, idx);
}

static void _allow_barrier(struct r1conf *conf, int idx)
{
        atomic_dec(&conf->nr_pending[idx]);
        wake_up(&conf->wait_barrier);
}

static void allow_barrier(struct r1conf *conf, sector_t sector_nr)

{
        int idx = sector_to_idx(sector_nr);

        _allow_barrier(conf, idx);
}

static void allow_all_barriers(struct r1conf *conf)
{
        int idx;

        for (idx = 0; idx < BARRIER_BUCKETS_NR; idx++)
                _allow_barrier(conf, idx);
}

/* conf->resync_lock should be held */
static int get_unqueued_pending(struct r1conf *conf)
{
        int idx, ret;

        for (ret = 0, idx = 0; idx < BARRIER_BUCKETS_NR; idx++)
                ret += atomic_read(&conf->nr_pending[idx]) -
                        atomic_read(&conf->nr_queued[idx]);

        return ret;
}

static void freeze_array(struct r1conf *conf, int extra)
{
        /* Stop sync I/O and normal I/O and wait for everything to
         * go quiet.
         * This is called in two situations:
         * 1) management command handlers (reshape, remove disk, quiesce).
         * 2) one normal I/O request failed.

         * After array_frozen is set to 1, new sync IO will be blocked at
         * raise_barrier(), and new normal I/O will blocked at _wait_barrier()
         * or wait_read_barrier(). The flying I/Os will either complete or be
         * queued. When everything goes quite, there are only queued I/Os left.

         * Every flying I/O contributes to a conf->nr_pending[idx], idx is the
         * barrier bucket index which this I/O request hits. When all sync and
         * normal I/O are queued, sum of all conf->nr_pending[] will match sum
         * of all conf->nr_queued[]. But normal I/O failure is an exception,
         * in handle_read_error(), we may call freeze_array() before trying to
         * fix the read error. In this case, the error read I/O is not queued,
         * so get_unqueued_pending() == 1.
         *
         * Therefore before this function returns, we need to wait until
         * get_unqueued_pendings(conf) gets equal to extra. For
         * normal I/O context, extra is 1, in rested situations extra is 0.
         */
        spin_lock_irq(&conf->resync_lock);
        conf->array_frozen = 1;
        raid1_log(conf->mddev, "wait freeze");
        wait_event_lock_irq_cmd(
                conf->wait_barrier,
                get_unqueued_pending(conf) == extra,
                conf->resync_lock,
                flush_pending_writes(conf));
        spin_unlock_irq(&conf->resync_lock);
}
static void unfreeze_array(struct r1conf *conf)
{
        /* reverse the effect of the freeze */
        spin_lock_irq(&conf->resync_lock);
        conf->array_frozen = 0;
        spin_unlock_irq(&conf->resync_lock);
        wake_up(&conf->wait_barrier);
}

/* duplicate the data pages for behind I/O
 */
static void alloc_behind_pages(struct bio *bio, struct r1bio *r1_bio)
{
        int i;
        struct bio_vec *bvec;
        struct bio_vec *bvecs = kzalloc(bio->bi_vcnt * sizeof(struct bio_vec),
                                        GFP_NOIO);
        if (unlikely(!bvecs))
                return;

        bio_for_each_segment_all(bvec, bio, i) {
                bvecs[i] = *bvec;
                bvecs[i].bv_page = alloc_page(GFP_NOIO);
                if (unlikely(!bvecs[i].bv_page))
                        goto do_sync_io;
                memcpy(kmap(bvecs[i].bv_page) + bvec->bv_offset,
                       kmap(bvec->bv_page) + bvec->bv_offset, bvec->bv_len);
                kunmap(bvecs[i].bv_page);
                kunmap(bvec->bv_page);
        }
        r1_bio->behind_bvecs = bvecs;
        r1_bio->behind_page_count = bio->bi_vcnt;
        set_bit(R1BIO_BehindIO, &r1_bio->state);
        return;

do_sync_io:
        for (i = 0; i < bio->bi_vcnt; i++)
                if (bvecs[i].bv_page)
                        put_page(bvecs[i].bv_page);
        kfree(bvecs);
        pr_debug("%dB behind alloc failed, doing sync I/O\n",
                 bio->bi_iter.bi_size);
}

struct raid1_plug_cb {
        struct blk_plug_cb      cb;
        struct bio_list         pending;
        int                     pending_cnt;
};

static void raid1_unplug(struct blk_plug_cb *cb, bool from_schedule)
{
        struct raid1_plug_cb *plug = container_of(cb, struct raid1_plug_cb,
                                                  cb);
        struct mddev *mddev = plug->cb.data;
        struct r1conf *conf = mddev->private;
        struct bio *bio;

        if (from_schedule || current->bio_list) {
                spin_lock_irq(&conf->device_lock);
                bio_list_merge(&conf->pending_bio_list, &plug->pending);
                conf->pending_count += plug->pending_cnt;
                spin_unlock_irq(&conf->device_lock);
                wake_up(&conf->wait_barrier);
                md_wakeup_thread(mddev->thread);
                kfree(plug);
                return;
        }

        /* we aren't scheduling, so we can do the write-out directly. */
        bio = bio_list_get(&plug->pending);
        bitmap_unplug(mddev->bitmap);
        wake_up(&conf->wait_barrier);

        while (bio) { /* submit pending writes */
                struct bio *next = bio->bi_next;
                struct md_rdev *rdev = (void*)bio->bi_bdev;
                bio->bi_next = NULL;
                bio->bi_bdev = rdev->bdev;
                if (test_bit(Faulty, &rdev->flags)) {
                        bio->bi_error = -EIO;
                        bio_endio(bio);
                } else if (unlikely((bio_op(bio) == REQ_OP_DISCARD) &&
                                    !blk_queue_discard(bdev_get_queue(bio->bi_bdev))))
                        /* Just ignore it */
                        bio_endio(bio);
                else
                        generic_make_request(bio);
                bio = next;
        }
        kfree(plug);
}

static inline struct r1bio *
alloc_r1bio(struct mddev *mddev, struct bio *bio, sector_t sectors_handled)
{
        struct r1conf *conf = mddev->private;
        struct r1bio *r1_bio;

        r1_bio = mempool_alloc(conf->r1bio_pool, GFP_NOIO);

        r1_bio->master_bio = bio;
        r1_bio->sectors = bio_sectors(bio) - sectors_handled;
        r1_bio->state = 0;
        r1_bio->mddev = mddev;
        r1_bio->sector = bio->bi_iter.bi_sector + sectors_handled;

        return r1_bio;
}

static void raid1_read_request(struct mddev *mddev, struct bio *bio)
{
        struct r1conf *conf = mddev->private;
        struct raid1_info *mirror;
        struct r1bio *r1_bio;
        struct bio *read_bio;
        struct bitmap *bitmap = mddev->bitmap;
        const int op = bio_op(bio);
        const unsigned long do_sync = (bio->bi_opf & REQ_SYNC);
        int sectors_handled;
        int max_sectors;
        int rdisk;

        /*
         * Still need barrier for READ in case that whole
         * array is frozen.
         */
        wait_read_barrier(conf, bio->bi_iter.bi_sector);

        r1_bio = alloc_r1bio(mddev, bio, 0);

        /*
         * We might need to issue multiple reads to different
         * devices if there are bad blocks around, so we keep
         * track of the number of reads in bio->bi_phys_segments.
         * If this is 0, there is only one r1_bio and no locking
         * will be needed when requests complete.  If it is
         * non-zero, then it is the number of not-completed requests.
         */
        bio->bi_phys_segments = 0;
        bio_clear_flag(bio, BIO_SEG_VALID);

        /*
         * make_request() can abort the operation when read-ahead is being
         * used and no empty request is available.
         */
read_again:
        rdisk = read_balance(conf, r1_bio, &max_sectors);

        if (rdisk < 0) {
                /* couldn't find anywhere to read from */
                raid_end_bio_io(r1_bio);
                return;
        }
        mirror = conf->mirrors + rdisk;

        if (test_bit(WriteMostly, &mirror->rdev->flags) &&
            bitmap) {
                /*
                 * Reading from a write-mostly device must take care not to
                 * over-take any writes that are 'behind'
                 */
                raid1_log(mddev, "wait behind writes");
                wait_event(bitmap->behind_wait,
                           atomic_read(&bitmap->behind_writes) == 0);
        }
        r1_bio->read_disk = rdisk;

        read_bio = bio_clone_fast(bio, GFP_NOIO, mddev->bio_set);
        bio_trim(read_bio, r1_bio->sector - bio->bi_iter.bi_sector,
                 max_sectors);

        r1_bio->bios[rdisk] = read_bio;

        read_bio->bi_iter.bi_sector = r1_bio->sector +
                mirror->rdev->data_offset;
        read_bio->bi_bdev = mirror->rdev->bdev;
        read_bio->bi_end_io = raid1_end_read_request;
        bio_set_op_attrs(read_bio, op, do_sync);
        if (test_bit(FailFast, &mirror->rdev->flags) &&
            test_bit(R1BIO_FailFast, &r1_bio->state))
                read_bio->bi_opf |= MD_FAILFAST;
        read_bio->bi_private = r1_bio;

        if (mddev->gendisk)
                trace_block_bio_remap(bdev_get_queue(read_bio->bi_bdev),
                                      read_bio, disk_devt(mddev->gendisk),
                                      r1_bio->sector);

        if (max_sectors < r1_bio->sectors) {
                /*
                 * could not read all from this device, so we will need another
                 * r1_bio.
                 */
                sectors_handled = (r1_bio->sector + max_sectors
                                   - bio->bi_iter.bi_sector);
                r1_bio->sectors = max_sectors;
                spin_lock_irq(&conf->device_lock);
                if (bio->bi_phys_segments == 0)
                        bio->bi_phys_segments = 2;
                else
                        bio->bi_phys_segments++;
                spin_unlock_irq(&conf->device_lock);

                /*
                 * Cannot call generic_make_request directly as that will be
                 * queued in __make_request and subsequent mempool_alloc might
                 * block waiting for it.  So hand bio over to raid1d.
                 */
                reschedule_retry(r1_bio);

                r1_bio = alloc_r1bio(mddev, bio, sectors_handled);
                goto read_again;
        } else
                generic_make_request(read_bio);
}

static void raid1_write_request(struct mddev *mddev, struct bio *bio)
{
        struct r1conf *conf = mddev->private;
        struct r1bio *r1_bio;
        int i, disks;
        struct bitmap *bitmap = mddev->bitmap;
        unsigned long flags;
        struct md_rdev *blocked_rdev;
        struct blk_plug_cb *cb;
        struct raid1_plug_cb *plug = NULL;
        int first_clone;
        int sectors_handled;
        int max_sectors;

        /*
         * Register the new request and wait if the reconstruction
         * thread has put up a bar for new requests.
         * Continue immediately if no resync is active currently.
         */

        md_write_start(mddev, bio); /* wait on superblock update early */

        if ((bio_end_sector(bio) > mddev->suspend_lo &&
            bio->bi_iter.bi_sector < mddev->suspend_hi) ||
            (mddev_is_clustered(mddev) &&
             md_cluster_ops->area_resyncing(mddev, WRITE,
                     bio->bi_iter.bi_sector, bio_end_sector(bio)))) {

                /*
                 * As the suspend_* range is controlled by userspace, we want
                 * an interruptible wait.
                 */
                DEFINE_WAIT(w);
                for (;;) {
                        flush_signals(current);
                        prepare_to_wait(&conf->wait_barrier,
                                        &w, TASK_INTERRUPTIBLE);
                        if (bio_end_sector(bio) <= mddev->suspend_lo ||
                            bio->bi_iter.bi_sector >= mddev->suspend_hi ||
                            (mddev_is_clustered(mddev) &&
                             !md_cluster_ops->area_resyncing(mddev, WRITE,
                                     bio->bi_iter.bi_sector,
                                     bio_end_sector(bio))))
                                break;
                        schedule();
                }
                finish_wait(&conf->wait_barrier, &w);
        }
        wait_barrier(conf, bio->bi_iter.bi_sector);

        r1_bio = alloc_r1bio(mddev, bio, 0);

        /* We might need to issue multiple writes to different
         * devices if there are bad blocks around, so we keep
         * track of the number of writes in bio->bi_phys_segments.
         * If this is 0, there is only one r1_bio and no locking
         * will be needed when requests complete.  If it is
         * non-zero, then it is the number of not-completed requests.
         */
        bio->bi_phys_segments = 0;
        bio_clear_flag(bio, BIO_SEG_VALID);

        if (conf->pending_count >= max_queued_requests) {
                md_wakeup_thread(mddev->thread);
                raid1_log(mddev, "wait queued");
                wait_event(conf->wait_barrier,
                           conf->pending_count < max_queued_requests);
        }
        /* first select target devices under rcu_lock and
         * inc refcount on their rdev.  Record them by setting
         * bios[x] to bio
         * If there are known/acknowledged bad blocks on any device on
         * which we have seen a write error, we want to avoid writing those
         * blocks.
         * This potentially requires several writes to write around
         * the bad blocks.  Each set of writes gets it's own r1bio
         * with a set of bios attached.
         */

        disks = conf->raid_disks * 2;
 retry_write:
        blocked_rdev = NULL;
        rcu_read_lock();
        max_sectors = r1_bio->sectors;
        for (i = 0;  i < disks; i++) {
                struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev);
                if (rdev && unlikely(test_bit(Blocked, &rdev->flags))) {
                        atomic_inc(&rdev->nr_pending);
                        blocked_rdev = rdev;
                        break;
                }
                r1_bio->bios[i] = NULL;
                if (!rdev || test_bit(Faulty, &rdev->flags)) {
                        if (i < conf->raid_disks)
                                set_bit(R1BIO_Degraded, &r1_bio->state);
                        continue;
                }

                atomic_inc(&rdev->nr_pending);
                if (test_bit(WriteErrorSeen, &rdev->flags)) {
                        sector_t first_bad;
                        int bad_sectors;
                        int is_bad;

                        is_bad = is_badblock(rdev, r1_bio->sector, max_sectors,
                                             &first_bad, &bad_sectors);
                        if (is_bad < 0) {
                                /* mustn't write here until the bad block is
                                 * acknowledged*/
                                set_bit(BlockedBadBlocks, &rdev->flags);
                                blocked_rdev = rdev;
                                break;
                        }
                        if (is_bad && first_bad <= r1_bio->sector) {
                                /* Cannot write here at all */
                                bad_sectors -= (r1_bio->sector - first_bad);
                                if (bad_sectors < max_sectors)
                                        /* mustn't write more than bad_sectors
                                         * to other devices yet
                                         */
                                        max_sectors = bad_sectors;
                                rdev_dec_pending(rdev, mddev);
                                /* We don't set R1BIO_Degraded as that
                                 * only applies if the disk is
                                 * missing, so it might be re-added,
                                 * and we want to know to recover this
                                 * chunk.
                                 * In this case the device is here,
                                 * and the fact that this chunk is not
                                 * in-sync is recorded in the bad
                                 * block log
                                 */
                                continue;
                        }
                        if (is_bad) {
                                int good_sectors = first_bad - r1_bio->sector;
                                if (good_sectors < max_sectors)
                                        max_sectors = good_sectors;
                        }
                }
                r1_bio->bios[i] = bio;
        }
        rcu_read_unlock();

        if (unlikely(blocked_rdev)) {
                /* Wait for this device to become unblocked */
                int j;

                for (j = 0; j < i; j++)
                        if (r1_bio->bios[j])
                                rdev_dec_pending(conf->mirrors[j].rdev, mddev);
                r1_bio->state = 0;
                allow_barrier(conf, bio->bi_iter.bi_sector);
                raid1_log(mddev, "wait rdev %d blocked", blocked_rdev->raid_disk);
                md_wait_for_blocked_rdev(blocked_rdev, mddev);
                wait_barrier(conf, bio->bi_iter.bi_sector);
                goto retry_write;
        }

        if (max_sectors < r1_bio->sectors) {
                /* We are splitting this write into multiple parts, so
                 * we need to prepare for allocating another r1_bio.
                 */
                r1_bio->sectors = max_sectors;
                spin_lock_irq(&conf->device_lock);
                if (bio->bi_phys_segments == 0)
                        bio->bi_phys_segments = 2;
                else
                        bio->bi_phys_segments++;
                spin_unlock_irq(&conf->device_lock);
        }
        sectors_handled = r1_bio->sector + max_sectors - bio->bi_iter.bi_sector;

        atomic_set(&r1_bio->remaining, 1);
        atomic_set(&r1_bio->behind_remaining, 0);

        first_clone = 1;
        for (i = 0; i < disks; i++) {
                struct bio *mbio = NULL;
                sector_t offset;
                if (!r1_bio->bios[i])
                        continue;

                offset = r1_bio->sector - bio->bi_iter.bi_sector;

                if (first_clone) {
                        /* do behind I/O ?
                         * Not if there are too many, or cannot
                         * allocate memory, or a reader on WriteMostly
                         * is waiting for behind writes to flush */
                        if (bitmap &&
                            (atomic_read(&bitmap->behind_writes)
                             < mddev->bitmap_info.max_write_behind) &&
                            !waitqueue_active(&bitmap->behind_wait)) {
                                mbio = bio_clone_bioset_partial(bio, GFP_NOIO,
                                                                mddev->bio_set,
                                                                offset << 9,
                                                                max_sectors << 9);
                                alloc_behind_pages(mbio, r1_bio);
                        }

                        bitmap_startwrite(bitmap, r1_bio->sector,
                                          r1_bio->sectors,
                                          test_bit(R1BIO_BehindIO,
                                                   &r1_bio->state));
                        first_clone = 0;
                }

                if (!mbio) {
                        if (r1_bio->behind_bvecs)
                                mbio = bio_clone_bioset_partial(bio, GFP_NOIO,
                                                                mddev->bio_set,
                                                                offset << 9,
                                                                max_sectors << 9);
                        else {
                                mbio = bio_clone_fast(bio, GFP_NOIO, mddev->bio_set);
                                bio_trim(mbio, offset, max_sectors);
                        }
                }

                if (r1_bio->behind_bvecs) {
                        struct bio_vec *bvec;
                        int j;

                        /*
                         * We trimmed the bio, so _all is legit
                         */
                        bio_for_each_segment_all(bvec, mbio, j)
                                bvec->bv_page = r1_bio->behind_bvecs[j].bv_page;
                        if (test_bit(WriteMostly, &conf->mirrors[i].rdev->flags))
                                atomic_inc(&r1_bio->behind_remaining);
                }

                r1_bio->bios[i] = mbio;

                mbio->bi_iter.bi_sector = (r1_bio->sector +
                                   conf->mirrors[i].rdev->data_offset);
                mbio->bi_bdev = conf->mirrors[i].rdev->bdev;
                mbio->bi_end_io = raid1_end_write_request;
                mbio->bi_opf = bio_op(bio) | (bio->bi_opf & (REQ_SYNC | REQ_FUA));
                if (test_bit(FailFast, &conf->mirrors[i].rdev->flags) &&
                    !test_bit(WriteMostly, &conf->mirrors[i].rdev->flags) &&
                    conf->raid_disks - mddev->degraded > 1)
                        mbio->bi_opf |= MD_FAILFAST;
                mbio->bi_private = r1_bio;

                atomic_inc(&r1_bio->remaining);

                if (mddev->gendisk)
                        trace_block_bio_remap(bdev_get_queue(mbio->bi_bdev),
                                              mbio, disk_devt(mddev->gendisk),
                                              r1_bio->sector);
                /* flush_pending_writes() needs access to the rdev so...*/
                mbio->bi_bdev = (void*)conf->mirrors[i].rdev;

                cb = blk_check_plugged(raid1_unplug, mddev, sizeof(*plug));
                if (cb)
                        plug = container_of(cb, struct raid1_plug_cb, cb);
                else
                        plug = NULL;
                spin_lock_irqsave(&conf->device_lock, flags);
                if (plug) {
                        bio_list_add(&plug->pending, mbio);
                        plug->pending_cnt++;
                } else {
                        bio_list_add(&conf->pending_bio_list, mbio);
                        conf->pending_count++;
                }
                spin_unlock_irqrestore(&conf->device_lock, flags);
                if (!plug)
                        md_wakeup_thread(mddev->thread);
        }
        /* Mustn't call r1_bio_write_done before this next test,
         * as it could result in the bio being freed.
         */
        if (sectors_handled < bio_sectors(bio)) {
                r1_bio_write_done(r1_bio);
                /* We need another r1_bio.  It has already been counted
                 * in bio->bi_phys_segments
                 */
                r1_bio = alloc_r1bio(mddev, bio, sectors_handled);
                goto retry_write;
        }

        r1_bio_write_done(r1_bio);

        /* In case raid1d snuck in to freeze_array */
        wake_up(&conf->wait_barrier);
}

static void raid1_make_request(struct mddev *mddev, struct bio *bio)
{
        struct bio *split;
        sector_t sectors;

        if (unlikely(bio->bi_opf & REQ_PREFLUSH)) {
                md_flush_request(mddev, bio);
                return;
        }

        /* if bio exceeds barrier unit boundary, split it */
        do {
                sectors = align_to_barrier_unit_end(
                                bio->bi_iter.bi_sector, bio_sectors(bio));
                if (sectors < bio_sectors(bio)) {
                        split = bio_split(bio, sectors, GFP_NOIO, fs_bio_set);
                        bio_chain(split, bio);
                } else {
                        split = bio;
                }

                if (bio_data_dir(split) == READ) {
                        raid1_read_request(mddev, split);

                        /*
                         * If a bio is splitted, the first part of bio will
                         * pass barrier but the bio is queued in
                         * current->bio_list (see generic_make_request). If
                         * there is a raise_barrier() called here, the second
                         * part of bio can't pass barrier. But since the first
                         * part bio isn't dispatched to underlaying disks yet,
                         * the barrier is never released, hence raise_barrier
                         * will alays wait. We have a deadlock.
                         * Note, this only happens in read path. For write
                         * path, the first part of bio is dispatched in a
                         * schedule() call (because of blk plug) or offloaded
                         * to raid10d.
                         * Quitting from the function immediately can change
                         * the bio order queued in bio_list and avoid the deadlock.
                         */
                        if (split != bio) {
                                generic_make_request(bio);
                                break;
                        }
                } else
                        raid1_write_request(mddev, split);
        } while (split != bio);
}

static void raid1_status(struct seq_file *seq, struct mddev *mddev)
{
        struct r1conf *conf = mddev->private;
        int i;

        seq_printf(seq, " [%d/%d] [", conf->raid_disks,
                   conf->raid_disks - mddev->degraded);
        rcu_read_lock();
        for (i = 0; i < conf->raid_disks; i++) {
                struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev);
                seq_printf(seq, "%s",
                           rdev && test_bit(In_sync, &rdev->flags) ? "U" : "_");
        }
        rcu_read_unlock();
        seq_printf(seq, "]");
}

static void raid1_error(struct mddev *mddev, struct md_rdev *rdev)
{
        char b[BDEVNAME_SIZE];
        struct r1conf *conf = mddev->private;
        unsigned long flags;

        /*
         * If it is not operational, then we have already marked it as dead
         * else if it is the last working disks, ignore the error, let the
         * next level up know.
         * else mark the drive as failed
         */
        spin_lock_irqsave(&conf->device_lock, flags);
        if (test_bit(In_sync, &rdev->flags)
            && (conf->raid_disks - mddev->degraded) == 1) {
                /*
                 * Don't fail the drive, act as though we were just a
                 * normal single drive.
                 * However don't try a recovery from this drive as
                 * it is very likely to fail.
                 */
                conf->recovery_disabled = mddev->recovery_disabled;
                spin_unlock_irqrestore(&conf->device_lock, flags);
                return;
        }
        set_bit(Blocked, &rdev->flags);
        if (test_and_clear_bit(In_sync, &rdev->flags)) {
                mddev->degraded++;
                set_bit(Faulty, &rdev->flags);
        } else
                set_bit(Faulty, &rdev->flags);
        spin_unlock_irqrestore(&conf->device_lock, flags);
        /*
         * if recovery is running, make sure it aborts.
         */
        set_bit(MD_RECOVERY_INTR, &mddev->recovery);
        set_mask_bits(&mddev->sb_flags, 0,
                      BIT(MD_SB_CHANGE_DEVS) | BIT(MD_SB_CHANGE_PENDING));
        pr_crit("md/raid1:%s: Disk failure on %s, disabling device.\n"
                "md/raid1:%s: Operation continuing on %d devices.\n",
                mdname(mddev), bdevname(rdev->bdev, b),
                mdname(mddev), conf->raid_disks - mddev->degraded);
}

static void print_conf(struct r1conf *conf)
{
        int i;

        pr_debug("RAID1 conf printout:\n");
        if (!conf) {
                pr_debug("(!conf)\n");
                return;
        }
        pr_debug(" --- wd:%d rd:%d\n", conf->raid_disks - conf->mddev->degraded,
                 conf->raid_disks);

        rcu_read_lock();
        for (i = 0; i < conf->raid_disks; i++) {
                char b[BDEVNAME_SIZE];
                struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev);
                if (rdev)
                        pr_debug(" disk %d, wo:%d, o:%d, dev:%s\n",
                                 i, !test_bit(In_sync, &rdev->flags),
                                 !test_bit(Faulty, &rdev->flags),
                                 bdevname(rdev->bdev,b));
        }
        rcu_read_unlock();
}

static void close_sync(struct r1conf *conf)
{
        wait_all_barriers(conf);
        allow_all_barriers(conf);

        mempool_destroy(conf->r1buf_pool);
        conf->r1buf_pool = NULL;
}

static int raid1_spare_active(struct mddev *mddev)
{
        int i;
        struct r1conf *conf = mddev->private;
        int count = 0;
        unsigned long flags;

        /*
         * Find all failed disks within the RAID1 configuration
         * and mark them readable.
         * Called under mddev lock, so rcu protection not needed.
         * device_lock used to avoid races with raid1_end_read_request
         * which expects 'In_sync' flags and ->degraded to be consistent.
         */
        spin_lock_irqsave(&conf->device_lock, flags);
        for (i = 0; i < conf->raid_disks; i++) {
                struct md_rdev *rdev = conf->mirrors[i].rdev;
                struct md_rdev *repl = conf->mirrors[conf->raid_disks + i].rdev;
                if (repl
                    && !test_bit(Candidate, &repl->flags)
                    && repl->recovery_offset == MaxSector
                    && !test_bit(Faulty, &repl->flags)
                    && !test_and_set_bit(In_sync, &repl->flags)) {
                        /* replacement has just become active */
                        if (!rdev ||
                            !test_and_clear_bit(In_sync, &rdev->flags))
                                count++;
                        if (rdev) {
                                /* Replaced device not technically
                                 * faulty, but we need to be sure
                                 * it gets removed and never re-added
                                 */
                                set_bit(Faulty, &rdev->flags);
                                sysfs_notify_dirent_safe(
                                        rdev->sysfs_state);
                        }
                }
                if (rdev
                    && rdev->recovery_offset == MaxSector
                    && !test_bit(Faulty, &rdev->flags)
                    && !test_and_set_bit(In_sync, &rdev->flags)) {
                        count++;
                        sysfs_notify_dirent_safe(rdev->sysfs_state);
                }
        }
        mddev->degraded -= count;
        spin_unlock_irqrestore(&conf->device_lock, flags);

        print_conf(conf);
        return count;
}

static int raid1_add_disk(struct mddev *mddev, struct md_rdev *rdev)
{
        struct r1conf *conf = mddev->private;
        int err = -EEXIST;
        int mirror = 0;
        struct raid1_info *p;
        int first = 0;
        int last = conf->raid_disks - 1;

        if (mddev->recovery_disabled == conf->recovery_disabled)
                return -EBUSY;

        if (md_integrity_add_rdev(rdev, mddev))
                return -ENXIO;

        if (rdev->raid_disk >= 0)
                first = last = rdev->raid_disk;

        /*
         * find the disk ... but prefer rdev->saved_raid_disk
         * if possible.
         */
        if (rdev->saved_raid_disk >= 0 &&
            rdev->saved_raid_disk >= first &&
            conf->mirrors[rdev->saved_raid_disk].rdev == NULL)
                first = last = rdev->saved_raid_disk;

        for (mirror = first; mirror <= last; mirror++) {
                p = conf->mirrors+mirror;
                if (!p->rdev) {

                        if (mddev->gendisk)
                                disk_stack_limits(mddev->gendisk, rdev->bdev,
                                                  rdev->data_offset << 9);

                        p->head_position = 0;
                        rdev->raid_disk = mirror;
                        err = 0;
                        /* As all devices are equivalent, we don't need a full recovery
                         * if this was recently any drive of the array
                         */
                        if (rdev->saved_raid_disk < 0)
                                conf->fullsync = 1;
                        rcu_assign_pointer(p->rdev, rdev);
                        break;
                }
                if (test_bit(WantReplacement, &p->rdev->flags) &&
                    p[conf->raid_disks].rdev == NULL) {
                        /* Add this device as a replacement */
                        clear_bit(In_sync, &rdev->flags);
                        set_bit(Replacement, &rdev->flags);
                        rdev->raid_disk = mirror;
                        err = 0;
                        conf->fullsync = 1;
                        rcu_assign_pointer(p[conf->raid_disks].rdev, rdev);
                        break;
                }
        }
        if (mddev->queue && blk_queue_discard(bdev_get_queue(rdev->bdev)))
                queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, mddev->queue);
        print_conf(conf);
        return err;
}

static int raid1_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
{
        struct r1conf *conf = mddev->private;
        int err = 0;
        int number = rdev->raid_disk;
        struct raid1_info *p = conf->mirrors + number;

        if (rdev != p->rdev)
                p = conf->mirrors + conf->raid_disks + number;

        print_conf(conf);
        if (rdev == p->rdev) {
                if (test_bit(In_sync, &rdev->flags) ||
                    atomic_read(&rdev->nr_pending)) {
                        err = -EBUSY;
                        goto abort;
                }
                /* Only remove non-faulty devices if recovery
                 * is not possible.
                 */
                if (!test_bit(Faulty, &rdev->flags) &&
                    mddev->recovery_disabled != conf->recovery_disabled &&
                    mddev->degraded < conf->raid_disks) {
                        err = -EBUSY;
                        goto abort;
                }
                p->rdev = NULL;
                if (!test_bit(RemoveSynchronized, &rdev->flags)) {
                        synchronize_rcu();
                        if (atomic_read(&rdev->nr_pending)) {
                                /* lost the race, try later */
                                err = -EBUSY;
                                p->rdev = rdev;
                                goto abort;
                        }
                }
                if (conf->mirrors[conf->raid_disks + number].rdev) {
                        /* We just removed a device that is being replaced.
                         * Move down the replacement.  We drain all IO before
                         * doing this to avoid confusion.
                         */
                        struct md_rdev *repl =
                                conf->mirrors[conf->raid_disks + number].rdev;
                        freeze_array(conf, 0);
                        clear_bit(Replacement, &repl->flags);
                        p->rdev = repl;
                        conf->mirrors[conf->raid_disks + number].rdev = NULL;
                        unfreeze_array(conf);
                        clear_bit(WantReplacement, &rdev->flags);
                } else
                        clear_bit(WantReplacement, &rdev->flags);
                err = md_integrity_register(mddev);
        }
abort:

        print_conf(conf);
        return err;
}

static void end_sync_read(struct bio *bio)
{
        struct r1bio *r1_bio = bio->bi_private;

        update_head_pos(r1_bio->read_disk, r1_bio);

        /*
         * we have read a block, now it needs to be re-written,
         * or re-read if the read failed.
         * We don't do much here, just schedule handling by raid1d
         */
        if (!bio->bi_error)
                set_bit(R1BIO_Uptodate, &r1_bio->state);

        if (atomic_dec_and_test(&r1_bio->remaining))
                reschedule_retry(r1_bio);
}

static void end_sync_write(struct bio *bio)
{
        int uptodate = !bio->bi_error;
        struct r1bio *r1_bio = bio->bi_private;
        struct mddev *mddev = r1_bio->mddev;
        struct r1conf *conf = mddev->private;
        sector_t first_bad;
        int bad_sectors;
        struct md_rdev *rdev = conf->mirrors[find_bio_disk(r1_bio, bio)].rdev;

        if (!uptodate) {
                sector_t sync_blocks = 0;
                sector_t s = r1_bio->sector;
                long sectors_to_go = r1_bio->sectors;
                /* make sure these bits doesn't get cleared. */
                do {
                        bitmap_end_sync(mddev->bitmap, s,
                                        &sync_blocks, 1);
                        s += sync_blocks;
                        sectors_to_go -= sync_blocks;
                } while (sectors_to_go > 0);
                set_bit(WriteErrorSeen, &rdev->flags);
                if (!test_and_set_bit(WantReplacement, &rdev->flags))
                        set_bit(MD_RECOVERY_NEEDED, &
                                mddev->recovery);
                set_bit(R1BIO_WriteError, &r1_bio->state);
        } else if (is_badblock(rdev, r1_bio->sector, r1_bio->sectors,
                               &first_bad, &bad_sectors) &&
                   !is_badblock(conf->mirrors[r1_bio->read_disk].rdev,
                                r1_bio->sector,
                                r1_bio->sectors,
                                &first_bad, &bad_sectors)
                )
                set_bit(R1BIO_MadeGood, &r1_bio->state);

        if (atomic_dec_and_test(&r1_bio->remaining)) {
                int s = r1_bio->sectors;
                if (test_bit(R1BIO_MadeGood, &r1_bio->state) ||
                    test_bit(R1BIO_WriteError, &r1_bio->state))
                        reschedule_retry(r1_bio);
                else {
                        put_buf(r1_bio);
                        md_done_sync(mddev, s, uptodate);
                }
        }
}

static int r1_sync_page_io(struct md_rdev *rdev, sector_t sector,
                            int sectors, struct page *page, int rw)
{
        if (sync_page_io(rdev, sector, sectors << 9, page, rw, 0, false))
                /* success */
                return 1;
        if (rw == WRITE) {
                set_bit(WriteErrorSeen, &rdev->flags);
                if (!test_and_set_bit(WantReplacement,
                                      &rdev->flags))
                        set_bit(MD_RECOVERY_NEEDED, &
                                rdev->mddev->recovery);
        }
        /* need to record an error - either for the block or the device */
        if (!rdev_set_badblocks(rdev, sector, sectors, 0))
                md_error(rdev->mddev, rdev);
        return 0;
}

static int fix_sync_read_error(struct r1bio *r1_bio)
{
        /* Try some synchronous reads of other devices to get
         * good data, much like with normal read errors.  Only
         * read into the pages we already have so we don't
         * need to re-issue the read request.
         * We don't need to freeze the array, because being in an
         * active sync request, there is no normal IO, and
         * no overlapping syncs.
         * We don't need to check is_badblock() again as we
         * made sure that anything with a bad block in range
         * will have bi_end_io clear.
         */
        struct mddev *mddev = r1_bio->mddev;
        struct r1conf *conf = mddev->private;
        struct bio *bio = r1_bio->bios[r1_bio->read_disk];
        sector_t sect = r1_bio->sector;
        int sectors = r1_bio->sectors;
        int idx = 0;
        struct md_rdev *rdev;

        rdev = conf->mirrors[r1_bio->read_disk].rdev;
        if (test_bit(FailFast, &rdev->flags)) {
                /* Don't try recovering from here - just fail it
                 * ... unless it is the last working device of course */
                md_error(mddev, rdev);
                if (test_bit(Faulty, &rdev->flags))
                        /* Don't try to read from here, but make sure
                         * put_buf does it's thing

                         */
                        bio->bi_end_io = end_sync_write;
        }

        while(sectors) {
                int s = sectors;
                int d = r1_bio->read_disk;
                int success = 0;
                int start;

                if (s > (PAGE_SIZE>>9))
                        s = PAGE_SIZE >> 9;
                do {
                        if (r1_bio->bios[d]->bi_end_io == end_sync_read) {
                                /* No rcu protection needed here devices
                                 * can only be removed when no resync is
                                 * active, and resync is currently active
                                 */
                                rdev = conf->mirrors[d].rdev;
                                if (sync_page_io(rdev, sect, s<<9,
                                                 bio->bi_io_vec[idx].bv_page,
                                                 REQ_OP_READ, 0, false)) {
                                        success = 1;
                                        break;
                                }
                        }
                        d++;
                        if (d == conf->raid_disks * 2)
                                d = 0;
                } while (!success && d != r1_bio->read_disk);

                if (!success) {
                        char b[BDEVNAME_SIZE];
                        int abort = 0;
                        /* Cannot read from anywhere, this block is lost.
                         * Record a bad block on each device.  If that doesn't
                         * work just disable and interrupt the recovery.
                         * Don't fail devices as that won't really help.
                         */
                        pr_crit_ratelimited("md/raid1:%s: %s: unrecoverable I/O read error for block %llu\n",
                                            mdname(mddev),
                                            bdevname(bio->bi_bdev, b),
                                            (unsigned long long)r1_bio->sector);
                        for (d = 0; d < conf->raid_disks * 2; d++) {
                                rdev = conf->mirrors[d].rdev;
                                if (!rdev || test_bit(Faulty, &rdev->flags))
                                        continue;
                                if (!rdev_set_badblocks(rdev, sect, s, 0))
                                        abort = 1;
                        }
                        if (abort) {
                                conf->recovery_disabled =
                                        mddev->recovery_disabled;
                                set_bit(MD_RECOVERY_INTR, &mddev->recovery);
                                md_done_sync(mddev, r1_bio->sectors, 0);
                                put_buf(r1_bio);
                                return 0;
                        }
                        /* Try next page */
                        sectors -= s;
                        sect += s;
                        idx++;
                        continue;
                }

                start = d;
                /* write it back and re-read */
                while (d != r1_bio->read_disk) {
                        if (d == 0)
                                d = conf->raid_disks * 2;
                        d--;
                        if (r1_bio->bios[d]->bi_end_io != end_sync_read)
                                continue;
                        rdev = conf->mirrors[d].rdev;
                        if (r1_sync_page_io(rdev, sect, s,
                                            bio->bi_io_vec[idx].bv_page,
                                            WRITE) == 0) {
                                r1_bio->bios[d]->bi_end_io = NULL;
                                rdev_dec_pending(rdev, mddev);
                        }
                }
                d = start;
                while (d != r1_bio->read_disk) {
                        if (d == 0)
                                d = conf->raid_disks * 2;
                        d--;
                        if (r1_bio->bios[d]->bi_end_io != end_sync_read)
                                continue;
                        rdev = conf->mirrors[d].rdev;
                        if (r1_sync_page_io(rdev, sect, s,
                                            bio->bi_io_vec[idx].bv_page,
                                            READ) != 0)
                                atomic_add(s, &rdev->corrected_errors);
                }
                sectors -= s;
                sect += s;
                idx ++;
        }
        set_bit(R1BIO_Uptodate, &r1_bio->state);
        bio->bi_error = 0;
        return 1;
}

static void process_checks(struct r1bio *r1_bio)
{
        /* We have read all readable devices.  If we haven't
         * got the block, then there is no hope left.
         * If we have, then we want to do a comparison
         * and skip the write if everything is the same.
         * If any blocks failed to read, then we need to
         * attempt an over-write
         */
        struct mddev *mddev = r1_bio->mddev;
        struct r1conf *conf = mddev->private;
        int primary;
        int i;
        int vcnt;

        /* Fix variable parts of all bios */
        vcnt = (r1_bio->sectors + PAGE_SIZE / 512 - 1) >> (PAGE_SHIFT - 9);
        for (i = 0; i < conf->raid_disks * 2; i++) {
                int j;
                int size;
                int error;
                struct bio *b = r1_bio->bios[i];
                if (b->bi_end_io != end_sync_read)
                        continue;
                /* fixup the bio for reuse, but preserve errno */
                error = b->bi_error;
                bio_reset(b);
                b->bi_error = error;
                b->bi_vcnt = vcnt;
                b->bi_iter.bi_size = r1_bio->sectors << 9;
                b->bi_iter.bi_sector = r1_bio->sector +
                        conf->mirrors[i].rdev->data_offset;
                b->bi_bdev = conf->mirrors[i].rdev->bdev;
                b->bi_end_io = end_sync_read;
                b->bi_private = r1_bio;

                size = b->bi_iter.bi_size;
                for (j = 0; j < vcnt ; j++) {
                        struct bio_vec *bi;
                        bi = &b->bi_io_vec[j];
                        bi->bv_offset = 0;
                        if (size > PAGE_SIZE)
                                bi->bv_len = PAGE_SIZE;
                        else
                                bi->bv_len = size;
                        size -= PAGE_SIZE;
                }
        }
        for (primary = 0; primary < conf->raid_disks * 2; primary++)
                if (r1_bio->bios[primary]->bi_end_io == end_sync_read &&
                    !r1_bio->bios[primary]->bi_error) {
                        r1_bio->bios[primary]->bi_end_io = NULL;
                        rdev_dec_pending(conf->mirrors[primary].rdev, mddev);
                        break;
                }
        r1_bio->read_disk = primary;
        for (i = 0; i < conf->raid_disks * 2; i++) {
                int j;
                struct bio *pbio = r1_bio->bios[primary];
                struct bio *sbio = r1_bio->bios[i];
                int error = sbio->bi_error;

                if (sbio->bi_end_io != end_sync_read)
                        continue;
                /* Now we can 'fixup' the error value */
                sbio->bi_error = 0;

                if (!error) {
                        for (j = vcnt; j-- ; ) {
                                struct page *p, *s;
                                p = pbio->bi_io_vec[j].bv_page;
                                s = sbio->bi_io_vec[j].bv_page;
                                if (memcmp(page_address(p),
                                           page_address(s),
                                           sbio->bi_io_vec[j].bv_len))
                                        break;
                        }
                } else
                        j = 0;
                if (j >= 0)
                        atomic64_add(r1_bio->sectors, &mddev->resync_mismatches);
                if (j < 0 || (test_bit(MD_RECOVERY_CHECK, &mddev->recovery)
                              && !error)) {
                        /* No need to write to this device. */
                        sbio->bi_end_io = NULL;
                        rdev_dec_pending(conf->mirrors[i].rdev, mddev);
                        continue;
                }

                bio_copy_data(sbio, pbio);
        }
}

static void sync_request_write(struct mddev *mddev, struct r1bio *r1_bio)
{
        struct r1conf *conf = mddev->private;
        int i;
        int disks = conf->raid_disks * 2;
        struct bio *bio, *wbio;

        bio = r1_bio->bios[r1_bio->read_disk];

        if (!test_bit(R1BIO_Uptodate, &r1_bio->state))
                /* ouch - failed to read all of that. */
                if (!fix_sync_read_error(r1_bio))
                        return;

        if (test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery))
                process_checks(r1_bio);

        /*
         * schedule writes
         */
        atomic_set(&r1_bio->remaining, 1);
        for (i = 0; i < disks ; i++) {
                wbio = r1_bio->bios[i];
                if (wbio->bi_end_io == NULL ||
                    (wbio->bi_end_io == end_sync_read &&
                     (i == r1_bio->read_disk ||
                      !test_bit(MD_RECOVERY_SYNC, &mddev->recovery))))
                        continue;

                bio_set_op_attrs(wbio, REQ_OP_WRITE, 0);
                if (test_bit(FailFast, &conf->mirrors[i].rdev->flags))
                        wbio->bi_opf |= MD_FAILFAST;

                wbio->bi_end_io = end_sync_write;
                atomic_inc(&r1_bio->remaining);
                md_sync_acct(conf->mirrors[i].rdev->bdev, bio_sectors(wbio));

                generic_make_request(wbio);
        }

        if (atomic_dec_and_test(&r1_bio->remaining)) {
                /* if we're here, all write(s) have completed, so clean up */
                int s = r1_bio->sectors;
                if (test_bit(R1BIO_MadeGood, &r1_bio->state) ||
                    test_bit(R1BIO_WriteError, &r1_bio->state))
                        reschedule_retry(r1_bio);
                else {
                        put_buf(r1_bio);
                        md_done_sync(mddev, s, 1);
                }
        }
}

/*
 * This is a kernel thread which:
 *
 *      1.      Retries failed read operations on working mirrors.
 *      2.      Updates the raid superblock when problems encounter.
 *      3.      Performs writes following reads for array synchronising.
 */

static void fix_read_error(struct r1conf *conf, int read_disk,
                           sector_t sect, int sectors)
{
        struct mddev *mddev = conf->mddev;
        while(sectors) {
                int s = sectors;
                int d = read_disk;
                int success = 0;
                int start;
                struct md_rdev *rdev;

                if (s > (PAGE_SIZE>>9))
                        s = PAGE_SIZE >> 9;

                do {
                        sector_t first_bad;
                        int bad_sectors;

                        rcu_read_lock();
                        rdev = rcu_dereference(conf->mirrors[d].rdev);
                        if (rdev &&
                            (test_bit(In_sync, &rdev->flags) ||
                             (!test_bit(Faulty, &rdev->flags) &&
                              rdev->recovery_offset >= sect + s)) &&
                            is_badblock(rdev, sect, s,
                                        &first_bad, &bad_sectors) == 0) {
                                atomic_inc(&rdev->nr_pending);
                                rcu_read_unlock();
                                if (sync_page_io(rdev, sect, s<<9,
                                         conf->tmppage, REQ_OP_READ, 0, false))
                                        success = 1;
                                rdev_dec_pending(rdev, mddev);
                                if (success)
                                        break;
                        } else
                                rcu_read_unlock();
                        d++;
                        if (d == conf->raid_disks * 2)
                                d = 0;
                } while (!success && d != read_disk);

                if (!success) {
                        /* Cannot read from anywhere - mark it bad */
                        struct md_rdev *rdev = conf->mirrors[read_disk].rdev;
                        if (!rdev_set_badblocks(rdev, sect, s, 0))
                                md_error(mddev, rdev);
                        break;
                }
                /* write it back and re-read */
                start = d;
                while (d != read_disk) {
                        if (d==0)
                                d = conf->raid_disks * 2;
                        d--;
                        rcu_read_lock();
                        rdev = rcu_dereference(conf->mirrors[d].rdev);
                        if (rdev &&
                            !test_bit(Faulty, &rdev->flags)) {
                                atomic_inc(&rdev->nr_pending);
                                rcu_read_unlock();
                                r1_sync_page_io(rdev, sect, s,
                                                conf->tmppage, WRITE);
                                rdev_dec_pending(rdev, mddev);
                        } else
                                rcu_read_unlock();
                }
                d = start;
                while (d != read_disk) {
                        char b[BDEVNAME_SIZE];
                        if (d==0)
                                d = conf->raid_disks * 2;
                        d--;
                        rcu_read_lock();
                        rdev = rcu_dereference(conf->mirrors[d].rdev);
                        if (rdev &&
                            !test_bit(Faulty, &rdev->flags)) {
                                atomic_inc(&rdev->nr_pending);
                                rcu_read_unlock();
                                if (r1_sync_page_io(rdev, sect, s,
                                                    conf->tmppage, READ)) {
                                        atomic_add(s, &rdev->corrected_errors);
                                        pr_info("md/raid1:%s: read error corrected (%d sectors at %llu on %s)\n",
                                                mdname(mddev), s,
                                                (unsigned long long)(sect +
                                                                     rdev->data_offset),
                                                bdevname(rdev->bdev, b));
                                }
                                rdev_dec_pending(rdev, mddev);
                        } else
                                rcu_read_unlock();
                }
                sectors -= s;
                sect += s;
        }
}

static int narrow_write_error(struct r1bio *r1_bio, int i)
{
        struct mddev *mddev = r1_bio->mddev;
        struct r1conf *conf = mddev->private;
        struct md_rdev *rdev = conf->mirrors[i].rdev;

        /* bio has the data to be written to device 'i' where
         * we just recently had a write error.
         * We repeatedly clone the bio and trim down to one block,
         * then try the write.  Where the write fails we record
         * a bad block.
         * It is conceivable that the bio doesn't exactly align with
         * blocks.  We must handle this somehow.
         *
         * We currently own a reference on the rdev.
         */

        int block_sectors;
        sector_t sector;
        int sectors;
        int sect_to_write = r1_bio->sectors;
        int ok = 1;

        if (rdev->badblocks.shift < 0)
                return 0;

        block_sectors = roundup(1 << rdev->badblocks.shift,
                                bdev_logical_block_size(rdev->bdev) >> 9);
        sector = r1_bio->sector;
        sectors = ((sector + block_sectors)
                   & ~(sector_t)(block_sectors - 1))
                - sector;

        while (sect_to_write) {
                struct bio *wbio;
                if (sectors > sect_to_write)
                        sectors = sect_to_write;
                /* Write at 'sector' for 'sectors'*/

                if (test_bit(R1BIO_BehindIO, &r1_bio->state)) {
                        unsigned vcnt = r1_bio->behind_page_count;
                        struct bio_vec *vec = r1_bio->behind_bvecs;

                        while (!vec->bv_page) {
                                vec++;
                                vcnt--;
                        }

                        wbio = bio_alloc_mddev(GFP_NOIO, vcnt, mddev);
                        memcpy(wbio->bi_io_vec, vec, vcnt * sizeof(struct bio_vec));

                        wbio->bi_vcnt = vcnt;
                } else {
                        wbio = bio_clone_fast(r1_bio->master_bio, GFP_NOIO,
                                              mddev->bio_set);
                }

                bio_set_op_attrs(wbio, REQ_OP_WRITE, 0);
                wbio->bi_iter.bi_sector = r1_bio->sector;
                wbio->bi_iter.bi_size = r1_bio->sectors << 9;

                bio_trim(wbio, sector - r1_bio->sector, sectors);
                wbio->bi_iter.bi_sector += rdev->data_offset;
                wbio->bi_bdev = rdev->bdev;

                if (submit_bio_wait(wbio) < 0)
                        /* failure! */
                        ok = rdev_set_badblocks(rdev, sector,
                                                sectors, 0)
                                && ok;

                bio_put(wbio);
                sect_to_write -= sectors;
                sector += sectors;
                sectors = block_sectors;
        }
        return ok;
}

static void handle_sync_write_finished(struct r1conf *conf, struct r1bio *r1_bio)
{
        int m;
        int s = r1_bio->sectors;
        for (m = 0; m < conf->raid_disks * 2 ; m++) {
                struct md_rdev *rdev = conf->mirrors[m].rdev;
                struct bio *bio = r1_bio->bios[m];
                if (bio->bi_end_io == NULL)
                        continue;
                if (!bio->bi_error &&
                    test_bit(R1BIO_MadeGood, &r1_bio->state)) {
                        rdev_clear_badblocks(rdev, r1_bio->sector, s, 0);
                }
                if (bio->bi_error &&
                    test_bit(R1BIO_WriteError, &r1_bio->state)) {
                        if (!rdev_set_badblocks(rdev, r1_bio->sector, s, 0))
                                md_error(conf->mddev, rdev);
                }
        }
        put_buf(r1_bio);
        md_done_sync(conf->mddev, s, 1);
}

static void handle_write_finished(struct r1conf *conf, struct r1bio *r1_bio)
{
        int m, idx;
        bool fail = false;

        for (m = 0; m < conf->raid_disks * 2 ; m++)
                if (r1_bio->bios[m] == IO_MADE_GOOD) {
                        struct md_rdev *rdev = conf->mirrors[m].rdev;
                        rdev_clear_badblocks(rdev,
                                             r1_bio->sector,
                                             r1_bio->sectors, 0);
                        rdev_dec_pending(rdev, conf->mddev);
                } else if (r1_bio->bios[m] != NULL) {
                        /* This drive got a write error.  We need to
                         * narrow down and record precise write
                         * errors.
                         */
                        fail = true;
                        if (!narrow_write_error(r1_bio, m)) {
                                md_error(conf->mddev,
                                         conf->mirrors[m].rdev);
                                /* an I/O failed, we can't clear the bitmap */
                                set_bit(R1BIO_Degraded, &r1_bio->state);
                        }
                        rdev_dec_pending(conf->mirrors[m].rdev,
                                         conf->mddev);
                }
        if (fail) {
                spin_lock_irq(&conf->device_lock);
                list_add(&r1_bio->retry_list, &conf->bio_end_io_list);
                idx = sector_to_idx(r1_bio->sector);
                atomic_inc(&conf->nr_queued[idx]);
                spin_unlock_irq(&conf->device_lock);
                /*
                 * In case freeze_array() is waiting for condition
                 * get_unqueued_pending() == extra to be true.
                 */
                wake_up(&conf->wait_barrier);
                md_wakeup_thread(conf->mddev->thread);
        } else {
                if (test_bit(R1BIO_WriteError, &r1_bio->state))
                        close_write(r1_bio);
                raid_end_bio_io(r1_bio);
        }
}

static void handle_read_error(struct r1conf *conf, struct r1bio *r1_bio)
{
        int disk;
        int max_sectors;
        struct mddev *mddev = conf->mddev;
        struct bio *bio;
        char b[BDEVNAME_SIZE];
        struct md_rdev *rdev;
        dev_t bio_dev;
        sector_t bio_sector;

        clear_bit(R1BIO_ReadError, &r1_bio->state);
        /* we got a read error. Maybe the drive is bad.  Maybe just
         * the block and we can fix it.
         * We freeze all other IO, and try reading the block from
         * other devices.  When we find one, we re-write
         * and check it that fixes the read error.
         * This is all done synchronously while the array is
         * frozen
         */

        bio = r1_bio->bios[r1_bio->read_disk];
        bdevname(bio->bi_bdev, b);
        bio_dev = bio->bi_bdev->bd_dev;
        bio_sector = conf->mirrors[r1_bio->read_disk].rdev->data_offset + r1_bio->sector;
        bio_put(bio);
        r1_bio->bios[r1_bio->read_disk] = NULL;

        rdev = conf->mirrors[r1_bio->read_disk].rdev;
        if (mddev->ro == 0
            && !test_bit(FailFast, &rdev->flags)) {
                freeze_array(conf, 1);
                fix_read_error(conf, r1_bio->read_disk,
                               r1_bio->sector, r1_bio->sectors);
                unfreeze_array(conf);
        } else {
                r1_bio->bios[r1_bio->read_disk] = IO_BLOCKED;
        }

        rdev_dec_pending(rdev, conf->mddev);

read_more:
        disk = read_balance(conf, r1_bio, &max_sectors);
        if (disk == -1) {
                pr_crit_ratelimited("md/raid1:%s: %s: unrecoverable I/O read error for block %llu\n",
                                    mdname(mddev), b, (unsigned long long)r1_bio->sector);
                raid_end_bio_io(r1_bio);
        } else {
                const unsigned long do_sync
                        = r1_bio->master_bio->bi_opf & REQ_SYNC;
                r1_bio->read_disk = disk;
                bio = bio_clone_fast(r1_bio->master_bio, GFP_NOIO,
                                     mddev->bio_set);
                bio_trim(bio, r1_bio->sector - bio->bi_iter.bi_sector,
                         max_sectors);
                r1_bio->bios[r1_bio->read_disk] = bio;
                rdev = conf->mirrors[disk].rdev;
                pr_info_ratelimited("md/raid1:%s: redirecting sector %llu to other mirror: %s\n",
                                    mdname(mddev),
                                    (unsigned long long)r1_bio->sector,
                                    bdevname(rdev->bdev, b));
                bio->bi_iter.bi_sector = r1_bio->sector + rdev->data_offset;
                bio->bi_bdev = rdev->bdev;
                bio->bi_end_io = raid1_end_read_request;
                bio_set_op_attrs(bio, REQ_OP_READ, do_sync);
                if (test_bit(FailFast, &rdev->flags) &&
                    test_bit(R1BIO_FailFast, &r1_bio->state))
                        bio->bi_opf |= MD_FAILFAST;
                bio->bi_private = r1_bio;
                if (max_sectors < r1_bio->sectors) {
                        /* Drat - have to split this up more */
                        struct bio *mbio = r1_bio->master_bio;
                        int sectors_handled = (r1_bio->sector + max_sectors
                                               - mbio->bi_iter.bi_sector);
                        r1_bio->sectors = max_sectors;
                        spin_lock_irq(&conf->device_lock);
                        if (mbio->bi_phys_segments == 0)
                                mbio->bi_phys_segments = 2;
                        else
                                mbio->bi_phys_segments++;
                        spin_unlock_irq(&conf->device_lock);
                        trace_block_bio_remap(bdev_get_queue(bio->bi_bdev),
                                              bio, bio_dev, bio_sector);
                        generic_make_request(bio);
                        bio = NULL;

                        r1_bio = alloc_r1bio(mddev, mbio, sectors_handled);
                        set_bit(R1BIO_ReadError, &r1_bio->state);

                        goto read_more;
                } else {
                        trace_block_bio_remap(bdev_get_queue(bio->bi_bdev),
                                              bio, bio_dev, bio_sector);
                        generic_make_request(bio);
                }
        }
}

static void raid1d(struct md_thread *thread)
{
        struct mddev *mddev = thread->mddev;
        struct r1bio *r1_bio;
        unsigned long flags;
        struct r1conf *conf = mddev->private;
        struct list_head *head = &conf->retry_list;
        struct blk_plug plug;
        int idx;

        md_check_recovery(mddev);

        if (!list_empty_careful(&conf->bio_end_io_list) &&
            !test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags)) {
                LIST_HEAD(tmp);
                spin_lock_irqsave(&conf->device_lock, flags);
                if (!test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags))
                        list_splice_init(&conf->bio_end_io_list, &tmp);
                spin_unlock_irqrestore(&conf->device_lock, flags);
                while (!list_empty(&tmp)) {
                        r1_bio = list_first_entry(&tmp, struct r1bio,
                                                  retry_list);
                        list_del(&r1_bio->retry_list);
                        idx = sector_to_idx(r1_bio->sector);
                        atomic_dec(&conf->nr_queued[idx]);
                        if (mddev->degraded)
                                set_bit(R1BIO_Degraded, &r1_bio->state);
                        if (test_bit(R1BIO_WriteError, &r1_bio->state))
                                close_write(r1_bio);
                        raid_end_bio_io(r1_bio);
                }
        }

        blk_start_plug(&plug);
        for (;;) {

                flush_pending_writes(conf);

                spin_lock_irqsave(&conf->device_lock, flags);
                if (list_empty(head)) {
                        spin_unlock_irqrestore(&conf->device_lock, flags);
                        break;
                }
                r1_bio = list_entry(head->prev, struct r1bio, retry_list);
                list_del(head->prev);
                idx = sector_to_idx(r1_bio->sector);
                atomic_dec(&conf->nr_queued[idx]);
                spin_unlock_irqrestore(&conf->device_lock, flags);

                mddev = r1_bio->mddev;
                conf = mddev->private;
                if (test_bit(R1BIO_IsSync, &r1_bio->state)) {
                        if (test_bit(R1BIO_MadeGood, &r1_bio->state) ||
                            test_bit(R1BIO_WriteError, &r1_bio->state))
                                handle_sync_write_finished(conf, r1_bio);
                        else
                                sync_request_write(mddev, r1_bio);
                } else if (test_bit(R1BIO_MadeGood, &r1_bio->state) ||
                           test_bit(R1BIO_WriteError, &r1_bio->state))
                        handle_write_finished(conf, r1_bio);
                else if (test_bit(R1BIO_ReadError, &r1_bio->state))
                        handle_read_error(conf, r1_bio);
                else
                        /* just a partial read to be scheduled from separate
                         * context
                         */
                        generic_make_request(r1_bio->bios[r1_bio->read_disk]);

                cond_resched();
                if (mddev->sb_flags & ~(1<<MD_SB_CHANGE_PENDING))
                        md_check_recovery(mddev);
        }
        blk_finish_plug(&plug);
}

static int init_resync(struct r1conf *conf)
{
        int buffs;

        buffs = RESYNC_WINDOW / RESYNC_BLOCK_SIZE;
        BUG_ON(conf->r1buf_pool);
        conf->r1buf_pool = mempool_create(buffs, r1buf_pool_alloc, r1buf_pool_free,
                                          conf->poolinfo);
        if (!conf->r1buf_pool)
                return -ENOMEM;
        return 0;
}

/*
 * perform a "sync" on one "block"
 *
 * We need to make sure that no normal I/O request - particularly write
 * requests - conflict with active sync requests.
 *
 * This is achieved by tracking pending requests and a 'barrier' concept
 * that can be installed to exclude normal IO requests.
 */

static sector_t raid1_sync_request(struct mddev *mddev, sector_t sector_nr,
                                   int *skipped)
{
        struct r1conf *conf = mddev->private;
        struct r1bio *r1_bio;
        struct bio *bio;
        sector_t max_sector, nr_sectors;
        int disk = -1;
        int i;
        int wonly = -1;
        int write_targets = 0, read_targets = 0;
        sector_t sync_blocks;
        int still_degraded = 0;
        int good_sectors = RESYNC_SECTORS;
        int min_bad = 0; /* number of sectors that are bad in all devices */
        int idx = sector_to_idx(sector_nr);

        if (!conf->r1buf_pool)
                if (init_resync(conf))
                        return 0;

        max_sector = mddev->dev_sectors;
        if (sector_nr >= max_sector) {
                /* If we aborted, we need to abort the
                 * sync on the 'current' bitmap chunk (there will
                 * only be one in raid1 resync.
                 * We can find the current addess in mddev->curr_resync
                 */
                if (mddev->curr_resync < max_sector) /* aborted */
                        bitmap_end_sync(mddev->bitmap, mddev->curr_resync,
                                                &sync_blocks, 1);
                else /* completed sync */
                        conf->fullsync = 0;

                bitmap_close_sync(mddev->bitmap);
                close_sync(conf);

                if (mddev_is_clustered(mddev)) {
                        conf->cluster_sync_low = 0;
                        conf->cluster_sync_high = 0;
                }
                return 0;
        }

        if (mddev->bitmap == NULL &&
            mddev->recovery_cp == MaxSector &&
            !test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery) &&
            conf->fullsync == 0) {
                *skipped = 1;
                return max_sector - sector_nr;
        }
        /* before building a request, check if we can skip these blocks..
         * This call the bitmap_start_sync doesn't actually record anything
         */
        if (!bitmap_start_sync(mddev->bitmap, sector_nr, &sync_blocks, 1) &&
            !conf->fullsync && !test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery)) {
                /* We can skip this block, and probably several more */
                *skipped = 1;
                return sync_blocks;
        }

        /*
         * If there is non-resync activity waiting for a turn, then let it
         * though before starting on this new sync request.
         */
        if (atomic_read(&conf->nr_waiting[idx]))
                schedule_timeout_uninterruptible(1);

        /* we are incrementing sector_nr below. To be safe, we check against
         * sector_nr + two times RESYNC_SECTORS
         */

        bitmap_cond_end_sync(mddev->bitmap, sector_nr,
                mddev_is_clustered(mddev) && (sector_nr + 2 * RESYNC_SECTORS > conf->cluster_sync_high));
        r1_bio = mempool_alloc(conf->r1buf_pool, GFP_NOIO);

        raise_barrier(conf, sector_nr);

        rcu_read_lock();
        /*
         * If we get a correctably read error during resync or recovery,
         * we might want to read from a different device.  So we
         * flag all drives that could conceivably be read from for READ,
         * and any others (which will be non-In_sync devices) for WRITE.
         * If a read fails, we try reading from something else for which READ
         * is OK.
         */

        r1_bio->mddev = mddev;
        r1_bio->sector = sector_nr;
        r1_bio->state = 0;
        set_bit(R1BIO_IsSync, &r1_bio->state);
        /* make sure good_sectors won't go across barrier unit boundary */
        good_sectors = align_to_barrier_unit_end(sector_nr, good_sectors);

        for (i = 0; i < conf->raid_disks * 2; i++) {
                struct md_rdev *rdev;
                bio = r1_bio->bios[i];
                bio_reset(bio);

                rdev = rcu_dereference(conf->mirrors[i].rdev);
                if (rdev == NULL ||
                    test_bit(Faulty, &rdev->flags)) {
                        if (i < conf->raid_disks)
                                still_degraded = 1;
                } else if (!test_bit(In_sync, &rdev->flags)) {
                        bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
                        bio->bi_end_io = end_sync_write;
                        write_targets ++;
                } else {
                        /* may need to read from here */
                        sector_t first_bad = MaxSector;
                        int bad_sectors;

                        if (is_badblock(rdev, sector_nr, good_sectors,
                                        &first_bad, &bad_sectors)) {
                                if (first_bad > sector_nr)
                                        good_sectors = first_bad - sector_nr;
                                else {
                                        bad_sectors -= (sector_nr - first_bad);
                                        if (min_bad == 0 ||
                                            min_bad > bad_sectors)
                                                min_bad = bad_sectors;
                                }
                        }
                        if (sector_nr < first_bad) {
                                if (test_bit(WriteMostly, &rdev->flags)) {
                                        if (wonly < 0)
                                                wonly = i;
                                } else {
                                        if (disk < 0)
                                                disk = i;
                                }
                                bio_set_op_attrs(bio, REQ_OP_READ, 0);
                                bio->bi_end_io = end_sync_read;
                                read_targets++;
                        } else if (!test_bit(WriteErrorSeen, &rdev->flags) &&
                                test_bit(MD_RECOVERY_SYNC, &mddev->recovery) &&
                                !test_bit(MD_RECOVERY_CHECK, &mddev->recovery)) {
                                /*
                                 * The device is suitable for reading (InSync),
                                 * but has bad block(s) here. Let's try to correct them,
                                 * if we are doing resync or repair. Otherwise, leave
                                 * this device alone for this sync request.
                                 */
                                bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
                                bio->bi_end_io = end_sync_write;
                                write_targets++;
                        }
                }
                if (bio->bi_end_io) {
                        atomic_inc(&rdev->nr_pending);
                        bio->bi_iter.bi_sector = sector_nr + rdev->data_offset;
                        bio->bi_bdev = rdev->bdev;
                        bio->bi_private = r1_bio;
                        if (test_bit(FailFast, &rdev->flags))
                                bio->bi_opf |= MD_FAILFAST;
                }
        }
        rcu_read_unlock();
        if (disk < 0)
                disk = wonly;
        r1_bio->read_disk = disk;

        if (read_targets == 0 && min_bad > 0) {
                /* These sectors are bad on all InSync devices, so we
                 * need to mark them bad on all write targets
                 */
                int ok = 1;
                for (i = 0 ; i < conf->raid_disks * 2 ; i++)
                        if (r1_bio->bios[i]->bi_end_io == end_sync_write) {
                                struct md_rdev *rdev = conf->mirrors[i].rdev;
                                ok = rdev_set_badblocks(rdev, sector_nr,
                                                        min_bad, 0
                                        ) && ok;
                        }
                set_bit(MD_SB_CHANGE_DEVS, &mddev->sb_flags);
                *skipped = 1;
                put_buf(r1_bio);

                if (!ok) {
                        /* Cannot record the badblocks, so need to
                         * abort the resync.
                         * If there are multiple read targets, could just
                         * fail the really bad ones ???
                         */
                        conf->recovery_disabled = mddev->recovery_disabled;
                        set_bit(MD_RECOVERY_INTR, &mddev->recovery);
                        return 0;
                } else
                        return min_bad;

        }
        if (min_bad > 0 && min_bad < good_sectors) {
                /* only resync enough to reach the next bad->good
                 * transition */
                good_sectors = min_bad;
        }

        if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery) && read_targets > 0)
                /* extra read targets are also write targets */
                write_targets += read_targets-1;

        if (write_targets == 0 || read_targets == 0) {
                /* There is nowhere to write, so all non-sync
                 * drives must be failed - so we are finished
                 */
                sector_t rv;
                if (min_bad > 0)
                        max_sector = sector_nr + min_bad;
                rv = max_sector - sector_nr;
                *skipped = 1;
                put_buf(r1_bio);
                return rv;
        }

        if (max_sector > mddev->resync_max)
                max_sector = mddev->resync_max; /* Don't do IO beyond here */
        if (max_sector > sector_nr + good_sectors)
                max_sector = sector_nr + good_sectors;
        nr_sectors = 0;
        sync_blocks = 0;
        do {
                struct page *page;
                int len = PAGE_SIZE;
                if (sector_nr + (len>>9) > max_sector)
                        len = (max_sector - sector_nr) << 9;
                if (len == 0)
                        break;
                if (sync_blocks == 0) {
                        if (!bitmap_start_sync(mddev->bitmap, sector_nr,
                                               &sync_blocks, still_degraded) &&
                            !conf->fullsync &&
                            !test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery))
                                break;
                        if ((len >> 9) > sync_blocks)
                                len = sync_blocks<<9;
                }

                for (i = 0 ; i < conf->raid_disks * 2; i++) {
                        bio = r1_bio->bios[i];
                        if (bio->bi_end_io) {
                                page = bio->bi_io_vec[bio->bi_vcnt].bv_page;
                                if (bio_add_page(bio, page, len, 0) == 0) {
                                        /* stop here */
                                        bio->bi_io_vec[bio->bi_vcnt].bv_page = page;
                                        while (i > 0) {
                                                i--;
                                                bio = r1_bio->bios[i];
                                                if (bio->bi_end_io==NULL)
                                                        continue;
                                                /* remove last page from this bio */
                                                bio->bi_vcnt--;
                                                bio->bi_iter.bi_size -= len;
                                                bio_clear_flag(bio, BIO_SEG_VALID);
                                        }
                                        goto bio_full;
                                }
                        }
                }
                nr_sectors += len>>9;
                sector_nr += len>>9;
                sync_blocks -= (len>>9);
        } while (r1_bio->bios[disk]->bi_vcnt < RESYNC_PAGES);
 bio_full:
        r1_bio->sectors = nr_sectors;

        if (mddev_is_clustered(mddev) &&
                        conf->cluster_sync_high < sector_nr + nr_sectors) {
                conf->cluster_sync_low = mddev->curr_resync_completed;
                conf->cluster_sync_high = conf->cluster_sync_low + CLUSTER_RESYNC_WINDOW_SECTORS;
                /* Send resync message */
                md_cluster_ops->resync_info_update(mddev,
                                conf->cluster_sync_low,
                                conf->cluster_sync_high);
        }

        /* For a user-requested sync, we read all readable devices and do a
         * compare
         */
        if (test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery)) {
                atomic_set(&r1_bio->remaining, read_targets);
                for (i = 0; i < conf->raid_disks * 2 && read_targets; i++) {
                        bio = r1_bio->bios[i];
                        if (bio->bi_end_io == end_sync_read) {
                                read_targets--;
                                md_sync_acct(bio->bi_bdev, nr_sectors);
                                if (read_targets == 1)
                                        bio->bi_opf &= ~MD_FAILFAST;
                                generic_make_request(bio);
                        }
                }
        } else {
                atomic_set(&r1_bio->remaining, 1);
                bio = r1_bio->bios[r1_bio->read_disk];
                md_sync_acct(bio->bi_bdev, nr_sectors);
                if (read_targets == 1)
                        bio->bi_opf &= ~MD_FAILFAST;
                generic_make_request(bio);

        }
        return nr_sectors;
}