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	Version: linux-6.0.1 spark-3.0.0 hadoop-3.2.0-src hadoop-3.3.0-src spark-2.4.7 linux-4.15.13 hadoop-2.7.4-src Revert   Change

 // SPDX-License-Identifier: GPL-2.0-or-later
 /*
  * raid10.c : Multiple Devices driver for Linux
  *
  * Copyright (C) 2000-2004 Neil Brown
  *
  * RAID-10 support for md.
  *
  * Base on code in raid1.c.  See raid1.c for further copyright information.
  */
 
 #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/kthread.h>
 #include <linux/raid/md_p.h>
 #include <trace/events/block.h>
 #include "md.h"
 #include "raid10.h"
 #include "raid0.h"
 #include "md-bitmap.h"
 
 /*
  * RAID10 provides a combination of RAID0 and RAID1 functionality.
  * The layout of data is defined by
  *    chunk_size
  *    raid_disks
  *    near_copies (stored in low byte of layout)
  *    far_copies (stored in second byte of layout)
  *    far_offset (stored in bit 16 of layout )
  *    use_far_sets (stored in bit 17 of layout )
  *    use_far_sets_bugfixed (stored in bit 18 of layout )
  *
  * The data to be stored is divided into chunks using chunksize.  Each device
  * is divided into far_copies sections.   In each section, chunks are laid out
  * in a style similar to raid0, but near_copies copies of each chunk is stored
  * (each on a different drive).  The starting device for each section is offset
  * near_copies from the starting device of the previous section.  Thus there
  * are (near_copies * far_copies) of each chunk, and each is on a different
  * drive.  near_copies and far_copies must be at least one, and their product
  * is at most raid_disks.
  *
  * If far_offset is true, then the far_copies are handled a bit differently.
  * The copies are still in different stripes, but instead of being very far
  * apart on disk, there are adjacent stripes.
  *
  * The far and offset algorithms are handled slightly differently if
  * 'use_far_sets' is true.  In this case, the array's devices are grouped into
  * sets that are (near_copies * far_copies) in size.  The far copied stripes
  * are still shifted by 'near_copies' devices, but this shifting stays confined
  * to the set rather than the entire array.  This is done to improve the number
  * of device combinations that can fail without causing the array to fail.
  * Example 'far' algorithm w/o 'use_far_sets' (each letter represents a chunk
  * on a device):
  *    A B C D    A B C D E
  *      ...         ...
  *    D A B C    E A B C D
  * Example 'far' algorithm w/ 'use_far_sets' enabled (sets illustrated w/ []'s):
  *    [A B] [C D]    [A B] [C D E]
  *    |...| |...|    |...| | ... |
  *    [B A] [D C]    [B A] [E C D]
  */
 
 static void allow_barrier(struct r10conf *conf);
 static void lower_barrier(struct r10conf *conf);
 static int _enough(struct r10conf *conf, int previous, int ignore);
 static int enough(struct r10conf *conf, int ignore);
 static sector_t reshape_request(struct mddev *mddev, sector_t sector_nr,
                 int *skipped);
 static void reshape_request_write(struct mddev *mddev, struct r10bio *r10_bio);
 static void end_reshape_write(struct bio *bio);
 static void end_reshape(struct r10conf *conf);
 
 #define raid10_log(md, fmt, args...)                \
     do { if ((md)->queue) blk_add_trace_msg((md)->queue, "raid10 " fmt, ##args); } while (0)
 
 #include "raid1-10.c"
 
 /*
  * for resync bio, r10bio pointer can be retrieved from the per-bio
  * 'struct resync_pages'.
  */
 static inline struct r10bio *get_resync_r10bio(struct bio *bio)
 {
     return get_resync_pages(bio)->raid_bio;
 }
 
 static void * r10bio_pool_alloc(gfp_t gfp_flags, void *data)
 {
     struct r10conf *conf = data;
     int size = offsetof(struct r10bio, devs[conf->geo.raid_disks]);
 
     /* allocate a r10bio with room for raid_disks entries in the
      * bios array */
     return kzalloc(size, gfp_flags);
 }
 
 #define RESYNC_SECTORS (RESYNC_BLOCK_SIZE >> 9)
 /* amount of memory to reserve for resync requests */
 #define RESYNC_WINDOW (1024*1024)
 /* maximum number of concurrent requests, memory permitting */
 #define RESYNC_DEPTH (32*1024*1024/RESYNC_BLOCK_SIZE)
 #define CLUSTER_RESYNC_WINDOW (32 * RESYNC_WINDOW)
 #define CLUSTER_RESYNC_WINDOW_SECTORS (CLUSTER_RESYNC_WINDOW >> 9)
 
 /*
  * When performing a resync, we need to read and compare, so
  * we need as many pages are there are copies.
  * When performing a recovery, we need 2 bios, one for read,
  * one for write (we recover only one drive per r10buf)
  *
  */
 static void * r10buf_pool_alloc(gfp_t gfp_flags, void *data)
 {
     struct r10conf *conf = data;
     struct r10bio *r10_bio;
     struct bio *bio;
     int j;
     int nalloc, nalloc_rp;
     struct resync_pages *rps;
 
     r10_bio = r10bio_pool_alloc(gfp_flags, conf);
     if (!r10_bio)
         return NULL;
 
     if (test_bit(MD_RECOVERY_SYNC, &conf->mddev->recovery) ||
         test_bit(MD_RECOVERY_RESHAPE, &conf->mddev->recovery))
         nalloc = conf->copies; /* resync */
     else
         nalloc = 2; /* recovery */
 
     /* allocate once for all bios */
     if (!conf->have_replacement)
         nalloc_rp = nalloc;
     else
         nalloc_rp = nalloc * 2;
     rps = kmalloc_array(nalloc_rp, sizeof(struct resync_pages), gfp_flags);
     if (!rps)
         goto out_free_r10bio;
 
     /*
      * Allocate bios.
      */
     for (j = nalloc ; j-- ; ) {
         bio = bio_kmalloc(RESYNC_PAGES, gfp_flags);
         if (!bio)
             goto out_free_bio;
         bio_init(bio, NULL, bio->bi_inline_vecs, RESYNC_PAGES, 0);
         r10_bio->devs[j].bio = bio;
         if (!conf->have_replacement)
             continue;
         bio = bio_kmalloc(RESYNC_PAGES, gfp_flags);
         if (!bio)
             goto out_free_bio;
         bio_init(bio, NULL, bio->bi_inline_vecs, RESYNC_PAGES, 0);
         r10_bio->devs[j].repl_bio = bio;
     }
     /*
      * Allocate RESYNC_PAGES data pages and attach them
      * where needed.
      */
     for (j = 0; j < nalloc; j++) {
         struct bio *rbio = r10_bio->devs[j].repl_bio;
         struct resync_pages *rp, *rp_repl;
 
         rp = &rps[j];
         if (rbio)
             rp_repl = &rps[nalloc + j];
 
         bio = r10_bio->devs[j].bio;
 
         if (!j || test_bit(MD_RECOVERY_SYNC,
                    &conf->mddev->recovery)) {
             if (resync_alloc_pages(rp, gfp_flags))
                 goto out_free_pages;
         } else {
             memcpy(rp, &rps[0], sizeof(*rp));
             resync_get_all_pages(rp);
         }
 
         rp->raid_bio = r10_bio;
         bio->bi_private = rp;
         if (rbio) {
             memcpy(rp_repl, rp, sizeof(*rp));
             rbio->bi_private = rp_repl;
         }
     }
 
     return r10_bio;
 
 out_free_pages:
     while (--j >= 0)
         resync_free_pages(&rps[j]);
 
     j = 0;
 out_free_bio:
     for ( ; j < nalloc; j++) {
         if (r10_bio->devs[j].bio)
             bio_uninit(r10_bio->devs[j].bio);
         kfree(r10_bio->devs[j].bio);
         if (r10_bio->devs[j].repl_bio)
             bio_uninit(r10_bio->devs[j].repl_bio);
         kfree(r10_bio->devs[j].repl_bio);
     }
     kfree(rps);
 out_free_r10bio:
     rbio_pool_free(r10_bio, conf);
     return NULL;
 }
 
 static void r10buf_pool_free(void *__r10_bio, void *data)
 {
     struct r10conf *conf = data;
     struct r10bio *r10bio = __r10_bio;
     int j;
     struct resync_pages *rp = NULL;
 
     for (j = conf->copies; j--; ) {
         struct bio *bio = r10bio->devs[j].bio;
 
         if (bio) {
             rp = get_resync_pages(bio);
             resync_free_pages(rp);
             bio_uninit(bio);
             kfree(bio);
         }
 
         bio = r10bio->devs[j].repl_bio;
         if (bio) {
             bio_uninit(bio);
             kfree(bio);
         }
     }
 
     /* resync pages array stored in the 1st bio's .bi_private */
     kfree(rp);
 
     rbio_pool_free(r10bio, conf);
 }
 
 static void put_all_bios(struct r10conf *conf, struct r10bio *r10_bio)
 {
     int i;
 
     for (i = 0; i < conf->geo.raid_disks; i++) {
         struct bio **bio = & r10_bio->devs[i].bio;
         if (!BIO_SPECIAL(*bio))
             bio_put(*bio);
         *bio = NULL;
         bio = &r10_bio->devs[i].repl_bio;
         if (r10_bio->read_slot < 0 && !BIO_SPECIAL(*bio))
             bio_put(*bio);
         *bio = NULL;
     }
 }
 
 static void free_r10bio(struct r10bio *r10_bio)
 {
     struct r10conf *conf = r10_bio->mddev->private;
 
     put_all_bios(conf, r10_bio);
     mempool_free(r10_bio, &conf->r10bio_pool);
 }
 
 static void put_buf(struct r10bio *r10_bio)
 {
     struct r10conf *conf = r10_bio->mddev->private;
 
     mempool_free(r10_bio, &conf->r10buf_pool);
 
     lower_barrier(conf);
 }
 
 static void reschedule_retry(struct r10bio *r10_bio)
 {
     unsigned long flags;
     struct mddev *mddev = r10_bio->mddev;
     struct r10conf *conf = mddev->private;
 
     spin_lock_irqsave(&conf->device_lock, flags);
     list_add(&r10_bio->retry_list, &conf->retry_list);
     conf->nr_queued ++;
     spin_unlock_irqrestore(&conf->device_lock, flags);
 
     /* wake up frozen array... */
     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 raid_end_bio_io(struct r10bio *r10_bio)
 {
     struct bio *bio = r10_bio->master_bio;
     struct r10conf *conf = r10_bio->mddev->private;
 
     if (!test_bit(R10BIO_Uptodate, &r10_bio->state))
         bio->bi_status = BLK_STS_IOERR;
 
     if (blk_queue_io_stat(bio->bi_bdev->bd_disk->queue))
         bio_end_io_acct(bio, r10_bio->start_time);
     bio_endio(bio);
     /*
      * Wake up any possible resync thread that waits for the device
      * to go idle.
      */
     allow_barrier(conf);
 
     free_r10bio(r10_bio);
 }
 
 /*
  * Update disk head position estimator based on IRQ completion info.
  */
 static inline void update_head_pos(int slot, struct r10bio *r10_bio)
 {
     struct r10conf *conf = r10_bio->mddev->private;
 
     conf->mirrors[r10_bio->devs[slot].devnum].head_position =
         r10_bio->devs[slot].addr + (r10_bio->sectors);
 }
 
 /*
  * Find the disk number which triggered given bio
  */
 static int find_bio_disk(struct r10conf *conf, struct r10bio *r10_bio,
              struct bio *bio, int *slotp, int *replp)
 {
     int slot;
     int repl = 0;
 
     for (slot = 0; slot < conf->geo.raid_disks; slot++) {
         if (r10_bio->devs[slot].bio == bio)
             break;
         if (r10_bio->devs[slot].repl_bio == bio) {
             repl = 1;
             break;
         }
     }
 
     update_head_pos(slot, r10_bio);
 
     if (slotp)
         *slotp = slot;
     if (replp)
         *replp = repl;
     return r10_bio->devs[slot].devnum;
 }
 
 static void raid10_end_read_request(struct bio *bio)
 {
     int uptodate = !bio->bi_status;
     struct r10bio *r10_bio = bio->bi_private;
     int slot;
     struct md_rdev *rdev;
     struct r10conf *conf = r10_bio->mddev->private;
 
     slot = r10_bio->read_slot;
     rdev = r10_bio->devs[slot].rdev;
     /*
      * this branch is our 'one mirror IO has finished' event handler:
      */
     update_head_pos(slot, r10_bio);
 
     if (uptodate) {
         /*
          * Set R10BIO_Uptodate in our master bio, so that
          * we will return a good error code 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.
          */
         set_bit(R10BIO_Uptodate, &r10_bio->state);
     } else {
         /* If all other devices that store this block 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"
          */
         if (!_enough(conf, test_bit(R10BIO_Previous, &r10_bio->state),
                  rdev->raid_disk))
             uptodate = 1;
     }
     if (uptodate) {
         raid_end_bio_io(r10_bio);
         rdev_dec_pending(rdev, conf->mddev);
     } else {
         /*
          * oops, read error - keep the refcount on the rdev
          */
         pr_err_ratelimited("md/raid10:%s: %pg: rescheduling sector %llu\n",
                    mdname(conf->mddev),
                    rdev->bdev,
                    (unsigned long long)r10_bio->sector);
         set_bit(R10BIO_ReadError, &r10_bio->state);
         reschedule_retry(r10_bio);
     }
 }
 
 static void close_write(struct r10bio *r10_bio)
 {
     /* clear the bitmap if all writes complete successfully */
     md_bitmap_endwrite(r10_bio->mddev->bitmap, r10_bio->sector,
                r10_bio->sectors,
                !test_bit(R10BIO_Degraded, &r10_bio->state),
                0);
     md_write_end(r10_bio->mddev);
 }
 
 static void one_write_done(struct r10bio *r10_bio)
 {
     if (atomic_dec_and_test(&r10_bio->remaining)) {
         if (test_bit(R10BIO_WriteError, &r10_bio->state))
             reschedule_retry(r10_bio);
         else {
             close_write(r10_bio);
             if (test_bit(R10BIO_MadeGood, &r10_bio->state))
                 reschedule_retry(r10_bio);
             else
                 raid_end_bio_io(r10_bio);
         }
     }
 }
 
 static void raid10_end_write_request(struct bio *bio)
 {
     struct r10bio *r10_bio = bio->bi_private;
     int dev;
     int dec_rdev = 1;
     struct r10conf *conf = r10_bio->mddev->private;
     int slot, repl;
     struct md_rdev *rdev = NULL;
     struct bio *to_put = NULL;
     bool discard_error;
 
     discard_error = bio->bi_status && bio_op(bio) == REQ_OP_DISCARD;
 
     dev = find_bio_disk(conf, r10_bio, bio, &slot, &repl);
 
     if (repl)
         rdev = conf->mirrors[dev].replacement;
     if (!rdev) {
         smp_rmb();
         repl = 0;
         rdev = conf->mirrors[dev].rdev;
     }
     /*
      * this branch is our 'one mirror IO has finished' event handler:
      */
     if (bio->bi_status && !discard_error) {
         if (repl)
             /* Never record new bad blocks to replacement,
              * just fail it.
              */
             md_error(rdev->mddev, rdev);
         else {
             set_bit(WriteErrorSeen, &rdev->flags);
             if (!test_and_set_bit(WantReplacement, &rdev->flags))
                 set_bit(MD_RECOVERY_NEEDED,
                     &rdev->mddev->recovery);
 
             dec_rdev = 0;
             if (test_bit(FailFast, &rdev->flags) &&
                 (bio->bi_opf & MD_FAILFAST)) {
                 md_error(rdev->mddev, rdev);
             }
 
             /*
              * When the device is faulty, it is not necessary to
              * handle write error.
              */
             if (!test_bit(Faulty, &rdev->flags))
                 set_bit(R10BIO_WriteError, &r10_bio->state);
             else {
                 /* Fail the request */
                 set_bit(R10BIO_Degraded, &r10_bio->state);
                 r10_bio->devs[slot].bio = NULL;
                 to_put = bio;
                 dec_rdev = 1;
             }
         }
     } else {
         /*
          * Set R10BIO_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;
 
         /*
          * Do not set R10BIO_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(R10BIO_Uptodate, &r10_bio->state);
 
         /* Maybe we can clear some bad blocks. */
         if (is_badblock(rdev,
                 r10_bio->devs[slot].addr,
                 r10_bio->sectors,
                 &first_bad, &bad_sectors) && !discard_error) {
             bio_put(bio);
             if (repl)
                 r10_bio->devs[slot].repl_bio = IO_MADE_GOOD;
             else
                 r10_bio->devs[slot].bio = IO_MADE_GOOD;
             dec_rdev = 0;
             set_bit(R10BIO_MadeGood, &r10_bio->state);
         }
     }
 
     /*
      *
      * Let's see if all mirrored write operations have finished
      * already.
      */
     one_write_done(r10_bio);
     if (dec_rdev)
         rdev_dec_pending(rdev, conf->mddev);
     if (to_put)
         bio_put(to_put);
 }
 
 /*
  * RAID10 layout manager
  * As well as the chunksize and raid_disks count, there are two
  * parameters: near_copies and far_copies.
  * near_copies * far_copies must be <= raid_disks.
  * Normally one of these will be 1.
  * If both are 1, we get raid0.
  * If near_copies == raid_disks, we get raid1.
  *
  * Chunks are laid out in raid0 style with near_copies copies of the
  * first chunk, followed by near_copies copies of the next chunk and
  * so on.
  * If far_copies > 1, then after 1/far_copies of the array has been assigned
  * as described above, we start again with a device offset of near_copies.
  * So we effectively have another copy of the whole array further down all
  * the drives, but with blocks on different drives.
  * With this layout, and block is never stored twice on the one device.
  *
  * raid10_find_phys finds the sector offset of a given virtual sector
  * on each device that it is on.
  *
  * raid10_find_virt does the reverse mapping, from a device and a
  * sector offset to a virtual address
  */
 
 static void __raid10_find_phys(struct geom *geo, struct r10bio *r10bio)
 {
     int n,f;
     sector_t sector;
     sector_t chunk;
     sector_t stripe;
     int dev;
     int slot = 0;
     int last_far_set_start, last_far_set_size;
 
     last_far_set_start = (geo->raid_disks / geo->far_set_size) - 1;
     last_far_set_start *= geo->far_set_size;
 
     last_far_set_size = geo->far_set_size;
     last_far_set_size += (geo->raid_disks % geo->far_set_size);
 
     /* now calculate first sector/dev */
     chunk = r10bio->sector >> geo->chunk_shift;
     sector = r10bio->sector & geo->chunk_mask;
 
     chunk *= geo->near_copies;
     stripe = chunk;
     dev = sector_div(stripe, geo->raid_disks);
     if (geo->far_offset)
         stripe *= geo->far_copies;
 
     sector += stripe << geo->chunk_shift;
 
     /* and calculate all the others */
     for (n = 0; n < geo->near_copies; n++) {
         int d = dev;
         int set;
         sector_t s = sector;
         r10bio->devs[slot].devnum = d;
         r10bio->devs[slot].addr = s;
         slot++;
 
         for (f = 1; f < geo->far_copies; f++) {
             set = d / geo->far_set_size;
             d += geo->near_copies;
 
             if ((geo->raid_disks % geo->far_set_size) &&
                 (d > last_far_set_start)) {
                 d -= last_far_set_start;
                 d %= last_far_set_size;
                 d += last_far_set_start;
             } else {
                 d %= geo->far_set_size;
                 d += geo->far_set_size * set;
             }
             s += geo->stride;
             r10bio->devs[slot].devnum = d;
             r10bio->devs[slot].addr = s;
             slot++;
         }
         dev++;
         if (dev >= geo->raid_disks) {
             dev = 0;
             sector += (geo->chunk_mask + 1);
         }
     }
 }
 
 static void raid10_find_phys(struct r10conf *conf, struct r10bio *r10bio)
 {
     struct geom *geo = &conf->geo;
 
     if (conf->reshape_progress != MaxSector &&
         ((r10bio->sector >= conf->reshape_progress) !=
          conf->mddev->reshape_backwards)) {
         set_bit(R10BIO_Previous, &r10bio->state);
         geo = &conf->prev;
     } else
         clear_bit(R10BIO_Previous, &r10bio->state);
 
     __raid10_find_phys(geo, r10bio);
 }
 
 static sector_t raid10_find_virt(struct r10conf *conf, sector_t sector, int dev)
 {
     sector_t offset, chunk, vchunk;
     /* Never use conf->prev as this is only called during resync
      * or recovery, so reshape isn't happening
      */
     struct geom *geo = &conf->geo;
     int far_set_start = (dev / geo->far_set_size) * geo->far_set_size;
     int far_set_size = geo->far_set_size;
     int last_far_set_start;
 
     if (geo->raid_disks % geo->far_set_size) {
         last_far_set_start = (geo->raid_disks / geo->far_set_size) - 1;
         last_far_set_start *= geo->far_set_size;
 
         if (dev >= last_far_set_start) {
             far_set_size = geo->far_set_size;
             far_set_size += (geo->raid_disks % geo->far_set_size);
             far_set_start = last_far_set_start;
         }
     }
 
     offset = sector & geo->chunk_mask;
     if (geo->far_offset) {
         int fc;
         chunk = sector >> geo->chunk_shift;
         fc = sector_div(chunk, geo->far_copies);
         dev -= fc * geo->near_copies;
         if (dev < far_set_start)
             dev += far_set_size;
     } else {
         while (sector >= geo->stride) {
             sector -= geo->stride;
             if (dev < (geo->near_copies + far_set_start))
                 dev += far_set_size - geo->near_copies;
             else
                 dev -= geo->near_copies;
         }
         chunk = sector >> geo->chunk_shift;
     }
     vchunk = chunk * geo->raid_disks + dev;
     sector_div(vchunk, geo->near_copies);
     return (vchunk << geo->chunk_shift) + offset;
 }
 
 /*
  * 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.
  */
 
 /*
  * FIXME: possibly should rethink readbalancing and do it differently
  * depending on near_copies / far_copies geometry.
  */
 static struct md_rdev *read_balance(struct r10conf *conf,
                     struct r10bio *r10_bio,
                     int *max_sectors)
 {
     const sector_t this_sector = r10_bio->sector;
     int disk, slot;
     int sectors = r10_bio->sectors;
     int best_good_sectors;
     sector_t new_distance, best_dist;
     struct md_rdev *best_dist_rdev, *best_pending_rdev, *rdev = NULL;
     int do_balance;
     int best_dist_slot, best_pending_slot;
     bool has_nonrot_disk = false;
     unsigned int min_pending;
     struct geom *geo = &conf->geo;
 
     raid10_find_phys(conf, r10_bio);
     rcu_read_lock();
     best_dist_slot = -1;
     min_pending = UINT_MAX;
     best_dist_rdev = NULL;
     best_pending_rdev = NULL;
     best_dist = MaxSector;
     best_good_sectors = 0;
     do_balance = 1;
     clear_bit(R10BIO_FailFast, &r10_bio->state);
     /*
      * Check if we can balance. We can balance on the whole
      * device if no resync is going on (recovery is ok), or below
      * the resync window. We take the first readable disk when
      * above the resync window.
      */
     if ((conf->mddev->recovery_cp < MaxSector
          && (this_sector + sectors >= conf->next_resync)) ||
         (mddev_is_clustered(conf->mddev) &&
          md_cluster_ops->area_resyncing(conf->mddev, READ, this_sector,
                         this_sector + sectors)))
         do_balance = 0;
 
     for (slot = 0; slot < conf->copies ; slot++) {
         sector_t first_bad;
         int bad_sectors;
         sector_t dev_sector;
         unsigned int pending;
         bool nonrot;
 
         if (r10_bio->devs[slot].bio == IO_BLOCKED)
             continue;
         disk = r10_bio->devs[slot].devnum;
         rdev = rcu_dereference(conf->mirrors[disk].replacement);
         if (rdev == NULL || test_bit(Faulty, &rdev->flags) ||
             r10_bio->devs[slot].addr + sectors > rdev->recovery_offset)
             rdev = rcu_dereference(conf->mirrors[disk].rdev);
         if (rdev == NULL ||
             test_bit(Faulty, &rdev->flags))
             continue;
         if (!test_bit(In_sync, &rdev->flags) &&
             r10_bio->devs[slot].addr + sectors > rdev->recovery_offset)
             continue;
 
         dev_sector = r10_bio->devs[slot].addr;
         if (is_badblock(rdev, dev_sector, sectors,
                 &first_bad, &bad_sectors)) {
             if (best_dist < MaxSector)
                 /* Already have a better slot */
                 continue;
             if (first_bad <= dev_sector) {
                 /* Cannot read here.  If this is the
                  * 'primary' device, then we must not read
                  * beyond 'bad_sectors' from another device.
                  */
                 bad_sectors -= (dev_sector - first_bad);
                 if (!do_balance && sectors > bad_sectors)
                     sectors = bad_sectors;
                 if (best_good_sectors > sectors)
                     best_good_sectors = sectors;
             } else {
                 sector_t good_sectors =
                     first_bad - dev_sector;
                 if (good_sectors > best_good_sectors) {
                     best_good_sectors = good_sectors;
                     best_dist_slot = slot;
                     best_dist_rdev = rdev;
                 }
                 if (!do_balance)
                     /* Must read from here */
                     break;
             }
             continue;
         } else
             best_good_sectors = sectors;
 
         if (!do_balance)
             break;
 
         nonrot = bdev_nonrot(rdev->bdev);
         has_nonrot_disk |= nonrot;
         pending = atomic_read(&rdev->nr_pending);
         if (min_pending > pending && nonrot) {
             min_pending = pending;
             best_pending_slot = slot;
             best_pending_rdev = rdev;
         }
 
         if (best_dist_slot >= 0)
             /* At least 2 disks to choose from so failfast is OK */
             set_bit(R10BIO_FailFast, &r10_bio->state);
         /* This optimisation is debatable, and completely destroys
          * sequential read speed for 'far copies' arrays.  So only
          * keep it for 'near' arrays, and review those later.
          */
         if (geo->near_copies > 1 && !pending)
             new_distance = 0;
 
         /* for far > 1 always use the lowest address */
         else if (geo->far_copies > 1)
             new_distance = r10_bio->devs[slot].addr;
         else
             new_distance = abs(r10_bio->devs[slot].addr -
                        conf->mirrors[disk].head_position);
 
         if (new_distance < best_dist) {
             best_dist = new_distance;
             best_dist_slot = slot;
             best_dist_rdev = rdev;
         }
     }
     if (slot >= conf->copies) {
         if (has_nonrot_disk) {
             slot = best_pending_slot;
             rdev = best_pending_rdev;
         } else {
             slot = best_dist_slot;
             rdev = best_dist_rdev;
         }
     }
 
     if (slot >= 0) {
         atomic_inc(&rdev->nr_pending);
         r10_bio->read_slot = slot;
     } else
         rdev = NULL;
     rcu_read_unlock();
     *max_sectors = best_good_sectors;
 
     return rdev;
 }
 
 static void flush_pending_writes(struct r10conf *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 blk_plug plug;
         struct bio *bio;
 
         bio = bio_list_get(&conf->pending_bio_list);
         spin_unlock_irq(&conf->device_lock);
 
         /*
          * As this is called in a wait_event() loop (see freeze_array),
          * current->state might be TASK_UNINTERRUPTIBLE which will
          * cause a warning when we prepare to wait again.  As it is
          * rare that this path is taken, it is perfectly safe to force
          * us to go around the wait_event() loop again, so the warning
          * is a false-positive. Silence the warning by resetting
          * thread state
          */
         __set_current_state(TASK_RUNNING);
 
         blk_start_plug(&plug);
         /* flush any pending bitmap writes to disk
          * before proceeding w/ I/O */
         md_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_set_dev(bio, rdev->bdev);
             if (test_bit(Faulty, &rdev->flags)) {
                 bio_io_error(bio);
             } else if (unlikely((bio_op(bio) ==  REQ_OP_DISCARD) &&
                         !bdev_max_discard_sectors(bio->bi_bdev)))
                 /* Just ignore it */
                 bio_endio(bio);
             else
                 submit_bio_noacct(bio);
             bio = next;
         }
         blk_finish_plug(&plug);
     } 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 r10conf *conf, int force)
 {
     BUG_ON(force && !conf->barrier);
     spin_lock_irq(&conf->resync_lock);
 
     /* Wait until no block IO is waiting (unless 'force') */
     wait_event_lock_irq(conf->wait_barrier, force || !conf->nr_waiting,
                 conf->resync_lock);
 
     /* block any new IO from starting */
     conf->barrier++;
 
     /* Now wait for all pending IO to complete */
     wait_event_lock_irq(conf->wait_barrier,
                 !atomic_read(&conf->nr_pending) && conf->barrier < RESYNC_DEPTH,
                 conf->resync_lock);
 
     spin_unlock_irq(&conf->resync_lock);
 }
 
 static void lower_barrier(struct r10conf *conf)
 {
     unsigned long flags;
     spin_lock_irqsave(&conf->resync_lock, flags);
     conf->barrier--;
     spin_unlock_irqrestore(&conf->resync_lock, flags);
     wake_up(&conf->wait_barrier);
 }
 
 static bool wait_barrier(struct r10conf *conf, bool nowait)
 {
     bool ret = true;
 
     spin_lock_irq(&conf->resync_lock);
     if (conf->barrier) {
         struct bio_list *bio_list = current->bio_list;
         conf->nr_waiting++;
         /* Wait for the barrier to drop.
          * However if there are already pending
          * requests (preventing the barrier from
          * rising completely), and the
          * pre-process bio queue isn't empty,
          * then don't wait, as we need to empty
          * that queue to get the nr_pending
          * count down.
          */
         /* Return false when nowait flag is set */
         if (nowait) {
             ret = false;
         } else {
             raid10_log(conf->mddev, "wait barrier");
             wait_event_lock_irq(conf->wait_barrier,
                         !conf->barrier ||
                         (atomic_read(&conf->nr_pending) &&
                          bio_list &&
                          (!bio_list_empty(&bio_list[0]) ||
                           !bio_list_empty(&bio_list[1]))) ||
                          /* move on if recovery thread is
                           * blocked by us
                           */
                          (conf->mddev->thread->tsk == current &&
                           test_bit(MD_RECOVERY_RUNNING,
                                &conf->mddev->recovery) &&
                           conf->nr_queued > 0),
                         conf->resync_lock);
         }
         conf->nr_waiting--;
         if (!conf->nr_waiting)
             wake_up(&conf->wait_barrier);
     }
     /* Only increment nr_pending when we wait */
     if (ret)
         atomic_inc(&conf->nr_pending);
     spin_unlock_irq(&conf->resync_lock);
     return ret;
 }
 
 static void allow_barrier(struct r10conf *conf)
 {
     if ((atomic_dec_and_test(&conf->nr_pending)) ||
             (conf->array_freeze_pending))
         wake_up(&conf->wait_barrier);
 }
 
 static void freeze_array(struct r10conf *conf, int extra)
 {
     /* stop syncio and normal IO and wait for everything to
      * go quiet.
      * We increment barrier and nr_waiting, and then
      * wait until nr_pending match nr_queued+extra
      * This is called in the context of one normal IO request
      * that has failed. Thus any sync request that might be pending
      * will be blocked by nr_pending, and we need to wait for
      * pending IO requests to complete or be queued for re-try.
      * Thus the number queued (nr_queued) plus this request (extra)
      * must match the number of pending IOs (nr_pending) before
      * we continue.
      */
     spin_lock_irq(&conf->resync_lock);
     conf->array_freeze_pending++;
     conf->barrier++;
     conf->nr_waiting++;
     wait_event_lock_irq_cmd(conf->wait_barrier,
                 atomic_read(&conf->nr_pending) == conf->nr_queued+extra,
                 conf->resync_lock,
                 flush_pending_writes(conf));
 
     conf->array_freeze_pending--;
     spin_unlock_irq(&conf->resync_lock);
 }
 
 static void unfreeze_array(struct r10conf *conf)
 {
     /* reverse the effect of the freeze */
     spin_lock_irq(&conf->resync_lock);
     conf->barrier--;
     conf->nr_waiting--;
     wake_up(&conf->wait_barrier);
     spin_unlock_irq(&conf->resync_lock);
 }
 
 static sector_t choose_data_offset(struct r10bio *r10_bio,
                    struct md_rdev *rdev)
 {
     if (!test_bit(MD_RECOVERY_RESHAPE, &rdev->mddev->recovery) ||
         test_bit(R10BIO_Previous, &r10_bio->state))
         return rdev->data_offset;
     else
         return rdev->new_data_offset;
 }
 
 static void raid10_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 r10conf *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);
         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);
     md_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_set_dev(bio, rdev->bdev);
         if (test_bit(Faulty, &rdev->flags)) {
             bio_io_error(bio);
         } else if (unlikely((bio_op(bio) ==  REQ_OP_DISCARD) &&
                     !bdev_max_discard_sectors(bio->bi_bdev)))
             /* Just ignore it */
             bio_endio(bio);
         else
             submit_bio_noacct(bio);
         bio = next;
     }
     kfree(plug);
 }
 
 /*
  * 1. 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.
  * 2. If IO spans the reshape position.  Need to wait for reshape to pass.
  */
 static bool regular_request_wait(struct mddev *mddev, struct r10conf *conf,
                  struct bio *bio, sector_t sectors)
 {
     /* Bail out if REQ_NOWAIT is set for the bio */
     if (!wait_barrier(conf, bio->bi_opf & REQ_NOWAIT)) {
         bio_wouldblock_error(bio);
         return false;
     }
     while (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery) &&
         bio->bi_iter.bi_sector < conf->reshape_progress &&
         bio->bi_iter.bi_sector + sectors > conf->reshape_progress) {
         allow_barrier(conf);
         if (bio->bi_opf & REQ_NOWAIT) {
             bio_wouldblock_error(bio);
             return false;
         }
         raid10_log(conf->mddev, "wait reshape");
         wait_event(conf->wait_barrier,
                conf->reshape_progress <= bio->bi_iter.bi_sector ||
                conf->reshape_progress >= bio->bi_iter.bi_sector +
                sectors);
         wait_barrier(conf, false);
     }
     return true;
 }
 
 static void raid10_read_request(struct mddev *mddev, struct bio *bio,
                 struct r10bio *r10_bio)
 {
     struct r10conf *conf = mddev->private;
     struct bio *read_bio;
     const enum req_op op = bio_op(bio);
     const blk_opf_t do_sync = bio->bi_opf & REQ_SYNC;
     int max_sectors;
     struct md_rdev *rdev;
     char b[BDEVNAME_SIZE];
     int slot = r10_bio->read_slot;
     struct md_rdev *err_rdev = NULL;
     gfp_t gfp = GFP_NOIO;
 
     if (slot >= 0 && r10_bio->devs[slot].rdev) {
         /*
          * This is an error retry, but we cannot
          * safely dereference the rdev in the r10_bio,
          * we must use the one in conf.
          * If it has already been disconnected (unlikely)
          * we lose the device name in error messages.
          */
         int disk;
         /*
          * As we are blocking raid10, it is a little safer to
          * use __GFP_HIGH.
          */
         gfp = GFP_NOIO | __GFP_HIGH;
 
         rcu_read_lock();
         disk = r10_bio->devs[slot].devnum;
         err_rdev = rcu_dereference(conf->mirrors[disk].rdev);
         if (err_rdev)
             snprintf(b, sizeof(b), "%pg", err_rdev->bdev);
         else {
             strcpy(b, "???");
             /* This never gets dereferenced */
             err_rdev = r10_bio->devs[slot].rdev;
         }
         rcu_read_unlock();
     }
 
     if (!regular_request_wait(mddev, conf, bio, r10_bio->sectors))
         return;
     rdev = read_balance(conf, r10_bio, &max_sectors);
     if (!rdev) {
         if (err_rdev) {
             pr_crit_ratelimited("md/raid10:%s: %s: unrecoverable I/O read error for block %llu\n",
                         mdname(mddev), b,
                         (unsigned long long)r10_bio->sector);
         }
         raid_end_bio_io(r10_bio);
         return;
     }
     if (err_rdev)
         pr_err_ratelimited("md/raid10:%s: %pg: redirecting sector %llu to another mirror\n",
                    mdname(mddev),
                    rdev->bdev,
                    (unsigned long long)r10_bio->sector);
     if (max_sectors < bio_sectors(bio)) {
         struct bio *split = bio_split(bio, max_sectors,
                           gfp, &conf->bio_split);
         bio_chain(split, bio);
         allow_barrier(conf);
         submit_bio_noacct(bio);
         wait_barrier(conf, false);
         bio = split;
         r10_bio->master_bio = bio;
         r10_bio->sectors = max_sectors;
     }
     slot = r10_bio->read_slot;
 
     if (blk_queue_io_stat(bio->bi_bdev->bd_disk->queue))
         r10_bio->start_time = bio_start_io_acct(bio);
     read_bio = bio_alloc_clone(rdev->bdev, bio, gfp, &mddev->bio_set);
 
     r10_bio->devs[slot].bio = read_bio;
     r10_bio->devs[slot].rdev = rdev;
 
     read_bio->bi_iter.bi_sector = r10_bio->devs[slot].addr +
         choose_data_offset(r10_bio, rdev);
     read_bio->bi_end_io = raid10_end_read_request;
     bio_set_op_attrs(read_bio, op, do_sync);
     if (test_bit(FailFast, &rdev->flags) &&
         test_bit(R10BIO_FailFast, &r10_bio->state))
             read_bio->bi_opf |= MD_FAILFAST;
     read_bio->bi_private = r10_bio;
 
     if (mddev->gendisk)
             trace_block_bio_remap(read_bio, disk_devt(mddev->gendisk),
                                   r10_bio->sector);
     submit_bio_noacct(read_bio);
     return;
 }
 
 static void raid10_write_one_disk(struct mddev *mddev, struct r10bio *r10_bio,
                   struct bio *bio, bool replacement,
                   int n_copy)
 {
     const enum req_op op = bio_op(bio);
     const blk_opf_t do_sync = bio->bi_opf & REQ_SYNC;
     const blk_opf_t do_fua = bio->bi_opf & REQ_FUA;
     unsigned long flags;
     struct blk_plug_cb *cb;
     struct raid1_plug_cb *plug = NULL;
     struct r10conf *conf = mddev->private;
     struct md_rdev *rdev;
     int devnum = r10_bio->devs[n_copy].devnum;
     struct bio *mbio;
 
     if (replacement) {
         rdev = conf->mirrors[devnum].replacement;
         if (rdev == NULL) {
             /* Replacement just got moved to main 'rdev' */
             smp_mb();
             rdev = conf->mirrors[devnum].rdev;
         }
     } else
         rdev = conf->mirrors[devnum].rdev;
 
     mbio = bio_alloc_clone(rdev->bdev, bio, GFP_NOIO, &mddev->bio_set);
     if (replacement)
         r10_bio->devs[n_copy].repl_bio = mbio;
     else
         r10_bio->devs[n_copy].bio = mbio;
 
     mbio->bi_iter.bi_sector = (r10_bio->devs[n_copy].addr +
                    choose_data_offset(r10_bio, rdev));
     mbio->bi_end_io = raid10_end_write_request;
     bio_set_op_attrs(mbio, op, do_sync | do_fua);
     if (!replacement && test_bit(FailFast,
                      &conf->mirrors[devnum].rdev->flags)
              && enough(conf, devnum))
         mbio->bi_opf |= MD_FAILFAST;
     mbio->bi_private = r10_bio;
 
     if (conf->mddev->gendisk)
         trace_block_bio_remap(mbio, disk_devt(conf->mddev->gendisk),
                       r10_bio->sector);
     /* flush_pending_writes() needs access to the rdev so...*/
     mbio->bi_bdev = (void *)rdev;
 
     atomic_inc(&r10_bio->remaining);
 
     cb = blk_check_plugged(raid10_unplug, mddev, sizeof(*plug));
     if (cb)
         plug = container_of(cb, struct raid1_plug_cb, cb);
     else
         plug = NULL;
     if (plug) {
         bio_list_add(&plug->pending, mbio);
     } else {
         spin_lock_irqsave(&conf->device_lock, flags);
         bio_list_add(&conf->pending_bio_list, mbio);
         spin_unlock_irqrestore(&conf->device_lock, flags);
         md_wakeup_thread(mddev->thread);
     }
 }
 
 static void wait_blocked_dev(struct mddev *mddev, struct r10bio *r10_bio)
 {
     int i;
     struct r10conf *conf = mddev->private;
     struct md_rdev *blocked_rdev;
 
 retry_wait:
     blocked_rdev = NULL;
     rcu_read_lock();
     for (i = 0; i < conf->copies; i++) {
         struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev);
         struct md_rdev *rrdev = rcu_dereference(
             conf->mirrors[i].replacement);
         if (rdev == rrdev)
             rrdev = NULL;
         if (rdev && unlikely(test_bit(Blocked, &rdev->flags))) {
             atomic_inc(&rdev->nr_pending);
             blocked_rdev = rdev;
             break;
         }
         if (rrdev && unlikely(test_bit(Blocked, &rrdev->flags))) {
             atomic_inc(&rrdev->nr_pending);
             blocked_rdev = rrdev;
             break;
         }
 
         if (rdev && test_bit(WriteErrorSeen, &rdev->flags)) {
             sector_t first_bad;
             sector_t dev_sector = r10_bio->devs[i].addr;
             int bad_sectors;
             int is_bad;
 
             /*
              * Discard request doesn't care the write result
              * so it doesn't need to wait blocked disk here.
              */
             if (!r10_bio->sectors)
                 continue;
 
             is_bad = is_badblock(rdev, dev_sector, r10_bio->sectors,
                          &first_bad, &bad_sectors);
             if (is_bad < 0) {
                 /*
                  * Mustn't write here until the bad block
                  * is acknowledged
                  */
                 atomic_inc(&rdev->nr_pending);
                 set_bit(BlockedBadBlocks, &rdev->flags);
                 blocked_rdev = rdev;
                 break;
             }
         }
     }
     rcu_read_unlock();
 
     if (unlikely(blocked_rdev)) {
         /* Have to wait for this device to get unblocked, then retry */
         allow_barrier(conf);
         raid10_log(conf->mddev, "%s wait rdev %d blocked",
                 __func__, blocked_rdev->raid_disk);
         md_wait_for_blocked_rdev(blocked_rdev, mddev);
         wait_barrier(conf, false);
         goto retry_wait;
     }
 }
 
 static void raid10_write_request(struct mddev *mddev, struct bio *bio,
                  struct r10bio *r10_bio)
 {
     struct r10conf *conf = mddev->private;
     int i;
     sector_t sectors;
     int max_sectors;
 
     if ((mddev_is_clustered(mddev) &&
          md_cluster_ops->area_resyncing(mddev, WRITE,
                         bio->bi_iter.bi_sector,
                         bio_end_sector(bio)))) {
         DEFINE_WAIT(w);
         /* Bail out if REQ_NOWAIT is set for the bio */
         if (bio->bi_opf & REQ_NOWAIT) {
             bio_wouldblock_error(bio);
             return;
         }
         for (;;) {
             prepare_to_wait(&conf->wait_barrier,
                     &w, TASK_IDLE);
             if (!md_cluster_ops->area_resyncing(mddev, WRITE,
                  bio->bi_iter.bi_sector, bio_end_sector(bio)))
                 break;
             schedule();
         }
         finish_wait(&conf->wait_barrier, &w);
     }
 
     sectors = r10_bio->sectors;
     if (!regular_request_wait(mddev, conf, bio, sectors))
         return;
     if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery) &&
         (mddev->reshape_backwards
          ? (bio->bi_iter.bi_sector < conf->reshape_safe &&
         bio->bi_iter.bi_sector + sectors > conf->reshape_progress)
          : (bio->bi_iter.bi_sector + sectors > conf->reshape_safe &&
         bio->bi_iter.bi_sector < conf->reshape_progress))) {
         /* Need to update reshape_position in metadata */
         mddev->reshape_position = conf->reshape_progress;
         set_mask_bits(&mddev->sb_flags, 0,
                   BIT(MD_SB_CHANGE_DEVS) | BIT(MD_SB_CHANGE_PENDING));
         md_wakeup_thread(mddev->thread);
         if (bio->bi_opf & REQ_NOWAIT) {
             allow_barrier(conf);
             bio_wouldblock_error(bio);
             return;
         }
         raid10_log(conf->mddev, "wait reshape metadata");
         wait_event(mddev->sb_wait,
                !test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags));
 
         conf->reshape_safe = mddev->reshape_position;
     }
 
     /* 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 to those blocks.  This potentially requires several
      * writes to write around the bad blocks.  Each set of writes
      * gets its own r10_bio with a set of bios attached.
      */
 
     r10_bio->read_slot = -1; /* make sure repl_bio gets freed */
     raid10_find_phys(conf, r10_bio);
 
     wait_blocked_dev(mddev, r10_bio);
 
     rcu_read_lock();
     max_sectors = r10_bio->sectors;
 
     for (i = 0;  i < conf->copies; i++) {
         int d = r10_bio->devs[i].devnum;
         struct md_rdev *rdev = rcu_dereference(conf->mirrors[d].rdev);
         struct md_rdev *rrdev = rcu_dereference(
             conf->mirrors[d].replacement);
         if (rdev == rrdev)
             rrdev = NULL;
         if (rdev && (test_bit(Faulty, &rdev->flags)))
             rdev = NULL;
         if (rrdev && (test_bit(Faulty, &rrdev->flags)))
             rrdev = NULL;
 
         r10_bio->devs[i].bio = NULL;
         r10_bio->devs[i].repl_bio = NULL;
 
         if (!rdev && !rrdev) {
             set_bit(R10BIO_Degraded, &r10_bio->state);
             continue;
         }
         if (rdev && test_bit(WriteErrorSeen, &rdev->flags)) {
             sector_t first_bad;
             sector_t dev_sector = r10_bio->devs[i].addr;
             int bad_sectors;
             int is_bad;
 
             is_bad = is_badblock(rdev, dev_sector, max_sectors,
                          &first_bad, &bad_sectors);
             if (is_bad && first_bad <= dev_sector) {
                 /* Cannot write here at all */
                 bad_sectors -= (dev_sector - first_bad);
                 if (bad_sectors < max_sectors)
                     /* Mustn't write more than bad_sectors
                      * to other devices yet
                      */
                     max_sectors = bad_sectors;
                 /* We don't set R10BIO_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 - dev_sector;
                 if (good_sectors < max_sectors)
                     max_sectors = good_sectors;
             }
         }
         if (rdev) {
             r10_bio->devs[i].bio = bio;
             atomic_inc(&rdev->nr_pending);
         }
         if (rrdev) {
             r10_bio->devs[i].repl_bio = bio;
             atomic_inc(&rrdev->nr_pending);
         }
     }
     rcu_read_unlock();
 
     if (max_sectors < r10_bio->sectors)
         r10_bio->sectors = max_sectors;
 
     if (r10_bio->sectors < bio_sectors(bio)) {
         struct bio *split = bio_split(bio, r10_bio->sectors,
                           GFP_NOIO, &conf->bio_split);
         bio_chain(split, bio);
         allow_barrier(conf);
         submit_bio_noacct(bio);
         wait_barrier(conf, false);
         bio = split;
         r10_bio->master_bio = bio;
     }
 
     if (blk_queue_io_stat(bio->bi_bdev->bd_disk->queue))
         r10_bio->start_time = bio_start_io_acct(bio);
     atomic_set(&r10_bio->remaining, 1);
     md_bitmap_startwrite(mddev->bitmap, r10_bio->sector, r10_bio->sectors, 0);
 
     for (i = 0; i < conf->copies; i++) {
         if (r10_bio->devs[i].bio)
             raid10_write_one_disk(mddev, r10_bio, bio, false, i);
         if (r10_bio->devs[i].repl_bio)
             raid10_write_one_disk(mddev, r10_bio, bio, true, i);
     }
     one_write_done(r10_bio);
 }
 
 static void __make_request(struct mddev *mddev, struct bio *bio, int sectors)
 {
     struct r10conf *conf = mddev->private;
     struct r10bio *r10_bio;
 
     r10_bio = mempool_alloc(&conf->r10bio_pool, GFP_NOIO);
 
     r10_bio->master_bio = bio;
     r10_bio->sectors = sectors;
 
     r10_bio->mddev = mddev;
     r10_bio->sector = bio->bi_iter.bi_sector;
     r10_bio->state = 0;
     r10_bio->read_slot = -1;
     memset(r10_bio->devs, 0, sizeof(r10_bio->devs[0]) *
             conf->geo.raid_disks);
 
     if (bio_data_dir(bio) == READ)
         raid10_read_request(mddev, bio, r10_bio);
     else
         raid10_write_request(mddev, bio, r10_bio);
 }
 
 static void raid_end_discard_bio(struct r10bio *r10bio)
 {
     struct r10conf *conf = r10bio->mddev->private;
     struct r10bio *first_r10bio;
 
     while (atomic_dec_and_test(&r10bio->remaining)) {
 
         allow_barrier(conf);
 
         if (!test_bit(R10BIO_Discard, &r10bio->state)) {
             first_r10bio = (struct r10bio *)r10bio->master_bio;
             free_r10bio(r10bio);
             r10bio = first_r10bio;
         } else {
             md_write_end(r10bio->mddev);
             bio_endio(r10bio->master_bio);
             free_r10bio(r10bio);
             break;
         }
     }
 }
 
 static void raid10_end_discard_request(struct bio *bio)
 {
     struct r10bio *r10_bio = bio->bi_private;
     struct r10conf *conf = r10_bio->mddev->private;
     struct md_rdev *rdev = NULL;
     int dev;
     int slot, repl;
 
     /*
      * We don't care the return value of discard bio
      */
     if (!test_bit(R10BIO_Uptodate, &r10_bio->state))
         set_bit(R10BIO_Uptodate, &r10_bio->state);
 
     dev = find_bio_disk(conf, r10_bio, bio, &slot, &repl);
     if (repl)
         rdev = conf->mirrors[dev].replacement;
     if (!rdev) {
         /*
          * raid10_remove_disk uses smp_mb to make sure rdev is set to
          * replacement before setting replacement to NULL. It can read
          * rdev first without barrier protect even replacment is NULL
          */
         smp_rmb();
         rdev = conf->mirrors[dev].rdev;
     }
 
     raid_end_discard_bio(r10_bio);
     rdev_dec_pending(rdev, conf->mddev);
 }
 
 /*
  * There are some limitations to handle discard bio
  * 1st, the discard size is bigger than stripe_size*2.
  * 2st, if the discard bio spans reshape progress, we use the old way to
  * handle discard bio
  */
 static int raid10_handle_discard(struct mddev *mddev, struct bio *bio)
 {
     struct r10conf *conf = mddev->private;
     struct geom *geo = &conf->geo;
     int far_copies = geo->far_copies;
     bool first_copy = true;
     struct r10bio *r10_bio, *first_r10bio;
     struct bio *split;
     int disk;
     sector_t chunk;
     unsigned int stripe_size;
     unsigned int stripe_data_disks;
     sector_t split_size;
     sector_t bio_start, bio_end;
     sector_t first_stripe_index, last_stripe_index;
     sector_t start_disk_offset;
     unsigned int start_disk_index;
     sector_t end_disk_offset;
     unsigned int end_disk_index;
     unsigned int remainder;
 
     if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery))
         return -EAGAIN;
 
     if (WARN_ON_ONCE(bio->bi_opf & REQ_NOWAIT)) {
         bio_wouldblock_error(bio);
         return 0;
     }
     wait_barrier(conf, false);
 
     /*
      * Check reshape again to avoid reshape happens after checking
      * MD_RECOVERY_RESHAPE and before wait_barrier
      */
     if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery))
         goto out;
 
     if (geo->near_copies)
         stripe_data_disks = geo->raid_disks / geo->near_copies +
                     geo->raid_disks % geo->near_copies;
     else
         stripe_data_disks = geo->raid_disks;
 
     stripe_size = stripe_data_disks << geo->chunk_shift;
 
     bio_start = bio->bi_iter.bi_sector;
     bio_end = bio_end_sector(bio);
 
     /*
      * Maybe one discard bio is smaller than strip size or across one
      * stripe and discard region is larger than one stripe size. For far
      * offset layout, if the discard region is not aligned with stripe
      * size, there is hole when we submit discard bio to member disk.
      * For simplicity, we only handle discard bio which discard region
      * is bigger than stripe_size * 2
      */
     if (bio_sectors(bio) < stripe_size*2)
         goto out;
 
     /*
      * Keep bio aligned with strip size.
      */
     div_u64_rem(bio_start, stripe_size, &remainder);
     if (remainder) {
         split_size = stripe_size - remainder;
         split = bio_split(bio, split_size, GFP_NOIO, &conf->bio_split);
         bio_chain(split, bio);
         allow_barrier(conf);
         /* Resend the fist split part */
         submit_bio_noacct(split);
         wait_barrier(conf, false);
     }
     div_u64_rem(bio_end, stripe_size, &remainder);
     if (remainder) {
         split_size = bio_sectors(bio) - remainder;
         split = bio_split(bio, split_size, GFP_NOIO, &conf->bio_split);
         bio_chain(split, bio);
         allow_barrier(conf);
         /* Resend the second split part */
         submit_bio_noacct(bio);
         bio = split;
         wait_barrier(conf, false);
     }
 
     bio_start = bio->bi_iter.bi_sector;
     bio_end = bio_end_sector(bio);
 
     /*
      * Raid10 uses chunk as the unit to store data. It's similar like raid0.
      * One stripe contains the chunks from all member disk (one chunk from
      * one disk at the same HBA address). For layout detail, see 'man md 4'
      */
     chunk = bio_start >> geo->chunk_shift;
     chunk *= geo->near_copies;
     first_stripe_index = chunk;
     start_disk_index = sector_div(first_stripe_index, geo->raid_disks);
     if (geo->far_offset)
         first_stripe_index *= geo->far_copies;
     start_disk_offset = (bio_start & geo->chunk_mask) +
                 (first_stripe_index << geo->chunk_shift);
 
     chunk = bio_end >> geo->chunk_shift;
     chunk *= geo->near_copies;
     last_stripe_index = chunk;
     end_disk_index = sector_div(last_stripe_index, geo->raid_disks);
     if (geo->far_offset)
         last_stripe_index *= geo->far_copies;
     end_disk_offset = (bio_end & geo->chunk_mask) +
                 (last_stripe_index << geo->chunk_shift);
 
 retry_discard:
     r10_bio = mempool_alloc(&conf->r10bio_pool, GFP_NOIO);
     r10_bio->mddev = mddev;
     r10_bio->state = 0;
     r10_bio->sectors = 0;
     memset(r10_bio->devs, 0, sizeof(r10_bio->devs[0]) * geo->raid_disks);
     wait_blocked_dev(mddev, r10_bio);
 
     /*
      * For far layout it needs more than one r10bio to cover all regions.
      * Inspired by raid10_sync_request, we can use the first r10bio->master_bio
      * to record the discard bio. Other r10bio->master_bio record the first
      * r10bio. The first r10bio only release after all other r10bios finish.
      * The discard bio returns only first r10bio finishes
      */
     if (first_copy) {
         r10_bio->master_bio = bio;
         set_bit(R10BIO_Discard, &r10_bio->state);
         first_copy = false;
         first_r10bio = r10_bio;
     } else
         r10_bio->master_bio = (struct bio *)first_r10bio;
 
     /*
      * first select target devices under rcu_lock and
      * inc refcount on their rdev.  Record them by setting
      * bios[x] to bio
      */
     rcu_read_lock();
     for (disk = 0; disk < geo->raid_disks; disk++) {
         struct md_rdev *rdev = rcu_dereference(conf->mirrors[disk].rdev);
         struct md_rdev *rrdev = rcu_dereference(
             conf->mirrors[disk].replacement);
 
         r10_bio->devs[disk].bio = NULL;
         r10_bio->devs[disk].repl_bio = NULL;
 
         if (rdev && (test_bit(Faulty, &rdev->flags)))
             rdev = NULL;
         if (rrdev && (test_bit(Faulty, &rrdev->flags)))
             rrdev = NULL;
         if (!rdev && !rrdev)
             continue;
 
         if (rdev) {
             r10_bio->devs[disk].bio = bio;
             atomic_inc(&rdev->nr_pending);
         }
         if (rrdev) {
             r10_bio->devs[disk].repl_bio = bio;
             atomic_inc(&rrdev->nr_pending);
         }
     }
     rcu_read_unlock();
 
     atomic_set(&r10_bio->remaining, 1);
     for (disk = 0; disk < geo->raid_disks; disk++) {
         sector_t dev_start, dev_end;
         struct bio *mbio, *rbio = NULL;
 
         /*
          * Now start to calculate the start and end address for each disk.
          * The space between dev_start and dev_end is the discard region.
          *
          * For dev_start, it needs to consider three conditions:
          * 1st, the disk is before start_disk, you can imagine the disk in
          * the next stripe. So the dev_start is the start address of next
          * stripe.
          * 2st, the disk is after start_disk, it means the disk is at the
          * same stripe of first disk
          * 3st, the first disk itself, we can use start_disk_offset directly
          */
         if (disk < start_disk_index)
             dev_start = (first_stripe_index + 1) * mddev->chunk_sectors;
         else if (disk > start_disk_index)
             dev_start = first_stripe_index * mddev->chunk_sectors;
         else
             dev_start = start_disk_offset;
 
         if (disk < end_disk_index)
             dev_end = (last_stripe_index + 1) * mddev->chunk_sectors;
         else if (disk > end_disk_index)
             dev_end = last_stripe_index * mddev->chunk_sectors;
         else
             dev_end = end_disk_offset;
 
         /*
          * It only handles discard bio which size is >= stripe size, so
          * dev_end > dev_start all the time.
          * It doesn't need to use rcu lock to get rdev here. We already
          * add rdev->nr_pending in the first loop.
          */
         if (r10_bio->devs[disk].bio) {
             struct md_rdev *rdev = conf->mirrors[disk].rdev;
             mbio = bio_alloc_clone(bio->bi_bdev, bio, GFP_NOIO,
                            &mddev->bio_set);
             mbio->bi_end_io = raid10_end_discard_request;
             mbio->bi_private = r10_bio;
             r10_bio->devs[disk].bio = mbio;
             r10_bio->devs[disk].devnum = disk;
             atomic_inc(&r10_bio->remaining);
             md_submit_discard_bio(mddev, rdev, mbio,
                     dev_start + choose_data_offset(r10_bio, rdev),
                     dev_end - dev_start);
             bio_endio(mbio);
         }
         if (r10_bio->devs[disk].repl_bio) {
             struct md_rdev *rrdev = conf->mirrors[disk].replacement;
             rbio = bio_alloc_clone(bio->bi_bdev, bio, GFP_NOIO,
                            &mddev->bio_set);
             rbio->bi_end_io = raid10_end_discard_request;
             rbio->bi_private = r10_bio;
             r10_bio->devs[disk].repl_bio = rbio;
             r10_bio->devs[disk].devnum = disk;
             atomic_inc(&r10_bio->remaining);
             md_submit_discard_bio(mddev, rrdev, rbio,
                     dev_start + choose_data_offset(r10_bio, rrdev),
                     dev_end - dev_start);
             bio_endio(rbio);
         }
     }
 
     if (!geo->far_offset && --far_copies) {
         first_stripe_index += geo->stride >> geo->chunk_shift;
         start_disk_offset += geo->stride;
         last_stripe_index += geo->stride >> geo->chunk_shift;
         end_disk_offset += geo->stride;
         atomic_inc(&first_r10bio->remaining);
         raid_end_discard_bio(r10_bio);
         wait_barrier(conf, false);
         goto retry_discard;
     }
 
     raid_end_discard_bio(r10_bio);
 
     return 0;
 out:
     allow_barrier(conf);
     return -EAGAIN;
 }
 
 static bool raid10_make_request(struct mddev *mddev, struct bio *bio)
 {
     struct r10conf *conf = mddev->private;
     sector_t chunk_mask = (conf->geo.chunk_mask & conf->prev.chunk_mask);
     int chunk_sects = chunk_mask + 1;
     int sectors = bio_sectors(bio);
 
     if (unlikely(bio->bi_opf & REQ_PREFLUSH)
         && md_flush_request(mddev, bio))
         return true;
 
     if (!md_write_start(mddev, bio))
         return false;
 
     if (unlikely(bio_op(bio) == REQ_OP_DISCARD))
         if (!raid10_handle_discard(mddev, bio))
             return true;
 
     /*
      * If this request crosses a chunk boundary, we need to split
      * it.
      */
     if (unlikely((bio->bi_iter.bi_sector & chunk_mask) +
              sectors > chunk_sects
              && (conf->geo.near_copies < conf->geo.raid_disks
              || conf->prev.near_copies <
              conf->prev.raid_disks)))
         sectors = chunk_sects -
             (bio->bi_iter.bi_sector &
              (chunk_sects - 1));
     __make_request(mddev, bio, sectors);
 
     /* In case raid10d snuck in to freeze_array */
     wake_up(&conf->wait_barrier);
     return true;
 }
 
 static void raid10_status(struct seq_file *seq, struct mddev *mddev)
 {
     struct r10conf *conf = mddev->private;
     int i;
 
     if (conf->geo.near_copies < conf->geo.raid_disks)
         seq_printf(seq, " %dK chunks", mddev->chunk_sectors / 2);
     if (conf->geo.near_copies > 1)
         seq_printf(seq, " %d near-copies", conf->geo.near_copies);
     if (conf->geo.far_copies > 1) {
         if (conf->geo.far_offset)
             seq_printf(seq, " %d offset-copies", conf->geo.far_copies);
         else
             seq_printf(seq, " %d far-copies", conf->geo.far_copies);
         if (conf->geo.far_set_size != conf->geo.raid_disks)
             seq_printf(seq, " %d devices per set", conf->geo.far_set_size);
     }
     seq_printf(seq, " [%d/%d] [", conf->geo.raid_disks,
                     conf->geo.raid_disks - mddev->degraded);
     rcu_read_lock();
     for (i = 0; i < conf->geo.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, "]");
 }
 
 /* check if there are enough drives for
  * every block to appear on atleast one.
  * Don't consider the device numbered 'ignore'
  * as we might be about to remove it.
  */
 static int _enough(struct r10conf *conf, int previous, int ignore)
 {
     int first = 0;
     int has_enough = 0;
     int disks, ncopies;
     if (previous) {
         disks = conf->prev.raid_disks;
         ncopies = conf->prev.near_copies;
     } else {
         disks = conf->geo.raid_disks;
         ncopies = conf->geo.near_copies;
     }
 
     rcu_read_lock();
     do {
         int n = conf->copies;
         int cnt = 0;
         int this = first;
         while (n--) {
             struct md_rdev *rdev;
             if (this != ignore &&
                 (rdev = rcu_dereference(conf->mirrors[this].rdev)) &&
                 test_bit(In_sync, &rdev->flags))
                 cnt++;
             this = (this+1) % disks;
         }
         if (cnt == 0)
             goto out;
         first = (first + ncopies) % disks;
     } while (first != 0);
     has_enough = 1;
 out:
     rcu_read_unlock();
     return has_enough;
 }
 
 static int enough(struct r10conf *conf, int ignore)
 {
     /* when calling 'enough', both 'prev' and 'geo' must
      * be stable.
      * This is ensured if ->reconfig_mutex or ->device_lock
      * is held.
      */
     return _enough(conf, 0, ignore) &&
         _enough(conf, 1, ignore);
 }
 
 /**
  * raid10_error() - RAID10 error handler.
  * @mddev: affected md device.
  * @rdev: member device to fail.
  *
  * The routine acknowledges &rdev failure and determines new @mddev state.
  * If it failed, then:
  *  - &MD_BROKEN flag is set in &mddev->flags.
  * Otherwise, it must be degraded:
  *  - recovery is interrupted.
  *  - &mddev->degraded is bumped.
 
  * @rdev is marked as &Faulty excluding case when array is failed and
  * &mddev->fail_last_dev is off.
  */
 static void raid10_error(struct mddev *mddev, struct md_rdev *rdev)
 {
     struct r10conf *conf = mddev->private;
     unsigned long flags;
 
     spin_lock_irqsave(&conf->device_lock, flags);
 
     if (test_bit(In_sync, &rdev->flags) && !enough(conf, rdev->raid_disk)) {
         set_bit(MD_BROKEN, &mddev->flags);
 
         if (!mddev->fail_last_dev) {
             spin_unlock_irqrestore(&conf->device_lock, flags);
             return;
         }
     }
     if (test_and_clear_bit(In_sync, &rdev->flags))
         mddev->degraded++;
 
     set_bit(MD_RECOVERY_INTR, &mddev->recovery);
     set_bit(Blocked, &rdev->flags);
     set_bit(Faulty, &rdev->flags);
     set_mask_bits(&mddev->sb_flags, 0,
               BIT(MD_SB_CHANGE_DEVS) | BIT(MD_SB_CHANGE_PENDING));
     spin_unlock_irqrestore(&conf->device_lock, flags);
     pr_crit("md/raid10:%s: Disk failure on %pg, disabling device.\n"
         "md/raid10:%s: Operation continuing on %d devices.\n",
         mdname(mddev), rdev->bdev,
         mdname(mddev), conf->geo.raid_disks - mddev->degraded);
 }
 
 static void print_conf(struct r10conf *conf)
 {
     int i;
     struct md_rdev *rdev;
 
     pr_debug("RAID10 conf printout:\n");
     if (!conf) {
         pr_debug("(!conf)\n");
         return;
     }
     pr_debug(" --- wd:%d rd:%d\n", conf->geo.raid_disks - conf->mddev->degraded,
          conf->geo.raid_disks);
 
     /* This is only called with ->reconfix_mutex held, so
      * rcu protection of rdev is not needed */
     for (i = 0; i < conf->geo.raid_disks; i++) {
         rdev = conf->mirrors[i].rdev;
         if (rdev)
             pr_debug(" disk %d, wo:%d, o:%d, dev:%pg\n",
                  i, !test_bit(In_sync, &rdev->flags),
                  !test_bit(Faulty, &rdev->flags),
                  rdev->bdev);
     }
 }
 
 static void close_sync(struct r10conf *conf)
 {
     wait_barrier(conf, false);
     allow_barrier(conf);
 
     mempool_exit(&conf->r10buf_pool);
 }
 
 static int raid10_spare_active(struct mddev *mddev)
 {
     int i;
     struct r10conf *conf = mddev->private;
     struct raid10_info *tmp;
     int count = 0;
     unsigned long flags;
 
     /*
      * Find all non-in_sync disks within the RAID10 configuration
      * and mark them in_sync
      */
     for (i = 0; i < conf->geo.raid_disks; i++) {
         tmp = conf->mirrors + i;
         if (tmp->replacement
             && tmp->replacement->recovery_offset == MaxSector
             && !test_bit(Faulty, &tmp->replacement->flags)
             && !test_and_set_bit(In_sync, &tmp->replacement->flags)) {
             /* Replacement has just become active */
             if (!tmp->rdev
                 || !test_and_clear_bit(In_sync, &tmp->rdev->flags))
                 count++;
             if (tmp->rdev) {
                 /* Replaced device not technically faulty,
                  * but we need to be sure it gets removed
                  * and never re-added.
                  */
                 set_bit(Faulty, &tmp->rdev->flags);
                 sysfs_notify_dirent_safe(
                     tmp->rdev->sysfs_state);
             }
             sysfs_notify_dirent_safe(tmp->replacement->sysfs_state);
         } else if (tmp->rdev
                && tmp->rdev->recovery_offset == MaxSector
                && !test_bit(Faulty, &tmp->rdev->flags)
                && !test_and_set_bit(In_sync, &tmp->rdev->flags)) {
             count++;
             sysfs_notify_dirent_safe(tmp->rdev->sysfs_state);
         }
     }
     spin_lock_irqsave(&conf->device_lock, flags);
     mddev->degraded -= count;
     spin_unlock_irqrestore(&conf->device_lock, flags);
 
     print_conf(conf);
     return count;
 }
 
 static int raid10_add_disk(struct mddev *mddev, struct md_rdev *rdev)
 {
     struct r10conf *conf = mddev->private;
     int err = -EEXIST;
     int mirror;
     int first = 0;
     int last = conf->geo.raid_disks - 1;
 
     if (mddev->recovery_cp < MaxSector)
         /* only hot-add to in-sync arrays, as recovery is
          * very different from resync
          */
         return -EBUSY;
     if (rdev->saved_raid_disk < 0 && !_enough(conf, 1, -1))
         return -EINVAL;
 
     if (md_integrity_add_rdev(rdev, mddev))
         return -ENXIO;
 
     if (rdev->raid_disk >= 0)
         first = last = rdev->raid_disk;
 
     if (rdev->saved_raid_disk >= first &&
         rdev->saved_raid_disk < conf->geo.raid_disks &&
         conf->mirrors[rdev->saved_raid_disk].rdev == NULL)
         mirror = rdev->saved_raid_disk;
     else
         mirror = first;
     for ( ; mirror <= last ; mirror++) {
         struct raid10_info *p = &conf->mirrors[mirror];
         if (p->recovery_disabled == mddev->recovery_disabled)
             continue;
         if (p->rdev) {
             if (!test_bit(WantReplacement, &p->rdev->flags) ||
                 p->replacement != NULL)
                 continue;
             clear_bit(In_sync, &rdev->flags);
             set_bit(Replacement, &rdev->flags);
             rdev->raid_disk = mirror;
             err = 0;
             if (mddev->gendisk)
                 disk_stack_limits(mddev->gendisk, rdev->bdev,
                           rdev->data_offset << 9);
             conf->fullsync = 1;
             rcu_assign_pointer(p->replacement, rdev);
             break;
         }
 
         if (mddev->gendisk)
             disk_stack_limits(mddev->gendisk, rdev->bdev,
                       rdev->data_offset << 9);
 
         p->head_position = 0;
         p->recovery_disabled = mddev->recovery_disabled - 1;
         rdev->raid_disk = mirror;
         err = 0;
         if (rdev->saved_raid_disk != mirror)
             conf->fullsync = 1;
         rcu_assign_pointer(p->rdev, rdev);
         break;
     }
 
     print_conf(conf);
     return err;
 }
 
 static int raid10_remove_disk(struct mddev *mddev, struct md_rdev *rdev)
 {
     struct r10conf *conf = mddev->private;
     int err = 0;
     int number = rdev->raid_disk;
     struct md_rdev **rdevp;
     struct raid10_info *p;
 
     print_conf(conf);
     if (unlikely(number >= mddev->raid_disks))
         return 0;
     p = conf->mirrors + number;
     if (rdev == p->rdev)
         rdevp = &p->rdev;
     else if (rdev == p->replacement)
         rdevp = &p->replacement;
     else
         return 0;
 
     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 != p->recovery_disabled &&
         (!p->replacement || p->replacement == rdev) &&
         number < conf->geo.raid_disks &&
         enough(conf, -1)) {
         err = -EBUSY;
         goto abort;
     }
     *rdevp = NULL;
     if (!test_bit(RemoveSynchronized, &rdev->flags)) {
         synchronize_rcu();
         if (atomic_read(&rdev->nr_pending)) {
             /* lost the race, try later */
             err = -EBUSY;
             *rdevp = rdev;
             goto abort;
         }
     }
     if (p->replacement) {
         /* We must have just cleared 'rdev' */
         p->rdev = p->replacement;
         clear_bit(Replacement, &p->replacement->flags);
         smp_mb(); /* Make sure other CPUs may see both as identical
                * but will never see neither -- if they are careful.
                */
         p->replacement = NULL;
     }
 
     clear_bit(WantReplacement, &rdev->flags);
     err = md_integrity_register(mddev);
 
 abort:
 
     print_conf(conf);
     return err;
 }
 
 static void __end_sync_read(struct r10bio *r10_bio, struct bio *bio, int d)
 {
     struct r10conf *conf = r10_bio->mddev->private;
 
     if (!bio->bi_status)
         set_bit(R10BIO_Uptodate, &r10_bio->state);
     else
         /* The write handler will notice the lack of
          * R10BIO_Uptodate and record any errors etc
          */
         atomic_add(r10_bio->sectors,
                &conf->mirrors[d].rdev->corrected_errors);
 
     /* for reconstruct, we always reschedule after a read.
      * for resync, only after all reads
      */
     rdev_dec_pending(conf->mirrors[d].rdev, conf->mddev);
     if (test_bit(R10BIO_IsRecover, &r10_bio->state) ||
         atomic_dec_and_test(&r10_bio->remaining)) {
         /* we have read all the blocks,
          * do the comparison in process context in raid10d
          */
         reschedule_retry(r10_bio);
     }
 }
 
 static void end_sync_read(struct bio *bio)
 {
     struct r10bio *r10_bio = get_resync_r10bio(bio);
     struct r10conf *conf = r10_bio->mddev->private;
     int d = find_bio_disk(conf, r10_bio, bio, NULL, NULL);
 
     __end_sync_read(r10_bio, bio, d);
 }
 
 static void end_reshape_read(struct bio *bio)
 {
     /* reshape read bio isn't allocated from r10buf_pool */
     struct r10bio *r10_bio = bio->bi_private;
 
     __end_sync_read(r10_bio, bio, r10_bio->read_slot);
 }
 
 static void end_sync_request(struct r10bio *r10_bio)
 {
     struct mddev *mddev = r10_bio->mddev;
 
     while (atomic_dec_and_test(&r10_bio->remaining)) {
         if (r10_bio->master_bio == NULL) {
             /* the primary of several recovery bios */
             sector_t s = r10_bio->sectors;
             if (test_bit(R10BIO_MadeGood, &r10_bio->state) ||
                 test_bit(R10BIO_WriteError, &r10_bio->state))
                 reschedule_retry(r10_bio);
             else
                 put_buf(r10_bio);
             md_done_sync(mddev, s, 1);
             break;
         } else {
             struct r10bio *r10_bio2 = (struct r10bio *)r10_bio->master_bio;
             if (test_bit(R10BIO_MadeGood, &r10_bio->state) ||
                 test_bit(R10BIO_WriteError, &r10_bio->state))
                 reschedule_retry(r10_bio);
             else
                 put_buf(r10_bio);
             r10_bio = r10_bio2;
         }
     }
 }
 
 static void end_sync_write(struct bio *bio)
 {
     struct r10bio *r10_bio = get_resync_r10bio(bio);
     struct mddev *mddev = r10_bio->mddev;
     struct r10conf *conf = mddev->private;
     int d;
     sector_t first_bad;
     int bad_sectors;
     int slot;
     int repl;
     struct md_rdev *rdev = NULL;
 
     d = find_bio_disk(conf, r10_bio, bio, &slot, &repl);
     if (repl)
         rdev = conf->mirrors[d].replacement;
     else
         rdev = conf->mirrors[d].rdev;
 
     if (bio->bi_status) {
         if (repl)
             md_error(mddev, rdev);
         else {
             set_bit(WriteErrorSeen, &rdev->flags);
             if (!test_and_set_bit(WantReplacement, &rdev->flags))
                 set_bit(MD_RECOVERY_NEEDED,
                     &rdev->mddev->recovery);
             set_bit(R10BIO_WriteError, &r10_bio->state);
         }
     } else if (is_badblock(rdev,
                  r10_bio->devs[slot].addr,
                  r10_bio->sectors,
                  &first_bad, &bad_sectors))
         set_bit(R10BIO_MadeGood, &r10_bio->state);
 
     rdev_dec_pending(rdev, mddev);
 
     end_sync_request(r10_bio);
 }
 
 /*
  * Note: sync and recover and handled very differently for raid10
  * This code is for resync.
  * For resync, we read through virtual addresses and read all blocks.
  * If there is any error, we schedule a write.  The lowest numbered
  * drive is authoritative.
  * However requests come for physical address, so we need to map.
  * For every physical address there are raid_disks/copies virtual addresses,
  * which is always are least one, but is not necessarly an integer.
  * This means that a physical address can span multiple chunks, so we may
  * have to submit multiple io requests for a single sync request.
  */
 /*
  * We check if all blocks are in-sync and only write to blocks that
  * aren't in sync
  */
 static void sync_request_write(struct mddev *mddev, struct r10bio *r10_bio)
 {
     struct r10conf *conf = mddev->private;
     int i, first;
     struct bio *tbio, *fbio;
     int vcnt;
     struct page **tpages, **fpages;
 
     atomic_set(&r10_bio->remaining, 1);
 
     /* find the first device with a block */
     for (i=0; i<conf->copies; i++)
         if (!r10_bio->devs[i].bio->bi_status)
             break;
 
     if (i == conf->copies)
         goto done;
 
     first = i;
     fbio = r10_bio->devs[i].bio;
     fbio->bi_iter.bi_size = r10_bio->sectors << 9;
     fbio->bi_iter.bi_idx = 0;
     fpages = get_resync_pages(fbio)->pages;
 
     vcnt = (r10_bio->sectors + (PAGE_SIZE >> 9) - 1) >> (PAGE_SHIFT - 9);
     /* now find blocks with errors */
     for (i=0 ; i < conf->copies ; i++) {
         int  j, d;
         struct md_rdev *rdev;
         struct resync_pages *rp;
 
         tbio = r10_bio->devs[i].bio;
 
         if (tbio->bi_end_io != end_sync_read)
             continue;
         if (i == first)
             continue;
 
         tpages = get_resync_pages(tbio)->pages;
         d = r10_bio->devs[i].devnum;
         rdev = conf->mirrors[d].rdev;
         if (!r10_bio->devs[i].bio->bi_status) {
             /* We know that the bi_io_vec layout is the same for
              * both 'first' and 'i', so we just compare them.
              * All vec entries are PAGE_SIZE;
              */
             int sectors = r10_bio->sectors;
             for (j = 0; j < vcnt; j++) {
                 int len = PAGE_SIZE;
                 if (sectors < (len / 512))
                     len = sectors * 512;
                 if (memcmp(page_address(fpages[j]),
                        page_address(tpages[j]),
                        len))
                     break;
                 sectors -= len/512;
             }
             if (j == vcnt)
                 continue;
             atomic64_add(r10_bio->sectors, &mddev->resync_mismatches);
             if (test_bit(MD_RECOVERY_CHECK, &mddev->recovery))
                 /* Don't fix anything. */
                 continue;
         } else if (test_bit(FailFast, &rdev->flags)) {
             /* Just give up on this device */
             md_error(rdev->mddev, rdev);
             continue;
         }
         /* Ok, we need to write this bio, either to correct an
          * inconsistency or to correct an unreadable block.
          * First we need to fixup bv_offset, bv_len and
          * bi_vecs, as the read request might have corrupted these
          */
         rp = get_resync_pages(tbio);
         bio_reset(tbio, conf->mirrors[d].rdev->bdev, REQ_OP_WRITE);
 
         md_bio_reset_resync_pages(tbio, rp, fbio->bi_iter.bi_size);
 
         rp->raid_bio = r10_bio;
         tbio->bi_private = rp;
         tbio->bi_iter.bi_sector = r10_bio->devs[i].addr;
         tbio->bi_end_io = end_sync_write;
 
         bio_copy_data(tbio, fbio);
 
         atomic_inc(&conf->mirrors[d].rdev->nr_pending);
         atomic_inc(&r10_bio->remaining);
         md_sync_acct(conf->mirrors[d].rdev->bdev, bio_sectors(tbio));
 
         if (test_bit(FailFast, &conf->mirrors[d].rdev->flags))
             tbio->bi_opf |= MD_FAILFAST;
         tbio->bi_iter.bi_sector += conf->mirrors[d].rdev->data_offset;
         submit_bio_noacct(tbio);
     }
 
     /* Now write out to any replacement devices
      * that are active
      */
     for (i = 0; i < conf->copies; i++) {
         int d;
 
         tbio = r10_bio->devs[i].repl_bio;
         if (!tbio || !tbio->bi_end_io)
             continue;
         if (r10_bio->devs[i].bio->bi_end_io != end_sync_write
             && r10_bio->devs[i].bio != fbio)
             bio_copy_data(tbio, fbio);
         d = r10_bio->devs[i].devnum;
         atomic_inc(&r10_bio->remaining);
         md_sync_acct(conf->mirrors[d].replacement->bdev,
                  bio_sectors(tbio));
         submit_bio_noacct(tbio);
     }
 
 done:
     if (atomic_dec_and_test(&r10_bio->remaining)) {
         md_done_sync(mddev, r10_bio->sectors, 1);
         put_buf(r10_bio);
     }
 }
 
 /*
  * Now for the recovery code.
  * Recovery happens across physical sectors.
  * We recover all non-is_sync drives by finding the virtual address of
  * each, and then choose a working drive that also has that virt address.
  * There is a separate r10_bio for each non-in_sync drive.
  * Only the first two slots are in use. The first for reading,
  * The second for writing.
  *
  */
 static void fix_recovery_read_error(struct r10bio *r10_bio)
 {
     /* We got a read error during recovery.
      * We repeat the read in smaller page-sized sections.
      * If a read succeeds, write it to the new device or record
      * a bad block if we cannot.
      * If a read fails, record a bad block on both old and
      * new devices.
      */
     struct mddev *mddev = r10_bio->mddev;
     struct r10conf *conf = mddev->private;
     struct bio *bio = r10_bio->devs[0].bio;
     sector_t sect = 0;
     int sectors = r10_bio->sectors;
     int idx = 0;
     int dr = r10_bio->devs[0].devnum;
     int dw = r10_bio->devs[1].devnum;
     struct page **pages = get_resync_pages(bio)->pages;
 
     while (sectors) {
         int s = sectors;
         struct md_rdev *rdev;
         sector_t addr;
         int ok;
 
         if (s > (PAGE_SIZE>>9))
             s = PAGE_SIZE >> 9;
 
         rdev = conf->mirrors[dr].rdev;
         addr = r10_bio->devs[0].addr + sect,
         ok = sync_page_io(rdev,
                   addr,
                   s << 9,
                   pages[idx],
                   REQ_OP_READ, false);
         if (ok) {
             rdev = conf->mirrors[dw].rdev;
             addr = r10_bio->devs[1].addr + sect;
             ok = sync_page_io(rdev,
                       addr,
                       s << 9,
                       pages[idx],
                       REQ_OP_WRITE, false);
             if (!ok) {
                 set_bit(WriteErrorSeen, &rdev->flags);
                 if (!test_and_set_bit(WantReplacement,
                               &rdev->flags))
                     set_bit(MD_RECOVERY_NEEDED,
                         &rdev->mddev->recovery);
             }
         }
         if (!ok) {
             /* We don't worry if we cannot set a bad block -
              * it really is bad so there is no loss in not
              * recording it yet
              */
             rdev_set_badblocks(rdev, addr, s, 0);
 
             if (rdev != conf->mirrors[dw].rdev) {
                 /* need bad block on destination too */
                 struct md_rdev *rdev2 = conf->mirrors[dw].rdev;
                 addr = r10_bio->devs[1].addr + sect;
                 ok = rdev_set_badblocks(rdev2, addr, s, 0);
                 if (!ok) {
                     /* just abort the recovery */
                     pr_notice("md/raid10:%s: recovery aborted due to read error\n",
                           mdname(mddev));
 
                     conf->mirrors[dw].recovery_disabled
                         = mddev->recovery_disabled;
                     set_bit(MD_RECOVERY_INTR,
                         &mddev->recovery);
                     break;
                 }
             }
         }
 
         sectors -= s;
         sect += s;
         idx++;
     }
 }
 
 static void recovery_request_write(struct mddev *mddev, struct r10bio *r10_bio)
 {
     struct r10conf *conf = mddev->private;
     int d;
     struct bio *wbio, *wbio2;
 
     if (!test_bit(R10BIO_Uptodate, &r10_bio->state)) {
         fix_recovery_read_error(r10_bio);
         end_sync_request(r10_bio);
         return;
     }
 
     /*
      * share the pages with the first bio
      * and submit the write request
      */
     d = r10_bio->devs[1].devnum;
     wbio = r10_bio->devs[1].bio;
     wbio2 = r10_bio->devs[1].repl_bio;
     /* Need to test wbio2->bi_end_io before we call
      * submit_bio_noacct as if the former is NULL,
      * the latter is free to free wbio2.
      */
     if (wbio2 && !wbio2->bi_end_io)
         wbio2 = NULL;
     if (wbio->bi_end_io) {
         atomic_inc(&conf->mirrors[d].rdev->nr_pending);
         md_sync_acct(conf->mirrors[d].rdev->bdev, bio_sectors(wbio));
         submit_bio_noacct(wbio);
     }
     if (wbio2) {
         atomic_inc(&conf->mirrors[d].replacement->nr_pending);
         md_sync_acct(conf->mirrors[d].replacement->bdev,
                  bio_sectors(wbio2));
         submit_bio_noacct(wbio2);
     }
 }
 
 /*
  * Used by fix_read_error() to decay the per rdev read_errors.
  * We halve the read error count for every hour that has elapsed
  * since the last recorded read error.
  *
  */
 static void check_decay_read_errors(struct mddev *mddev, struct md_rdev *rdev)
 {
     long cur_time_mon;
     unsigned long hours_since_last;
     unsigned int read_errors = atomic_read(&rdev->read_errors);
 
     cur_time_mon = ktime_get_seconds();
 
     if (rdev->last_read_error == 0) {
         /* first time we've seen a read error */
         rdev->last_read_error = cur_time_mon;
         return;
     }
 
     hours_since_last = (long)(cur_time_mon -
                 rdev->last_read_error) / 3600;
 
     rdev->last_read_error = cur_time_mon;
 
     /*
      * if hours_since_last is > the number of bits in read_errors
      * just set read errors to 0. We do this to avoid
      * overflowing the shift of read_errors by hours_since_last.
      */
     if (hours_since_last >= 8 * sizeof(read_errors))
         atomic_set(&rdev->read_errors, 0);
     else
         atomic_set(&rdev->read_errors, read_errors >> hours_since_last);
 }
 
 static int r10_sync_page_io(struct md_rdev *rdev, sector_t sector,
                 int sectors, struct page *page, enum req_op op)
 {
     sector_t first_bad;
     int bad_sectors;
 
     if (is_badblock(rdev, sector, sectors, &first_bad, &bad_sectors)
         && (op == REQ_OP_READ || test_bit(WriteErrorSeen, &rdev->flags)))
         return -1;
     if (sync_page_io(rdev, sector, sectors << 9, page, op, false))
         /* success */
         return 1;
     if (op == REQ_OP_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;
 }
 
 /*
  * 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 r10conf *conf, struct mddev *mddev, struct r10bio *r10_bio)
 {
     int sect = 0; /* Offset from r10_bio->sector */
     int sectors = r10_bio->sectors;
     struct md_rdev *rdev;
     int max_read_errors = atomic_read(&mddev->max_corr_read_errors);
     int d = r10_bio->devs[r10_bio->read_slot].devnum;
 
     /* still own a reference to this rdev, so it cannot
      * have been cleared recently.
      */
     rdev = conf->mirrors[d].rdev;
 
     if (test_bit(Faulty, &rdev->flags))
         /* drive has already been failed, just ignore any
            more fix_read_error() attempts */
         return;
 
     check_decay_read_errors(mddev, rdev);
     atomic_inc(&rdev->read_errors);
     if (atomic_read(&rdev->read_errors) > max_read_errors) {
         pr_notice("md/raid10:%s: %pg: Raid device exceeded read_error threshold [cur %d:max %d]\n",
               mdname(mddev), rdev->bdev,
               atomic_read(&rdev->read_errors), max_read_errors);
         pr_notice("md/raid10:%s: %pg: Failing raid device\n",
               mdname(mddev), rdev->bdev);
         md_error(mddev, rdev);
         r10_bio->devs[r10_bio->read_slot].bio = IO_BLOCKED;
         return;
     }
 
     while(sectors) {
         int s = sectors;
         int sl = r10_bio->read_slot;
         int success = 0;
         int start;
 
         if (s > (PAGE_SIZE>>9))
             s = PAGE_SIZE >> 9;
 
         rcu_read_lock();
         do {
             sector_t first_bad;
             int bad_sectors;
 
             d = r10_bio->devs[sl].devnum;
             rdev = rcu_dereference(conf->mirrors[d].rdev);
             if (rdev &&
                 test_bit(In_sync, &rdev->flags) &&
                 !test_bit(Faulty, &rdev->flags) &&
                 is_badblock(rdev, r10_bio->devs[sl].addr + sect, s,
                     &first_bad, &bad_sectors) == 0) {
                 atomic_inc(&rdev->nr_pending);
                 rcu_read_unlock();
                 success = sync_page_io(rdev,
                                r10_bio->devs[sl].addr +
                                sect,
                                s<<9,
                                conf->tmppage,
                                REQ_OP_READ, false);
                 rdev_dec_pending(rdev, mddev);
                 rcu_read_lock();
                 if (success)
                     break;
             }
             sl++;
             if (sl == conf->copies)
                 sl = 0;
         } while (!success && sl != r10_bio->read_slot);
         rcu_read_unlock();
 
         if (!success) {
             /* Cannot read from anywhere, just mark the block
              * as bad on the first device to discourage future
              * reads.
              */
             int dn = r10_bio->devs[r10_bio->read_slot].devnum;
             rdev = conf->mirrors[dn].rdev;
 
             if (!rdev_set_badblocks(
                     rdev,
                     r10_bio->devs[r10_bio->read_slot].addr
                     + sect,
                     s, 0)) {
                 md_error(mddev, rdev);
                 r10_bio->devs[r10_bio->read_slot].bio
                     = IO_BLOCKED;
             }
             break;
         }
 
         start = sl;
         /* write it back and re-read */
         rcu_read_lock();
         while (sl != r10_bio->read_slot) {
             if (sl==0)
                 sl = conf->copies;
             sl--;
             d = r10_bio->devs[sl].devnum;
             rdev = rcu_dereference(conf->mirrors[d].rdev);
             if (!rdev ||
                 test_bit(Faulty, &rdev->flags) ||
                 !test_bit(In_sync, &rdev->flags))
                 continue;
 
             atomic_inc(&rdev->nr_pending);
             rcu_read_unlock();
             if (r10_sync_page_io(rdev,
                          r10_bio->devs[sl].addr +
                          sect,
                          s, conf->tmppage, REQ_OP_WRITE)
                 == 0) {
                 /* Well, this device is dead */
                 pr_notice("md/raid10:%s: read correction write failed (%d sectors at %llu on %pg)\n",
                       mdname(mddev), s,
                       (unsigned long long)(
                           sect +
                           choose_data_offset(r10_bio,
                                      rdev)),
                       rdev->bdev);
                 pr_notice("md/raid10:%s: %pg: failing drive\n",
                       mdname(mddev),
                       rdev->bdev);
             }
             rdev_dec_pending(rdev, mddev);
             rcu_read_lock();
         }
         sl = start;
         while (sl != r10_bio->read_slot) {
             if (sl==0)
                 sl = conf->copies;
             sl--;
             d = r10_bio->devs[sl].devnum;
             rdev = rcu_dereference(conf->mirrors[d].rdev);
             if (!rdev ||
                 test_bit(Faulty, &rdev->flags) ||
                 !test_bit(In_sync, &rdev->flags))
                 continue;
 
             atomic_inc(&rdev->nr_pending);
             rcu_read_unlock();
             switch (r10_sync_page_io(rdev,
                          r10_bio->devs[sl].addr +
                          sect,
                          s, conf->tmppage, REQ_OP_READ)) {
             case 0:
                 /* Well, this device is dead */
                 pr_notice("md/raid10:%s: unable to read back corrected sectors (%d sectors at %llu on %pg)\n",
                        mdname(mddev), s,
                        (unsigned long long)(
                            sect +
                            choose_data_offset(r10_bio, rdev)),
                        rdev->bdev);
                 pr_notice("md/raid10:%s: %pg: failing drive\n",
                        mdname(mddev),
                        rdev->bdev);
                 break;
             case 1:
                 pr_info("md/raid10:%s: read error corrected (%d sectors at %llu on %pg)\n",
                        mdname(mddev), s,
                        (unsigned long long)(
                            sect +
                            choose_data_offset(r10_bio, rdev)),
                        rdev->bdev);
                 atomic_add(s, &rdev->corrected_errors);
             }
 
             rdev_dec_pending(rdev, mddev);
             rcu_read_lock();
         }
         rcu_read_unlock();
 
         sectors -= s;
         sect += s;
     }
 }
 
 static int narrow_write_error(struct r10bio *r10_bio, int i)
 {
     struct bio *bio = r10_bio->master_bio;
     struct mddev *mddev = r10_bio->mddev;
     struct r10conf *conf = mddev->private;
     struct md_rdev *rdev = conf->mirrors[r10_bio->devs[i].devnum].rdev;
     /* bio has the data to be written to slot '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.
      *
      * We currently own a reference to the rdev.
      */
 
     int block_sectors;
     sector_t sector;
     int sectors;
     int sect_to_write = r10_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 = r10_bio->sector;
     sectors = ((r10_bio->sector + block_sectors)
            & ~(sector_t)(block_sectors - 1))
         - sector;
 
     while (sect_to_write) {
         struct bio *wbio;
         sector_t wsector;
         if (sectors > sect_to_write)
             sectors = sect_to_write;
         /* Write at 'sector' for 'sectors' */
         wbio = bio_alloc_clone(rdev->bdev, bio, GFP_NOIO,
                        &mddev->bio_set);
         bio_trim(wbio, sector - bio->bi_iter.bi_sector, sectors);
         wsector = r10_bio->devs[i].addr + (sector - r10_bio->sector);
         wbio->bi_iter.bi_sector = wsector +
                    choose_data_offset(r10_bio, rdev);
         bio_set_op_attrs(wbio, REQ_OP_WRITE, 0);
 
         if (submit_bio_wait(wbio) < 0)
             /* Failure! */
             ok = rdev_set_badblocks(rdev, wsector,
                         sectors, 0)
                 && ok;
 
         bio_put(wbio);
         sect_to_write -= sectors;
         sector += sectors;
         sectors = block_sectors;
     }
     return ok;
 }
 
 static void handle_read_error(struct mddev *mddev, struct r10bio *r10_bio)
 {
     int slot = r10_bio->read_slot;
     struct bio *bio;
     struct r10conf *conf = mddev->private;
     struct md_rdev *rdev = r10_bio->devs[slot].rdev;
 
     /* 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 = r10_bio->devs[slot].bio;
     bio_put(bio);
     r10_bio->devs[slot].bio = NULL;
 
     if (mddev->ro)
         r10_bio->devs[slot].bio = IO_BLOCKED;
     else if (!test_bit(FailFast, &rdev->flags)) {
         freeze_array(conf, 1);
         fix_read_error(conf, mddev, r10_bio);
         unfreeze_array(conf);
     } else
         md_error(mddev, rdev);
 
     rdev_dec_pending(rdev, mddev);
     allow_barrier(conf);
     r10_bio->state = 0;
     raid10_read_request(mddev, r10_bio->master_bio, r10_bio);
 }
 
 static void handle_write_completed(struct r10conf *conf, struct r10bio *r10_bio)
 {
     /* Some sort of write request has finished and it
      * succeeded in writing where we thought there was a
      * bad block.  So forget the bad block.
      * Or possibly if failed and we need to record
      * a bad block.
      */
     int m;
     struct md_rdev *rdev;
 
     if (test_bit(R10BIO_IsSync, &r10_bio->state) ||
         test_bit(R10BIO_IsRecover, &r10_bio->state)) {
         for (m = 0; m < conf->copies; m++) {
             int dev = r10_bio->devs[m].devnum;
             rdev = conf->mirrors[dev].rdev;
             if (r10_bio->devs[m].bio == NULL ||
                 r10_bio->devs[m].bio->bi_end_io == NULL)
                 continue;
             if (!r10_bio->devs[m].bio->bi_status) {
                 rdev_clear_badblocks(
                     rdev,
                     r10_bio->devs[m].addr,
                     r10_bio->sectors, 0);
             } else {
                 if (!rdev_set_badblocks(
                         rdev,
                         r10_bio->devs[m].addr,
                         r10_bio->sectors, 0))
                     md_error(conf->mddev, rdev);
             }
             rdev = conf->mirrors[dev].replacement;
             if (r10_bio->devs[m].repl_bio == NULL ||
                 r10_bio->devs[m].repl_bio->bi_end_io == NULL)
                 continue;
 
             if (!r10_bio->devs[m].repl_bio->bi_status) {
                 rdev_clear_badblocks(
                     rdev,
                     r10_bio->devs[m].addr,
                     r10_bio->sectors, 0);
             } else {
                 if (!rdev_set_badblocks(
                         rdev,
                         r10_bio->devs[m].addr,
                         r10_bio->sectors, 0))
                     md_error(conf->mddev, rdev);
             }
         }
         put_buf(r10_bio);
     } else {
         bool fail = false;
         for (m = 0; m < conf->copies; m++) {
             int dev = r10_bio->devs[m].devnum;
             struct bio *bio = r10_bio->devs[m].bio;
             rdev = conf->mirrors[dev].rdev;
             if (bio == IO_MADE_GOOD) {
                 rdev_clear_badblocks(
                     rdev,
                     r10_bio->devs[m].addr,
                     r10_bio->sectors, 0);
                 rdev_dec_pending(rdev, conf->mddev);
             } else if (bio != NULL && bio->bi_status) {
                 fail = true;
                 if (!narrow_write_error(r10_bio, m)) {
                     md_error(conf->mddev, rdev);
                     set_bit(R10BIO_Degraded,
                         &r10_bio->state);
                 }
                 rdev_dec_pending(rdev, conf->mddev);
             }
             bio = r10_bio->devs[m].repl_bio;
             rdev = conf->mirrors[dev].replacement;
             if (rdev && bio == IO_MADE_GOOD) {
                 rdev_clear_badblocks(
                     rdev,
                     r10_bio->devs[m].addr,
                     r10_bio->sectors, 0);
                 rdev_dec_pending(rdev, conf->mddev);
             }
         }
         if (fail) {
             spin_lock_irq(&conf->device_lock);
             list_add(&r10_bio->retry_list, &conf->bio_end_io_list);
             conf->nr_queued++;
             spin_unlock_irq(&conf->device_lock);
             /*
              * In case freeze_array() is waiting for condition
              * nr_pending == nr_queued + extra to be true.
              */
             wake_up(&conf->wait_barrier);
             md_wakeup_thread(conf->mddev->thread);
         } else {
             if (test_bit(R10BIO_WriteError,
                      &r10_bio->state))
                 close_write(r10_bio);
             raid_end_bio_io(r10_bio);
         }
     }
 }
 
 static void raid10d(struct md_thread *thread)
 {
     struct mddev *mddev = thread->mddev;
     struct r10bio *r10_bio;
     unsigned long flags;
     struct r10conf *conf = mddev->private;
     struct list_head *head = &conf->retry_list;
     struct blk_plug plug;
 
     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)) {
             while (!list_empty(&conf->bio_end_io_list)) {
                 list_move(conf->bio_end_io_list.prev, &tmp);
                 conf->nr_queued--;
             }
         }
         spin_unlock_irqrestore(&conf->device_lock, flags);
         while (!list_empty(&tmp)) {
             r10_bio = list_first_entry(&tmp, struct r10bio,
                            retry_list);
             list_del(&r10_bio->retry_list);
             if (mddev->degraded)
                 set_bit(R10BIO_Degraded, &r10_bio->state);
 
             if (test_bit(R10BIO_WriteError,
                      &r10_bio->state))
                 close_write(r10_bio);
             raid_end_bio_io(r10_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;
         }
         r10_bio = list_entry(head->prev, struct r10bio, retry_list);
         list_del(head->prev);
         conf->nr_queued--;
         spin_unlock_irqrestore(&conf->device_lock, flags);
 
         mddev = r10_bio->mddev;
         conf = mddev->private;
         if (test_bit(R10BIO_MadeGood, &r10_bio->state) ||
             test_bit(R10BIO_WriteError, &r10_bio->state))
             handle_write_completed(conf, r10_bio);
         else if (test_bit(R10BIO_IsReshape, &r10_bio->state))
             reshape_request_write(mddev, r10_bio);
         else if (test_bit(R10BIO_IsSync, &r10_bio->state))
             sync_request_write(mddev, r10_bio);
         else if (test_bit(R10BIO_IsRecover, &r10_bio->state))
             recovery_request_write(mddev, r10_bio);
         else if (test_bit(R10BIO_ReadError, &r10_bio->state))
             handle_read_error(mddev, r10_bio);
         else
             WARN_ON_ONCE(1);
 
         cond_resched();
         if (mddev->sb_flags & ~(1<<MD_SB_CHANGE_PENDING))
             md_check_recovery(mddev);
     }
     blk_finish_plug(&plug);
 }
 
 static int init_resync(struct r10conf *conf)
 {
     int ret, buffs, i;
 
     buffs = RESYNC_WINDOW / RESYNC_BLOCK_SIZE;
     BUG_ON(mempool_initialized(&conf->r10buf_pool));
     conf->have_replacement = 0;
     for (i = 0; i < conf->geo.raid_disks; i++)
         if (conf->mirrors[i].replacement)
             conf->have_replacement = 1;
     ret = mempool_init(&conf->r10buf_pool, buffs,
                r10buf_pool_alloc, r10buf_pool_free, conf);
     if (ret)
         return ret;
     conf->next_resync = 0;
     return 0;
 }
 
 static struct r10bio *raid10_alloc_init_r10buf(struct r10conf *conf)
 {
     struct r10bio *r10bio = mempool_alloc(&conf->r10buf_pool, GFP_NOIO);
     struct rsync_pages *rp;
     struct bio *bio;
     int nalloc;
     int i;
 
     if (test_bit(MD_RECOVERY_SYNC, &conf->mddev->recovery) ||
         test_bit(MD_RECOVERY_RESHAPE, &conf->mddev->recovery))
         nalloc = conf->copies; /* resync */
     else
         nalloc = 2; /* recovery */
 
     for (i = 0; i < nalloc; i++) {
         bio = r10bio->devs[i].bio;
         rp = bio->bi_private;
         bio_reset(bio, NULL, 0);
         bio->bi_private = rp;
         bio = r10bio->devs[i].repl_bio;
         if (bio) {
             rp = bio->bi_private;
             bio_reset(bio, NULL, 0);
             bio->bi_private = rp;
         }
     }
     return r10bio;
 }
 
 /*
  * Set cluster_sync_high since we need other nodes to add the
  * range [cluster_sync_low, cluster_sync_high] to suspend list.
  */
 static void raid10_set_cluster_sync_high(struct r10conf *conf)
 {
     sector_t window_size;
     int extra_chunk, chunks;
 
     /*
      * First, here we define "stripe" as a unit which across
      * all member devices one time, so we get chunks by use
      * raid_disks / near_copies. Otherwise, if near_copies is
      * close to raid_disks, then resync window could increases
      * linearly with the increase of raid_disks, which means
      * we will suspend a really large IO window while it is not
      * necessary. If raid_disks is not divisible by near_copies,
      * an extra chunk is needed to ensure the whole "stripe" is
      * covered.
      */
 
     chunks = conf->geo.raid_disks / conf->geo.near_copies;
     if (conf->geo.raid_disks % conf->geo.near_copies == 0)
         extra_chunk = 0;
     else
         extra_chunk = 1;
     window_size = (chunks + extra_chunk) * conf->mddev->chunk_sectors;
 
     /*
      * At least use a 32M window to align with raid1's resync window
      */
     window_size = (CLUSTER_RESYNC_WINDOW_SECTORS > window_size) ?
             CLUSTER_RESYNC_WINDOW_SECTORS : window_size;
 
     conf->cluster_sync_high = conf->cluster_sync_low + window_size;
 }
 
 /*
  * 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.
  *
  * Resync and recovery are handled very differently.
  * We differentiate by looking at MD_RECOVERY_SYNC in mddev->recovery.
  *
  * For resync, we iterate over virtual addresses, read all copies,
  * and update if there are differences.  If only one copy is live,
  * skip it.
  * For recovery, we iterate over physical addresses, read a good
  * value for each non-in_sync drive, and over-write.
  *
  * So, for recovery we may have several outstanding complex requests for a
  * given address, one for each out-of-sync device.  We model this by allocating
  * a number of r10_bio structures, one for each out-of-sync device.
  * As we setup these structures, we collect all bio's together into a list
  * which we then process collectively to add pages, and then process again
  * to pass to submit_bio_noacct.
  *
  * The r10_bio structures are linked using a borrowed master_bio pointer.
  * This link is counted in ->remaining.  When the r10_bio that points to NULL
  * has its remaining count decremented to 0, the whole complex operation
  * is complete.
  *
  */
 
 static sector_t raid10_sync_request(struct mddev *mddev, sector_t sector_nr,
                  int *skipped)
 {
     struct r10conf *conf = mddev->private;
     struct r10bio *r10_bio;
     struct bio *biolist = NULL, *bio;
     sector_t max_sector, nr_sectors;
     int i;
     int max_sync;
     sector_t sync_blocks;
     sector_t sectors_skipped = 0;
     int chunks_skipped = 0;
     sector_t chunk_mask = conf->geo.chunk_mask;
     int page_idx = 0;
 
     if (!mempool_initialized(&conf->r10buf_pool))
         if (init_resync(conf))
             return 0;
 
     /*
      * Allow skipping a full rebuild for incremental assembly
      * of a clean array, like RAID1 does.
      */
     if (mddev->bitmap == NULL &&
         mddev->recovery_cp == MaxSector &&
         mddev->reshape_position == MaxSector &&
         !test_bit(MD_RECOVERY_SYNC, &mddev->recovery) &&
         !test_bit(MD_RECOVERY_REQUESTED, &mddev->recovery) &&
         !test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery) &&
         conf->fullsync == 0) {
         *skipped = 1;
         return mddev->dev_sectors - sector_nr;
     }
 
  skipped:
     max_sector = mddev->dev_sectors;
     if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery) ||
         test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery))
         max_sector = mddev->resync_max_sectors;
     if (sector_nr >= max_sector) {
         conf->cluster_sync_low = 0;
         conf->cluster_sync_high = 0;
 
         /* If we aborted, we need to abort the
          * sync on the 'current' bitmap chucks (there can
          * be several when recovering multiple devices).
          * as we may have started syncing it but not finished.
          * We can find the current address in
          * mddev->curr_resync, but for recovery,
          * we need to convert that to several
          * virtual addresses.
          */
         if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery)) {
             end_reshape(conf);
             close_sync(conf);
             return 0;
         }
 
         if (mddev->curr_resync < max_sector) { /* aborted */
             if (test_bit(MD_RECOVERY_SYNC, &mddev->recovery))
                 md_bitmap_end_sync(mddev->bitmap, mddev->curr_resync,
                            &sync_blocks, 1);
             else for (i = 0; i < conf->geo.raid_disks; i++) {
                 sector_t sect =
                     raid10_find_virt(conf, mddev->curr_resync, i);
                 md_bitmap_end_sync(mddev->bitmap, sect,
                            &sync_blocks, 1);
             }
         } else {
             /* completed sync */
             if ((!mddev->bitmap || conf->fullsync)
                 && conf->have_replacement
                 && test_bit(MD_RECOVERY_SYNC, &mddev->recovery)) {
                 /* Completed a full sync so the replacements
                  * are now fully recovered.
                  */
                 rcu_read_lock();
                 for (i = 0; i < conf->geo.raid_disks; i++) {
                     struct md_rdev *rdev =
                         rcu_dereference(conf->mirrors[i].replacement);
                     if (rdev)
                         rdev->recovery_offset = MaxSector;
                 }
                 rcu_read_unlock();
             }
             conf->fullsync = 0;
         }
         md_bitmap_close_sync(mddev->bitmap);
         close_sync(conf);
         *skipped = 1;
         return sectors_skipped;
     }
 
     if (test_bit(MD_RECOVERY_RESHAPE, &mddev->recovery))
         return reshape_request(mddev, sector_nr, skipped);
 
     if (chunks_skipped >= conf->geo.raid_disks) {
         /* if there has been nothing to do on any drive,
          * then there is nothing to do at all..
          */
         *skipped = 1;
         return (max_sector - sector_nr) + sectors_skipped;
     }
 
     if (max_sector > mddev->resync_max)
         max_sector = mddev->resync_max; /* Don't do IO beyond here */
 
     /* make sure whole request will fit in a chunk - if chunks
      * are meaningful
      */
     if (conf->geo.near_copies < conf->geo.raid_disks &&
         max_sector > (sector_nr | chunk_mask))
         max_sector = (sector_nr | chunk_mask) + 1;
 
     /*
      * If there is non-resync activity waiting for a turn, then let it
      * though before starting on this new sync request.
      */
     if (conf->nr_waiting)
         schedule_timeout_uninterruptible(1);
 
     /* Again, very different code for resync and recovery.
      * Both must result in an r10bio with a list of bios that
      * have bi_end_io, bi_sector, bi_bdev set,
      * and bi_private set to the r10bio.
      * For recovery, we may actually create several r10bios
      * with 2 bios in each, that correspond to the bios in the main one.
      * In this case, the subordinate r10bios link back through a
      * borrowed master_bio pointer, and the counter in the master
      * includes a ref from each subordinate.
      */
     /* First, we decide what to do and set ->bi_end_io
      * To end_sync_read if we want to read, and
      * end_sync_write if we will want to write.
      */
 
     max_sync = RESYNC_PAGES << (PAGE_SHIFT-9);
     if (!test_bit(MD_RECOVERY_SYNC, &mddev->recovery)) {
         /* recovery... the complicated one */
         int j;
         r10_bio = NULL;
 
         for (i = 0 ; i < conf->geo.raid_disks; i++) {
             int still_degraded;
             struct r10bio *rb2;
             sector_t sect;
             int must_sync;
             int any_working;
             int need_recover = 0;
             int need_replace = 0;
             struct raid10_info *mirror = &conf->mirrors[i];
             struct md_rdev *mrdev, *mreplace;
 
             rcu_read_lock();
             mrdev = rcu_dereference(mirror->rdev);
             mreplace = rcu_dereference(mirror->replacement);
 
             if (mrdev != NULL &&
                 !test_bit(Faulty, &mrdev->flags) &&
                 !test_bit(In_sync, &mrdev->flags))
                 need_recover = 1;
             if (mreplace != NULL &&
                 !test_bit(Faulty, &mreplace->flags))
                 need_replace = 1;
 
             if (!need_recover && !need_replace) {
                 rcu_read_unlock();
                 continue;
             }
 
             still_degraded = 0;
             /* want to reconstruct this device */
             rb2 = r10_bio;
             sect = raid10_find_virt(conf, sector_nr, i);
             if (sect >= mddev->resync_max_sectors) {
                 /* last stripe is not complete - don't
                  * try to recover this sector.
                  */
                 rcu_read_unlock();
                 continue;
             }
             if (mreplace && test_bit(Faulty, &mreplace->flags))
                 mreplace = NULL;
             /* Unless we are doing a full sync, or a replacement
              * we only need to recover the block if it is set in
              * the bitmap
              */
             must_sync = md_bitmap_start_sync(mddev->bitmap, sect,
                              &sync_blocks, 1);
             if (sync_blocks < max_sync)
                 max_sync = sync_blocks;
             if (!must_sync &&
                 mreplace == NULL &&
                 !conf->fullsync) {
                 /* yep, skip the sync_blocks here, but don't assume
                  * that there will never be anything to do here
                  */
                 chunks_skipped = -1;
                 rcu_read_unlock();
                 continue;
             }
             atomic_inc(&mrdev->nr_pending);
             if (mreplace)
                 atomic_inc(&mreplace->nr_pending);
             rcu_read_unlock();
 
             r10_bio = raid10_alloc_init_r10buf(conf);
             r10_bio->state = 0;
             raise_barrier(conf, rb2 != NULL);
             atomic_set(&r10_bio->remaining, 0);
 
             r10_bio->master_bio = (struct bio*)rb2;
             if (rb2)
                 atomic_inc(&rb2->remaining);
             r10_bio->mddev = mddev;
             set_bit(R10BIO_IsRecover, &r10_bio->state);
             r10_bio->sector = sect;
 
             raid10_find_phys(conf, r10_bio);
 
             /* Need to check if the array will still be
              * degraded
              */
             rcu_read_lock();
             for (j = 0; j < conf->geo.raid_disks; j++) {
                 struct md_rdev *rdev = rcu_dereference(
                     conf->mirrors[j].rdev);
                 if (rdev == NULL || test_bit(Faulty, &rdev->flags)) {
                     still_degraded = 1;
                     break;
                 }
             }
 
             must_sync = md_bitmap_start_sync(mddev->bitmap, sect,
                              &sync_blocks, still_degraded);
 
             any_working = 0;
             for (j=0; j<conf->copies;j++) {
                 int k;
                 int d = r10_bio->devs[j].devnum;
                 sector_t from_addr, to_addr;
                 struct md_rdev *rdev =
                     rcu_dereference(conf->mirrors[d].rdev);
                 sector_t sector, first_bad;
                 int bad_sectors;
                 if (!rdev ||
                     !test_bit(In_sync, &rdev->flags))
                     continue;
                 /* This is where we read from */
                 any_working = 1;
                 sector = r10_bio->devs[j].addr;
 
                 if (is_badblock(rdev, sector, max_sync,
                         &first_bad, &bad_sectors)) {
                     if (first_bad > sector)
                         max_sync = first_bad - sector;
                     else {
                         bad_sectors -= (sector
                                 - first_bad);
                         if (max_sync > bad_sectors)
                             max_sync = bad_sectors;
                         continue;
                     }
                 }
                 bio = r10_bio->devs[0].bio;
                 bio->bi_next = biolist;
                 biolist = bio;
                 bio->bi_end_io = end_sync_read;
                 bio_set_op_attrs(bio, REQ_OP_READ, 0);
                 if (test_bit(FailFast, &rdev->flags))
                     bio->bi_opf |= MD_FAILFAST;
                 from_addr = r10_bio->devs[j].addr;
                 bio->bi_iter.bi_sector = from_addr +
                     rdev->data_offset;
                 bio_set_dev(bio, rdev->bdev);
                 atomic_inc(&rdev->nr_pending);
                 /* and we write to 'i' (if not in_sync) */
 
                 for (k=0; k<conf->copies; k++)
                     if (r10_bio->devs[k].devnum == i)
                         break;
                 BUG_ON(k == conf->copies);
                 to_addr = r10_bio->devs[k].addr;
                 r10_bio->devs[0].devnum = d;
                 r10_bio->devs[0].addr = from_addr;
                 r10_bio->devs[1].devnum = i;
                 r10_bio->devs[1].addr = to_addr;
 
                 if (need_recover) {
                     bio = r10_bio->devs[1].bio;
                     bio->bi_next = biolist;
                     biolist = bio;
                     bio->bi_end_io = end_sync_write;
                     bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
                     bio->bi_iter.bi_sector = to_addr
                         + mrdev->data_offset;
                     bio_set_dev(bio, mrdev->bdev);
                     atomic_inc(&r10_bio->remaining);
                 } else
                     r10_bio->devs[1].bio->bi_end_io = NULL;
 
                 /* and maybe write to replacement */
                 bio = r10_bio->devs[1].repl_bio;
                 if (bio)
                     bio->bi_end_io = NULL;
                 /* Note: if need_replace, then bio
                  * cannot be NULL as r10buf_pool_alloc will
                  * have allocated it.
                  */
                 if (!need_replace)
                     break;
                 bio->bi_next = biolist;
                 biolist = bio;
                 bio->bi_end_io = end_sync_write;
                 bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
                 bio->bi_iter.bi_sector = to_addr +
                     mreplace->data_offset;
                 bio_set_dev(bio, mreplace->bdev);
                 atomic_inc(&r10_bio->remaining);
                 break;
             }
             rcu_read_unlock();
             if (j == conf->copies) {
                 /* Cannot recover, so abort the recovery or
                  * record a bad block */
                 if (any_working) {
                     /* problem is that there are bad blocks
                      * on other device(s)
                      */
                     int k;
                     for (k = 0; k < conf->copies; k++)
                         if (r10_bio->devs[k].devnum == i)
                             break;
                     if (!test_bit(In_sync,
                               &mrdev->flags)
                         && !rdev_set_badblocks(
                             mrdev,
                             r10_bio->devs[k].addr,
                             max_sync, 0))
                         any_working = 0;
                     if (mreplace &&
                         !rdev_set_badblocks(
                             mreplace,
                             r10_bio->devs[k].addr,
                             max_sync, 0))
                         any_working = 0;
                 }
                 if (!any_working)  {
                     if (!test_and_set_bit(MD_RECOVERY_INTR,
                                   &mddev->recovery))
                         pr_warn("md/raid10:%s: insufficient working devices for recovery.\n",
                                mdname(mddev));
                     mirror->recovery_disabled
                         = mddev->recovery_disabled;
                 }
                 put_buf(r10_bio);
                 if (rb2)
                     atomic_dec(&rb2->remaining);
                 r10_bio = rb2;
                 rdev_dec_pending(mrdev, mddev);
                 if (mreplace)
                     rdev_dec_pending(mreplace, mddev);
                 break;
             }
             rdev_dec_pending(mrdev, mddev);
             if (mreplace)
                 rdev_dec_pending(mreplace, mddev);
             if (r10_bio->devs[0].bio->bi_opf & MD_FAILFAST) {
                 /* Only want this if there is elsewhere to
                  * read from. 'j' is currently the first
                  * readable copy.
                  */
                 int targets = 1;
                 for (; j < conf->copies; j++) {
                     int d = r10_bio->devs[j].devnum;
                     if (conf->mirrors[d].rdev &&
                         test_bit(In_sync,
                               &conf->mirrors[d].rdev->flags))
                         targets++;
                 }
                 if (targets == 1)
                     r10_bio->devs[0].bio->bi_opf
                         &= ~MD_FAILFAST;
             }
         }
         if (biolist == NULL) {
             while (r10_bio) {
                 struct r10bio *rb2 = r10_bio;
                 r10_bio = (struct r10bio*) rb2->master_bio;
                 rb2->master_bio = NULL;
                 put_buf(rb2);
             }
             goto giveup;
         }
     } else {
         /* resync. Schedule a read for every block at this virt offset */
         int count = 0;
 
         /*
          * Since curr_resync_completed could probably not update in
          * time, and we will set cluster_sync_low based on it.
          * Let's check against "sector_nr + 2 * RESYNC_SECTORS" for
          * safety reason, which ensures curr_resync_completed is
          * updated in bitmap_cond_end_sync.
          */
         md_bitmap_cond_end_sync(mddev->bitmap, sector_nr,
                     mddev_is_clustered(mddev) &&
                     (sector_nr + 2 * RESYNC_SECTORS > conf->cluster_sync_high));
 
         if (!md_bitmap_start_sync(mddev->bitmap, sector_nr,
                       &sync_blocks, mddev->degraded) &&
             !conf->fullsync && !test_bit(MD_RECOVERY_REQUESTED,
                          &mddev->recovery)) {
             /* We can skip this block */
             *skipped = 1;
             return sync_blocks + sectors_skipped;
         }
         if (sync_blocks < max_sync)
             max_sync = sync_blocks;
         r10_bio = raid10_alloc_init_r10buf(conf);
         r10_bio->state = 0;
 
         r10_bio->mddev = mddev;
         atomic_set(&r10_bio->remaining, 0);
         raise_barrier(conf, 0);
         conf->next_resync = sector_nr;
 
         r10_bio->master_bio = NULL;
         r10_bio->sector = sector_nr;
         set_bit(R10BIO_IsSync, &r10_bio->state);
         raid10_find_phys(conf, r10_bio);
         r10_bio->sectors = (sector_nr | chunk_mask) - sector_nr + 1;
 
         for (i = 0; i < conf->copies; i++) {
             int d = r10_bio->devs[i].devnum;
             sector_t first_bad, sector;
             int bad_sectors;
             struct md_rdev *rdev;
 
             if (r10_bio->devs[i].repl_bio)
                 r10_bio->devs[i].repl_bio->bi_end_io = NULL;
 
             bio = r10_bio->devs[i].bio;
             bio->bi_status = BLK_STS_IOERR;
             rcu_read_lock();
             rdev = rcu_dereference(conf->mirrors[d].rdev);
             if (rdev == NULL || test_bit(Faulty, &rdev->flags)) {
                 rcu_read_unlock();
                 continue;
             }
             sector = r10_bio->devs[i].addr;
             if (is_badblock(rdev, sector, max_sync,
                     &first_bad, &bad_sectors)) {
                 if (first_bad > sector)
                     max_sync = first_bad - sector;
                 else {
                     bad_sectors -= (sector - first_bad);
                     if (max_sync > bad_sectors)
                         max_sync = bad_sectors;
                     rcu_read_unlock();
                     continue;
                 }
             }
             atomic_inc(&rdev->nr_pending);
             atomic_inc(&r10_bio->remaining);
             bio->bi_next = biolist;
             biolist = bio;
             bio->bi_end_io = end_sync_read;
             bio_set_op_attrs(bio, REQ_OP_READ, 0);
             if (test_bit(FailFast, &rdev->flags))
                 bio->bi_opf |= MD_FAILFAST;
             bio->bi_iter.bi_sector = sector + rdev->data_offset;
             bio_set_dev(bio, rdev->bdev);
             count++;
 
             rdev = rcu_dereference(conf->mirrors[d].replacement);
             if (rdev == NULL || test_bit(Faulty, &rdev->flags)) {
                 rcu_read_unlock();
                 continue;
             }
             atomic_inc(&rdev->nr_pending);
 
             /* Need to set up for writing to the replacement */
             bio = r10_bio->devs[i].repl_bio;
             bio->bi_status = BLK_STS_IOERR;
 
             sector = r10_bio->devs[i].addr;
             bio->bi_next = biolist;
             biolist = bio;
             bio->bi_end_io = end_sync_write;
             bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
             if (test_bit(FailFast, &rdev->flags))
                 bio->bi_opf |= MD_FAILFAST;
             bio->bi_iter.bi_sector = sector + rdev->data_offset;
             bio_set_dev(bio, rdev->bdev);
             count++;
             rcu_read_unlock();
         }
 
         if (count < 2) {
             for (i=0; i<conf->copies; i++) {
                 int d = r10_bio->devs[i].devnum;
                 if (r10_bio->devs[i].bio->bi_end_io)
                     rdev_dec_pending(conf->mirrors[d].rdev,
                              mddev);
                 if (r10_bio->devs[i].repl_bio &&
                     r10_bio->devs[i].repl_bio->bi_end_io)
                     rdev_dec_pending(
                         conf->mirrors[d].replacement,
                         mddev);
             }
             put_buf(r10_bio);
             biolist = NULL;
             goto giveup;
         }
     }
 
     nr_sectors = 0;
     if (sector_nr + max_sync < max_sector)
         max_sector = sector_nr + max_sync;
     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;
         for (bio= biolist ; bio ; bio=bio->bi_next) {
             struct resync_pages *rp = get_resync_pages(bio);
             page = resync_fetch_page(rp, page_idx);
             /*
              * won't fail because the vec table is big enough
              * to hold all these pages
              */
             bio_add_page(bio, page, len, 0);
         }
         nr_sectors += len>>9;
         sector_nr += len>>9;
     } while (++page_idx < RESYNC_PAGES);
     r10_bio->sectors = nr_sectors;
 
     if (mddev_is_clustered(mddev) &&
         test_bit(MD_RECOVERY_SYNC, &mddev->recovery)) {
         /* It is resync not recovery */
         if (conf->cluster_sync_high < sector_nr + nr_sectors) {
             conf->cluster_sync_low = mddev->curr_resync_completed;
             raid10_set_cluster_sync_high(conf);
             /* Send resync message */
             md_cluster_ops->resync_info_update(mddev,
                         conf->cluster_sync_low,
                         conf->cluster_sync_high);
         }
     } else if (mddev_is_clustered(mddev)) {
         /* This is recovery not resync */
         sector_t sect_va1, sect_va2;
         bool broadcast_msg = false;
 
         for (i = 0; i < conf->geo.raid_disks; i++) {
             /*
              * sector_nr is a device address for recovery, so we
              * need translate it to array address before compare
              * with cluster_sync_high.
              */
             sect_va1 = raid10_find_virt(conf, sector_nr, i);
 
             if (conf->cluster_sync_high < sect_va1 + nr_sectors) {
                 broadcast_msg = true;
                 /*
                  * curr_resync_completed is similar as
                  * sector_nr, so make the translation too.
                  */
                 sect_va2 = raid10_find_virt(conf,
                     mddev->curr_resync_completed, i);
 
                 if (conf->cluster_sync_low == 0 ||
                     conf->cluster_sync_low > sect_va2)
                     conf->cluster_sync_low = sect_va2;
             }
         }
         if (broadcast_msg) {
             raid10_set_cluster_sync_high(conf);
             md_cluster_ops->resync_info_update(mddev,
                         conf->cluster_sync_low,
                         conf->cluster_sync_high);
         }
     }
 
     while (biolist) {
         bio = biolist;
         biolist = biolist->bi_next;
 
         bio->bi_next = NULL;
         r10_bio = get_resync_r10bio(bio);
         r10_bio->sectors = nr_sectors;
 
         if (bio->bi_end_io == end_sync_read) {
             md_sync_acct_bio(bio, nr_sectors);
             bio->bi_status = 0;
             submit_bio_noacct(bio);
         }
     }
 
     if (sectors_skipped)
         /* pretend they weren't skipped, it makes
          * no important difference in this case
          */
         md_done_sync(mddev, sectors_skipped, 1);
 
     return sectors_skipped + nr_sectors;
  giveup:
     /* There is nowhere to write, so all non-sync
      * drives must be failed or in resync, all drives
      * have a bad block, so try the next chunk...
      */
     if (sector_nr + max_sync < max_sector)
         max_sector = sector_nr + max_sync;
 
     sectors_skipped += (max_sector - sector_nr);
     chunks_skipped ++;
     sector_nr = max_sector;
     goto skipped;
 }
 
 static sector_t
 raid10_size(struct mddev *mddev, sector_t sectors, int raid_disks)
 {
     sector_t size;
     struct r10conf *conf = mddev->private;
 
     if (!raid_disks)
         raid_disks = min(conf->geo.raid_disks,
                  conf->prev.raid_disks);
     if (!sectors)
         sectors = conf->dev_sectors;
 
     size = sectors >> conf->geo.chunk_shift;
     sector_div(size, conf->geo.far_copies);
     size = size * raid_disks;
     sector_div(size, conf->geo.near_copies);
 
     return size << conf->geo.chunk_shift;
 }
 
 static void calc_sectors(struct r10conf *conf, sector_t size)
 {
     /* Calculate the number of sectors-per-device that will
      * actually be used, and set conf->dev_sectors and
      * conf->stride
      */
 
     size = size >> conf->geo.chunk_shift;
     sector_div(size, conf->geo.far_copies);
     size = size * conf->geo.raid_disks;
     sector_div(size, conf->geo.near_copies);
     /* 'size' is now the number of chunks in the array */
     /* calculate "used chunks per device" */
     size = size * conf->copies;
 
     /* We need to round up when dividing by raid_disks to
      * get the stride size.
      */
     size = DIV_ROUND_UP_SECTOR_T(size, conf->geo.raid_disks);
 
     conf->dev_sectors = size << conf->geo.chunk_shift;
 
     if (conf->geo.far_offset)
         conf->geo.stride = 1 << conf->geo.chunk_shift;
     else {
         sector_div(size, conf->geo.far_copies);
         conf->geo.stride = size << conf->geo.chunk_shift;
     }
 }
 
 enum geo_type {geo_new, geo_old, geo_start};
 static int setup_geo(struct geom *geo, struct mddev *mddev, enum geo_type new)
 {
     int nc, fc, fo;
     int layout, chunk, disks;
     switch (new) {
     case geo_old:
         layout = mddev->layout;
         chunk = mddev->chunk_sectors;
         disks = mddev->raid_disks - mddev->delta_disks;
         break;
     case geo_new:
         layout = mddev->new_layout;
         chunk = mddev->new_chunk_sectors;
         disks = mddev->raid_disks;
         break;
     default: /* avoid 'may be unused' warnings */
     case geo_start: /* new when starting reshape - raid_disks not
              * updated yet. */
         layout = mddev->new_layout;
         chunk = mddev->new_chunk_sectors;
         disks = mddev->raid_disks + mddev->delta_disks;
         break;
     }
     if (layout >> 19)
         return -1;
     if (chunk < (PAGE_SIZE >> 9) ||
         !is_power_of_2(chunk))
         return -2;
     nc = layout & 255;
     fc = (layout >> 8) & 255;
     fo = layout & (1<<16);
     geo->raid_disks = disks;
     geo->near_copies = nc;
     geo->far_copies = fc;
     geo->far_offset = fo;
     switch (layout >> 17) {
     case 0: /* original layout.  simple but not always optimal */
         geo->far_set_size = disks;
         break;
     case 1: /* "improved" layout which was buggy.  Hopefully no-one is
          * actually using this, but leave code here just in case.*/
         geo->far_set_size = disks/fc;
         WARN(geo->far_set_size < fc,
              "This RAID10 layout does not provide data safety - please backup and create new array\n");
         break;
     case 2: /* "improved" layout fixed to match documentation */
         geo->far_set_size = fc * nc;
         break;
     default: /* Not a valid layout */
         return -1;
     }
     geo->chunk_mask = chunk - 1;
     geo->chunk_shift = ffz(~chunk);
     return nc*fc;
 }
 
 static struct r10conf *setup_conf(struct mddev *mddev)
 {
     struct r10conf *conf = NULL;
     int err = -EINVAL;
     struct geom geo;
     int copies;
 
     copies = setup_geo(&geo, mddev, geo_new);
 
     if (copies == -2) {
         pr_warn("md/raid10:%s: chunk size must be at least PAGE_SIZE(%ld) and be a power of 2.\n",
             mdname(mddev), PAGE_SIZE);
         goto out;
     }
 
     if (copies < 2 || copies > mddev->raid_disks) {
         pr_warn("md/raid10:%s: unsupported raid10 layout: 0x%8x\n",
             mdname(mddev), mddev->new_layout);
         goto out;
     }
 
     err = -ENOMEM;
     conf = kzalloc(sizeof(struct r10conf), GFP_KERNEL);
     if (!conf)
         goto out;
 
     /* FIXME calc properly */
     conf->mirrors = kcalloc(mddev->raid_disks + max(0, -mddev->delta_disks),
                 sizeof(struct raid10_info),
                 GFP_KERNEL);
     if (!conf->mirrors)
         goto out;
 
     conf->tmppage = alloc_page(GFP_KERNEL);
     if (!conf->tmppage)
         goto out;
 
     conf->geo = geo;
     conf->copies = copies;
     err = mempool_init(&conf->r10bio_pool, NR_RAID_BIOS, r10bio_pool_alloc,
                rbio_pool_free, conf);
     if (err)
         goto out;
 
     err = bioset_init(&conf->bio_split, BIO_POOL_SIZE, 0, 0);
     if (err)
         goto out;
 
     calc_sectors(conf, mddev->dev_sectors);
     if (mddev->reshape_position == MaxSector) {
         conf->prev = conf->geo;
         conf->reshape_progress = MaxSector;
     } else {
         if (setup_geo(&conf->prev, mddev, geo_old) != conf->copies) {
             err = -EINVAL;
             goto out;
         }
         conf->reshape_progress = mddev->reshape_position;
         if (conf->prev.far_offset)
             conf->prev.stride = 1 << conf->prev.chunk_shift;
         else
             /* far_copies must be 1 */
             conf->prev.stride = conf->dev_sectors;
     }
     conf->reshape_safe = conf->reshape_progress;
     spin_lock_init(&conf->device_lock);
     INIT_LIST_HEAD(&conf->retry_list);
     INIT_LIST_HEAD(&conf->bio_end_io_list);
 
     spin_lock_init(&conf->resync_lock);
     init_waitqueue_head(&conf->wait_barrier);
     atomic_set(&conf->nr_pending, 0);
 
     err = -ENOMEM;
     conf->thread = md_register_thread(raid10d, mddev, "raid10");
     if (!conf->thread)
         goto out;
 
     conf->mddev = mddev;
     return conf;
 
  out:
     if (conf) {
         mempool_exit(&conf->r10bio_pool);
         kfree(conf->mirrors);
         safe_put_page(conf->tmppage);
         bioset_exit(&conf->bio_split);
         kfree(conf);
     }
     return ERR_PTR(err);
 }
 
 static void raid10_set_io_opt(struct r10conf *conf)
 {
     int raid_disks = conf->geo.raid_disks;
 
     if (!(conf->geo.raid_disks % conf->geo.near_copies))
         raid_disks /= conf->geo.near_copies;
     blk_queue_io_opt(conf->mddev->queue, (conf->mddev->chunk_sectors << 9) *
              raid_disks);
 }
 
 static int raid10_run(struct mddev *mddev)
 {
     struct r10conf *conf;
     int i, disk_idx;
     struct raid10_info *disk;
     struct md_rdev *rdev;
     sector_t size;
     sector_t min_offset_diff = 0;
     int first = 1;
 
     if (mddev_init_writes_pending(mddev) < 0)
         return -ENOMEM;
 
     if (mddev->private == NULL) {
         conf = setup_conf(mddev);
         if (IS_ERR(conf))
             return PTR_ERR(conf);
         mddev->private = conf;
     }
     conf = mddev->private;
     if (!conf)
         goto out;
 
     if (mddev_is_clustered(conf->mddev)) {
         int fc, fo;
 
         fc = (mddev->layout >> 8) & 255;
         fo = mddev->layout & (1<<16);
         if (fc > 1 || fo > 0) {
             pr_err("only near layout is supported by clustered"
                 " raid10\n");
             goto out_free_conf;
         }
     }
 
     mddev->thread = conf->thread;
     conf->thread = NULL;
 
     if (mddev->queue) {
         blk_queue_max_discard_sectors(mddev->queue,
                           UINT_MAX);
         blk_queue_max_write_zeroes_sectors(mddev->queue, 0);
         blk_queue_io_min(mddev->queue, mddev->chunk_sectors << 9);
         raid10_set_io_opt(conf);
     }
 
     rdev_for_each(rdev, mddev) {
         long long diff;
 
         disk_idx = rdev->raid_disk;
         if (disk_idx < 0)
             continue;
         if (disk_idx >= conf->geo.raid_disks &&
             disk_idx >= conf->prev.raid_disks)
             continue;
         disk = conf->mirrors + disk_idx;
 
         if (test_bit(Replacement, &rdev->flags)) {
             if (disk->replacement)
                 goto out_free_conf;
             disk->replacement = rdev;
         } else {
             if (disk->rdev)
                 goto out_free_conf;
             disk->rdev = rdev;
         }
         diff = (rdev->new_data_offset - rdev->data_offset);
         if (!mddev->reshape_backwards)
             diff = -diff;
         if (diff < 0)
             diff = 0;
         if (first || diff < min_offset_diff)
             min_offset_diff = diff;
 
         if (mddev->gendisk)
             disk_stack_limits(mddev->gendisk, rdev->bdev,
                       rdev->data_offset << 9);
 
         disk->head_position = 0;
         first = 0;
     }
 
     /* need to check that every block has at least one working mirror */
     if (!enough(conf, -1)) {
         pr_err("md/raid10:%s: not enough operational mirrors.\n",
                mdname(mddev));
         goto out_free_conf;
     }
 
     if (conf->reshape_progress != MaxSector) {
         /* must ensure that shape change is supported */
         if (conf->geo.far_copies != 1 &&
             conf->geo.far_offset == 0)
             goto out_free_conf;
         if (conf->prev.far_copies != 1 &&
             conf->prev.far_offset == 0)
             goto out_free_conf;
     }
 
     mddev->degraded = 0;
     for (i = 0;
          i < conf->geo.raid_disks
              || i < conf->prev.raid_disks;
          i++) {
 
         disk = conf->mirrors + i;
 
         if (!disk->rdev && disk->replacement) {
             /* The replacement is all we have - use it */
             disk->rdev = disk->replacement;
             disk->replacement = NULL;
             clear_bit(Replacement, &disk->rdev->flags);
         }
 
         if (!disk->rdev ||
             !test_bit(In_sync, &disk->rdev->flags)) {
             disk->head_position = 0;
             mddev->degraded++;
             if (disk->rdev &&
                 disk->rdev->saved_raid_disk < 0)
                 conf->fullsync = 1;
         }
 
         if (disk->replacement &&
             !test_bit(In_sync, &disk->replacement->flags) &&
             disk->replacement->saved_raid_disk < 0) {
             conf->fullsync = 1;
         }
 
         disk->recovery_disabled = mddev->recovery_disabled - 1;
     }
 
     if (mddev->recovery_cp != MaxSector)
         pr_notice("md/raid10:%s: not clean -- starting background reconstruction\n",
               mdname(mddev));
     pr_info("md/raid10:%s: active with %d out of %d devices\n",
         mdname(mddev), conf->geo.raid_disks - mddev->degraded,
         conf->geo.raid_disks);
     /*
      * Ok, everything is just fine now
      */
     mddev->dev_sectors = conf->dev_sectors;
     size = raid10_size(mddev, 0, 0);
     md_set_array_sectors(mddev, size);
     mddev->resync_max_sectors = size;
     set_bit(MD_FAILFAST_SUPPORTED, &mddev->flags);
 
     if (md_integrity_register(mddev))
         goto out_free_conf;
 
     if (conf->reshape_progress != MaxSector) {
         unsigned long before_length, after_length;
 
         before_length = ((1 << conf->prev.chunk_shift) *
                  conf->prev.far_copies);
         after_length = ((1 << conf->geo.chunk_shift) *
                 conf->geo.far_copies);
 
         if (max(before_length, after_length) > min_offset_diff) {
             /* This cannot work */
             pr_warn("md/raid10: offset difference not enough to continue reshape\n");
             goto out_free_conf;
         }
         conf->offset_diff = min_offset_diff;
 
         clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
         clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
         set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
         set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
         mddev->sync_thread = md_register_thread(md_do_sync, mddev,
                             "reshape");
         if (!mddev->sync_thread)
             goto out_free_conf;
     }
 
     return 0;
 
 out_free_conf:
     md_unregister_thread(&mddev->thread);
     mempool_exit(&conf->r10bio_pool);
     safe_put_page(conf->tmppage);
     kfree(conf->mirrors);
     kfree(conf);
     mddev->private = NULL;
 out:
     return -EIO;
 }
 
 static void raid10_free(struct mddev *mddev, void *priv)
 {
     struct r10conf *conf = priv;
 
     mempool_exit(&conf->r10bio_pool);
     safe_put_page(conf->tmppage);
     kfree(conf->mirrors);
     kfree(conf->mirrors_old);
     kfree(conf->mirrors_new);
     bioset_exit(&conf->bio_split);
     kfree(conf);
 }
 
 static void raid10_quiesce(struct mddev *mddev, int quiesce)
 {
     struct r10conf *conf = mddev->private;
 
     if (quiesce)
         raise_barrier(conf, 0);
     else
         lower_barrier(conf);
 }
 
 static int raid10_resize(struct mddev *mddev, sector_t sectors)
 {
     /* Resize of 'far' arrays is not supported.
      * For 'near' and 'offset' arrays we can set the
      * number of sectors used to be an appropriate multiple
      * of the chunk size.
      * For 'offset', this is far_copies*chunksize.
      * For 'near' the multiplier is the LCM of
      * near_copies and raid_disks.
      * So if far_copies > 1 && !far_offset, fail.
      * Else find LCM(raid_disks, near_copy)*far_copies and
      * multiply by chunk_size.  Then round to this number.
      * This is mostly done by raid10_size()
      */
     struct r10conf *conf = mddev->private;
     sector_t oldsize, size;
 
     if (mddev->reshape_position != MaxSector)
         return -EBUSY;
 
     if (conf->geo.far_copies > 1 && !conf->geo.far_offset)
         return -EINVAL;
 
     oldsize = raid10_size(mddev, 0, 0);
     size = raid10_size(mddev, sectors, 0);
     if (mddev->external_size &&
         mddev->array_sectors > size)
         return -EINVAL;
     if (mddev->bitmap) {
         int ret = md_bitmap_resize(mddev->bitmap, size, 0, 0);
         if (ret)
             return ret;
     }
     md_set_array_sectors(mddev, size);
     if (sectors > mddev->dev_sectors &&
         mddev->recovery_cp > oldsize) {
         mddev->recovery_cp = oldsize;
         set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
     }
     calc_sectors(conf, sectors);
     mddev->dev_sectors = conf->dev_sectors;
     mddev->resync_max_sectors = size;
     return 0;
 }
 
 static void *raid10_takeover_raid0(struct mddev *mddev, sector_t size, int devs)
 {
     struct md_rdev *rdev;
     struct r10conf *conf;
 
     if (mddev->degraded > 0) {
         pr_warn("md/raid10:%s: Error: degraded raid0!\n",
             mdname(mddev));
         return ERR_PTR(-EINVAL);
     }
     sector_div(size, devs);
 
     /* Set new parameters */
     mddev->new_level = 10;
     /* new layout: far_copies = 1, near_copies = 2 */
     mddev->new_layout = (1<<8) + 2;
     mddev->new_chunk_sectors = mddev->chunk_sectors;
     mddev->delta_disks = mddev->raid_disks;
     mddev->raid_disks *= 2;
     /* make sure it will be not marked as dirty */
     mddev->recovery_cp = MaxSector;
     mddev->dev_sectors = size;
 
     conf = setup_conf(mddev);
     if (!IS_ERR(conf)) {
         rdev_for_each(rdev, mddev)
             if (rdev->raid_disk >= 0) {
                 rdev->new_raid_disk = rdev->raid_disk * 2;
                 rdev->sectors = size;
             }
         conf->barrier = 1;
     }
 
     return conf;
 }
 
 static void *raid10_takeover(struct mddev *mddev)
 {
     struct r0conf *raid0_conf;
 
     /* raid10 can take over:
      *  raid0 - providing it has only two drives
      */
     if (mddev->level == 0) {
         /* for raid0 takeover only one zone is supported */
         raid0_conf = mddev->private;
         if (raid0_conf->nr_strip_zones > 1) {
             pr_warn("md/raid10:%s: cannot takeover raid 0 with more than one zone.\n",
                 mdname(mddev));
             return ERR_PTR(-EINVAL);
         }
         return raid10_takeover_raid0(mddev,
             raid0_conf->strip_zone->zone_end,
             raid0_conf->strip_zone->nb_dev);
     }
     return ERR_PTR(-EINVAL);
 }
 
 static int raid10_check_reshape(struct mddev *mddev)
 {
     /* Called when there is a request to change
      * - layout (to ->new_layout)
      * - chunk size (to ->new_chunk_sectors)
      * - raid_disks (by delta_disks)
      * or when trying to restart a reshape that was ongoing.
      *
      * We need to validate the request and possibly allocate
      * space if that might be an issue later.
      *
      * Currently we reject any reshape of a 'far' mode array,
      * allow chunk size to change if new is generally acceptable,
      * allow raid_disks to increase, and allow
      * a switch between 'near' mode and 'offset' mode.
      */
     struct r10conf *conf = mddev->private;
     struct geom geo;
 
     if (conf->geo.far_copies != 1 && !conf->geo.far_offset)
         return -EINVAL;
 
     if (setup_geo(&geo, mddev, geo_start) != conf->copies)
         /* mustn't change number of copies */
         return -EINVAL;
     if (geo.far_copies > 1 && !geo.far_offset)
         /* Cannot switch to 'far' mode */
         return -EINVAL;
 
     if (mddev->array_sectors & geo.chunk_mask)
             /* not factor of array size */
             return -EINVAL;
 
     if (!enough(conf, -1))
         return -EINVAL;
 
     kfree(conf->mirrors_new);
     conf->mirrors_new = NULL;
     if (mddev->delta_disks > 0) {
         /* allocate new 'mirrors' list */
         conf->mirrors_new =
             kcalloc(mddev->raid_disks + mddev->delta_disks,
                 sizeof(struct raid10_info),
                 GFP_KERNEL);
         if (!conf->mirrors_new)
             return -ENOMEM;
     }
     return 0;
 }
 
 /*
  * Need to check if array has failed when deciding whether to:
  *  - start an array
  *  - remove non-faulty devices
  *  - add a spare
  *  - allow a reshape
  * This determination is simple when no reshape is happening.
  * However if there is a reshape, we need to carefully check
  * both the before and after sections.
  * This is because some failed devices may only affect one
  * of the two sections, and some non-in_sync devices may
  * be insync in the section most affected by failed devices.
  */
 static int calc_degraded(struct r10conf *conf)
 {
     int degraded, degraded2;
     int i;
 
     rcu_read_lock();
     degraded = 0;
     /* 'prev' section first */
     for (i = 0; i < conf->prev.raid_disks; i++) {
         struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev);
         if (!rdev || test_bit(Faulty, &rdev->flags))
             degraded++;
         else if (!test_bit(In_sync, &rdev->flags))
             /* When we can reduce the number of devices in
              * an array, this might not contribute to
              * 'degraded'.  It does now.
              */
             degraded++;
     }
     rcu_read_unlock();
     if (conf->geo.raid_disks == conf->prev.raid_disks)
         return degraded;
     rcu_read_lock();
     degraded2 = 0;
     for (i = 0; i < conf->geo.raid_disks; i++) {
         struct md_rdev *rdev = rcu_dereference(conf->mirrors[i].rdev);
         if (!rdev || test_bit(Faulty, &rdev->flags))
             degraded2++;
         else if (!test_bit(In_sync, &rdev->flags)) {
             /* If reshape is increasing the number of devices,
              * this section has already been recovered, so
              * it doesn't contribute to degraded.
              * else it does.
              */
             if (conf->geo.raid_disks <= conf->prev.raid_disks)
                 degraded2++;
         }
     }
     rcu_read_unlock();
     if (degraded2 > degraded)
         return degraded2;
     return degraded;
 }
 
 static int raid10_start_reshape(struct mddev *mddev)
 {
     /* A 'reshape' has been requested. This commits
      * the various 'new' fields and sets MD_RECOVER_RESHAPE
      * This also checks if there are enough spares and adds them
      * to the array.
      * We currently require enough spares to make the final
      * array non-degraded.  We also require that the difference
      * between old and new data_offset - on each device - is
      * enough that we never risk over-writing.
      */
 
     unsigned long before_length, after_length;
     sector_t min_offset_diff = 0;
     int first = 1;
     struct geom new;
     struct r10conf *conf = mddev->private;
     struct md_rdev *rdev;
     int spares = 0;
     int ret;
 
     if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery))
         return -EBUSY;
 
     if (setup_geo(&new, mddev, geo_start) != conf->copies)
         return -EINVAL;
 
     before_length = ((1 << conf->prev.chunk_shift) *
              conf->prev.far_copies);
     after_length = ((1 << conf->geo.chunk_shift) *
             conf->geo.far_copies);
 
     rdev_for_each(rdev, mddev) {
         if (!test_bit(In_sync, &rdev->flags)
             && !test_bit(Faulty, &rdev->flags))
             spares++;
         if (rdev->raid_disk >= 0) {
             long long diff = (rdev->new_data_offset
                       - rdev->data_offset);
             if (!mddev->reshape_backwards)
                 diff = -diff;
             if (diff < 0)
                 diff = 0;
             if (first || diff < min_offset_diff)
                 min_offset_diff = diff;
             first = 0;
         }
     }
 
     if (max(before_length, after_length) > min_offset_diff)
         return -EINVAL;
 
     if (spares < mddev->delta_disks)
         return -EINVAL;
 
     conf->offset_diff = min_offset_diff;
     spin_lock_irq(&conf->device_lock);
     if (conf->mirrors_new) {
         memcpy(conf->mirrors_new, conf->mirrors,
                sizeof(struct raid10_info)*conf->prev.raid_disks);
         smp_mb();
         kfree(conf->mirrors_old);
         conf->mirrors_old = conf->mirrors;
         conf->mirrors = conf->mirrors_new;
         conf->mirrors_new = NULL;
     }
     setup_geo(&conf->geo, mddev, geo_start);
     smp_mb();
     if (mddev->reshape_backwards) {
         sector_t size = raid10_size(mddev, 0, 0);
         if (size < mddev->array_sectors) {
             spin_unlock_irq(&conf->device_lock);
             pr_warn("md/raid10:%s: array size must be reduce before number of disks\n",
                 mdname(mddev));
             return -EINVAL;
         }
         mddev->resync_max_sectors = size;
         conf->reshape_progress = size;
     } else
         conf->reshape_progress = 0;
     conf->reshape_safe = conf->reshape_progress;
     spin_unlock_irq(&conf->device_lock);
 
     if (mddev->delta_disks && mddev->bitmap) {
         struct mdp_superblock_1 *sb = NULL;
         sector_t oldsize, newsize;
 
         oldsize = raid10_size(mddev, 0, 0);
         newsize = raid10_size(mddev, 0, conf->geo.raid_disks);
 
         if (!mddev_is_clustered(mddev)) {
             ret = md_bitmap_resize(mddev->bitmap, newsize, 0, 0);
             if (ret)
                 goto abort;
             else
                 goto out;
         }
 
         rdev_for_each(rdev, mddev) {
             if (rdev->raid_disk > -1 &&
                 !test_bit(Faulty, &rdev->flags))
                 sb = page_address(rdev->sb_page);
         }
 
         /*
          * some node is already performing reshape, and no need to
          * call md_bitmap_resize again since it should be called when
          * receiving BITMAP_RESIZE msg
          */
         if ((sb && (le32_to_cpu(sb->feature_map) &
                 MD_FEATURE_RESHAPE_ACTIVE)) || (oldsize == newsize))
             goto out;
 
         ret = md_bitmap_resize(mddev->bitmap, newsize, 0, 0);
         if (ret)
             goto abort;
 
         ret = md_cluster_ops->resize_bitmaps(mddev, newsize, oldsize);
         if (ret) {
             md_bitmap_resize(mddev->bitmap, oldsize, 0, 0);
             goto abort;
         }
     }
 out:
     if (mddev->delta_disks > 0) {
         rdev_for_each(rdev, mddev)
             if (rdev->raid_disk < 0 &&
                 !test_bit(Faulty, &rdev->flags)) {
                 if (raid10_add_disk(mddev, rdev) == 0) {
                     if (rdev->raid_disk >=
                         conf->prev.raid_disks)
                         set_bit(In_sync, &rdev->flags);
                     else
                         rdev->recovery_offset = 0;
 
                     /* Failure here is OK */
                     sysfs_link_rdev(mddev, rdev);
                 }
             } else if (rdev->raid_disk >= conf->prev.raid_disks
                    && !test_bit(Faulty, &rdev->flags)) {
                 /* This is a spare that was manually added */
                 set_bit(In_sync, &rdev->flags);
             }
     }
     /* When a reshape changes the number of devices,
      * ->degraded is measured against the larger of the
      * pre and  post numbers.
      */
     spin_lock_irq(&conf->device_lock);
     mddev->degraded = calc_degraded(conf);
     spin_unlock_irq(&conf->device_lock);
     mddev->raid_disks = conf->geo.raid_disks;
     mddev->reshape_position = conf->reshape_progress;
     set_bit(MD_SB_CHANGE_DEVS, &mddev->sb_flags);
 
     clear_bit(MD_RECOVERY_SYNC, &mddev->recovery);
     clear_bit(MD_RECOVERY_CHECK, &mddev->recovery);
     clear_bit(MD_RECOVERY_DONE, &mddev->recovery);
     set_bit(MD_RECOVERY_RESHAPE, &mddev->recovery);
     set_bit(MD_RECOVERY_RUNNING, &mddev->recovery);
 
     mddev->sync_thread = md_register_thread(md_do_sync, mddev,
                         "reshape");
     if (!mddev->sync_thread) {
         ret = -EAGAIN;
         goto abort;
     }
     conf->reshape_checkpoint = jiffies;
     md_wakeup_thread(mddev->sync_thread);
     md_new_event();
     return 0;
 
 abort:
     mddev->recovery = 0;
     spin_lock_irq(&conf->device_lock);
     conf->geo = conf->prev;
     mddev->raid_disks = conf->geo.raid_disks;
     rdev_for_each(rdev, mddev)
         rdev->new_data_offset = rdev->data_offset;
     smp_wmb();
     conf->reshape_progress = MaxSector;
     conf->reshape_safe = MaxSector;
     mddev->reshape_position = MaxSector;
     spin_unlock_irq(&conf->device_lock);
     return ret;
 }
 
 /* Calculate the last device-address that could contain
  * any block from the chunk that includes the array-address 's'
  * and report the next address.
  * i.e. the address returned will be chunk-aligned and after
  * any data that is in the chunk containing 's'.
  */
 static sector_t last_dev_address(sector_t s, struct geom *geo)
 {
     s = (s | geo->chunk_mask) + 1;
     s >>= geo->chunk_shift;
     s *= geo->near_copies;
     s = DIV_ROUND_UP_SECTOR_T(s, geo->raid_disks);
     s *= geo->far_copies;
     s <<= geo->chunk_shift;
     return s;
 }
 
 /* Calculate the first device-address that could contain
  * any block from the chunk that includes the array-address 's'.
  * This too will be the start of a chunk
  */
 static sector_t first_dev_address(sector_t s, struct geom *geo)
 {
     s >>= geo->chunk_shift;
     s *= geo->near_copies;
     sector_div(s, geo->raid_disks);
     s *= geo->far_copies;
     s <<= geo->chunk_shift;
     return s;
 }
 
 static sector_t reshape_request(struct mddev *mddev, sector_t sector_nr,
                 int *skipped)
 {
     /* We simply copy at most one chunk (smallest of old and new)
      * at a time, possibly less if that exceeds RESYNC_PAGES,
      * or we hit a bad block or something.
      * This might mean we pause for normal IO in the middle of
      * a chunk, but that is not a problem as mddev->reshape_position
      * can record any location.
      *
      * If we will want to write to a location that isn't
      * yet recorded as 'safe' (i.e. in metadata on disk) then
      * we need to flush all reshape requests and update the metadata.
      *
      * When reshaping forwards (e.g. to more devices), we interpret
      * 'safe' as the earliest block which might not have been copied
      * down yet.  We divide this by previous stripe size and multiply
      * by previous stripe length to get lowest device offset that we
      * cannot write to yet.
      * We interpret 'sector_nr' as an address that we want to write to.
      * From this we use last_device_address() to find where we might
      * write to, and first_device_address on the  'safe' position.
      * If this 'next' write position is after the 'safe' position,
      * we must update the metadata to increase the 'safe' position.
      *
      * When reshaping backwards, we round in the opposite direction
      * and perform the reverse test:  next write position must not be
      * less than current safe position.
      *
      * In all this the minimum difference in data offsets
      * (conf->offset_diff - always positive) allows a bit of slack,
      * so next can be after 'safe', but not by more than offset_diff
      *
      * We need to prepare all the bios here before we start any IO
      * to ensure the size we choose is acceptable to all devices.
      * The means one for each copy for write-out and an extra one for
      * read-in.
      * We store the read-in bio in ->master_bio and the others in
      * ->devs[x].bio and ->devs[x].repl_bio.
      */
     struct r10conf *conf = mddev->private;
     struct r10bio *r10_bio;
     sector_t next, safe, last;
     int max_sectors;
     int nr_sectors;
     int s;
     struct md_rdev *rdev;
     int need_flush = 0;
     struct bio *blist;
     struct bio *bio, *read_bio;
     int sectors_done = 0;
     struct page **pages;
 
     if (sector_nr == 0) {
         /* If restarting in the middle, skip the initial sectors */
         if (mddev->reshape_backwards &&
             conf->reshape_progress < raid10_size(mddev, 0, 0)) {
             sector_nr = (raid10_size(mddev, 0, 0)
                      - conf->reshape_progress);
         } else if (!mddev->reshape_backwards &&
                conf->reshape_progress > 0)
             sector_nr = conf->reshape_progress;
         if (sector_nr) {
             mddev->curr_resync_completed = sector_nr;
             sysfs_notify_dirent_safe(mddev->sysfs_completed);
             *skipped = 1;
             return sector_nr;
         }
     }
 
     /* We don't use sector_nr to track where we are up to
      * as that doesn't work well for ->reshape_backwards.
      * So just use ->reshape_progress.
      */
     if (mddev->reshape_backwards) {
         /* 'next' is the earliest device address that we might
          * write to for this chunk in the new layout
          */
         next = first_dev_address(conf->reshape_progress - 1,
                      &conf->geo);
 
         /* 'safe' is the last device address that we might read from
          * in the old layout after a restart
          */
         safe = last_dev_address(conf->reshape_safe - 1,
                     &conf->prev);
 
         if (next + conf->offset_diff < safe)
             need_flush = 1;
 
         last = conf->reshape_progress - 1;
         sector_nr = last & ~(sector_t)(conf->geo.chunk_mask
                            & conf->prev.chunk_mask);
         if (sector_nr + RESYNC_SECTORS < last)
             sector_nr = last + 1 - RESYNC_SECTORS;
     } else {
         /* 'next' is after the last device address that we
          * might write to for this chunk in the new layout
          */
         next = last_dev_address(conf->reshape_progress, &conf->geo);
 
         /* 'safe' is the earliest device address that we might
          * read from in the old layout after a restart
          */
         safe = first_dev_address(conf->reshape_safe, &conf->prev);
 
         /* Need to update metadata if 'next' might be beyond 'safe'
          * as that would possibly corrupt data
          */
         if (next > safe + conf->offset_diff)
             need_flush = 1;
 
         sector_nr = conf->reshape_progress;
         last  = sector_nr | (conf->geo.chunk_mask
                      & conf->prev.chunk_mask);
 
         if (sector_nr + RESYNC_SECTORS <= last)
             last = sector_nr + RESYNC_SECTORS - 1;
     }
 
     if (need_flush ||
         time_after(jiffies, conf->reshape_checkpoint + 10*HZ)) {
         /* Need to update reshape_position in metadata */
         wait_barrier(conf, false);
         mddev->reshape_position = conf->reshape_progress;
         if (mddev->reshape_backwards)
             mddev->curr_resync_completed = raid10_size(mddev, 0, 0)
                 - conf->reshape_progress;
         else
             mddev->curr_resync_completed = conf->reshape_progress;
         conf->reshape_checkpoint = jiffies;
         set_bit(MD_SB_CHANGE_DEVS, &mddev->sb_flags);
         md_wakeup_thread(mddev->thread);
         wait_event(mddev->sb_wait, mddev->sb_flags == 0 ||
                test_bit(MD_RECOVERY_INTR, &mddev->recovery));
         if (test_bit(MD_RECOVERY_INTR, &mddev->recovery)) {
             allow_barrier(conf);
             return sectors_done;
         }
         conf->reshape_safe = mddev->reshape_position;
         allow_barrier(conf);
     }
 
     raise_barrier(conf, 0);
 read_more:
     /* Now schedule reads for blocks from sector_nr to last */
     r10_bio = raid10_alloc_init_r10buf(conf);
     r10_bio->state = 0;
     raise_barrier(conf, 1);
     atomic_set(&r10_bio->remaining, 0);
     r10_bio->mddev = mddev;
     r10_bio->sector = sector_nr;
     set_bit(R10BIO_IsReshape, &r10_bio->state);
     r10_bio->sectors = last - sector_nr + 1;
     rdev = read_balance(conf, r10_bio, &max_sectors);
     BUG_ON(!test_bit(R10BIO_Previous, &r10_bio->state));
 
     if (!rdev) {
         /* Cannot read from here, so need to record bad blocks
          * on all the target devices.
          */
         // FIXME
         mempool_free(r10_bio, &conf->r10buf_pool);
         set_bit(MD_RECOVERY_INTR, &mddev->recovery);
         return sectors_done;
     }
 
     read_bio = bio_alloc_bioset(rdev->bdev, RESYNC_PAGES, REQ_OP_READ,
                     GFP_KERNEL, &mddev->bio_set);
     read_bio->bi_iter.bi_sector = (r10_bio->devs[r10_bio->read_slot].addr
                    + rdev->data_offset);
     read_bio->bi_private = r10_bio;
     read_bio->bi_end_io = end_reshape_read;
     r10_bio->master_bio = read_bio;
     r10_bio->read_slot = r10_bio->devs[r10_bio->read_slot].devnum;
 
     /*
      * Broadcast RESYNC message to other nodes, so all nodes would not
      * write to the region to avoid conflict.
     */
     if (mddev_is_clustered(mddev) && conf->cluster_sync_high <= sector_nr) {
         struct mdp_superblock_1 *sb = NULL;
         int sb_reshape_pos = 0;
 
         conf->cluster_sync_low = sector_nr;
         conf->cluster_sync_high = sector_nr + CLUSTER_RESYNC_WINDOW_SECTORS;
         sb = page_address(rdev->sb_page);
         if (sb) {
             sb_reshape_pos = le64_to_cpu(sb->reshape_position);
             /*
              * Set cluster_sync_low again if next address for array
              * reshape is less than cluster_sync_low. Since we can't
              * update cluster_sync_low until it has finished reshape.
              */
             if (sb_reshape_pos < conf->cluster_sync_low)
                 conf->cluster_sync_low = sb_reshape_pos;
         }
 
         md_cluster_ops->resync_info_update(mddev, conf->cluster_sync_low,
                               conf->cluster_sync_high);
     }
 
     /* Now find the locations in the new layout */
     __raid10_find_phys(&conf->geo, r10_bio);
 
     blist = read_bio;
     read_bio->bi_next = NULL;
 
     rcu_read_lock();
     for (s = 0; s < conf->copies*2; s++) {
         struct bio *b;
         int d = r10_bio->devs[s/2].devnum;
         struct md_rdev *rdev2;
         if (s&1) {
             rdev2 = rcu_dereference(conf->mirrors[d].replacement);
             b = r10_bio->devs[s/2].repl_bio;
         } else {
             rdev2 = rcu_dereference(conf->mirrors[d].rdev);
             b = r10_bio->devs[s/2].bio;
         }
         if (!rdev2 || test_bit(Faulty, &rdev2->flags))
             continue;
 
         bio_set_dev(b, rdev2->bdev);
         b->bi_iter.bi_sector = r10_bio->devs[s/2].addr +
             rdev2->new_data_offset;
         b->bi_end_io = end_reshape_write;
         bio_set_op_attrs(b, REQ_OP_WRITE, 0);
         b->bi_next = blist;
         blist = b;
     }
 
     /* Now add as many pages as possible to all of these bios. */
 
     nr_sectors = 0;
     pages = get_resync_pages(r10_bio->devs[0].bio)->pages;
     for (s = 0 ; s < max_sectors; s += PAGE_SIZE >> 9) {
         struct page *page = pages[s / (PAGE_SIZE >> 9)];
         int len = (max_sectors - s) << 9;
         if (len > PAGE_SIZE)
             len = PAGE_SIZE;
         for (bio = blist; bio ; bio = bio->bi_next) {
             /*
              * won't fail because the vec table is big enough
              * to hold all these pages
              */
             bio_add_page(bio, page, len, 0);
         }
         sector_nr += len >> 9;
         nr_sectors += len >> 9;
     }
     rcu_read_unlock();
     r10_bio->sectors = nr_sectors;
 
     /* Now submit the read */
     md_sync_acct_bio(read_bio, r10_bio->sectors);
     atomic_inc(&r10_bio->remaining);
     read_bio->bi_next = NULL;
     submit_bio_noacct(read_bio);
     sectors_done += nr_sectors;
     if (sector_nr <= last)
         goto read_more;
 
     lower_barrier(conf);
 
     /* Now that we have done the whole section we can
      * update reshape_progress
      */
     if (mddev->reshape_backwards)
         conf->reshape_progress -= sectors_done;
     else
         conf->reshape_progress += sectors_done;
 
     return sectors_done;
 }
 
 static void end_reshape_request(struct r10bio *r10_bio);
 static int handle_reshape_read_error(struct mddev *mddev,
                      struct r10bio *r10_bio);
 static void reshape_request_write(struct mddev *mddev, struct r10bio *r10_bio)
 {
     /* Reshape read completed.  Hopefully we have a block
      * to write out.
      * If we got a read error then we do sync 1-page reads from
      * elsewhere until we find the data - or give up.
      */
     struct r10conf *conf = mddev->private;
     int s;
 
     if (!test_bit(R10BIO_Uptodate, &r10_bio->state))
         if (handle_reshape_read_error(mddev, r10_bio) < 0) {
             /* Reshape has been aborted */
             md_done_sync(mddev, r10_bio->sectors, 0);
             return;
         }
 
     /* We definitely have the data in the pages, schedule the
      * writes.
      */
     atomic_set(&r10_bio->remaining, 1);
     for (s = 0; s < conf->copies*2; s++) {
         struct bio *b;
         int d = r10_bio->devs[s/2].devnum;
         struct md_rdev *rdev;
         rcu_read_lock();
         if (s&1) {
             rdev = rcu_dereference(conf->mirrors[d].replacement);
             b = r10_bio->devs[s/2].repl_bio;
         } else {
             rdev = rcu_dereference(conf->mirrors[d].rdev);
             b = r10_bio->devs[s/2].bio;
         }
         if (!rdev || test_bit(Faulty, &rdev->flags)) {
             rcu_read_unlock();
             continue;
         }
         atomic_inc(&rdev->nr_pending);
         rcu_read_unlock();
         md_sync_acct_bio(b, r10_bio->sectors);
         atomic_inc(&r10_bio->remaining);
         b->bi_next = NULL;
         submit_bio_noacct(b);
     }
     end_reshape_request(r10_bio);
 }
 
 static void end_reshape(struct r10conf *conf)
 {
     if (test_bit(MD_RECOVERY_INTR, &conf->mddev->recovery))
         return;
 
     spin_lock_irq(&conf->device_lock);
     conf->prev = conf->geo;
     md_finish_reshape(conf->mddev);
     smp_wmb();
     conf->reshape_progress = MaxSector;
     conf->reshape_safe = MaxSector;
     spin_unlock_irq(&conf->device_lock);
 
     if (conf->mddev->queue)
         raid10_set_io_opt(conf);
     conf->fullsync = 0;
 }
 
 static void raid10_update_reshape_pos(struct mddev *mddev)
 {
     struct r10conf *conf = mddev->private;
     sector_t lo, hi;
 
     md_cluster_ops->resync_info_get(mddev, &lo, &hi);
     if (((mddev->reshape_position <= hi) && (mddev->reshape_position >= lo))
         || mddev->reshape_position == MaxSector)
         conf->reshape_progress = mddev->reshape_position;
     else
         WARN_ON_ONCE(1);
 }
 
 static int handle_reshape_read_error(struct mddev *mddev,
                      struct r10bio *r10_bio)
 {
     /* Use sync reads to get the blocks from somewhere else */
     int sectors = r10_bio->sectors;
     struct r10conf *conf = mddev->private;
     struct r10bio *r10b;
     int slot = 0;
     int idx = 0;
     struct page **pages;
 
     r10b = kmalloc(struct_size(r10b, devs, conf->copies), GFP_NOIO);
     if (!r10b) {
         set_bit(MD_RECOVERY_INTR, &mddev->recovery);
         return -ENOMEM;
     }
 
     /* reshape IOs share pages from .devs[0].bio */
     pages = get_resync_pages(r10_bio->devs[0].bio)->pages;
 
     r10b->sector = r10_bio->sector;
     __raid10_find_phys(&conf->prev, r10b);
 
     while (sectors) {
         int s = sectors;
         int success = 0;
         int first_slot = slot;
 
         if (s > (PAGE_SIZE >> 9))
             s = PAGE_SIZE >> 9;
 
         rcu_read_lock();
         while (!success) {
             int d = r10b->devs[slot].devnum;
             struct md_rdev *rdev = rcu_dereference(conf->mirrors[d].rdev);
             sector_t addr;
             if (rdev == NULL ||
                 test_bit(Faulty, &rdev->flags) ||
                 !test_bit(In_sync, &rdev->flags))
                 goto failed;
 
             addr = r10b->devs[slot].addr + idx * PAGE_SIZE;
             atomic_inc(&rdev->nr_pending);
             rcu_read_unlock();
             success = sync_page_io(rdev,
                            addr,
                            s << 9,
                            pages[idx],
                            REQ_OP_READ, false);
             rdev_dec_pending(rdev, mddev);
             rcu_read_lock();
             if (success)
                 break;
         failed:
             slot++;
             if (slot >= conf->copies)
                 slot = 0;
             if (slot == first_slot)
                 break;
         }
         rcu_read_unlock();
         if (!success) {
             /* couldn't read this block, must give up */
             set_bit(MD_RECOVERY_INTR,
                 &mddev->recovery);
             kfree(r10b);
             return -EIO;
         }
         sectors -= s;
         idx++;
     }
     kfree(r10b);
     return 0;
 }
 
 static void end_reshape_write(struct bio *bio)
 {
     struct r10bio *r10_bio = get_resync_r10bio(bio);
     struct mddev *mddev = r10_bio->mddev;
     struct r10conf *conf = mddev->private;
     int d;
     int slot;
     int repl;
     struct md_rdev *rdev = NULL;
 
     d = find_bio_disk(conf, r10_bio, bio, &slot, &repl);
     if (repl)
         rdev = conf->mirrors[d].replacement;
     if (!rdev) {
         smp_mb();
         rdev = conf->mirrors[d].rdev;
     }
 
     if (bio->bi_status) {
         /* FIXME should record badblock */
         md_error(mddev, rdev);
     }
 
     rdev_dec_pending(rdev, mddev);
     end_reshape_request(r10_bio);
 }
 
 static void end_reshape_request(struct r10bio *r10_bio)
 {
     if (!atomic_dec_and_test(&r10_bio->remaining))
         return;
     md_done_sync(r10_bio->mddev, r10_bio->sectors, 1);
     bio_put(r10_bio->master_bio);
     put_buf(r10_bio);
 }
 
 static void raid10_finish_reshape(struct mddev *mddev)
 {
     struct r10conf *conf = mddev->private;
 
     if (test_bit(MD_RECOVERY_INTR, &mddev->recovery))
         return;
 
     if (mddev->delta_disks > 0) {
         if (mddev->recovery_cp > mddev->resync_max_sectors) {
             mddev->recovery_cp = mddev->resync_max_sectors;
             set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
         }
         mddev->resync_max_sectors = mddev->array_sectors;
     } else {
         int d;
         rcu_read_lock();
         for (d = conf->geo.raid_disks ;
              d < conf->geo.raid_disks - mddev->delta_disks;
              d++) {
             struct md_rdev *rdev = rcu_dereference(conf->mirrors[d].rdev);
             if (rdev)
                 clear_bit(In_sync, &rdev->flags);
             rdev = rcu_dereference(conf->mirrors[d].replacement);
             if (rdev)
                 clear_bit(In_sync, &rdev->flags);
         }
         rcu_read_unlock();
     }
     mddev->layout = mddev->new_layout;
     mddev->chunk_sectors = 1 << conf->geo.chunk_shift;
     mddev->reshape_position = MaxSector;
     mddev->delta_disks = 0;
     mddev->reshape_backwards = 0;
 }
 
 static struct md_personality raid10_personality =
 {
     .name       = "raid10",
     .level      = 10,
     .owner      = THIS_MODULE,
     .make_request   = raid10_make_request,
     .run        = raid10_run,
     .free       = raid10_free,
     .status     = raid10_status,
     .error_handler  = raid10_error,
     .hot_add_disk   = raid10_add_disk,
     .hot_remove_disk= raid10_remove_disk,
     .spare_active   = raid10_spare_active,
     .sync_request   = raid10_sync_request,
     .quiesce    = raid10_quiesce,
     .size       = raid10_size,
     .resize     = raid10_resize,
     .takeover   = raid10_takeover,
     .check_reshape  = raid10_check_reshape,
     .start_reshape  = raid10_start_reshape,
     .finish_reshape = raid10_finish_reshape,
     .update_reshape_pos = raid10_update_reshape_pos,
 };
 
 static int __init raid_init(void)
 {
     return register_md_personality(&raid10_personality);
 }
 
 static void raid_exit(void)
 {
     unregister_md_personality(&raid10_personality);
 }
 
 module_init(raid_init);
 module_exit(raid_exit);
 MODULE_LICENSE("GPL");
 MODULE_DESCRIPTION("RAID10 (striped mirror) personality for MD");
 MODULE_ALIAS("md-personality-9"); /* RAID10 */
 MODULE_ALIAS("md-raid10");
 MODULE_ALIAS("md-level-10");