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[linux-2.6-microblaze.git] / fs / btrfs / raid56.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright (C) 2012 Fusion-io  All rights reserved.
 * Copyright (C) 2012 Intel Corp. All rights reserved.
 */

#include <linux/sched.h>
#include <linux/bio.h>
#include <linux/slab.h>
#include <linux/blkdev.h>
#include <linux/raid/pq.h>
#include <linux/hash.h>
#include <linux/list_sort.h>
#include <linux/raid/xor.h>
#include <linux/mm.h>
#include "misc.h"
#include "ctree.h"
#include "disk-io.h"
#include "volumes.h"
#include "raid56.h"
#include "async-thread.h"

/* set when additional merges to this rbio are not allowed */
#define RBIO_RMW_LOCKED_BIT     1

/*
 * set when this rbio is sitting in the hash, but it is just a cache
 * of past RMW
 */
#define RBIO_CACHE_BIT          2

/*
 * set when it is safe to trust the stripe_pages for caching
 */
#define RBIO_CACHE_READY_BIT    3

#define RBIO_CACHE_SIZE 1024

#define BTRFS_STRIPE_HASH_TABLE_BITS                            11

/* Used by the raid56 code to lock stripes for read/modify/write */
struct btrfs_stripe_hash {
        struct list_head hash_list;
        spinlock_t lock;
};

/* Used by the raid56 code to lock stripes for read/modify/write */
struct btrfs_stripe_hash_table {
        struct list_head stripe_cache;
        spinlock_t cache_lock;
        int cache_size;
        struct btrfs_stripe_hash table[];
};

/*
 * A bvec like structure to present a sector inside a page.
 *
 * Unlike bvec we don't need bvlen, as it's fixed to sectorsize.
 */
struct sector_ptr {
        struct page *page;
        unsigned int pgoff:24;
        unsigned int uptodate:8;
};

enum btrfs_rbio_ops {
        BTRFS_RBIO_WRITE,
        BTRFS_RBIO_READ_REBUILD,
        BTRFS_RBIO_PARITY_SCRUB,
        BTRFS_RBIO_REBUILD_MISSING,
};

struct btrfs_raid_bio {
        struct btrfs_io_context *bioc;

        /* while we're doing rmw on a stripe
         * we put it into a hash table so we can
         * lock the stripe and merge more rbios
         * into it.
         */
        struct list_head hash_list;

        /*
         * LRU list for the stripe cache
         */
        struct list_head stripe_cache;

        /*
         * for scheduling work in the helper threads
         */
        struct work_struct work;

        /*
         * bio list and bio_list_lock are used
         * to add more bios into the stripe
         * in hopes of avoiding the full rmw
         */
        struct bio_list bio_list;
        spinlock_t bio_list_lock;

        /* also protected by the bio_list_lock, the
         * plug list is used by the plugging code
         * to collect partial bios while plugged.  The
         * stripe locking code also uses it to hand off
         * the stripe lock to the next pending IO
         */
        struct list_head plug_list;

        /*
         * flags that tell us if it is safe to
         * merge with this bio
         */
        unsigned long flags;

        /*
         * set if we're doing a parity rebuild
         * for a read from higher up, which is handled
         * differently from a parity rebuild as part of
         * rmw
         */
        enum btrfs_rbio_ops operation;

        /* Size of each individual stripe on disk */
        u32 stripe_len;

        /* How many pages there are for the full stripe including P/Q */
        u16 nr_pages;

        /* How many sectors there are for the full stripe including P/Q */
        u16 nr_sectors;

        /* Number of data stripes (no p/q) */
        u8 nr_data;

        /* Numer of all stripes (including P/Q) */
        u8 real_stripes;

        /* How many pages there are for each stripe */
        u8 stripe_npages;

        /* How many sectors there are for each stripe */
        u8 stripe_nsectors;

        /* First bad stripe, -1 means no corruption */
        s8 faila;

        /* Second bad stripe (for RAID6 use) */
        s8 failb;

        /* Stripe number that we're scrubbing  */
        u8 scrubp;

        /*
         * size of all the bios in the bio_list.  This
         * helps us decide if the rbio maps to a full
         * stripe or not
         */
        int bio_list_bytes;

        int generic_bio_cnt;

        refcount_t refs;

        atomic_t stripes_pending;

        atomic_t error;
        /*
         * these are two arrays of pointers.  We allocate the
         * rbio big enough to hold them both and setup their
         * locations when the rbio is allocated
         */

        /* pointers to pages that we allocated for
         * reading/writing stripes directly from the disk (including P/Q)
         */
        struct page **stripe_pages;

        /* Pointers to the sectors in the bio_list, for faster lookup */
        struct sector_ptr *bio_sectors;

        /*
         * For subpage support, we need to map each sector to above
         * stripe_pages.
         */
        struct sector_ptr *stripe_sectors;

        /* Bitmap to record which horizontal stripe has data */
        unsigned long *dbitmap;

        /* allocated with real_stripes-many pointers for finish_*() calls */
        void **finish_pointers;

        /* Allocated with stripe_nsectors-many bits for finish_*() calls */
        unsigned long *finish_pbitmap;
};

static int __raid56_parity_recover(struct btrfs_raid_bio *rbio);
static noinline void finish_rmw(struct btrfs_raid_bio *rbio);
static void rmw_work(struct work_struct *work);
static void read_rebuild_work(struct work_struct *work);
static int fail_bio_stripe(struct btrfs_raid_bio *rbio, struct bio *bio);
static int fail_rbio_index(struct btrfs_raid_bio *rbio, int failed);
static void __free_raid_bio(struct btrfs_raid_bio *rbio);
static void index_rbio_pages(struct btrfs_raid_bio *rbio);
static int alloc_rbio_pages(struct btrfs_raid_bio *rbio);

static noinline void finish_parity_scrub(struct btrfs_raid_bio *rbio,
                                         int need_check);
static void scrub_parity_work(struct work_struct *work);

static void start_async_work(struct btrfs_raid_bio *rbio, work_func_t work_func)
{
        INIT_WORK(&rbio->work, work_func);
        queue_work(rbio->bioc->fs_info->rmw_workers, &rbio->work);
}

/*
 * the stripe hash table is used for locking, and to collect
 * bios in hopes of making a full stripe
 */
int btrfs_alloc_stripe_hash_table(struct btrfs_fs_info *info)
{
        struct btrfs_stripe_hash_table *table;
        struct btrfs_stripe_hash_table *x;
        struct btrfs_stripe_hash *cur;
        struct btrfs_stripe_hash *h;
        int num_entries = 1 << BTRFS_STRIPE_HASH_TABLE_BITS;
        int i;

        if (info->stripe_hash_table)
                return 0;

        /*
         * The table is large, starting with order 4 and can go as high as
         * order 7 in case lock debugging is turned on.
         *
         * Try harder to allocate and fallback to vmalloc to lower the chance
         * of a failing mount.
         */
        table = kvzalloc(struct_size(table, table, num_entries), GFP_KERNEL);
        if (!table)
                return -ENOMEM;

        spin_lock_init(&table->cache_lock);
        INIT_LIST_HEAD(&table->stripe_cache);

        h = table->table;

        for (i = 0; i < num_entries; i++) {
                cur = h + i;
                INIT_LIST_HEAD(&cur->hash_list);
                spin_lock_init(&cur->lock);
        }

        x = cmpxchg(&info->stripe_hash_table, NULL, table);
        kvfree(x);
        return 0;
}

/*
 * caching an rbio means to copy anything from the
 * bio_sectors array into the stripe_pages array.  We
 * use the page uptodate bit in the stripe cache array
 * to indicate if it has valid data
 *
 * once the caching is done, we set the cache ready
 * bit.
 */
static void cache_rbio_pages(struct btrfs_raid_bio *rbio)
{
        int i;
        int ret;

        ret = alloc_rbio_pages(rbio);
        if (ret)
                return;

        for (i = 0; i < rbio->nr_sectors; i++) {
                /* Some range not covered by bio (partial write), skip it */
                if (!rbio->bio_sectors[i].page)
                        continue;

                ASSERT(rbio->stripe_sectors[i].page);
                memcpy_page(rbio->stripe_sectors[i].page,
                            rbio->stripe_sectors[i].pgoff,
                            rbio->bio_sectors[i].page,
                            rbio->bio_sectors[i].pgoff,
                            rbio->bioc->fs_info->sectorsize);
                rbio->stripe_sectors[i].uptodate = 1;
        }
        set_bit(RBIO_CACHE_READY_BIT, &rbio->flags);
}

/*
 * we hash on the first logical address of the stripe
 */
static int rbio_bucket(struct btrfs_raid_bio *rbio)
{
        u64 num = rbio->bioc->raid_map[0];

        /*
         * we shift down quite a bit.  We're using byte
         * addressing, and most of the lower bits are zeros.
         * This tends to upset hash_64, and it consistently
         * returns just one or two different values.
         *
         * shifting off the lower bits fixes things.
         */
        return hash_64(num >> 16, BTRFS_STRIPE_HASH_TABLE_BITS);
}

static bool full_page_sectors_uptodate(struct btrfs_raid_bio *rbio,
                                       unsigned int page_nr)
{
        const u32 sectorsize = rbio->bioc->fs_info->sectorsize;
        const u32 sectors_per_page = PAGE_SIZE / sectorsize;
        int i;

        ASSERT(page_nr < rbio->nr_pages);

        for (i = sectors_per_page * page_nr;
             i < sectors_per_page * page_nr + sectors_per_page;
             i++) {
                if (!rbio->stripe_sectors[i].uptodate)
                        return false;
        }
        return true;
}

/*
 * Update the stripe_sectors[] array to use correct page and pgoff
 *
 * Should be called every time any page pointer in stripes_pages[] got modified.
 */
static void index_stripe_sectors(struct btrfs_raid_bio *rbio)
{
        const u32 sectorsize = rbio->bioc->fs_info->sectorsize;
        u32 offset;
        int i;

        for (i = 0, offset = 0; i < rbio->nr_sectors; i++, offset += sectorsize) {
                int page_index = offset >> PAGE_SHIFT;

                ASSERT(page_index < rbio->nr_pages);
                rbio->stripe_sectors[i].page = rbio->stripe_pages[page_index];
                rbio->stripe_sectors[i].pgoff = offset_in_page(offset);
        }
}

/*
 * Stealing an rbio means taking all the uptodate pages from the stripe array
 * in the source rbio and putting them into the destination rbio.
 *
 * This will also update the involved stripe_sectors[] which are referring to
 * the old pages.
 */
static void steal_rbio(struct btrfs_raid_bio *src, struct btrfs_raid_bio *dest)
{
        int i;
        struct page *s;
        struct page *d;

        if (!test_bit(RBIO_CACHE_READY_BIT, &src->flags))
                return;

        for (i = 0; i < dest->nr_pages; i++) {
                s = src->stripe_pages[i];
                if (!s || !full_page_sectors_uptodate(src, i))
                        continue;

                d = dest->stripe_pages[i];
                if (d)
                        __free_page(d);

                dest->stripe_pages[i] = s;
                src->stripe_pages[i] = NULL;
        }
        index_stripe_sectors(dest);
        index_stripe_sectors(src);
}

/*
 * merging means we take the bio_list from the victim and
 * splice it into the destination.  The victim should
 * be discarded afterwards.
 *
 * must be called with dest->rbio_list_lock held
 */
static void merge_rbio(struct btrfs_raid_bio *dest,
                       struct btrfs_raid_bio *victim)
{
        bio_list_merge(&dest->bio_list, &victim->bio_list);
        dest->bio_list_bytes += victim->bio_list_bytes;
        dest->generic_bio_cnt += victim->generic_bio_cnt;
        bio_list_init(&victim->bio_list);
}

/*
 * used to prune items that are in the cache.  The caller
 * must hold the hash table lock.
 */
static void __remove_rbio_from_cache(struct btrfs_raid_bio *rbio)
{
        int bucket = rbio_bucket(rbio);
        struct btrfs_stripe_hash_table *table;
        struct btrfs_stripe_hash *h;
        int freeit = 0;

        /*
         * check the bit again under the hash table lock.
         */
        if (!test_bit(RBIO_CACHE_BIT, &rbio->flags))
                return;

        table = rbio->bioc->fs_info->stripe_hash_table;
        h = table->table + bucket;

        /* hold the lock for the bucket because we may be
         * removing it from the hash table
         */
        spin_lock(&h->lock);

        /*
         * hold the lock for the bio list because we need
         * to make sure the bio list is empty
         */
        spin_lock(&rbio->bio_list_lock);

        if (test_and_clear_bit(RBIO_CACHE_BIT, &rbio->flags)) {
                list_del_init(&rbio->stripe_cache);
                table->cache_size -= 1;
                freeit = 1;

                /* if the bio list isn't empty, this rbio is
                 * still involved in an IO.  We take it out
                 * of the cache list, and drop the ref that
                 * was held for the list.
                 *
                 * If the bio_list was empty, we also remove
                 * the rbio from the hash_table, and drop
                 * the corresponding ref
                 */
                if (bio_list_empty(&rbio->bio_list)) {
                        if (!list_empty(&rbio->hash_list)) {
                                list_del_init(&rbio->hash_list);
                                refcount_dec(&rbio->refs);
                                BUG_ON(!list_empty(&rbio->plug_list));
                        }
                }
        }

        spin_unlock(&rbio->bio_list_lock);
        spin_unlock(&h->lock);

        if (freeit)
                __free_raid_bio(rbio);
}

/*
 * prune a given rbio from the cache
 */
static void remove_rbio_from_cache(struct btrfs_raid_bio *rbio)
{
        struct btrfs_stripe_hash_table *table;
        unsigned long flags;

        if (!test_bit(RBIO_CACHE_BIT, &rbio->flags))
                return;

        table = rbio->bioc->fs_info->stripe_hash_table;

        spin_lock_irqsave(&table->cache_lock, flags);
        __remove_rbio_from_cache(rbio);
        spin_unlock_irqrestore(&table->cache_lock, flags);
}

/*
 * remove everything in the cache
 */
static void btrfs_clear_rbio_cache(struct btrfs_fs_info *info)
{
        struct btrfs_stripe_hash_table *table;
        unsigned long flags;
        struct btrfs_raid_bio *rbio;

        table = info->stripe_hash_table;

        spin_lock_irqsave(&table->cache_lock, flags);
        while (!list_empty(&table->stripe_cache)) {
                rbio = list_entry(table->stripe_cache.next,
                                  struct btrfs_raid_bio,
                                  stripe_cache);
                __remove_rbio_from_cache(rbio);
        }
        spin_unlock_irqrestore(&table->cache_lock, flags);
}

/*
 * remove all cached entries and free the hash table
 * used by unmount
 */
void btrfs_free_stripe_hash_table(struct btrfs_fs_info *info)
{
        if (!info->stripe_hash_table)
                return;
        btrfs_clear_rbio_cache(info);
        kvfree(info->stripe_hash_table);
        info->stripe_hash_table = NULL;
}

/*
 * insert an rbio into the stripe cache.  It
 * must have already been prepared by calling
 * cache_rbio_pages
 *
 * If this rbio was already cached, it gets
 * moved to the front of the lru.
 *
 * If the size of the rbio cache is too big, we
 * prune an item.
 */
static void cache_rbio(struct btrfs_raid_bio *rbio)
{
        struct btrfs_stripe_hash_table *table;
        unsigned long flags;

        if (!test_bit(RBIO_CACHE_READY_BIT, &rbio->flags))
                return;

        table = rbio->bioc->fs_info->stripe_hash_table;

        spin_lock_irqsave(&table->cache_lock, flags);
        spin_lock(&rbio->bio_list_lock);

        /* bump our ref if we were not in the list before */
        if (!test_and_set_bit(RBIO_CACHE_BIT, &rbio->flags))
                refcount_inc(&rbio->refs);

        if (!list_empty(&rbio->stripe_cache)){
                list_move(&rbio->stripe_cache, &table->stripe_cache);
        } else {
                list_add(&rbio->stripe_cache, &table->stripe_cache);
                table->cache_size += 1;
        }

        spin_unlock(&rbio->bio_list_lock);

        if (table->cache_size > RBIO_CACHE_SIZE) {
                struct btrfs_raid_bio *found;

                found = list_entry(table->stripe_cache.prev,
                                  struct btrfs_raid_bio,
                                  stripe_cache);

                if (found != rbio)
                        __remove_rbio_from_cache(found);
        }

        spin_unlock_irqrestore(&table->cache_lock, flags);
}

/*
 * helper function to run the xor_blocks api.  It is only
 * able to do MAX_XOR_BLOCKS at a time, so we need to
 * loop through.
 */
static void run_xor(void **pages, int src_cnt, ssize_t len)
{
        int src_off = 0;
        int xor_src_cnt = 0;
        void *dest = pages[src_cnt];

        while(src_cnt > 0) {
                xor_src_cnt = min(src_cnt, MAX_XOR_BLOCKS);
                xor_blocks(xor_src_cnt, len, dest, pages + src_off);

                src_cnt -= xor_src_cnt;
                src_off += xor_src_cnt;
        }
}

/*
 * Returns true if the bio list inside this rbio covers an entire stripe (no
 * rmw required).
 */
static int rbio_is_full(struct btrfs_raid_bio *rbio)
{
        unsigned long flags;
        unsigned long size = rbio->bio_list_bytes;
        int ret = 1;

        spin_lock_irqsave(&rbio->bio_list_lock, flags);
        if (size != rbio->nr_data * rbio->stripe_len)
                ret = 0;
        BUG_ON(size > rbio->nr_data * rbio->stripe_len);
        spin_unlock_irqrestore(&rbio->bio_list_lock, flags);

        return ret;
}

/*
 * returns 1 if it is safe to merge two rbios together.
 * The merging is safe if the two rbios correspond to
 * the same stripe and if they are both going in the same
 * direction (read vs write), and if neither one is
 * locked for final IO
 *
 * The caller is responsible for locking such that
 * rmw_locked is safe to test
 */
static int rbio_can_merge(struct btrfs_raid_bio *last,
                          struct btrfs_raid_bio *cur)
{
        if (test_bit(RBIO_RMW_LOCKED_BIT, &last->flags) ||
            test_bit(RBIO_RMW_LOCKED_BIT, &cur->flags))
                return 0;

        /*
         * we can't merge with cached rbios, since the
         * idea is that when we merge the destination
         * rbio is going to run our IO for us.  We can
         * steal from cached rbios though, other functions
         * handle that.
         */
        if (test_bit(RBIO_CACHE_BIT, &last->flags) ||
            test_bit(RBIO_CACHE_BIT, &cur->flags))
                return 0;

        if (last->bioc->raid_map[0] != cur->bioc->raid_map[0])
                return 0;

        /* we can't merge with different operations */
        if (last->operation != cur->operation)
                return 0;
        /*
         * We've need read the full stripe from the drive.
         * check and repair the parity and write the new results.
         *
         * We're not allowed to add any new bios to the
         * bio list here, anyone else that wants to
         * change this stripe needs to do their own rmw.
         */
        if (last->operation == BTRFS_RBIO_PARITY_SCRUB)
                return 0;

        if (last->operation == BTRFS_RBIO_REBUILD_MISSING)
                return 0;

        if (last->operation == BTRFS_RBIO_READ_REBUILD) {
                int fa = last->faila;
                int fb = last->failb;
                int cur_fa = cur->faila;
                int cur_fb = cur->failb;

                if (last->faila >= last->failb) {
                        fa = last->failb;
                        fb = last->faila;
                }

                if (cur->faila >= cur->failb) {
                        cur_fa = cur->failb;
                        cur_fb = cur->faila;
                }

                if (fa != cur_fa || fb != cur_fb)
                        return 0;
        }
        return 1;
}

static unsigned int rbio_stripe_sector_index(const struct btrfs_raid_bio *rbio,
                                             unsigned int stripe_nr,
                                             unsigned int sector_nr)
{
        ASSERT(stripe_nr < rbio->real_stripes);
        ASSERT(sector_nr < rbio->stripe_nsectors);

        return stripe_nr * rbio->stripe_nsectors + sector_nr;
}

/* Return a sector from rbio->stripe_sectors, not from the bio list */
static struct sector_ptr *rbio_stripe_sector(const struct btrfs_raid_bio *rbio,
                                             unsigned int stripe_nr,
                                             unsigned int sector_nr)
{
        return &rbio->stripe_sectors[rbio_stripe_sector_index(rbio, stripe_nr,
                                                              sector_nr)];
}

/* Grab a sector inside P stripe */
static struct sector_ptr *rbio_pstripe_sector(const struct btrfs_raid_bio *rbio,
                                              unsigned int sector_nr)
{
        return rbio_stripe_sector(rbio, rbio->nr_data, sector_nr);
}

/* Grab a sector inside Q stripe, return NULL if not RAID6 */
static struct sector_ptr *rbio_qstripe_sector(const struct btrfs_raid_bio *rbio,
                                              unsigned int sector_nr)
{
        if (rbio->nr_data + 1 == rbio->real_stripes)
                return NULL;
        return rbio_stripe_sector(rbio, rbio->nr_data + 1, sector_nr);
}

/*
 * The first stripe in the table for a logical address
 * has the lock.  rbios are added in one of three ways:
 *
 * 1) Nobody has the stripe locked yet.  The rbio is given
 * the lock and 0 is returned.  The caller must start the IO
 * themselves.
 *
 * 2) Someone has the stripe locked, but we're able to merge
 * with the lock owner.  The rbio is freed and the IO will
 * start automatically along with the existing rbio.  1 is returned.
 *
 * 3) Someone has the stripe locked, but we're not able to merge.
 * The rbio is added to the lock owner's plug list, or merged into
 * an rbio already on the plug list.  When the lock owner unlocks,
 * the next rbio on the list is run and the IO is started automatically.
 * 1 is returned
 *
 * If we return 0, the caller still owns the rbio and must continue with
 * IO submission.  If we return 1, the caller must assume the rbio has
 * already been freed.
 */
static noinline int lock_stripe_add(struct btrfs_raid_bio *rbio)
{
        struct btrfs_stripe_hash *h;
        struct btrfs_raid_bio *cur;
        struct btrfs_raid_bio *pending;
        unsigned long flags;
        struct btrfs_raid_bio *freeit = NULL;
        struct btrfs_raid_bio *cache_drop = NULL;
        int ret = 0;

        h = rbio->bioc->fs_info->stripe_hash_table->table + rbio_bucket(rbio);

        spin_lock_irqsave(&h->lock, flags);
        list_for_each_entry(cur, &h->hash_list, hash_list) {
                if (cur->bioc->raid_map[0] != rbio->bioc->raid_map[0])
                        continue;

                spin_lock(&cur->bio_list_lock);

                /* Can we steal this cached rbio's pages? */
                if (bio_list_empty(&cur->bio_list) &&
                    list_empty(&cur->plug_list) &&
                    test_bit(RBIO_CACHE_BIT, &cur->flags) &&
                    !test_bit(RBIO_RMW_LOCKED_BIT, &cur->flags)) {
                        list_del_init(&cur->hash_list);
                        refcount_dec(&cur->refs);

                        steal_rbio(cur, rbio);
                        cache_drop = cur;
                        spin_unlock(&cur->bio_list_lock);

                        goto lockit;
                }

                /* Can we merge into the lock owner? */
                if (rbio_can_merge(cur, rbio)) {
                        merge_rbio(cur, rbio);
                        spin_unlock(&cur->bio_list_lock);
                        freeit = rbio;
                        ret = 1;
                        goto out;
                }


                /*
                 * We couldn't merge with the running rbio, see if we can merge
                 * with the pending ones.  We don't have to check for rmw_locked
                 * because there is no way they are inside finish_rmw right now
                 */
                list_for_each_entry(pending, &cur->plug_list, plug_list) {
                        if (rbio_can_merge(pending, rbio)) {
                                merge_rbio(pending, rbio);
                                spin_unlock(&cur->bio_list_lock);
                                freeit = rbio;
                                ret = 1;
                                goto out;
                        }
                }

                /*
                 * No merging, put us on the tail of the plug list, our rbio
                 * will be started with the currently running rbio unlocks
                 */
                list_add_tail(&rbio->plug_list, &cur->plug_list);
                spin_unlock(&cur->bio_list_lock);
                ret = 1;
                goto out;
        }
lockit:
        refcount_inc(&rbio->refs);
        list_add(&rbio->hash_list, &h->hash_list);
out:
        spin_unlock_irqrestore(&h->lock, flags);
        if (cache_drop)
                remove_rbio_from_cache(cache_drop);
        if (freeit)
                __free_raid_bio(freeit);
        return ret;
}

/*
 * called as rmw or parity rebuild is completed.  If the plug list has more
 * rbios waiting for this stripe, the next one on the list will be started
 */
static noinline void unlock_stripe(struct btrfs_raid_bio *rbio)
{
        int bucket;
        struct btrfs_stripe_hash *h;
        unsigned long flags;
        int keep_cache = 0;

        bucket = rbio_bucket(rbio);
        h = rbio->bioc->fs_info->stripe_hash_table->table + bucket;

        if (list_empty(&rbio->plug_list))
                cache_rbio(rbio);

        spin_lock_irqsave(&h->lock, flags);
        spin_lock(&rbio->bio_list_lock);

        if (!list_empty(&rbio->hash_list)) {
                /*
                 * if we're still cached and there is no other IO
                 * to perform, just leave this rbio here for others
                 * to steal from later
                 */
                if (list_empty(&rbio->plug_list) &&
                    test_bit(RBIO_CACHE_BIT, &rbio->flags)) {
                        keep_cache = 1;
                        clear_bit(RBIO_RMW_LOCKED_BIT, &rbio->flags);
                        BUG_ON(!bio_list_empty(&rbio->bio_list));
                        goto done;
                }

                list_del_init(&rbio->hash_list);
                refcount_dec(&rbio->refs);

                /*
                 * we use the plug list to hold all the rbios
                 * waiting for the chance to lock this stripe.
                 * hand the lock over to one of them.
                 */
                if (!list_empty(&rbio->plug_list)) {
                        struct btrfs_raid_bio *next;
                        struct list_head *head = rbio->plug_list.next;

                        next = list_entry(head, struct btrfs_raid_bio,
                                          plug_list);

                        list_del_init(&rbio->plug_list);

                        list_add(&next->hash_list, &h->hash_list);
                        refcount_inc(&next->refs);
                        spin_unlock(&rbio->bio_list_lock);
                        spin_unlock_irqrestore(&h->lock, flags);

                        if (next->operation == BTRFS_RBIO_READ_REBUILD)
                                start_async_work(next, read_rebuild_work);
                        else if (next->operation == BTRFS_RBIO_REBUILD_MISSING) {
                                steal_rbio(rbio, next);
                                start_async_work(next, read_rebuild_work);
                        } else if (next->operation == BTRFS_RBIO_WRITE) {
                                steal_rbio(rbio, next);
                                start_async_work(next, rmw_work);
                        } else if (next->operation == BTRFS_RBIO_PARITY_SCRUB) {
                                steal_rbio(rbio, next);
                                start_async_work(next, scrub_parity_work);
                        }

                        goto done_nolock;
                }
        }
done:
        spin_unlock(&rbio->bio_list_lock);
        spin_unlock_irqrestore(&h->lock, flags);

done_nolock:
        if (!keep_cache)
                remove_rbio_from_cache(rbio);
}

static void __free_raid_bio(struct btrfs_raid_bio *rbio)
{
        int i;

        if (!refcount_dec_and_test(&rbio->refs))
                return;

        WARN_ON(!list_empty(&rbio->stripe_cache));
        WARN_ON(!list_empty(&rbio->hash_list));
        WARN_ON(!bio_list_empty(&rbio->bio_list));

        for (i = 0; i < rbio->nr_pages; i++) {
                if (rbio->stripe_pages[i]) {
                        __free_page(rbio->stripe_pages[i]);
                        rbio->stripe_pages[i] = NULL;
                }
        }

        btrfs_put_bioc(rbio->bioc);
        kfree(rbio);
}

static void rbio_endio_bio_list(struct bio *cur, blk_status_t err)
{
        struct bio *next;

        while (cur) {
                next = cur->bi_next;
                cur->bi_next = NULL;
                cur->bi_status = err;
                bio_endio(cur);
                cur = next;
        }
}

/*
 * this frees the rbio and runs through all the bios in the
 * bio_list and calls end_io on them
 */
static void rbio_orig_end_io(struct btrfs_raid_bio *rbio, blk_status_t err)
{
        struct bio *cur = bio_list_get(&rbio->bio_list);
        struct bio *extra;

        if (rbio->generic_bio_cnt)
                btrfs_bio_counter_sub(rbio->bioc->fs_info, rbio->generic_bio_cnt);

        /*
         * At this moment, rbio->bio_list is empty, however since rbio does not
         * always have RBIO_RMW_LOCKED_BIT set and rbio is still linked on the
         * hash list, rbio may be merged with others so that rbio->bio_list
         * becomes non-empty.
         * Once unlock_stripe() is done, rbio->bio_list will not be updated any
         * more and we can call bio_endio() on all queued bios.
         */
        unlock_stripe(rbio);
        extra = bio_list_get(&rbio->bio_list);
        __free_raid_bio(rbio);

        rbio_endio_bio_list(cur, err);
        if (extra)
                rbio_endio_bio_list(extra, err);
}

/*
 * end io function used by finish_rmw.  When we finally
 * get here, we've written a full stripe
 */
static void raid_write_end_io(struct bio *bio)
{
        struct btrfs_raid_bio *rbio = bio->bi_private;
        blk_status_t err = bio->bi_status;
        int max_errors;

        if (err)
                fail_bio_stripe(rbio, bio);

        bio_put(bio);

        if (!atomic_dec_and_test(&rbio->stripes_pending))
                return;

        err = BLK_STS_OK;

        /* OK, we have read all the stripes we need to. */
        max_errors = (rbio->operation == BTRFS_RBIO_PARITY_SCRUB) ?
                     0 : rbio->bioc->max_errors;
        if (atomic_read(&rbio->error) > max_errors)
                err = BLK_STS_IOERR;

        rbio_orig_end_io(rbio, err);
}

/**
 * Get a sector pointer specified by its @stripe_nr and @sector_nr
 *
 * @rbio:               The raid bio
 * @stripe_nr:          Stripe number, valid range [0, real_stripe)
 * @sector_nr:          Sector number inside the stripe,
 *                      valid range [0, stripe_nsectors)
 * @bio_list_only:      Whether to use sectors inside the bio list only.
 *
 * The read/modify/write code wants to reuse the original bio page as much
 * as possible, and only use stripe_sectors as fallback.
 */
static struct sector_ptr *sector_in_rbio(struct btrfs_raid_bio *rbio,
                                         int stripe_nr, int sector_nr,
                                         bool bio_list_only)
{
        struct sector_ptr *sector;
        int index;

        ASSERT(stripe_nr >= 0 && stripe_nr < rbio->real_stripes);
        ASSERT(sector_nr >= 0 && sector_nr < rbio->stripe_nsectors);

        index = stripe_nr * rbio->stripe_nsectors + sector_nr;
        ASSERT(index >= 0 && index < rbio->nr_sectors);

        spin_lock_irq(&rbio->bio_list_lock);
        sector = &rbio->bio_sectors[index];
        if (sector->page || bio_list_only) {
                /* Don't return sector without a valid page pointer */
                if (!sector->page)
                        sector = NULL;
                spin_unlock_irq(&rbio->bio_list_lock);
                return sector;
        }
        spin_unlock_irq(&rbio->bio_list_lock);

        return &rbio->stripe_sectors[index];
}

/*
 * allocation and initial setup for the btrfs_raid_bio.  Not
 * this does not allocate any pages for rbio->pages.
 */
static struct btrfs_raid_bio *alloc_rbio(struct btrfs_fs_info *fs_info,
                                         struct btrfs_io_context *bioc,
                                         u32 stripe_len)
{
        const unsigned int real_stripes = bioc->num_stripes - bioc->num_tgtdevs;
        const unsigned int stripe_npages = stripe_len >> PAGE_SHIFT;
        const unsigned int num_pages = stripe_npages * real_stripes;
        const unsigned int stripe_nsectors = stripe_len >> fs_info->sectorsize_bits;
        const unsigned int num_sectors = stripe_nsectors * real_stripes;
        struct btrfs_raid_bio *rbio;
        int nr_data = 0;
        void *p;

        ASSERT(IS_ALIGNED(stripe_len, PAGE_SIZE));
        /* PAGE_SIZE must also be aligned to sectorsize for subpage support */
        ASSERT(IS_ALIGNED(PAGE_SIZE, fs_info->sectorsize));

        rbio = kzalloc(sizeof(*rbio) +
                       sizeof(*rbio->stripe_pages) * num_pages +
                       sizeof(*rbio->bio_sectors) * num_sectors +
                       sizeof(*rbio->stripe_sectors) * num_sectors +
                       sizeof(*rbio->finish_pointers) * real_stripes +
                       sizeof(*rbio->dbitmap) * BITS_TO_LONGS(stripe_nsectors) +
                       sizeof(*rbio->finish_pbitmap) * BITS_TO_LONGS(stripe_nsectors),
                       GFP_NOFS);
        if (!rbio)
                return ERR_PTR(-ENOMEM);

        bio_list_init(&rbio->bio_list);
        INIT_LIST_HEAD(&rbio->plug_list);
        spin_lock_init(&rbio->bio_list_lock);
        INIT_LIST_HEAD(&rbio->stripe_cache);
        INIT_LIST_HEAD(&rbio->hash_list);
        rbio->bioc = bioc;
        rbio->stripe_len = stripe_len;
        rbio->nr_pages = num_pages;
        rbio->nr_sectors = num_sectors;
        rbio->real_stripes = real_stripes;
        rbio->stripe_npages = stripe_npages;
        rbio->stripe_nsectors = stripe_nsectors;
        rbio->faila = -1;
        rbio->failb = -1;
        refcount_set(&rbio->refs, 1);
        atomic_set(&rbio->error, 0);
        atomic_set(&rbio->stripes_pending, 0);

        /*
         * The stripe_pages, bio_sectors, etc arrays point to the extra memory
         * we allocated past the end of the rbio.
         */
        p = rbio + 1;
#define CONSUME_ALLOC(ptr, count)       do {                            \
                ptr = p;                                                \
                p = (unsigned char *)p + sizeof(*(ptr)) * (count);      \
        } while (0)
        CONSUME_ALLOC(rbio->stripe_pages, num_pages);
        CONSUME_ALLOC(rbio->bio_sectors, num_sectors);
        CONSUME_ALLOC(rbio->stripe_sectors, num_sectors);
        CONSUME_ALLOC(rbio->finish_pointers, real_stripes);
        CONSUME_ALLOC(rbio->dbitmap, BITS_TO_LONGS(stripe_nsectors));
        CONSUME_ALLOC(rbio->finish_pbitmap, BITS_TO_LONGS(stripe_nsectors));
#undef  CONSUME_ALLOC

        if (bioc->map_type & BTRFS_BLOCK_GROUP_RAID5)
                nr_data = real_stripes - 1;
        else if (bioc->map_type & BTRFS_BLOCK_GROUP_RAID6)
                nr_data = real_stripes - 2;
        else
                BUG();

        rbio->nr_data = nr_data;
        return rbio;
}

/* allocate pages for all the stripes in the bio, including parity */
static int alloc_rbio_pages(struct btrfs_raid_bio *rbio)
{
        int ret;

        ret = btrfs_alloc_page_array(rbio->nr_pages, rbio->stripe_pages);
        if (ret < 0)
                return ret;
        /* Mapping all sectors */
        index_stripe_sectors(rbio);
        return 0;
}

/* only allocate pages for p/q stripes */
static int alloc_rbio_parity_pages(struct btrfs_raid_bio *rbio)
{
        const int data_pages = rbio->nr_data * rbio->stripe_npages;
        int ret;

        ret = btrfs_alloc_page_array(rbio->nr_pages - data_pages,
                                     rbio->stripe_pages + data_pages);
        if (ret < 0)
                return ret;

        index_stripe_sectors(rbio);
        return 0;
}

/*
 * Add a single sector @sector into our list of bios for IO.
 *
 * Return 0 if everything went well.
 * Return <0 for error.
 */
static int rbio_add_io_sector(struct btrfs_raid_bio *rbio,
                              struct bio_list *bio_list,
                              struct sector_ptr *sector,
                              unsigned int stripe_nr,
                              unsigned int sector_nr,
                              unsigned long bio_max_len,
                              unsigned int opf)
{
        const u32 sectorsize = rbio->bioc->fs_info->sectorsize;
        struct bio *last = bio_list->tail;
        int ret;
        struct bio *bio;
        struct btrfs_io_stripe *stripe;
        u64 disk_start;

        /*
         * Note: here stripe_nr has taken device replace into consideration,
         * thus it can be larger than rbio->real_stripe.
         * So here we check against bioc->num_stripes, not rbio->real_stripes.
         */
        ASSERT(stripe_nr >= 0 && stripe_nr < rbio->bioc->num_stripes);
        ASSERT(sector_nr >= 0 && sector_nr < rbio->stripe_nsectors);
        ASSERT(sector->page);

        stripe = &rbio->bioc->stripes[stripe_nr];
        disk_start = stripe->physical + sector_nr * sectorsize;

        /* if the device is missing, just fail this stripe */
        if (!stripe->dev->bdev)
                return fail_rbio_index(rbio, stripe_nr);

        /* see if we can add this page onto our existing bio */
        if (last) {
                u64 last_end = last->bi_iter.bi_sector << 9;
                last_end += last->bi_iter.bi_size;

                /*
                 * we can't merge these if they are from different
                 * devices or if they are not contiguous
                 */
                if (last_end == disk_start && !last->bi_status &&
                    last->bi_bdev == stripe->dev->bdev) {
                        ret = bio_add_page(last, sector->page, sectorsize,
                                           sector->pgoff);
                        if (ret == sectorsize)
                                return 0;
                }
        }

        /* put a new bio on the list */
        bio = bio_alloc(stripe->dev->bdev, max(bio_max_len >> PAGE_SHIFT, 1UL),
                        opf, GFP_NOFS);
        bio->bi_iter.bi_sector = disk_start >> 9;
        bio->bi_private = rbio;

        bio_add_page(bio, sector->page, sectorsize, sector->pgoff);
        bio_list_add(bio_list, bio);
        return 0;
}

/*
 * while we're doing the read/modify/write cycle, we could
 * have errors in reading pages off the disk.  This checks
 * for errors and if we're not able to read the page it'll
 * trigger parity reconstruction.  The rmw will be finished
 * after we've reconstructed the failed stripes
 */
static void validate_rbio_for_rmw(struct btrfs_raid_bio *rbio)
{
        if (rbio->faila >= 0 || rbio->failb >= 0) {
                BUG_ON(rbio->faila == rbio->real_stripes - 1);
                __raid56_parity_recover(rbio);
        } else {
                finish_rmw(rbio);
        }
}

static void index_one_bio(struct btrfs_raid_bio *rbio, struct bio *bio)
{
        const u32 sectorsize = rbio->bioc->fs_info->sectorsize;
        struct bio_vec bvec;
        struct bvec_iter iter;
        u32 offset = (bio->bi_iter.bi_sector << SECTOR_SHIFT) -
                     rbio->bioc->raid_map[0];

        if (bio_flagged(bio, BIO_CLONED))
                bio->bi_iter = btrfs_bio(bio)->iter;

        bio_for_each_segment(bvec, bio, iter) {
                u32 bvec_offset;

                for (bvec_offset = 0; bvec_offset < bvec.bv_len;
                     bvec_offset += sectorsize, offset += sectorsize) {
                        int index = offset / sectorsize;
                        struct sector_ptr *sector = &rbio->bio_sectors[index];

                        sector->page = bvec.bv_page;
                        sector->pgoff = bvec.bv_offset + bvec_offset;
                        ASSERT(sector->pgoff < PAGE_SIZE);
                }
        }
}

/*
 * helper function to walk our bio list and populate the bio_pages array with
 * the result.  This seems expensive, but it is faster than constantly
 * searching through the bio list as we setup the IO in finish_rmw or stripe
 * reconstruction.
 *
 * This must be called before you trust the answers from page_in_rbio
 */
static void index_rbio_pages(struct btrfs_raid_bio *rbio)
{
        struct bio *bio;

        spin_lock_irq(&rbio->bio_list_lock);
        bio_list_for_each(bio, &rbio->bio_list)
                index_one_bio(rbio, bio);

        spin_unlock_irq(&rbio->bio_list_lock);
}

/*
 * this is called from one of two situations.  We either
 * have a full stripe from the higher layers, or we've read all
 * the missing bits off disk.
 *
 * This will calculate the parity and then send down any
 * changed blocks.
 */
static noinline void finish_rmw(struct btrfs_raid_bio *rbio)
{
        struct btrfs_io_context *bioc = rbio->bioc;
        const u32 sectorsize = bioc->fs_info->sectorsize;
        void **pointers = rbio->finish_pointers;
        int nr_data = rbio->nr_data;
        int stripe;
        int sectornr;
        bool has_qstripe;
        struct bio_list bio_list;
        struct bio *bio;
        int ret;

        bio_list_init(&bio_list);

        if (rbio->real_stripes - rbio->nr_data == 1)
                has_qstripe = false;
        else if (rbio->real_stripes - rbio->nr_data == 2)
                has_qstripe = true;
        else
                BUG();

        /* at this point we either have a full stripe,
         * or we've read the full stripe from the drive.
         * recalculate the parity and write the new results.
         *
         * We're not allowed to add any new bios to the
         * bio list here, anyone else that wants to
         * change this stripe needs to do their own rmw.
         */
        spin_lock_irq(&rbio->bio_list_lock);
        set_bit(RBIO_RMW_LOCKED_BIT, &rbio->flags);
        spin_unlock_irq(&rbio->bio_list_lock);

        atomic_set(&rbio->error, 0);

        /*
         * now that we've set rmw_locked, run through the
         * bio list one last time and map the page pointers
         *
         * We don't cache full rbios because we're assuming
         * the higher layers are unlikely to use this area of
         * the disk again soon.  If they do use it again,
         * hopefully they will send another full bio.
         */
        index_rbio_pages(rbio);
        if (!rbio_is_full(rbio))
                cache_rbio_pages(rbio);
        else
                clear_bit(RBIO_CACHE_READY_BIT, &rbio->flags);

        for (sectornr = 0; sectornr < rbio->stripe_nsectors; sectornr++) {
                struct sector_ptr *sector;

                /* First collect one sector from each data stripe */
                for (stripe = 0; stripe < nr_data; stripe++) {
                        sector = sector_in_rbio(rbio, stripe, sectornr, 0);
                        pointers[stripe] = kmap_local_page(sector->page) +
                                           sector->pgoff;
                }

                /* Then add the parity stripe */
                sector = rbio_pstripe_sector(rbio, sectornr);
                sector->uptodate = 1;
                pointers[stripe++] = kmap_local_page(sector->page) + sector->pgoff;

                if (has_qstripe) {
                        /*
                         * RAID6, add the qstripe and call the library function
                         * to fill in our p/q
                         */
                        sector = rbio_qstripe_sector(rbio, sectornr);
                        sector->uptodate = 1;
                        pointers[stripe++] = kmap_local_page(sector->page) +
                                             sector->pgoff;

                        raid6_call.gen_syndrome(rbio->real_stripes, sectorsize,
                                                pointers);
                } else {
                        /* raid5 */
                        memcpy(pointers[nr_data], pointers[0], sectorsize);
                        run_xor(pointers + 1, nr_data - 1, sectorsize);
                }
                for (stripe = stripe - 1; stripe >= 0; stripe--)
                        kunmap_local(pointers[stripe]);
        }

        /*
         * time to start writing.  Make bios for everything from the
         * higher layers (the bio_list in our rbio) and our p/q.  Ignore
         * everything else.
         */
        for (stripe = 0; stripe < rbio->real_stripes; stripe++) {
                for (sectornr = 0; sectornr < rbio->stripe_nsectors; sectornr++) {
                        struct sector_ptr *sector;

                        if (stripe < rbio->nr_data) {
                                sector = sector_in_rbio(rbio, stripe, sectornr, 1);
                                if (!sector)
                                        continue;
                        } else {
                                sector = rbio_stripe_sector(rbio, stripe, sectornr);
                        }

                        ret = rbio_add_io_sector(rbio, &bio_list, sector, stripe,
                                                 sectornr, rbio->stripe_len,
                                                 REQ_OP_WRITE);
                        if (ret)
                                goto cleanup;
                }
        }

        if (likely(!bioc->num_tgtdevs))
                goto write_data;

        for (stripe = 0; stripe < rbio->real_stripes; stripe++) {
                if (!bioc->tgtdev_map[stripe])
                        continue;

                for (sectornr = 0; sectornr < rbio->stripe_nsectors; sectornr++) {
                        struct sector_ptr *sector;

                        if (stripe < rbio->nr_data) {
                                sector = sector_in_rbio(rbio, stripe, sectornr, 1);
                                if (!sector)
                                        continue;
                        } else {
                                sector = rbio_stripe_sector(rbio, stripe, sectornr);
                        }

                        ret = rbio_add_io_sector(rbio, &bio_list, sector,
                                               rbio->bioc->tgtdev_map[stripe],
                                               sectornr, rbio->stripe_len,
                                               REQ_OP_WRITE);
                        if (ret)
                                goto cleanup;
                }
        }

write_data:
        atomic_set(&rbio->stripes_pending, bio_list_size(&bio_list));
        BUG_ON(atomic_read(&rbio->stripes_pending) == 0);

        while ((bio = bio_list_pop(&bio_list))) {
                bio->bi_end_io = raid_write_end_io;

                submit_bio(bio);
        }
        return;

cleanup:
        rbio_orig_end_io(rbio, BLK_STS_IOERR);

        while ((bio = bio_list_pop(&bio_list)))
                bio_put(bio);
}

/*
 * helper to find the stripe number for a given bio.  Used to figure out which
 * stripe has failed.  This expects the bio to correspond to a physical disk,
 * so it looks up based on physical sector numbers.
 */
static int find_bio_stripe(struct btrfs_raid_bio *rbio,
                           struct bio *bio)
{
        u64 physical = bio->bi_iter.bi_sector;
        int i;
        struct btrfs_io_stripe *stripe;

        physical <<= 9;

        for (i = 0; i < rbio->bioc->num_stripes; i++) {
                stripe = &rbio->bioc->stripes[i];
                if (in_range(physical, stripe->physical, rbio->stripe_len) &&
                    stripe->dev->bdev && bio->bi_bdev == stripe->dev->bdev) {
                        return i;
                }
        }
        return -1;
}

/*
 * helper to find the stripe number for a given
 * bio (before mapping).  Used to figure out which stripe has
 * failed.  This looks up based on logical block numbers.
 */
static int find_logical_bio_stripe(struct btrfs_raid_bio *rbio,
                                   struct bio *bio)
{
        u64 logical = bio->bi_iter.bi_sector << 9;
        int i;

        for (i = 0; i < rbio->nr_data; i++) {
                u64 stripe_start = rbio->bioc->raid_map[i];

                if (in_range(logical, stripe_start, rbio->stripe_len))
                        return i;
        }
        return -1;
}

/*
 * returns -EIO if we had too many failures
 */
static int fail_rbio_index(struct btrfs_raid_bio *rbio, int failed)
{
        unsigned long flags;
        int ret = 0;

        spin_lock_irqsave(&rbio->bio_list_lock, flags);

        /* we already know this stripe is bad, move on */
        if (rbio->faila == failed || rbio->failb == failed)
                goto out;

        if (rbio->faila == -1) {
                /* first failure on this rbio */
                rbio->faila = failed;
                atomic_inc(&rbio->error);
        } else if (rbio->failb == -1) {
                /* second failure on this rbio */
                rbio->failb = failed;
                atomic_inc(&rbio->error);
        } else {
                ret = -EIO;
        }
out:
        spin_unlock_irqrestore(&rbio->bio_list_lock, flags);

        return ret;
}

/*
 * helper to fail a stripe based on a physical disk
 * bio.
 */
static int fail_bio_stripe(struct btrfs_raid_bio *rbio,
                           struct bio *bio)
{
        int failed = find_bio_stripe(rbio, bio);

        if (failed < 0)
                return -EIO;

        return fail_rbio_index(rbio, failed);
}

/*
 * For subpage case, we can no longer set page Uptodate directly for
 * stripe_pages[], thus we need to locate the sector.
 */
static struct sector_ptr *find_stripe_sector(struct btrfs_raid_bio *rbio,
                                             struct page *page,
                                             unsigned int pgoff)
{
        int i;

        for (i = 0; i < rbio->nr_sectors; i++) {
                struct sector_ptr *sector = &rbio->stripe_sectors[i];

                if (sector->page == page && sector->pgoff == pgoff)
                        return sector;
        }
        return NULL;
}

/*
 * this sets each page in the bio uptodate.  It should only be used on private
 * rbio pages, nothing that comes in from the higher layers
 */
static void set_bio_pages_uptodate(struct btrfs_raid_bio *rbio, struct bio *bio)
{
        const u32 sectorsize = rbio->bioc->fs_info->sectorsize;
        struct bio_vec *bvec;
        struct bvec_iter_all iter_all;

        ASSERT(!bio_flagged(bio, BIO_CLONED));

        bio_for_each_segment_all(bvec, bio, iter_all) {
                struct sector_ptr *sector;
                int pgoff;

                for (pgoff = bvec->bv_offset; pgoff - bvec->bv_offset < bvec->bv_len;
                     pgoff += sectorsize) {
                        sector = find_stripe_sector(rbio, bvec->bv_page, pgoff);
                        ASSERT(sector);
                        if (sector)
                                sector->uptodate = 1;
                }
        }
}

/*
 * end io for the read phase of the rmw cycle.  All the bios here are physical
 * stripe bios we've read from the disk so we can recalculate the parity of the
 * stripe.
 *
 * This will usually kick off finish_rmw once all the bios are read in, but it
 * may trigger parity reconstruction if we had any errors along the way
 */
static void raid_rmw_end_io(struct bio *bio)
{
        struct btrfs_raid_bio *rbio = bio->bi_private;

        if (bio->bi_status)
                fail_bio_stripe(rbio, bio);
        else
                set_bio_pages_uptodate(rbio, bio);

        bio_put(bio);

        if (!atomic_dec_and_test(&rbio->stripes_pending))
                return;

        if (atomic_read(&rbio->error) > rbio->bioc->max_errors)
                goto cleanup;

        /*
         * this will normally call finish_rmw to start our write
         * but if there are any failed stripes we'll reconstruct
         * from parity first
         */
        validate_rbio_for_rmw(rbio);
        return;

cleanup:

        rbio_orig_end_io(rbio, BLK_STS_IOERR);
}

/*
 * the stripe must be locked by the caller.  It will
 * unlock after all the writes are done
 */
static int raid56_rmw_stripe(struct btrfs_raid_bio *rbio)
{
        int bios_to_read = 0;
        struct bio_list bio_list;
        int ret;
        int sectornr;
        int stripe;
        struct bio *bio;

        bio_list_init(&bio_list);

        ret = alloc_rbio_pages(rbio);
        if (ret)
                goto cleanup;

        index_rbio_pages(rbio);

        atomic_set(&rbio->error, 0);
        /*
         * build a list of bios to read all the missing parts of this
         * stripe
         */
        for (stripe = 0; stripe < rbio->nr_data; stripe++) {
                for (sectornr = 0; sectornr < rbio->stripe_nsectors; sectornr++) {
                        struct sector_ptr *sector;

                        /*
                         * We want to find all the sectors missing from the
                         * rbio and read them from the disk.  If * sector_in_rbio()
                         * finds a page in the bio list we don't need to read
                         * it off the stripe.
                         */
                        sector = sector_in_rbio(rbio, stripe, sectornr, 1);
                        if (sector)
                                continue;

                        sector = rbio_stripe_sector(rbio, stripe, sectornr);
                        /*
                         * The bio cache may have handed us an uptodate page.
                         * If so, be happy and use it.
                         */
                        if (sector->uptodate)
                                continue;

                        ret = rbio_add_io_sector(rbio, &bio_list, sector,
                                       stripe, sectornr, rbio->stripe_len,
                                       REQ_OP_READ);
                        if (ret)
                                goto cleanup;
                }
        }

        bios_to_read = bio_list_size(&bio_list);
        if (!bios_to_read) {
                /*
                 * this can happen if others have merged with
                 * us, it means there is nothing left to read.
                 * But if there are missing devices it may not be
                 * safe to do the full stripe write yet.
                 */
                goto finish;
        }

        /*
         * The bioc may be freed once we submit the last bio. Make sure not to
         * touch it after that.
         */
        atomic_set(&rbio->stripes_pending, bios_to_read);
        while ((bio = bio_list_pop(&bio_list))) {
                bio->bi_end_io = raid_rmw_end_io;

                btrfs_bio_wq_end_io(rbio->bioc->fs_info, bio, BTRFS_WQ_ENDIO_RAID56);

                submit_bio(bio);
        }
        /* the actual write will happen once the reads are done */
        return 0;

cleanup:
        rbio_orig_end_io(rbio, BLK_STS_IOERR);

        while ((bio = bio_list_pop(&bio_list)))
                bio_put(bio);

        return -EIO;

finish:
        validate_rbio_for_rmw(rbio);
        return 0;
}

/*
 * if the upper layers pass in a full stripe, we thank them by only allocating
 * enough pages to hold the parity, and sending it all down quickly.
 */
static int full_stripe_write(struct btrfs_raid_bio *rbio)
{
        int ret;

        ret = alloc_rbio_parity_pages(rbio);
        if (ret) {
                __free_raid_bio(rbio);
                return ret;
        }

        ret = lock_stripe_add(rbio);
        if (ret == 0)
                finish_rmw(rbio);
        return 0;
}

/*
 * partial stripe writes get handed over to async helpers.
 * We're really hoping to merge a few more writes into this
 * rbio before calculating new parity
 */
static int partial_stripe_write(struct btrfs_raid_bio *rbio)
{
        int ret;

        ret = lock_stripe_add(rbio);
        if (ret == 0)
                start_async_work(rbio, rmw_work);
        return 0;
}

/*
 * sometimes while we were reading from the drive to
 * recalculate parity, enough new bios come into create
 * a full stripe.  So we do a check here to see if we can
 * go directly to finish_rmw
 */
static int __raid56_parity_write(struct btrfs_raid_bio *rbio)
{
        /* head off into rmw land if we don't have a full stripe */
        if (!rbio_is_full(rbio))
                return partial_stripe_write(rbio);
        return full_stripe_write(rbio);
}

/*
 * We use plugging call backs to collect full stripes.
 * Any time we get a partial stripe write while plugged
 * we collect it into a list.  When the unplug comes down,
 * we sort the list by logical block number and merge
 * everything we can into the same rbios
 */
struct btrfs_plug_cb {
        struct blk_plug_cb cb;
        struct btrfs_fs_info *info;
        struct list_head rbio_list;
        struct work_struct work;
};

/*
 * rbios on the plug list are sorted for easier merging.
 */
static int plug_cmp(void *priv, const struct list_head *a,
                    const struct list_head *b)
{
        const struct btrfs_raid_bio *ra = container_of(a, struct btrfs_raid_bio,
                                                       plug_list);
        const struct btrfs_raid_bio *rb = container_of(b, struct btrfs_raid_bio,
                                                       plug_list);
        u64 a_sector = ra->bio_list.head->bi_iter.bi_sector;
        u64 b_sector = rb->bio_list.head->bi_iter.bi_sector;

        if (a_sector < b_sector)
                return -1;
        if (a_sector > b_sector)
                return 1;
        return 0;
}

static void run_plug(struct btrfs_plug_cb *plug)
{
        struct btrfs_raid_bio *cur;
        struct btrfs_raid_bio *last = NULL;

        /*
         * sort our plug list then try to merge
         * everything we can in hopes of creating full
         * stripes.
         */
        list_sort(NULL, &plug->rbio_list, plug_cmp);
        while (!list_empty(&plug->rbio_list)) {
                cur = list_entry(plug->rbio_list.next,
                                 struct btrfs_raid_bio, plug_list);
                list_del_init(&cur->plug_list);

                if (rbio_is_full(cur)) {
                        int ret;

                        /* we have a full stripe, send it down */
                        ret = full_stripe_write(cur);
                        BUG_ON(ret);
                        continue;
                }
                if (last) {
                        if (rbio_can_merge(last, cur)) {
                                merge_rbio(last, cur);
                                __free_raid_bio(cur);
                                continue;

                        }
                        __raid56_parity_write(last);
                }
                last = cur;
        }
        if (last) {
                __raid56_parity_write(last);
        }
        kfree(plug);
}

/*
 * if the unplug comes from schedule, we have to push the
 * work off to a helper thread
 */
static void unplug_work(struct work_struct *work)
{
        struct btrfs_plug_cb *plug;
        plug = container_of(work, struct btrfs_plug_cb, work);
        run_plug(plug);
}

static void btrfs_raid_unplug(struct blk_plug_cb *cb, bool from_schedule)
{
        struct btrfs_plug_cb *plug;
        plug = container_of(cb, struct btrfs_plug_cb, cb);

        if (from_schedule) {
                INIT_WORK(&plug->work, unplug_work);
                queue_work(plug->info->rmw_workers, &plug->work);
                return;
        }
        run_plug(plug);
}

/*
 * our main entry point for writes from the rest of the FS.
 */
int raid56_parity_write(struct bio *bio, struct btrfs_io_context *bioc, u32 stripe_len)
{
        struct btrfs_fs_info *fs_info = bioc->fs_info;
        struct btrfs_raid_bio *rbio;
        struct btrfs_plug_cb *plug = NULL;
        struct blk_plug_cb *cb;
        int ret;

        rbio = alloc_rbio(fs_info, bioc, stripe_len);
        if (IS_ERR(rbio)) {
                btrfs_put_bioc(bioc);
                return PTR_ERR(rbio);
        }
        bio_list_add(&rbio->bio_list, bio);
        rbio->bio_list_bytes = bio->bi_iter.bi_size;
        rbio->operation = BTRFS_RBIO_WRITE;

        btrfs_bio_counter_inc_noblocked(fs_info);
        rbio->generic_bio_cnt = 1;

        /*
         * don't plug on full rbios, just get them out the door
         * as quickly as we can
         */
        if (rbio_is_full(rbio)) {
                ret = full_stripe_write(rbio);
                if (ret)
                        btrfs_bio_counter_dec(fs_info);
                return ret;
        }

        cb = blk_check_plugged(btrfs_raid_unplug, fs_info, sizeof(*plug));
        if (cb) {
                plug = container_of(cb, struct btrfs_plug_cb, cb);
                if (!plug->info) {
                        plug->info = fs_info;
                        INIT_LIST_HEAD(&plug->rbio_list);
                }
                list_add_tail(&rbio->plug_list, &plug->rbio_list);
                ret = 0;
        } else {
                ret = __raid56_parity_write(rbio);
                if (ret)
                        btrfs_bio_counter_dec(fs_info);
        }
        return ret;
}

/*
 * all parity reconstruction happens here.  We've read in everything
 * we can find from the drives and this does the heavy lifting of
 * sorting the good from the bad.
 */
static void __raid_recover_end_io(struct btrfs_raid_bio *rbio)
{
        const u32 sectorsize = rbio->bioc->fs_info->sectorsize;
        int sectornr, stripe;
        void **pointers;
        void **unmap_array;
        int faila = -1, failb = -1;
        blk_status_t err;
        int i;

        /*
         * This array stores the pointer for each sector, thus it has the extra
         * pgoff value added from each sector
         */
        pointers = kcalloc(rbio->real_stripes, sizeof(void *), GFP_NOFS);
        if (!pointers) {
                err = BLK_STS_RESOURCE;
                goto cleanup_io;
        }

        /*
         * Store copy of pointers that does not get reordered during
         * reconstruction so that kunmap_local works.
         */
        unmap_array = kcalloc(rbio->real_stripes, sizeof(void *), GFP_NOFS);
        if (!unmap_array) {
                err = BLK_STS_RESOURCE;
                goto cleanup_pointers;
        }

        faila = rbio->faila;
        failb = rbio->failb;

        if (rbio->operation == BTRFS_RBIO_READ_REBUILD ||
            rbio->operation == BTRFS_RBIO_REBUILD_MISSING) {
                spin_lock_irq(&rbio->bio_list_lock);
                set_bit(RBIO_RMW_LOCKED_BIT, &rbio->flags);
                spin_unlock_irq(&rbio->bio_list_lock);
        }

        index_rbio_pages(rbio);

        for (sectornr = 0; sectornr < rbio->stripe_nsectors; sectornr++) {
                struct sector_ptr *sector;

                /*
                 * Now we just use bitmap to mark the horizontal stripes in
                 * which we have data when doing parity scrub.
                 */
                if (rbio->operation == BTRFS_RBIO_PARITY_SCRUB &&
                    !test_bit(sectornr, rbio->dbitmap))
                        continue;

                /*
                 * Setup our array of pointers with sectors from each stripe
                 *
                 * NOTE: store a duplicate array of pointers to preserve the
                 * pointer order
                 */
                for (stripe = 0; stripe < rbio->real_stripes; stripe++) {
                        /*
                         * If we're rebuilding a read, we have to use
                         * pages from the bio list
                         */
                        if ((rbio->operation == BTRFS_RBIO_READ_REBUILD ||
                             rbio->operation == BTRFS_RBIO_REBUILD_MISSING) &&
                            (stripe == faila || stripe == failb)) {
                                sector = sector_in_rbio(rbio, stripe, sectornr, 0);
                        } else {
                                sector = rbio_stripe_sector(rbio, stripe, sectornr);
                        }
                        ASSERT(sector->page);
                        pointers[stripe] = kmap_local_page(sector->page) +
                                           sector->pgoff;
                        unmap_array[stripe] = pointers[stripe];
                }

                /* All raid6 handling here */
                if (rbio->bioc->map_type & BTRFS_BLOCK_GROUP_RAID6) {
                        /* Single failure, rebuild from parity raid5 style */
                        if (failb < 0) {
                                if (faila == rbio->nr_data) {
                                        /*
                                         * Just the P stripe has failed, without
                                         * a bad data or Q stripe.
                                         * TODO, we should redo the xor here.
                                         */
                                        err = BLK_STS_IOERR;
                                        goto cleanup;
                                }
                                /*
                                 * a single failure in raid6 is rebuilt
                                 * in the pstripe code below
                                 */
                                goto pstripe;
                        }

                        /* make sure our ps and qs are in order */
                        if (faila > failb)
                                swap(faila, failb);

                        /* if the q stripe is failed, do a pstripe reconstruction
                         * from the xors.
                         * If both the q stripe and the P stripe are failed, we're
                         * here due to a crc mismatch and we can't give them the
                         * data they want
                         */
                        if (rbio->bioc->raid_map[failb] == RAID6_Q_STRIPE) {
                                if (rbio->bioc->raid_map[faila] ==
                                    RAID5_P_STRIPE) {
                                        err = BLK_STS_IOERR;
                                        goto cleanup;
                                }
                                /*
                                 * otherwise we have one bad data stripe and
                                 * a good P stripe.  raid5!
                                 */
                                goto pstripe;
                        }

                        if (rbio->bioc->raid_map[failb] == RAID5_P_STRIPE) {
                                raid6_datap_recov(rbio->real_stripes,
                                                  sectorsize, faila, pointers);
                        } else {
                                raid6_2data_recov(rbio->real_stripes,
                                                  sectorsize, faila, failb,
                                                  pointers);
                        }
                } else {
                        void *p;

                        /* rebuild from P stripe here (raid5 or raid6) */
                        BUG_ON(failb != -1);
pstripe:
                        /* Copy parity block into failed block to start with */
                        memcpy(pointers[faila], pointers[rbio->nr_data], sectorsize);

                        /* rearrange the pointer array */
                        p = pointers[faila];
                        for (stripe = faila; stripe < rbio->nr_data - 1; stripe++)
                                pointers[stripe] = pointers[stripe + 1];
                        pointers[rbio->nr_data - 1] = p;

                        /* xor in the rest */
                        run_xor(pointers, rbio->nr_data - 1, sectorsize);
                }
                /* if we're doing this rebuild as part of an rmw, go through
                 * and set all of our private rbio pages in the
                 * failed stripes as uptodate.  This way finish_rmw will
                 * know they can be trusted.  If this was a read reconstruction,
                 * other endio functions will fiddle the uptodate bits
                 */
                if (rbio->operation == BTRFS_RBIO_WRITE) {
                        for (i = 0;  i < rbio->stripe_nsectors; i++) {
                                if (faila != -1) {
                                        sector = rbio_stripe_sector(rbio, faila, i);
                                        sector->uptodate = 1;
                                }
                                if (failb != -1) {
                                        sector = rbio_stripe_sector(rbio, failb, i);
                                        sector->uptodate = 1;
                                }
                        }
                }
                for (stripe = rbio->real_stripes - 1; stripe >= 0; stripe--)
                        kunmap_local(unmap_array[stripe]);
        }

        err = BLK_STS_OK;
cleanup:
        kfree(unmap_array);
cleanup_pointers:
        kfree(pointers);

cleanup_io:
        /*
         * Similar to READ_REBUILD, REBUILD_MISSING at this point also has a
         * valid rbio which is consistent with ondisk content, thus such a
         * valid rbio can be cached to avoid further disk reads.
         */
        if (rbio->operation == BTRFS_RBIO_READ_REBUILD ||
            rbio->operation == BTRFS_RBIO_REBUILD_MISSING) {
                /*
                 * - In case of two failures, where rbio->failb != -1:
                 *
                 *   Do not cache this rbio since the above read reconstruction
                 *   (raid6_datap_recov() or raid6_2data_recov()) may have
                 *   changed some content of stripes which are not identical to
                 *   on-disk content any more, otherwise, a later write/recover
                 *   may steal stripe_pages from this rbio and end up with
                 *   corruptions or rebuild failures.
                 *
                 * - In case of single failure, where rbio->failb == -1:
                 *
                 *   Cache this rbio iff the above read reconstruction is
                 *   executed without problems.
                 */
                if (err == BLK_STS_OK && rbio->failb < 0)
                        cache_rbio_pages(rbio);
                else
                        clear_bit(RBIO_CACHE_READY_BIT, &rbio->flags);

                rbio_orig_end_io(rbio, err);
        } else if (err == BLK_STS_OK) {
                rbio->faila = -1;
                rbio->failb = -1;

                if (rbio->operation == BTRFS_RBIO_WRITE)
                        finish_rmw(rbio);
                else if (rbio->operation == BTRFS_RBIO_PARITY_SCRUB)
                        finish_parity_scrub(rbio, 0);
                else
                        BUG();
        } else {
                rbio_orig_end_io(rbio, err);
        }
}

/*
 * This is called only for stripes we've read from disk to
 * reconstruct the parity.
 */
static void raid_recover_end_io(struct bio *bio)
{
        struct btrfs_raid_bio *rbio = bio->bi_private;

        /*
         * we only read stripe pages off the disk, set them
         * up to date if there were no errors
         */
        if (bio->bi_status)
                fail_bio_stripe(rbio, bio);
        else
                set_bio_pages_uptodate(rbio, bio);
        bio_put(bio);

        if (!atomic_dec_and_test(&rbio->stripes_pending))
                return;

        if (atomic_read(&rbio->error) > rbio->bioc->max_errors)
                rbio_orig_end_io(rbio, BLK_STS_IOERR);
        else
                __raid_recover_end_io(rbio);
}

/*
 * reads everything we need off the disk to reconstruct
 * the parity. endio handlers trigger final reconstruction
 * when the IO is done.
 *
 * This is used both for reads from the higher layers and for
 * parity construction required to finish a rmw cycle.
 */
static int __raid56_parity_recover(struct btrfs_raid_bio *rbio)
{
        int bios_to_read = 0;
        struct bio_list bio_list;
        int ret;
        int sectornr;
        int stripe;
        struct bio *bio;

        bio_list_init(&bio_list);

        ret = alloc_rbio_pages(rbio);
        if (ret)
                goto cleanup;

        atomic_set(&rbio->error, 0);

        /*
         * read everything that hasn't failed.  Thanks to the
         * stripe cache, it is possible that some or all of these
         * pages are going to be uptodate.
         */
        for (stripe = 0; stripe < rbio->real_stripes; stripe++) {
                if (rbio->faila == stripe || rbio->failb == stripe) {
                        atomic_inc(&rbio->error);
                        continue;
                }

                for (sectornr = 0; sectornr < rbio->stripe_nsectors; sectornr++) {
                        struct sector_ptr *sector;

                        /*
                         * the rmw code may have already read this
                         * page in
                         */
                        sector = rbio_stripe_sector(rbio, stripe, sectornr);
                        if (sector->uptodate)
                                continue;

                        ret = rbio_add_io_sector(rbio, &bio_list, sector,
                                                 stripe, sectornr, rbio->stripe_len,
                                                 REQ_OP_READ);
                        if (ret < 0)
                                goto cleanup;
                }
        }

        bios_to_read = bio_list_size(&bio_list);
        if (!bios_to_read) {
                /*
                 * we might have no bios to read just because the pages
                 * were up to date, or we might have no bios to read because
                 * the devices were gone.
                 */
                if (atomic_read(&rbio->error) <= rbio->bioc->max_errors) {
                        __raid_recover_end_io(rbio);
                        return 0;
                } else {
                        goto cleanup;
                }
        }

        /*
         * The bioc may be freed once we submit the last bio. Make sure not to
         * touch it after that.
         */
        atomic_set(&rbio->stripes_pending, bios_to_read);
        while ((bio = bio_list_pop(&bio_list))) {
                bio->bi_end_io = raid_recover_end_io;

                btrfs_bio_wq_end_io(rbio->bioc->fs_info, bio, BTRFS_WQ_ENDIO_RAID56);

                submit_bio(bio);
        }

        return 0;

cleanup:
        if (rbio->operation == BTRFS_RBIO_READ_REBUILD ||
            rbio->operation == BTRFS_RBIO_REBUILD_MISSING)
                rbio_orig_end_io(rbio, BLK_STS_IOERR);

        while ((bio = bio_list_pop(&bio_list)))
                bio_put(bio);

        return -EIO;
}

/*
 * the main entry point for reads from the higher layers.  This
 * is really only called when the normal read path had a failure,
 * so we assume the bio they send down corresponds to a failed part
 * of the drive.
 */
int raid56_parity_recover(struct bio *bio, struct btrfs_io_context *bioc,
                          u32 stripe_len, int mirror_num, int generic_io)
{
        struct btrfs_fs_info *fs_info = bioc->fs_info;
        struct btrfs_raid_bio *rbio;
        int ret;

        if (generic_io) {
                ASSERT(bioc->mirror_num == mirror_num);
                btrfs_bio(bio)->mirror_num = mirror_num;
        }

        rbio = alloc_rbio(fs_info, bioc, stripe_len);
        if (IS_ERR(rbio)) {
                if (generic_io)
                        btrfs_put_bioc(bioc);
                return PTR_ERR(rbio);
        }

        rbio->operation = BTRFS_RBIO_READ_REBUILD;
        bio_list_add(&rbio->bio_list, bio);
        rbio->bio_list_bytes = bio->bi_iter.bi_size;

        rbio->faila = find_logical_bio_stripe(rbio, bio);
        if (rbio->faila == -1) {
                btrfs_warn(fs_info,
"%s could not find the bad stripe in raid56 so that we cannot recover any more (bio has logical %llu len %llu, bioc has map_type %llu)",
                           __func__, bio->bi_iter.bi_sector << 9,
                           (u64)bio->bi_iter.bi_size, bioc->map_type);
                if (generic_io)
                        btrfs_put_bioc(bioc);
                kfree(rbio);
                return -EIO;
        }

        if (generic_io) {
                btrfs_bio_counter_inc_noblocked(fs_info);
                rbio->generic_bio_cnt = 1;
        } else {
                btrfs_get_bioc(bioc);
        }

        /*
         * Loop retry:
         * for 'mirror == 2', reconstruct from all other stripes.
         * for 'mirror_num > 2', select a stripe to fail on every retry.
         */
        if (mirror_num > 2) {
                /*
                 * 'mirror == 3' is to fail the p stripe and
                 * reconstruct from the q stripe.  'mirror > 3' is to
                 * fail a data stripe and reconstruct from p+q stripe.
                 */
                rbio->failb = rbio->real_stripes - (mirror_num - 1);
                ASSERT(rbio->failb > 0);
                if (rbio->failb <= rbio->faila)
                        rbio->failb--;
        }

        ret = lock_stripe_add(rbio);

        /*
         * __raid56_parity_recover will end the bio with
         * any errors it hits.  We don't want to return
         * its error value up the stack because our caller
         * will end up calling bio_endio with any nonzero
         * return
         */
        if (ret == 0)
                __raid56_parity_recover(rbio);
        /*
         * our rbio has been added to the list of
         * rbios that will be handled after the
         * currently lock owner is done
         */
        return 0;

}

static void rmw_work(struct work_struct *work)
{
        struct btrfs_raid_bio *rbio;

        rbio = container_of(work, struct btrfs_raid_bio, work);
        raid56_rmw_stripe(rbio);
}

static void read_rebuild_work(struct work_struct *work)
{
        struct btrfs_raid_bio *rbio;

        rbio = container_of(work, struct btrfs_raid_bio, work);
        __raid56_parity_recover(rbio);
}

/*
 * The following code is used to scrub/replace the parity stripe
 *
 * Caller must have already increased bio_counter for getting @bioc.
 *
 * Note: We need make sure all the pages that add into the scrub/replace
 * raid bio are correct and not be changed during the scrub/replace. That
 * is those pages just hold metadata or file data with checksum.
 */

struct btrfs_raid_bio *raid56_parity_alloc_scrub_rbio(struct bio *bio,
                                struct btrfs_io_context *bioc,
                                u32 stripe_len, struct btrfs_device *scrub_dev,
                                unsigned long *dbitmap, int stripe_nsectors)
{
        struct btrfs_fs_info *fs_info = bioc->fs_info;
        struct btrfs_raid_bio *rbio;
        int i;

        rbio = alloc_rbio(fs_info, bioc, stripe_len);
        if (IS_ERR(rbio))
                return NULL;
        bio_list_add(&rbio->bio_list, bio);
        /*
         * This is a special bio which is used to hold the completion handler
         * and make the scrub rbio is similar to the other types
         */
        ASSERT(!bio->bi_iter.bi_size);
        rbio->operation = BTRFS_RBIO_PARITY_SCRUB;

        /*
         * After mapping bioc with BTRFS_MAP_WRITE, parities have been sorted
         * to the end position, so this search can start from the first parity
         * stripe.
         */
        for (i = rbio->nr_data; i < rbio->real_stripes; i++) {
                if (bioc->stripes[i].dev == scrub_dev) {
                        rbio->scrubp = i;
                        break;
                }
        }
        ASSERT(i < rbio->real_stripes);

        bitmap_copy(rbio->dbitmap, dbitmap, stripe_nsectors);

        /*
         * We have already increased bio_counter when getting bioc, record it
         * so we can free it at rbio_orig_end_io().
         */
        rbio->generic_bio_cnt = 1;

        return rbio;
}

/* Used for both parity scrub and missing. */
void raid56_add_scrub_pages(struct btrfs_raid_bio *rbio, struct page *page,
                            unsigned int pgoff, u64 logical)
{
        const u32 sectorsize = rbio->bioc->fs_info->sectorsize;
        int stripe_offset;
        int index;

        ASSERT(logical >= rbio->bioc->raid_map[0]);
        ASSERT(logical + sectorsize <= rbio->bioc->raid_map[0] +
                                rbio->stripe_len * rbio->nr_data);
        stripe_offset = (int)(logical - rbio->bioc->raid_map[0]);
        index = stripe_offset / sectorsize;
        rbio->bio_sectors[index].page = page;
        rbio->bio_sectors[index].pgoff = pgoff;
}

/*
 * We just scrub the parity that we have correct data on the same horizontal,
 * so we needn't allocate all pages for all the stripes.
 */
static int alloc_rbio_essential_pages(struct btrfs_raid_bio *rbio)
{
        const u32 sectorsize = rbio->bioc->fs_info->sectorsize;
        int stripe;
        int sectornr;

        for_each_set_bit(sectornr, rbio->dbitmap, rbio->stripe_nsectors) {
                for (stripe = 0; stripe < rbio->real_stripes; stripe++) {
                        struct page *page;
                        int index = (stripe * rbio->stripe_nsectors + sectornr) *
                                    sectorsize >> PAGE_SHIFT;

                        if (rbio->stripe_pages[index])
                                continue;

                        page = alloc_page(GFP_NOFS);
                        if (!page)
                                return -ENOMEM;
                        rbio->stripe_pages[index] = page;
                }
        }
        index_stripe_sectors(rbio);
        return 0;
}

static noinline void finish_parity_scrub(struct btrfs_raid_bio *rbio,
                                         int need_check)
{
        struct btrfs_io_context *bioc = rbio->bioc;
        const u32 sectorsize = bioc->fs_info->sectorsize;
        void **pointers = rbio->finish_pointers;
        unsigned long *pbitmap = rbio->finish_pbitmap;
        int nr_data = rbio->nr_data;
        int stripe;
        int sectornr;
        bool has_qstripe;
        struct sector_ptr p_sector = { 0 };
        struct sector_ptr q_sector = { 0 };
        struct bio_list bio_list;
        struct bio *bio;
        int is_replace = 0;
        int ret;

        bio_list_init(&bio_list);

        if (rbio->real_stripes - rbio->nr_data == 1)
                has_qstripe = false;
        else if (rbio->real_stripes - rbio->nr_data == 2)
                has_qstripe = true;
        else
                BUG();

        if (bioc->num_tgtdevs && bioc->tgtdev_map[rbio->scrubp]) {
                is_replace = 1;
                bitmap_copy(pbitmap, rbio->dbitmap, rbio->stripe_nsectors);
        }

        /*
         * Because the higher layers(scrubber) are unlikely to
         * use this area of the disk again soon, so don't cache
         * it.
         */
        clear_bit(RBIO_CACHE_READY_BIT, &rbio->flags);

        if (!need_check)
                goto writeback;

        p_sector.page = alloc_page(GFP_NOFS);
        if (!p_sector.page)
                goto cleanup;
        p_sector.pgoff = 0;
        p_sector.uptodate = 1;

        if (has_qstripe) {
                /* RAID6, allocate and map temp space for the Q stripe */
                q_sector.page = alloc_page(GFP_NOFS);
                if (!q_sector.page) {
                        __free_page(p_sector.page);
                        p_sector.page = NULL;
                        goto cleanup;
                }
                q_sector.pgoff = 0;
                q_sector.uptodate = 1;
                pointers[rbio->real_stripes - 1] = kmap_local_page(q_sector.page);
        }

        atomic_set(&rbio->error, 0);

        /* Map the parity stripe just once */
        pointers[nr_data] = kmap_local_page(p_sector.page);

        for_each_set_bit(sectornr, rbio->dbitmap, rbio->stripe_nsectors) {
                struct sector_ptr *sector;
                void *parity;

                /* first collect one page from each data stripe */
                for (stripe = 0; stripe < nr_data; stripe++) {
                        sector = sector_in_rbio(rbio, stripe, sectornr, 0);
                        pointers[stripe] = kmap_local_page(sector->page) +
                                           sector->pgoff;
                }

                if (has_qstripe) {
                        /* RAID6, call the library function to fill in our P/Q */
                        raid6_call.gen_syndrome(rbio->real_stripes, sectorsize,
                                                pointers);
                } else {
                        /* raid5 */
                        memcpy(pointers[nr_data], pointers[0], sectorsize);
                        run_xor(pointers + 1, nr_data - 1, sectorsize);
                }

                /* Check scrubbing parity and repair it */
                sector = rbio_stripe_sector(rbio, rbio->scrubp, sectornr);
                parity = kmap_local_page(sector->page) + sector->pgoff;
                if (memcmp(parity, pointers[rbio->scrubp], sectorsize) != 0)
                        memcpy(parity, pointers[rbio->scrubp], sectorsize);
                else
                        /* Parity is right, needn't writeback */
                        bitmap_clear(rbio->dbitmap, sectornr, 1);
                kunmap_local(parity);

                for (stripe = nr_data - 1; stripe >= 0; stripe--)
                        kunmap_local(pointers[stripe]);
        }

        kunmap_local(pointers[nr_data]);
        __free_page(p_sector.page);
        p_sector.page = NULL;
        if (q_sector.page) {
                kunmap_local(pointers[rbio->real_stripes - 1]);
                __free_page(q_sector.page);
                q_sector.page = NULL;
        }

writeback:
        /*
         * time to start writing.  Make bios for everything from the
         * higher layers (the bio_list in our rbio) and our p/q.  Ignore
         * everything else.
         */
        for_each_set_bit(sectornr, rbio->dbitmap, rbio->stripe_nsectors) {
                struct sector_ptr *sector;

                sector = rbio_stripe_sector(rbio, rbio->scrubp, sectornr);
                ret = rbio_add_io_sector(rbio, &bio_list, sector, rbio->scrubp,
                                         sectornr, rbio->stripe_len, REQ_OP_WRITE);
                if (ret)
                        goto cleanup;
        }

        if (!is_replace)
                goto submit_write;

        for_each_set_bit(sectornr, pbitmap, rbio->stripe_nsectors) {
                struct sector_ptr *sector;

                sector = rbio_stripe_sector(rbio, rbio->scrubp, sectornr);
                ret = rbio_add_io_sector(rbio, &bio_list, sector,
                                       bioc->tgtdev_map[rbio->scrubp],
                                       sectornr, rbio->stripe_len, REQ_OP_WRITE);
                if (ret)
                        goto cleanup;
        }

submit_write:
        nr_data = bio_list_size(&bio_list);
        if (!nr_data) {
                /* Every parity is right */
                rbio_orig_end_io(rbio, BLK_STS_OK);
                return;
        }

        atomic_set(&rbio->stripes_pending, nr_data);

        while ((bio = bio_list_pop(&bio_list))) {
                bio->bi_end_io = raid_write_end_io;

                submit_bio(bio);
        }
        return;

cleanup:
        rbio_orig_end_io(rbio, BLK_STS_IOERR);

        while ((bio = bio_list_pop(&bio_list)))
                bio_put(bio);
}

static inline int is_data_stripe(struct btrfs_raid_bio *rbio, int stripe)
{
        if (stripe >= 0 && stripe < rbio->nr_data)
                return 1;
        return 0;
}

/*
 * While we're doing the parity check and repair, we could have errors
 * in reading pages off the disk.  This checks for errors and if we're
 * not able to read the page it'll trigger parity reconstruction.  The
 * parity scrub will be finished after we've reconstructed the failed
 * stripes
 */
static void validate_rbio_for_parity_scrub(struct btrfs_raid_bio *rbio)
{
        if (atomic_read(&rbio->error) > rbio->bioc->max_errors)
                goto cleanup;

        if (rbio->faila >= 0 || rbio->failb >= 0) {
                int dfail = 0, failp = -1;

                if (is_data_stripe(rbio, rbio->faila))
                        dfail++;
                else if (is_parity_stripe(rbio->faila))
                        failp = rbio->faila;

                if (is_data_stripe(rbio, rbio->failb))
                        dfail++;
                else if (is_parity_stripe(rbio->failb))
                        failp = rbio->failb;

                /*
                 * Because we can not use a scrubbing parity to repair
                 * the data, so the capability of the repair is declined.
                 * (In the case of RAID5, we can not repair anything)
                 */
                if (dfail > rbio->bioc->max_errors - 1)
                        goto cleanup;

                /*
                 * If all data is good, only parity is correctly, just
                 * repair the parity.
                 */
                if (dfail == 0) {
                        finish_parity_scrub(rbio, 0);
                        return;
                }

                /*
                 * Here means we got one corrupted data stripe and one
                 * corrupted parity on RAID6, if the corrupted parity
                 * is scrubbing parity, luckily, use the other one to repair
                 * the data, or we can not repair the data stripe.
                 */
                if (failp != rbio->scrubp)
                        goto cleanup;

                __raid_recover_end_io(rbio);
        } else {
                finish_parity_scrub(rbio, 1);
        }
        return;

cleanup:
        rbio_orig_end_io(rbio, BLK_STS_IOERR);
}

/*
 * end io for the read phase of the rmw cycle.  All the bios here are physical
 * stripe bios we've read from the disk so we can recalculate the parity of the
 * stripe.
 *
 * This will usually kick off finish_rmw once all the bios are read in, but it
 * may trigger parity reconstruction if we had any errors along the way
 */
static void raid56_parity_scrub_end_io(struct bio *bio)
{
        struct btrfs_raid_bio *rbio = bio->bi_private;

        if (bio->bi_status)
                fail_bio_stripe(rbio, bio);
        else
                set_bio_pages_uptodate(rbio, bio);

        bio_put(bio);

        if (!atomic_dec_and_test(&rbio->stripes_pending))
                return;

        /*
         * this will normally call finish_rmw to start our write
         * but if there are any failed stripes we'll reconstruct
         * from parity first
         */
        validate_rbio_for_parity_scrub(rbio);
}

static void raid56_parity_scrub_stripe(struct btrfs_raid_bio *rbio)
{
        int bios_to_read = 0;
        struct bio_list bio_list;
        int ret;
        int sectornr;
        int stripe;
        struct bio *bio;

        bio_list_init(&bio_list);

        ret = alloc_rbio_essential_pages(rbio);
        if (ret)
                goto cleanup;

        atomic_set(&rbio->error, 0);
        /*
         * build a list of bios to read all the missing parts of this
         * stripe
         */
        for (stripe = 0; stripe < rbio->real_stripes; stripe++) {
                for_each_set_bit(sectornr , rbio->dbitmap, rbio->stripe_nsectors) {
                        struct sector_ptr *sector;
                        /*
                         * We want to find all the sectors missing from the
                         * rbio and read them from the disk.  If * sector_in_rbio()
                         * finds a sector in the bio list we don't need to read
                         * it off the stripe.
                         */
                        sector = sector_in_rbio(rbio, stripe, sectornr, 1);
                        if (sector)
                                continue;

                        sector = rbio_stripe_sector(rbio, stripe, sectornr);
                        /*
                         * The bio cache may have handed us an uptodate sector.
                         * If so, be happy and use it.
                         */
                        if (sector->uptodate)
                                continue;

                        ret = rbio_add_io_sector(rbio, &bio_list, sector,
                                                 stripe, sectornr, rbio->stripe_len,
                                                 REQ_OP_READ);
                        if (ret)
                                goto cleanup;
                }
        }

        bios_to_read = bio_list_size(&bio_list);
        if (!bios_to_read) {
                /*
                 * this can happen if others have merged with
                 * us, it means there is nothing left to read.
                 * But if there are missing devices it may not be
                 * safe to do the full stripe write yet.
                 */
                goto finish;
        }

        /*
         * The bioc may be freed once we submit the last bio. Make sure not to
         * touch it after that.
         */
        atomic_set(&rbio->stripes_pending, bios_to_read);
        while ((bio = bio_list_pop(&bio_list))) {
                bio->bi_end_io = raid56_parity_scrub_end_io;

                btrfs_bio_wq_end_io(rbio->bioc->fs_info, bio, BTRFS_WQ_ENDIO_RAID56);

                submit_bio(bio);
        }
        /* the actual write will happen once the reads are done */
        return;

cleanup:
        rbio_orig_end_io(rbio, BLK_STS_IOERR);

        while ((bio = bio_list_pop(&bio_list)))
                bio_put(bio);

        return;

finish:
        validate_rbio_for_parity_scrub(rbio);
}

static void scrub_parity_work(struct work_struct *work)
{
        struct btrfs_raid_bio *rbio;

        rbio = container_of(work, struct btrfs_raid_bio, work);
        raid56_parity_scrub_stripe(rbio);
}

void raid56_parity_submit_scrub_rbio(struct btrfs_raid_bio *rbio)
{
        if (!lock_stripe_add(rbio))
                start_async_work(rbio, scrub_parity_work);
}

/* The following code is used for dev replace of a missing RAID 5/6 device. */

struct btrfs_raid_bio *
raid56_alloc_missing_rbio(struct bio *bio, struct btrfs_io_context *bioc,
                          u64 length)
{
        struct btrfs_fs_info *fs_info = bioc->fs_info;
        struct btrfs_raid_bio *rbio;

        rbio = alloc_rbio(fs_info, bioc, length);
        if (IS_ERR(rbio))
                return NULL;

        rbio->operation = BTRFS_RBIO_REBUILD_MISSING;
        bio_list_add(&rbio->bio_list, bio);
        /*
         * This is a special bio which is used to hold the completion handler
         * and make the scrub rbio is similar to the other types
         */
        ASSERT(!bio->bi_iter.bi_size);

        rbio->faila = find_logical_bio_stripe(rbio, bio);
        if (rbio->faila == -1) {
                BUG();
                kfree(rbio);
                return NULL;
        }

        /*
         * When we get bioc, we have already increased bio_counter, record it
         * so we can free it at rbio_orig_end_io()
         */
        rbio->generic_bio_cnt = 1;

        return rbio;
}

void raid56_submit_missing_rbio(struct btrfs_raid_bio *rbio)
{
        if (!lock_stripe_add(rbio))
                start_async_work(rbio, read_rebuild_work);
}