Linux 6.13-rc4

[linux.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 "messages.h"
#include "ctree.h"
#include "disk-io.h"
#include "volumes.h"
#include "raid56.h"
#include "async-thread.h"
#include "file-item.h"
#include "btrfs_inode.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

static void dump_bioc(const struct btrfs_fs_info *fs_info, const struct btrfs_io_context *bioc)
{
        if (unlikely(!bioc)) {
                btrfs_crit(fs_info, "bioc=NULL");
                return;
        }
        btrfs_crit(fs_info,
"bioc logical=%llu full_stripe=%llu size=%llu map_type=0x%llx mirror=%u replace_nr_stripes=%u replace_stripe_src=%d num_stripes=%u",
                bioc->logical, bioc->full_stripe_logical, bioc->size,
                bioc->map_type, bioc->mirror_num, bioc->replace_nr_stripes,
                bioc->replace_stripe_src, bioc->num_stripes);
        for (int i = 0; i < bioc->num_stripes; i++) {
                btrfs_crit(fs_info, "    nr=%d devid=%llu physical=%llu",
                           i, bioc->stripes[i].dev->devid,
                           bioc->stripes[i].physical);
        }
}

static void btrfs_dump_rbio(const struct btrfs_fs_info *fs_info,
                            const struct btrfs_raid_bio *rbio)
{
        if (!IS_ENABLED(CONFIG_BTRFS_ASSERT))
                return;

        dump_bioc(fs_info, rbio->bioc);
        btrfs_crit(fs_info,
"rbio flags=0x%lx nr_sectors=%u nr_data=%u real_stripes=%u stripe_nsectors=%u scrubp=%u dbitmap=0x%lx",
                rbio->flags, rbio->nr_sectors, rbio->nr_data,
                rbio->real_stripes, rbio->stripe_nsectors,
                rbio->scrubp, rbio->dbitmap);
}

#define ASSERT_RBIO(expr, rbio)                                         \
({                                                                      \
        if (IS_ENABLED(CONFIG_BTRFS_ASSERT) && unlikely(!(expr))) {     \
                const struct btrfs_fs_info *__fs_info = (rbio)->bioc ?  \
                                        (rbio)->bioc->fs_info : NULL;   \
                                                                        \
                btrfs_dump_rbio(__fs_info, (rbio));                     \
        }                                                               \
        ASSERT((expr));                                                 \
})

#define ASSERT_RBIO_STRIPE(expr, rbio, stripe_nr)                       \
({                                                                      \
        if (IS_ENABLED(CONFIG_BTRFS_ASSERT) && unlikely(!(expr))) {     \
                const struct btrfs_fs_info *__fs_info = (rbio)->bioc ?  \
                                        (rbio)->bioc->fs_info : NULL;   \
                                                                        \
                btrfs_dump_rbio(__fs_info, (rbio));                     \
                btrfs_crit(__fs_info, "stripe_nr=%d", (stripe_nr));     \
        }                                                               \
        ASSERT((expr));                                                 \
})

#define ASSERT_RBIO_SECTOR(expr, rbio, sector_nr)                       \
({                                                                      \
        if (IS_ENABLED(CONFIG_BTRFS_ASSERT) && unlikely(!(expr))) {     \
                const struct btrfs_fs_info *__fs_info = (rbio)->bioc ?  \
                                        (rbio)->bioc->fs_info : NULL;   \
                                                                        \
                btrfs_dump_rbio(__fs_info, (rbio));                     \
                btrfs_crit(__fs_info, "sector_nr=%d", (sector_nr));     \
        }                                                               \
        ASSERT((expr));                                                 \
})

#define ASSERT_RBIO_LOGICAL(expr, rbio, logical)                        \
({                                                                      \
        if (IS_ENABLED(CONFIG_BTRFS_ASSERT) && unlikely(!(expr))) {     \
                const struct btrfs_fs_info *__fs_info = (rbio)->bioc ?  \
                                        (rbio)->bioc->fs_info : NULL;   \
                                                                        \
                btrfs_dump_rbio(__fs_info, (rbio));                     \
                btrfs_crit(__fs_info, "logical=%llu", (logical));               \
        }                                                               \
        ASSERT((expr));                                                 \
})

/* 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;
};

static void rmw_rbio_work(struct work_struct *work);
static void rmw_rbio_work_locked(struct work_struct *work);
static void index_rbio_pages(struct btrfs_raid_bio *rbio);
static int alloc_rbio_pages(struct btrfs_raid_bio *rbio);

static int finish_parity_scrub(struct btrfs_raid_bio *rbio);
static void scrub_rbio_work_locked(struct work_struct *work);

static void free_raid_bio_pointers(struct btrfs_raid_bio *rbio)
{
        bitmap_free(rbio->error_bitmap);
        kfree(rbio->stripe_pages);
        kfree(rbio->bio_sectors);
        kfree(rbio->stripe_sectors);
        kfree(rbio->finish_pointers);
}

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);
        free_raid_bio_pointers(rbio);
        kfree(rbio);
}

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) {
                        /*
                         * Even if the sector is not covered by bio, if it is
                         * a data sector it should still be uptodate as it is
                         * read from disk.
                         */
                        if (i < rbio->nr_data * rbio->stripe_nsectors)
                                ASSERT(rbio->stripe_sectors[i].uptodate);
                        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->full_stripe_logical;

        /*
         * 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);
        }
}

static void steal_rbio_page(struct btrfs_raid_bio *src,
                            struct btrfs_raid_bio *dest, int page_nr)
{
        const u32 sectorsize = src->bioc->fs_info->sectorsize;
        const u32 sectors_per_page = PAGE_SIZE / sectorsize;
        int i;

        if (dest->stripe_pages[page_nr])
                __free_page(dest->stripe_pages[page_nr]);
        dest->stripe_pages[page_nr] = src->stripe_pages[page_nr];
        src->stripe_pages[page_nr] = NULL;

        /* Also update the sector->uptodate bits. */
        for (i = sectors_per_page * page_nr;
             i < sectors_per_page * page_nr + sectors_per_page; i++)
                dest->stripe_sectors[i].uptodate = true;
}

static bool is_data_stripe_page(struct btrfs_raid_bio *rbio, int page_nr)
{
        const int sector_nr = (page_nr << PAGE_SHIFT) >>
                              rbio->bioc->fs_info->sectorsize_bits;

        /*
         * We have ensured PAGE_SIZE is aligned with sectorsize, thus
         * we won't have a page which is half data half parity.
         *
         * Thus if the first sector of the page belongs to data stripes, then
         * the full page belongs to data stripes.
         */
        return (sector_nr < rbio->nr_data * rbio->stripe_nsectors);
}

/*
 * 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;

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

        for (i = 0; i < dest->nr_pages; i++) {
                struct page *p = src->stripe_pages[i];

                /*
                 * We don't need to steal P/Q pages as they will always be
                 * regenerated for RMW or full write anyway.
                 */
                if (!is_data_stripe_page(src, i))
                        continue;

                /*
                 * If @src already has RBIO_CACHE_READY_BIT, it should have
                 * all data stripe pages present and uptodate.
                 */
                ASSERT(p);
                ASSERT(full_page_sectors_uptodate(src, i));
                steal_rbio_page(src, dest, i);
        }
        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_init(&dest->bio_list, &victim->bio_list);
        dest->bio_list_bytes += victim->bio_list_bytes;
        /* Also inherit the bitmaps from @victim. */
        bitmap_or(&dest->dbitmap, &victim->dbitmap, &dest->dbitmap,
                  dest->stripe_nsectors);
}

/*
 * 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;

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

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

        spin_lock(&table->cache_lock);
        __remove_rbio_from_cache(rbio);
        spin_unlock(&table->cache_lock);
}

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

        table = info->stripe_hash_table;

        spin_lock(&table->cache_lock);
        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(&table->cache_lock);
}

/*
 * 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;

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

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

        spin_lock(&table->cache_lock);
        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(&table->cache_lock);
}

/*
 * 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 size = rbio->bio_list_bytes;
        int ret = 1;

        spin_lock(&rbio->bio_list_lock);
        if (size != rbio->nr_data * BTRFS_STRIPE_LEN)
                ret = 0;
        BUG_ON(size > rbio->nr_data * BTRFS_STRIPE_LEN);
        spin_unlock(&rbio->bio_list_lock);

        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->full_stripe_logical != cur->bioc->full_stripe_logical)
                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_READ_REBUILD)
                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_RBIO_STRIPE(stripe_nr < rbio->real_stripes, rbio, stripe_nr);
        ASSERT_RBIO_SECTOR(sector_nr < rbio->stripe_nsectors, rbio, sector_nr);

        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;
        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(&h->lock);
        list_for_each_entry(cur, &h->hash_list, hash_list) {
                if (cur->bioc->full_stripe_logical != rbio->bioc->full_stripe_logical)
                        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(&h->lock);
        if (cache_drop)
                remove_rbio_from_cache(cache_drop);
        if (freeit)
                free_raid_bio(freeit);
        return ret;
}

static void recover_rbio_work_locked(struct work_struct *work);

/*
 * 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;
        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(&h->lock);
        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(&h->lock);

                        if (next->operation == BTRFS_RBIO_READ_REBUILD) {
                                start_async_work(next, recover_rbio_work_locked);
                        } else if (next->operation == BTRFS_RBIO_WRITE) {
                                steal_rbio(rbio, next);
                                start_async_work(next, rmw_rbio_work_locked);
                        } else if (next->operation == BTRFS_RBIO_PARITY_SCRUB) {
                                steal_rbio(rbio, next);
                                start_async_work(next, scrub_rbio_work_locked);
                        }

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

done_nolock:
        if (!keep_cache)
                remove_rbio_from_cache(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;

        kfree(rbio->csum_buf);
        bitmap_free(rbio->csum_bitmap);
        rbio->csum_buf = NULL;
        rbio->csum_bitmap = NULL;

        /*
         * Clear the data bitmap, as the rbio may be cached for later usage.
         * do this before before unlock_stripe() so there will be no new bio
         * for this bio.
         */
        bitmap_clear(&rbio->dbitmap, 0, rbio->stripe_nsectors);

        /*
         * 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);
}

/*
 * 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_RBIO_STRIPE(stripe_nr >= 0 && stripe_nr < rbio->real_stripes,
                           rbio, stripe_nr);
        ASSERT_RBIO_SECTOR(sector_nr >= 0 && sector_nr < rbio->stripe_nsectors,
                           rbio, sector_nr);

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

        spin_lock(&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(&rbio->bio_list_lock);
                return sector;
        }
        spin_unlock(&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)
{
        const unsigned int real_stripes = bioc->num_stripes - bioc->replace_nr_stripes;
        const unsigned int stripe_npages = BTRFS_STRIPE_LEN >> PAGE_SHIFT;
        const unsigned int num_pages = stripe_npages * real_stripes;
        const unsigned int stripe_nsectors =
                BTRFS_STRIPE_LEN >> fs_info->sectorsize_bits;
        const unsigned int num_sectors = stripe_nsectors * real_stripes;
        struct btrfs_raid_bio *rbio;

        /* PAGE_SIZE must also be aligned to sectorsize for subpage support */
        ASSERT(IS_ALIGNED(PAGE_SIZE, fs_info->sectorsize));
        /*
         * Our current stripe len should be fixed to 64k thus stripe_nsectors
         * (at most 16) should be no larger than BITS_PER_LONG.
         */
        ASSERT(stripe_nsectors <= BITS_PER_LONG);

        /*
         * Real stripes must be between 2 (2 disks RAID5, aka RAID1) and 256
         * (limited by u8).
         */
        ASSERT(real_stripes >= 2);
        ASSERT(real_stripes <= U8_MAX);

        rbio = kzalloc(sizeof(*rbio), GFP_NOFS);
        if (!rbio)
                return ERR_PTR(-ENOMEM);
        rbio->stripe_pages = kcalloc(num_pages, sizeof(struct page *),
                                     GFP_NOFS);
        rbio->bio_sectors = kcalloc(num_sectors, sizeof(struct sector_ptr),
                                    GFP_NOFS);
        rbio->stripe_sectors = kcalloc(num_sectors, sizeof(struct sector_ptr),
                                       GFP_NOFS);
        rbio->finish_pointers = kcalloc(real_stripes, sizeof(void *), GFP_NOFS);
        rbio->error_bitmap = bitmap_zalloc(num_sectors, GFP_NOFS);

        if (!rbio->stripe_pages || !rbio->bio_sectors || !rbio->stripe_sectors ||
            !rbio->finish_pointers || !rbio->error_bitmap) {
                free_raid_bio_pointers(rbio);
                kfree(rbio);
                return ERR_PTR(-ENOMEM);
        }

        bio_list_init(&rbio->bio_list);
        init_waitqueue_head(&rbio->io_wait);
        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);
        btrfs_get_bioc(bioc);
        rbio->bioc = bioc;
        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;
        refcount_set(&rbio->refs, 1);
        atomic_set(&rbio->stripes_pending, 0);

        ASSERT(btrfs_nr_parity_stripes(bioc->map_type));
        rbio->nr_data = real_stripes - btrfs_nr_parity_stripes(bioc->map_type);
        ASSERT(rbio->nr_data > 0);

        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, false);
        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, false);
        if (ret < 0)
                return ret;

        index_stripe_sectors(rbio);
        return 0;
}

/*
 * Return the total number of errors found in the vertical stripe of @sector_nr.
 *
 * @faila and @failb will also be updated to the first and second stripe
 * number of the errors.
 */
static int get_rbio_veritical_errors(struct btrfs_raid_bio *rbio, int sector_nr,
                                     int *faila, int *failb)
{
        int stripe_nr;
        int found_errors = 0;

        if (faila || failb) {
                /*
                 * Both @faila and @failb should be valid pointers if any of
                 * them is specified.
                 */
                ASSERT(faila && failb);
                *faila = -1;
                *failb = -1;
        }

        for (stripe_nr = 0; stripe_nr < rbio->real_stripes; stripe_nr++) {
                int total_sector_nr = stripe_nr * rbio->stripe_nsectors + sector_nr;

                if (test_bit(total_sector_nr, rbio->error_bitmap)) {
                        found_errors++;
                        if (faila) {
                                /* Update faila and failb. */
                                if (*faila < 0)
                                        *faila = stripe_nr;
                                else if (*failb < 0)
                                        *failb = stripe_nr;
                        }
                }
        }
        return found_errors;
}

/*
 * 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,
                              enum req_op op)
{
        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_RBIO_STRIPE(stripe_nr >= 0 && stripe_nr < rbio->bioc->num_stripes,
                           rbio, stripe_nr);
        ASSERT_RBIO_SECTOR(sector_nr >= 0 && sector_nr < rbio->stripe_nsectors,
                           rbio, sector_nr);
        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) {
                int found_errors;

                set_bit(stripe_nr * rbio->stripe_nsectors + sector_nr,
                        rbio->error_bitmap);

                /* Check if we have reached tolerance early. */
                found_errors = get_rbio_veritical_errors(rbio, sector_nr,
                                                         NULL, NULL);
                if (found_errors > rbio->bioc->max_errors)
                        return -EIO;
                return 0;
        }

        /* see if we can add this page onto our existing bio */
        if (last) {
                u64 last_end = last->bi_iter.bi_sector << SECTOR_SHIFT;
                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(BTRFS_STRIPE_LEN >> PAGE_SHIFT, 1),
                        op, GFP_NOFS);
        bio->bi_iter.bi_sector = disk_start >> SECTOR_SHIFT;
        bio->bi_private = rbio;

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

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->full_stripe_logical;

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

        spin_unlock(&rbio->bio_list_lock);
}

static void bio_get_trace_info(struct btrfs_raid_bio *rbio, struct bio *bio,
                               struct raid56_bio_trace_info *trace_info)
{
        const struct btrfs_io_context *bioc = rbio->bioc;
        int i;

        ASSERT(bioc);

        /* We rely on bio->bi_bdev to find the stripe number. */
        if (!bio->bi_bdev)
                goto not_found;

        for (i = 0; i < bioc->num_stripes; i++) {
                if (bio->bi_bdev != bioc->stripes[i].dev->bdev)
                        continue;
                trace_info->stripe_nr = i;
                trace_info->devid = bioc->stripes[i].dev->devid;
                trace_info->offset = (bio->bi_iter.bi_sector << SECTOR_SHIFT) -
                                     bioc->stripes[i].physical;
                return;
        }

not_found:
        trace_info->devid = -1;
        trace_info->offset = -1;
        trace_info->stripe_nr = -1;
}

static inline void bio_list_put(struct bio_list *bio_list)
{
        struct bio *bio;

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

static void assert_rbio(struct btrfs_raid_bio *rbio)
{
        if (!IS_ENABLED(CONFIG_BTRFS_ASSERT))
                return;

        /*
         * At least two stripes (2 disks RAID5), and since real_stripes is U8,
         * we won't go beyond 256 disks anyway.
         */
        ASSERT_RBIO(rbio->real_stripes >= 2, rbio);
        ASSERT_RBIO(rbio->nr_data > 0, rbio);

        /*
         * This is another check to make sure nr data stripes is smaller
         * than total stripes.
         */
        ASSERT_RBIO(rbio->nr_data < rbio->real_stripes, rbio);
}

/* Generate PQ for one vertical stripe. */
static void generate_pq_vertical(struct btrfs_raid_bio *rbio, int sectornr)
{
        void **pointers = rbio->finish_pointers;
        const u32 sectorsize = rbio->bioc->fs_info->sectorsize;
        struct sector_ptr *sector;
        int stripe;
        const bool has_qstripe = rbio->bioc->map_type & BTRFS_BLOCK_GROUP_RAID6;

        /* First collect one sector from each data stripe */
        for (stripe = 0; stripe < rbio->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;

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

static int rmw_assemble_write_bios(struct btrfs_raid_bio *rbio,
                                   struct bio_list *bio_list)
{
        /* The total sector number inside the full stripe. */
        int total_sector_nr;
        int sectornr;
        int stripe;
        int ret;

        ASSERT(bio_list_size(bio_list) == 0);

        /* We should have at least one data sector. */
        ASSERT(bitmap_weight(&rbio->dbitmap, rbio->stripe_nsectors));

        /*
         * Reset errors, as we may have errors inherited from from degraded
         * write.
         */
        bitmap_clear(rbio->error_bitmap, 0, rbio->nr_sectors);

        /*
         * Start assembly.  Make bios for everything from the higher layers (the
         * bio_list in our rbio) and our P/Q.  Ignore everything else.
         */
        for (total_sector_nr = 0; total_sector_nr < rbio->nr_sectors;
             total_sector_nr++) {
                struct sector_ptr *sector;

                stripe = total_sector_nr / rbio->stripe_nsectors;
                sectornr = total_sector_nr % rbio->stripe_nsectors;

                /* This vertical stripe has no data, skip it. */
                if (!test_bit(sectornr, &rbio->dbitmap))
                        continue;

                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, REQ_OP_WRITE);
                if (ret)
                        goto error;
        }

        if (likely(!rbio->bioc->replace_nr_stripes))
                return 0;

        /*
         * Make a copy for the replace target device.
         *
         * Thus the source stripe number (in replace_stripe_src) should be valid.
         */
        ASSERT(rbio->bioc->replace_stripe_src >= 0);

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

                stripe = total_sector_nr / rbio->stripe_nsectors;
                sectornr = total_sector_nr % rbio->stripe_nsectors;

                /*
                 * For RAID56, there is only one device that can be replaced,
                 * and replace_stripe_src[0] indicates the stripe number we
                 * need to copy from.
                 */
                if (stripe != rbio->bioc->replace_stripe_src) {
                        /*
                         * We can skip the whole stripe completely, note
                         * total_sector_nr will be increased by one anyway.
                         */
                        ASSERT(sectornr == 0);
                        total_sector_nr += rbio->stripe_nsectors - 1;
                        continue;
                }

                /* This vertical stripe has no data, skip it. */
                if (!test_bit(sectornr, &rbio->dbitmap))
                        continue;

                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->real_stripes,
                                         sectornr, REQ_OP_WRITE);
                if (ret)
                        goto error;
        }

        return 0;
error:
        bio_list_put(bio_list);
        return -EIO;
}

static void set_rbio_range_error(struct btrfs_raid_bio *rbio, struct bio *bio)
{
        struct btrfs_fs_info *fs_info = rbio->bioc->fs_info;
        u32 offset = (bio->bi_iter.bi_sector << SECTOR_SHIFT) -
                     rbio->bioc->full_stripe_logical;
        int total_nr_sector = offset >> fs_info->sectorsize_bits;

        ASSERT(total_nr_sector < rbio->nr_data * rbio->stripe_nsectors);

        bitmap_set(rbio->error_bitmap, total_nr_sector,
                   bio->bi_iter.bi_size >> fs_info->sectorsize_bits);

        /*
         * Special handling for raid56_alloc_missing_rbio() used by
         * scrub/replace.  Unlike call path in raid56_parity_recover(), they
         * pass an empty bio here.  Thus we have to find out the missing device
         * and mark the stripe error instead.
         */
        if (bio->bi_iter.bi_size == 0) {
                bool found_missing = false;
                int stripe_nr;

                for (stripe_nr = 0; stripe_nr < rbio->real_stripes; stripe_nr++) {
                        if (!rbio->bioc->stripes[stripe_nr].dev->bdev) {
                                found_missing = true;
                                bitmap_set(rbio->error_bitmap,
                                           stripe_nr * rbio->stripe_nsectors,
                                           rbio->stripe_nsectors);
                        }
                }
                ASSERT(found_missing);
        }
}

/*
 * For subpage case, we can no longer set page Up-to-date 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;
                }
        }
}

static int get_bio_sector_nr(struct btrfs_raid_bio *rbio, struct bio *bio)
{
        struct bio_vec *bv = bio_first_bvec_all(bio);
        int i;

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

                sector = &rbio->stripe_sectors[i];
                if (sector->page == bv->bv_page && sector->pgoff == bv->bv_offset)
                        break;
                sector = &rbio->bio_sectors[i];
                if (sector->page == bv->bv_page && sector->pgoff == bv->bv_offset)
                        break;
        }
        ASSERT(i < rbio->nr_sectors);
        return i;
}

static void rbio_update_error_bitmap(struct btrfs_raid_bio *rbio, struct bio *bio)
{
        int total_sector_nr = get_bio_sector_nr(rbio, bio);
        u32 bio_size = 0;
        struct bio_vec *bvec;
        int i;

        bio_for_each_bvec_all(bvec, bio, i)
                bio_size += bvec->bv_len;

        /*
         * Since we can have multiple bios touching the error_bitmap, we cannot
         * call bitmap_set() without protection.
         *
         * Instead use set_bit() for each bit, as set_bit() itself is atomic.
         */
        for (i = total_sector_nr; i < total_sector_nr +
             (bio_size >> rbio->bioc->fs_info->sectorsize_bits); i++)
                set_bit(i, rbio->error_bitmap);
}

/* Verify the data sectors at read time. */
static void verify_bio_data_sectors(struct btrfs_raid_bio *rbio,
                                    struct bio *bio)
{
        struct btrfs_fs_info *fs_info = rbio->bioc->fs_info;
        int total_sector_nr = get_bio_sector_nr(rbio, bio);
        struct bio_vec *bvec;
        struct bvec_iter_all iter_all;

        /* No data csum for the whole stripe, no need to verify. */
        if (!rbio->csum_bitmap || !rbio->csum_buf)
                return;

        /* P/Q stripes, they have no data csum to verify against. */
        if (total_sector_nr >= rbio->nr_data * rbio->stripe_nsectors)
                return;

        bio_for_each_segment_all(bvec, bio, iter_all) {
                int bv_offset;

                for (bv_offset = bvec->bv_offset;
                     bv_offset < bvec->bv_offset + bvec->bv_len;
                     bv_offset += fs_info->sectorsize, total_sector_nr++) {
                        u8 csum_buf[BTRFS_CSUM_SIZE];
                        u8 *expected_csum = rbio->csum_buf +
                                            total_sector_nr * fs_info->csum_size;
                        int ret;

                        /* No csum for this sector, skip to the next sector. */
                        if (!test_bit(total_sector_nr, rbio->csum_bitmap))
                                continue;

                        ret = btrfs_check_sector_csum(fs_info, bvec->bv_page,
                                bv_offset, csum_buf, expected_csum);
                        if (ret < 0)
                                set_bit(total_sector_nr, rbio->error_bitmap);
                }
        }
}

static void raid_wait_read_end_io(struct bio *bio)
{
        struct btrfs_raid_bio *rbio = bio->bi_private;

        if (bio->bi_status) {
                rbio_update_error_bitmap(rbio, bio);
        } else {
                set_bio_pages_uptodate(rbio, bio);
                verify_bio_data_sectors(rbio, bio);
        }

        bio_put(bio);
        if (atomic_dec_and_test(&rbio->stripes_pending))
                wake_up(&rbio->io_wait);
}

static void submit_read_wait_bio_list(struct btrfs_raid_bio *rbio,
                             struct bio_list *bio_list)
{
        struct bio *bio;

        atomic_set(&rbio->stripes_pending, bio_list_size(bio_list));
        while ((bio = bio_list_pop(bio_list))) {
                bio->bi_end_io = raid_wait_read_end_io;

                if (trace_raid56_read_enabled()) {
                        struct raid56_bio_trace_info trace_info = { 0 };

                        bio_get_trace_info(rbio, bio, &trace_info);
                        trace_raid56_read(rbio, bio, &trace_info);
                }
                submit_bio(bio);
        }

        wait_event(rbio->io_wait, atomic_read(&rbio->stripes_pending) == 0);
}

static int alloc_rbio_data_pages(struct btrfs_raid_bio *rbio)
{
        const int data_pages = rbio->nr_data * rbio->stripe_npages;
        int ret;

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

        index_stripe_sectors(rbio);
        return 0;
}

/*
 * 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;
};

/*
 * 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 raid_unplug(struct blk_plug_cb *cb, bool from_schedule)
{
        struct btrfs_plug_cb *plug = container_of(cb, struct btrfs_plug_cb, cb);
        struct btrfs_raid_bio *cur;
        struct btrfs_raid_bio *last = NULL;

        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)) {
                        /* We have a full stripe, queue it down. */
                        start_async_work(cur, rmw_rbio_work);
                        continue;
                }
                if (last) {
                        if (rbio_can_merge(last, cur)) {
                                merge_rbio(last, cur);
                                free_raid_bio(cur);
                                continue;
                        }
                        start_async_work(last, rmw_rbio_work);
                }
                last = cur;
        }
        if (last)
                start_async_work(last, rmw_rbio_work);
        kfree(plug);
}

/* Add the original bio into rbio->bio_list, and update rbio::dbitmap. */
static void rbio_add_bio(struct btrfs_raid_bio *rbio, struct bio *orig_bio)
{
        const struct btrfs_fs_info *fs_info = rbio->bioc->fs_info;
        const u64 orig_logical = orig_bio->bi_iter.bi_sector << SECTOR_SHIFT;
        const u64 full_stripe_start = rbio->bioc->full_stripe_logical;
        const u32 orig_len = orig_bio->bi_iter.bi_size;
        const u32 sectorsize = fs_info->sectorsize;
        u64 cur_logical;

        ASSERT_RBIO_LOGICAL(orig_logical >= full_stripe_start &&
                            orig_logical + orig_len <= full_stripe_start +
                            rbio->nr_data * BTRFS_STRIPE_LEN,
                            rbio, orig_logical);

        bio_list_add(&rbio->bio_list, orig_bio);
        rbio->bio_list_bytes += orig_bio->bi_iter.bi_size;

        /* Update the dbitmap. */
        for (cur_logical = orig_logical; cur_logical < orig_logical + orig_len;
             cur_logical += sectorsize) {
                int bit = ((u32)(cur_logical - full_stripe_start) >>
                           fs_info->sectorsize_bits) % rbio->stripe_nsectors;

                set_bit(bit, &rbio->dbitmap);
        }
}

/*
 * our main entry point for writes from the rest of the FS.
 */
void raid56_parity_write(struct bio *bio, struct btrfs_io_context *bioc)
{
        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;

        rbio = alloc_rbio(fs_info, bioc);
        if (IS_ERR(rbio)) {
                bio->bi_status = errno_to_blk_status(PTR_ERR(rbio));
                bio_endio(bio);
                return;
        }
        rbio->operation = BTRFS_RBIO_WRITE;
        rbio_add_bio(rbio, bio);

        /*
         * Don't plug on full rbios, just get them out the door
         * as quickly as we can
         */
        if (!rbio_is_full(rbio)) {
                cb = blk_check_plugged(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);
                        return;
                }
        }

        /*
         * Either we don't have any existing plug, or we're doing a full stripe,
         * queue the rmw work now.
         */
        start_async_work(rbio, rmw_rbio_work);
}

static int verify_one_sector(struct btrfs_raid_bio *rbio,
                             int stripe_nr, int sector_nr)
{
        struct btrfs_fs_info *fs_info = rbio->bioc->fs_info;
        struct sector_ptr *sector;
        u8 csum_buf[BTRFS_CSUM_SIZE];
        u8 *csum_expected;
        int ret;

        if (!rbio->csum_bitmap || !rbio->csum_buf)
                return 0;

        /* No way to verify P/Q as they are not covered by data csum. */
        if (stripe_nr >= rbio->nr_data)
                return 0;
        /*
         * If we're rebuilding a read, we have to use pages from the
         * bio list if possible.
         */
        if (rbio->operation == BTRFS_RBIO_READ_REBUILD) {
                sector = sector_in_rbio(rbio, stripe_nr, sector_nr, 0);
        } else {
                sector = rbio_stripe_sector(rbio, stripe_nr, sector_nr);
        }

        ASSERT(sector->page);

        csum_expected = rbio->csum_buf +
                        (stripe_nr * rbio->stripe_nsectors + sector_nr) *
                        fs_info->csum_size;
        ret = btrfs_check_sector_csum(fs_info, sector->page, sector->pgoff,
                                      csum_buf, csum_expected);
        return ret;
}

/*
 * Recover a vertical stripe specified by @sector_nr.
 * @*pointers are the pre-allocated pointers by the caller, so we don't
 * need to allocate/free the pointers again and again.
 */
static int recover_vertical(struct btrfs_raid_bio *rbio, int sector_nr,
                            void **pointers, void **unmap_array)
{
        struct btrfs_fs_info *fs_info = rbio->bioc->fs_info;
        struct sector_ptr *sector;
        const u32 sectorsize = fs_info->sectorsize;
        int found_errors;
        int faila;
        int failb;
        int stripe_nr;
        int ret = 0;

        /*
         * 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(sector_nr, &rbio->dbitmap))
                return 0;

        found_errors = get_rbio_veritical_errors(rbio, sector_nr, &faila,
                                                 &failb);
        /*
         * No errors in the vertical stripe, skip it.  Can happen for recovery
         * which only part of a stripe failed csum check.
         */
        if (!found_errors)
                return 0;

        if (found_errors > rbio->bioc->max_errors)
                return -EIO;

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

        /* 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.
                                 * We have nothing to do, just skip the
                                 * recovery for this stripe.
                                 */
                                goto cleanup;
                        /*
                         * a single failure in raid6 is rebuilt
                         * in the pstripe code below
                         */
                        goto pstripe;
                }

                /*
                 * 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 (failb == rbio->real_stripes - 1) {
                        if (faila == rbio->real_stripes - 2)
                                /*
                                 * Only P and Q are corrupted.
                                 * We only care about data stripes recovery,
                                 * can skip this vertical stripe.
                                 */
                                goto cleanup;
                        /*
                         * Otherwise we have one bad data stripe and
                         * a good P stripe.  raid5!
                         */
                        goto pstripe;
                }

                if (failb == rbio->real_stripes - 2) {
                        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). */
                ASSERT(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_nr = faila; stripe_nr < rbio->nr_data - 1;
                     stripe_nr++)
                        pointers[stripe_nr] = pointers[stripe_nr + 1];
                pointers[rbio->nr_data - 1] = p;

                /* Xor in the rest */
                run_xor(pointers, rbio->nr_data - 1, sectorsize);

        }

        /*
         * No matter if this is a RMW or recovery, we should have all
         * failed sectors repaired in the vertical stripe, thus they are now
         * uptodate.
         * Especially if we determine to cache the rbio, we need to
         * have at least all data sectors uptodate.
         *
         * If possible, also check if the repaired sector matches its data
         * checksum.
         */
        if (faila >= 0) {
                ret = verify_one_sector(rbio, faila, sector_nr);
                if (ret < 0)
                        goto cleanup;

                sector = rbio_stripe_sector(rbio, faila, sector_nr);
                sector->uptodate = 1;
        }
        if (failb >= 0) {
                ret = verify_one_sector(rbio, failb, sector_nr);
                if (ret < 0)
                        goto cleanup;

                sector = rbio_stripe_sector(rbio, failb, sector_nr);
                sector->uptodate = 1;
        }

cleanup:
        for (stripe_nr = rbio->real_stripes - 1; stripe_nr >= 0; stripe_nr--)
                kunmap_local(unmap_array[stripe_nr]);
        return ret;
}

static int recover_sectors(struct btrfs_raid_bio *rbio)
{
        void **pointers = NULL;
        void **unmap_array = NULL;
        int sectornr;
        int ret = 0;

        /*
         * @pointers array stores the pointer for each sector.
         *
         * @unmap_array stores copy of pointers that does not get reordered
         * during reconstruction so that kunmap_local works.
         */
        pointers = kcalloc(rbio->real_stripes, sizeof(void *), GFP_NOFS);
        unmap_array = kcalloc(rbio->real_stripes, sizeof(void *), GFP_NOFS);
        if (!pointers || !unmap_array) {
                ret = -ENOMEM;
                goto out;
        }

        if (rbio->operation == BTRFS_RBIO_READ_REBUILD) {
                spin_lock(&rbio->bio_list_lock);
                set_bit(RBIO_RMW_LOCKED_BIT, &rbio->flags);
                spin_unlock(&rbio->bio_list_lock);
        }

        index_rbio_pages(rbio);

        for (sectornr = 0; sectornr < rbio->stripe_nsectors; sectornr++) {
                ret = recover_vertical(rbio, sectornr, pointers, unmap_array);
                if (ret < 0)
                        break;
        }

out:
        kfree(pointers);
        kfree(unmap_array);
        return ret;
}

static void recover_rbio(struct btrfs_raid_bio *rbio)
{
        struct bio_list bio_list = BIO_EMPTY_LIST;
        int total_sector_nr;
        int ret = 0;

        /*
         * Either we're doing recover for a read failure or degraded write,
         * caller should have set error bitmap correctly.
         */
        ASSERT(bitmap_weight(rbio->error_bitmap, rbio->nr_sectors));

        /* For recovery, we need to read all sectors including P/Q. */
        ret = alloc_rbio_pages(rbio);
        if (ret < 0)
                goto out;

        index_rbio_pages(rbio);

        /*
         * Read everything that hasn't failed. However this time we will
         * not trust any cached sector.
         * As we may read out some stale data but higher layer is not reading
         * that stale part.
         *
         * So here we always re-read everything in recovery path.
         */
        for (total_sector_nr = 0; total_sector_nr < rbio->nr_sectors;
             total_sector_nr++) {
                int stripe = total_sector_nr / rbio->stripe_nsectors;
                int sectornr = total_sector_nr % rbio->stripe_nsectors;
                struct sector_ptr *sector;

                /*
                 * Skip the range which has error.  It can be a range which is
                 * marked error (for csum mismatch), or it can be a missing
                 * device.
                 */
                if (!rbio->bioc->stripes[stripe].dev->bdev ||
                    test_bit(total_sector_nr, rbio->error_bitmap)) {
                        /*
                         * Also set the error bit for missing device, which
                         * may not yet have its error bit set.
                         */
                        set_bit(total_sector_nr, rbio->error_bitmap);
                        continue;
                }

                sector = rbio_stripe_sector(rbio, stripe, sectornr);
                ret = rbio_add_io_sector(rbio, &bio_list, sector, stripe,
                                         sectornr, REQ_OP_READ);
                if (ret < 0) {
                        bio_list_put(&bio_list);
                        goto out;
                }
        }

        submit_read_wait_bio_list(rbio, &bio_list);
        ret = recover_sectors(rbio);
out:
        rbio_orig_end_io(rbio, errno_to_blk_status(ret));
}

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

        rbio = container_of(work, struct btrfs_raid_bio, work);
        if (!lock_stripe_add(rbio))
                recover_rbio(rbio);
}

static void recover_rbio_work_locked(struct work_struct *work)
{
        recover_rbio(container_of(work, struct btrfs_raid_bio, work));
}

static void set_rbio_raid6_extra_error(struct btrfs_raid_bio *rbio, int mirror_num)
{
        bool found = false;
        int sector_nr;

        /*
         * This is for RAID6 extra recovery tries, thus mirror number should
         * be large than 2.
         * Mirror 1 means read from data stripes. Mirror 2 means rebuild using
         * RAID5 methods.
         */
        ASSERT(mirror_num > 2);
        for (sector_nr = 0; sector_nr < rbio->stripe_nsectors; sector_nr++) {
                int found_errors;
                int faila;
                int failb;

                found_errors = get_rbio_veritical_errors(rbio, sector_nr,
                                                         &faila, &failb);
                /* This vertical stripe doesn't have errors. */
                if (!found_errors)
                        continue;

                /*
                 * If we found errors, there should be only one error marked
                 * by previous set_rbio_range_error().
                 */
                ASSERT(found_errors == 1);
                found = true;

                /* Now select another stripe to mark as error. */
                failb = rbio->real_stripes - (mirror_num - 1);
                if (failb <= faila)
                        failb--;

                /* Set the extra bit in error bitmap. */
                if (failb >= 0)
                        set_bit(failb * rbio->stripe_nsectors + sector_nr,
                                rbio->error_bitmap);
        }

        /* We should found at least one vertical stripe with error.*/
        ASSERT(found);
}

/*
 * 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.
 */
void raid56_parity_recover(struct bio *bio, struct btrfs_io_context *bioc,
                           int mirror_num)
{
        struct btrfs_fs_info *fs_info = bioc->fs_info;
        struct btrfs_raid_bio *rbio;

        rbio = alloc_rbio(fs_info, bioc);
        if (IS_ERR(rbio)) {
                bio->bi_status = errno_to_blk_status(PTR_ERR(rbio));
                bio_endio(bio);
                return;
        }

        rbio->operation = BTRFS_RBIO_READ_REBUILD;
        rbio_add_bio(rbio, bio);

        set_rbio_range_error(rbio, bio);

        /*
         * 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)
                set_rbio_raid6_extra_error(rbio, mirror_num);

        start_async_work(rbio, recover_rbio_work);
}

static void fill_data_csums(struct btrfs_raid_bio *rbio)
{
        struct btrfs_fs_info *fs_info = rbio->bioc->fs_info;
        struct btrfs_root *csum_root = btrfs_csum_root(fs_info,
                                                       rbio->bioc->full_stripe_logical);
        const u64 start = rbio->bioc->full_stripe_logical;
        const u32 len = (rbio->nr_data * rbio->stripe_nsectors) <<
                        fs_info->sectorsize_bits;
        int ret;

        /* The rbio should not have its csum buffer initialized. */
        ASSERT(!rbio->csum_buf && !rbio->csum_bitmap);

        /*
         * Skip the csum search if:
         *
         * - The rbio doesn't belong to data block groups
         *   Then we are doing IO for tree blocks, no need to search csums.
         *
         * - The rbio belongs to mixed block groups
         *   This is to avoid deadlock, as we're already holding the full
         *   stripe lock, if we trigger a metadata read, and it needs to do
         *   raid56 recovery, we will deadlock.
         */
        if (!(rbio->bioc->map_type & BTRFS_BLOCK_GROUP_DATA) ||
            rbio->bioc->map_type & BTRFS_BLOCK_GROUP_METADATA)
                return;

        rbio->csum_buf = kzalloc(rbio->nr_data * rbio->stripe_nsectors *
                                 fs_info->csum_size, GFP_NOFS);
        rbio->csum_bitmap = bitmap_zalloc(rbio->nr_data * rbio->stripe_nsectors,
                                          GFP_NOFS);
        if (!rbio->csum_buf || !rbio->csum_bitmap) {
                ret = -ENOMEM;
                goto error;
        }

        ret = btrfs_lookup_csums_bitmap(csum_root, NULL, start, start + len - 1,
                                        rbio->csum_buf, rbio->csum_bitmap);
        if (ret < 0)
                goto error;
        if (bitmap_empty(rbio->csum_bitmap, len >> fs_info->sectorsize_bits))
                goto no_csum;
        return;

error:
        /*
         * We failed to allocate memory or grab the csum, but it's not fatal,
         * we can still continue.  But better to warn users that RMW is no
         * longer safe for this particular sub-stripe write.
         */
        btrfs_warn_rl(fs_info,
"sub-stripe write for full stripe %llu is not safe, failed to get csum: %d",
                        rbio->bioc->full_stripe_logical, ret);
no_csum:
        kfree(rbio->csum_buf);
        bitmap_free(rbio->csum_bitmap);
        rbio->csum_buf = NULL;
        rbio->csum_bitmap = NULL;
}

static int rmw_read_wait_recover(struct btrfs_raid_bio *rbio)
{
        struct bio_list bio_list = BIO_EMPTY_LIST;
        int total_sector_nr;
        int ret = 0;

        /*
         * Fill the data csums we need for data verification.  We need to fill
         * the csum_bitmap/csum_buf first, as our endio function will try to
         * verify the data sectors.
         */
        fill_data_csums(rbio);

        /*
         * Build a list of bios to read all sectors (including data and P/Q).
         *
         * This behavior is to compensate the later csum verification and recovery.
         */
        for (total_sector_nr = 0; total_sector_nr < rbio->nr_sectors;
             total_sector_nr++) {
                struct sector_ptr *sector;
                int stripe = total_sector_nr / rbio->stripe_nsectors;
                int sectornr = total_sector_nr % rbio->stripe_nsectors;

                sector = rbio_stripe_sector(rbio, stripe, sectornr);
                ret = rbio_add_io_sector(rbio, &bio_list, sector,
                               stripe, sectornr, REQ_OP_READ);
                if (ret) {
                        bio_list_put(&bio_list);
                        return ret;
                }
        }

        /*
         * We may or may not have any corrupted sectors (including missing dev
         * and csum mismatch), just let recover_sectors() to handle them all.
         */
        submit_read_wait_bio_list(rbio, &bio_list);
        return recover_sectors(rbio);
}

static void raid_wait_write_end_io(struct bio *bio)
{
        struct btrfs_raid_bio *rbio = bio->bi_private;
        blk_status_t err = bio->bi_status;

        if (err)
                rbio_update_error_bitmap(rbio, bio);
        bio_put(bio);
        if (atomic_dec_and_test(&rbio->stripes_pending))
                wake_up(&rbio->io_wait);
}

static void submit_write_bios(struct btrfs_raid_bio *rbio,
                              struct bio_list *bio_list)
{
        struct bio *bio;

        atomic_set(&rbio->stripes_pending, bio_list_size(bio_list));
        while ((bio = bio_list_pop(bio_list))) {
                bio->bi_end_io = raid_wait_write_end_io;

                if (trace_raid56_write_enabled()) {
                        struct raid56_bio_trace_info trace_info = { 0 };

                        bio_get_trace_info(rbio, bio, &trace_info);
                        trace_raid56_write(rbio, bio, &trace_info);
                }
                submit_bio(bio);
        }
}

/*
 * To determine if we need to read any sector from the disk.
 * Should only be utilized in RMW path, to skip cached rbio.
 */
static bool need_read_stripe_sectors(struct btrfs_raid_bio *rbio)
{
        int i;

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

                /*
                 * We have a sector which doesn't have page nor uptodate,
                 * thus this rbio can not be cached one, as cached one must
                 * have all its data sectors present and uptodate.
                 */
                if (!sector->page || !sector->uptodate)
                        return true;
        }
        return false;
}

static void rmw_rbio(struct btrfs_raid_bio *rbio)
{
        struct bio_list bio_list;
        int sectornr;
        int ret = 0;

        /*
         * Allocate the pages for parity first, as P/Q pages will always be
         * needed for both full-stripe and sub-stripe writes.
         */
        ret = alloc_rbio_parity_pages(rbio);
        if (ret < 0)
                goto out;

        /*
         * Either full stripe write, or we have every data sector already
         * cached, can go to write path immediately.
         */
        if (!rbio_is_full(rbio) && need_read_stripe_sectors(rbio)) {
                /*
                 * Now we're doing sub-stripe write, also need all data stripes
                 * to do the full RMW.
                 */
                ret = alloc_rbio_data_pages(rbio);
                if (ret < 0)
                        goto out;

                index_rbio_pages(rbio);

                ret = rmw_read_wait_recover(rbio);
                if (ret < 0)
                        goto out;
        }

        /*
         * At this stage we're not allowed to add any new bios to the
         * bio list any more, anyone else that wants to change this stripe
         * needs to do their own rmw.
         */
        spin_lock(&rbio->bio_list_lock);
        set_bit(RBIO_RMW_LOCKED_BIT, &rbio->flags);
        spin_unlock(&rbio->bio_list_lock);

        bitmap_clear(rbio->error_bitmap, 0, rbio->nr_sectors);

        index_rbio_pages(rbio);

        /*
         * 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.
         */
        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++)
                generate_pq_vertical(rbio, sectornr);

        bio_list_init(&bio_list);
        ret = rmw_assemble_write_bios(rbio, &bio_list);
        if (ret < 0)
                goto out;

        /* We should have at least one bio assembled. */
        ASSERT(bio_list_size(&bio_list));
        submit_write_bios(rbio, &bio_list);
        wait_event(rbio->io_wait, atomic_read(&rbio->stripes_pending) == 0);

        /* We may have more errors than our tolerance during the read. */
        for (sectornr = 0; sectornr < rbio->stripe_nsectors; sectornr++) {
                int found_errors;

                found_errors = get_rbio_veritical_errors(rbio, sectornr, NULL, NULL);
                if (found_errors > rbio->bioc->max_errors) {
                        ret = -EIO;
                        break;
                }
        }
out:
        rbio_orig_end_io(rbio, errno_to_blk_status(ret));
}

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

        rbio = container_of(work, struct btrfs_raid_bio, work);
        if (lock_stripe_add(rbio) == 0)
                rmw_rbio(rbio);
}

static void rmw_rbio_work_locked(struct work_struct *work)
{
        rmw_rbio(container_of(work, struct btrfs_raid_bio, work));
}

/*
 * 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,
                                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);
        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_RBIO_STRIPE(i < rbio->real_stripes, rbio, i);

        bitmap_copy(&rbio->dbitmap, dbitmap, stripe_nsectors);
        return rbio;
}

/*
 * 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 total_sector_nr;

        for (total_sector_nr = 0; total_sector_nr < rbio->nr_sectors;
             total_sector_nr++) {
                struct page *page;
                int sectornr = total_sector_nr % rbio->stripe_nsectors;
                int index = (total_sector_nr * sectorsize) >> PAGE_SHIFT;

                if (!test_bit(sectornr, &rbio->dbitmap))
                        continue;
                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 int finish_parity_scrub(struct btrfs_raid_bio *rbio)
{
        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;
        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();

        /*
         * Replace is running and our P/Q stripe is being replaced, then we
         * need to duplicate the final write to replace target.
         */
        if (bioc->replace_nr_stripes && bioc->replace_stripe_src == 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);

        p_sector.page = alloc_page(GFP_NOFS);
        if (!p_sector.page)
                return -ENOMEM;
        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;
                        return -ENOMEM;
                }
                q_sector.pgoff = 0;
                q_sector.uptodate = 1;
                pointers[rbio->real_stripes - 1] = kmap_local_page(q_sector.page);
        }

        bitmap_clear(rbio->error_bitmap, 0, rbio->nr_sectors);

        /* 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) {
                        assert_rbio(rbio);
                        /* 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;
        }

        /*
         * 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, REQ_OP_WRITE);
                if (ret)
                        goto cleanup;
        }

        if (!is_replace)
                goto submit_write;

        /*
         * Replace is running and our parity stripe needs to be duplicated to
         * the target device.  Check we have a valid source stripe number.
         */
        ASSERT_RBIO(rbio->bioc->replace_stripe_src >= 0, rbio);
        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,
                                         rbio->real_stripes,
                                         sectornr, REQ_OP_WRITE);
                if (ret)
                        goto cleanup;
        }

submit_write:
        submit_write_bios(rbio, &bio_list);
        return 0;

cleanup:
        bio_list_put(&bio_list);
        return ret;
}

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

static int recover_scrub_rbio(struct btrfs_raid_bio *rbio)
{
        void **pointers = NULL;
        void **unmap_array = NULL;
        int sector_nr;
        int ret = 0;

        /*
         * @pointers array stores the pointer for each sector.
         *
         * @unmap_array stores copy of pointers that does not get reordered
         * during reconstruction so that kunmap_local works.
         */
        pointers = kcalloc(rbio->real_stripes, sizeof(void *), GFP_NOFS);
        unmap_array = kcalloc(rbio->real_stripes, sizeof(void *), GFP_NOFS);
        if (!pointers || !unmap_array) {
                ret = -ENOMEM;
                goto out;
        }

        for (sector_nr = 0; sector_nr < rbio->stripe_nsectors; sector_nr++) {
                int dfail = 0, failp = -1;
                int faila;
                int failb;
                int found_errors;

                found_errors = get_rbio_veritical_errors(rbio, sector_nr,
                                                         &faila, &failb);
                if (found_errors > rbio->bioc->max_errors) {
                        ret = -EIO;
                        goto out;
                }
                if (found_errors == 0)
                        continue;

                /* We should have at least one error here. */
                ASSERT(faila >= 0 || failb >= 0);

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

                if (is_data_stripe(rbio, failb))
                        dfail++;
                else if (is_parity_stripe(failb))
                        failp = 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) {
                        ret = -EIO;
                        goto out;
                }
                /*
                 * If all data is good, only parity is correctly, just repair
                 * the parity, no need to recover data stripes.
                 */
                if (dfail == 0)
                        continue;

                /*
                 * 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) {
                        ret = -EIO;
                        goto out;
                }

                ret = recover_vertical(rbio, sector_nr, pointers, unmap_array);
                if (ret < 0)
                        goto out;
        }
out:
        kfree(pointers);
        kfree(unmap_array);
        return ret;
}

static int scrub_assemble_read_bios(struct btrfs_raid_bio *rbio)
{
        struct bio_list bio_list = BIO_EMPTY_LIST;
        int total_sector_nr;
        int ret = 0;

        /* Build a list of bios to read all the missing parts. */
        for (total_sector_nr = 0; total_sector_nr < rbio->nr_sectors;
             total_sector_nr++) {
                int sectornr = total_sector_nr % rbio->stripe_nsectors;
                int stripe = total_sector_nr / rbio->stripe_nsectors;
                struct sector_ptr *sector;

                /* No data in the vertical stripe, no need to read. */
                if (!test_bit(sectornr, &rbio->dbitmap))
                        continue;

                /*
                 * 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,
                 * use it.
                 */
                if (sector->uptodate)
                        continue;

                ret = rbio_add_io_sector(rbio, &bio_list, sector, stripe,
                                         sectornr, REQ_OP_READ);
                if (ret) {
                        bio_list_put(&bio_list);
                        return ret;
                }
        }

        submit_read_wait_bio_list(rbio, &bio_list);
        return 0;
}

static void scrub_rbio(struct btrfs_raid_bio *rbio)
{
        int sector_nr;
        int ret;

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

        bitmap_clear(rbio->error_bitmap, 0, rbio->nr_sectors);

        ret = scrub_assemble_read_bios(rbio);
        if (ret < 0)
                goto out;

        /* We may have some failures, recover the failed sectors first. */
        ret = recover_scrub_rbio(rbio);
        if (ret < 0)
                goto out;

        /*
         * We have every sector properly prepared. Can finish the scrub
         * and writeback the good content.
         */
        ret = finish_parity_scrub(rbio);
        wait_event(rbio->io_wait, atomic_read(&rbio->stripes_pending) == 0);
        for (sector_nr = 0; sector_nr < rbio->stripe_nsectors; sector_nr++) {
                int found_errors;

                found_errors = get_rbio_veritical_errors(rbio, sector_nr, NULL, NULL);
                if (found_errors > rbio->bioc->max_errors) {
                        ret = -EIO;
                        break;
                }
        }
out:
        rbio_orig_end_io(rbio, errno_to_blk_status(ret));
}

static void scrub_rbio_work_locked(struct work_struct *work)
{
        scrub_rbio(container_of(work, struct btrfs_raid_bio, work));
}

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

/*
 * This is for scrub call sites where we already have correct data contents.
 * This allows us to avoid reading data stripes again.
 *
 * Unfortunately here we have to do page copy, other than reusing the pages.
 * This is due to the fact rbio has its own page management for its cache.
 */
void raid56_parity_cache_data_pages(struct btrfs_raid_bio *rbio,
                                    struct page **data_pages, u64 data_logical)
{
        const u64 offset_in_full_stripe = data_logical -
                                          rbio->bioc->full_stripe_logical;
        const int page_index = offset_in_full_stripe >> PAGE_SHIFT;
        const u32 sectorsize = rbio->bioc->fs_info->sectorsize;
        const u32 sectors_per_page = PAGE_SIZE / sectorsize;
        int ret;

        /*
         * If we hit ENOMEM temporarily, but later at
         * raid56_parity_submit_scrub_rbio() time it succeeded, we just do
         * the extra read, not a big deal.
         *
         * If we hit ENOMEM later at raid56_parity_submit_scrub_rbio() time,
         * the bio would got proper error number set.
         */
        ret = alloc_rbio_data_pages(rbio);
        if (ret < 0)
                return;

        /* data_logical must be at stripe boundary and inside the full stripe. */
        ASSERT(IS_ALIGNED(offset_in_full_stripe, BTRFS_STRIPE_LEN));
        ASSERT(offset_in_full_stripe < (rbio->nr_data << BTRFS_STRIPE_LEN_SHIFT));

        for (int page_nr = 0; page_nr < (BTRFS_STRIPE_LEN >> PAGE_SHIFT); page_nr++) {
                struct page *dst = rbio->stripe_pages[page_nr + page_index];
                struct page *src = data_pages[page_nr];

                memcpy_page(dst, 0, src, 0, PAGE_SIZE);
                for (int sector_nr = sectors_per_page * page_index;
                     sector_nr < sectors_per_page * (page_index + 1);
                     sector_nr++)
                        rbio->stripe_sectors[sector_nr].uptodate = true;
        }
}