signal/alpha: Document a conflict with SI_USER for SIGTRAP

[cris-mirror.git] / drivers / md / raid5-cache.c

/*
 * Copyright (C) 2015 Shaohua Li <shli@fb.com>
 * Copyright (C) 2016 Song Liu <songliubraving@fb.com>
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms and conditions of the GNU General Public License,
 * version 2, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
 * more details.
 *
 */
#include <linux/kernel.h>
#include <linux/wait.h>
#include <linux/blkdev.h>
#include <linux/slab.h>
#include <linux/raid/md_p.h>
#include <linux/crc32c.h>
#include <linux/random.h>
#include <linux/kthread.h>
#include <linux/types.h>
#include "md.h"
#include "raid5.h"
#include "bitmap.h"
#include "raid5-log.h"

/*
 * metadata/data stored in disk with 4k size unit (a block) regardless
 * underneath hardware sector size. only works with PAGE_SIZE == 4096
 */
#define BLOCK_SECTORS (8)
#define BLOCK_SECTOR_SHIFT (3)

/*
 * log->max_free_space is min(1/4 disk size, 10G reclaimable space).
 *
 * In write through mode, the reclaim runs every log->max_free_space.
 * This can prevent the recovery scans for too long
 */
#define RECLAIM_MAX_FREE_SPACE (10 * 1024 * 1024 * 2) /* sector */
#define RECLAIM_MAX_FREE_SPACE_SHIFT (2)

/* wake up reclaim thread periodically */
#define R5C_RECLAIM_WAKEUP_INTERVAL (30 * HZ)
/* start flush with these full stripes */
#define R5C_FULL_STRIPE_FLUSH_BATCH(conf) (conf->max_nr_stripes / 4)
/* reclaim stripes in groups */
#define R5C_RECLAIM_STRIPE_GROUP (NR_STRIPE_HASH_LOCKS * 2)

/*
 * We only need 2 bios per I/O unit to make progress, but ensure we
 * have a few more available to not get too tight.
 */
#define R5L_POOL_SIZE   4

static char *r5c_journal_mode_str[] = {"write-through",
                                       "write-back"};
/*
 * raid5 cache state machine
 *
 * With the RAID cache, each stripe works in two phases:
 *      - caching phase
 *      - writing-out phase
 *
 * These two phases are controlled by bit STRIPE_R5C_CACHING:
 *   if STRIPE_R5C_CACHING == 0, the stripe is in writing-out phase
 *   if STRIPE_R5C_CACHING == 1, the stripe is in caching phase
 *
 * When there is no journal, or the journal is in write-through mode,
 * the stripe is always in writing-out phase.
 *
 * For write-back journal, the stripe is sent to caching phase on write
 * (r5c_try_caching_write). r5c_make_stripe_write_out() kicks off
 * the write-out phase by clearing STRIPE_R5C_CACHING.
 *
 * Stripes in caching phase do not write the raid disks. Instead, all
 * writes are committed from the log device. Therefore, a stripe in
 * caching phase handles writes as:
 *      - write to log device
 *      - return IO
 *
 * Stripes in writing-out phase handle writes as:
 *      - calculate parity
 *      - write pending data and parity to journal
 *      - write data and parity to raid disks
 *      - return IO for pending writes
 */

struct r5l_log {
        struct md_rdev *rdev;

        u32 uuid_checksum;

        sector_t device_size;           /* log device size, round to
                                         * BLOCK_SECTORS */
        sector_t max_free_space;        /* reclaim run if free space is at
                                         * this size */

        sector_t last_checkpoint;       /* log tail. where recovery scan
                                         * starts from */
        u64 last_cp_seq;                /* log tail sequence */

        sector_t log_start;             /* log head. where new data appends */
        u64 seq;                        /* log head sequence */

        sector_t next_checkpoint;

        struct mutex io_mutex;
        struct r5l_io_unit *current_io; /* current io_unit accepting new data */

        spinlock_t io_list_lock;
        struct list_head running_ios;   /* io_units which are still running,
                                         * and have not yet been completely
                                         * written to the log */
        struct list_head io_end_ios;    /* io_units which have been completely
                                         * written to the log but not yet written
                                         * to the RAID */
        struct list_head flushing_ios;  /* io_units which are waiting for log
                                         * cache flush */
        struct list_head finished_ios;  /* io_units which settle down in log disk */
        struct bio flush_bio;

        struct list_head no_mem_stripes;   /* pending stripes, -ENOMEM */

        struct kmem_cache *io_kc;
        mempool_t *io_pool;
        struct bio_set *bs;
        mempool_t *meta_pool;

        struct md_thread *reclaim_thread;
        unsigned long reclaim_target;   /* number of space that need to be
                                         * reclaimed.  if it's 0, reclaim spaces
                                         * used by io_units which are in
                                         * IO_UNIT_STRIPE_END state (eg, reclaim
                                         * dones't wait for specific io_unit
                                         * switching to IO_UNIT_STRIPE_END
                                         * state) */
        wait_queue_head_t iounit_wait;

        struct list_head no_space_stripes; /* pending stripes, log has no space */
        spinlock_t no_space_stripes_lock;

        bool need_cache_flush;

        /* for r5c_cache */
        enum r5c_journal_mode r5c_journal_mode;

        /* all stripes in r5cache, in the order of seq at sh->log_start */
        struct list_head stripe_in_journal_list;

        spinlock_t stripe_in_journal_lock;
        atomic_t stripe_in_journal_count;

        /* to submit async io_units, to fulfill ordering of flush */
        struct work_struct deferred_io_work;
        /* to disable write back during in degraded mode */
        struct work_struct disable_writeback_work;

        /* to for chunk_aligned_read in writeback mode, details below */
        spinlock_t tree_lock;
        struct radix_tree_root big_stripe_tree;
};

/*
 * Enable chunk_aligned_read() with write back cache.
 *
 * Each chunk may contain more than one stripe (for example, a 256kB
 * chunk contains 64 4kB-page, so this chunk contain 64 stripes). For
 * chunk_aligned_read, these stripes are grouped into one "big_stripe".
 * For each big_stripe, we count how many stripes of this big_stripe
 * are in the write back cache. These data are tracked in a radix tree
 * (big_stripe_tree). We use radix_tree item pointer as the counter.
 * r5c_tree_index() is used to calculate keys for the radix tree.
 *
 * chunk_aligned_read() calls r5c_big_stripe_cached() to look up
 * big_stripe of each chunk in the tree. If this big_stripe is in the
 * tree, chunk_aligned_read() aborts. This look up is protected by
 * rcu_read_lock().
 *
 * It is necessary to remember whether a stripe is counted in
 * big_stripe_tree. Instead of adding new flag, we reuses existing flags:
 * STRIPE_R5C_PARTIAL_STRIPE and STRIPE_R5C_FULL_STRIPE. If either of these
 * two flags are set, the stripe is counted in big_stripe_tree. This
 * requires moving set_bit(STRIPE_R5C_PARTIAL_STRIPE) to
 * r5c_try_caching_write(); and moving clear_bit of
 * STRIPE_R5C_PARTIAL_STRIPE and STRIPE_R5C_FULL_STRIPE to
 * r5c_finish_stripe_write_out().
 */

/*
 * radix tree requests lowest 2 bits of data pointer to be 2b'00.
 * So it is necessary to left shift the counter by 2 bits before using it
 * as data pointer of the tree.
 */
#define R5C_RADIX_COUNT_SHIFT 2

/*
 * calculate key for big_stripe_tree
 *
 * sect: align_bi->bi_iter.bi_sector or sh->sector
 */
static inline sector_t r5c_tree_index(struct r5conf *conf,
                                      sector_t sect)
{
        sector_t offset;

        offset = sector_div(sect, conf->chunk_sectors);
        return sect;
}

/*
 * an IO range starts from a meta data block and end at the next meta data
 * block. The io unit's the meta data block tracks data/parity followed it. io
 * unit is written to log disk with normal write, as we always flush log disk
 * first and then start move data to raid disks, there is no requirement to
 * write io unit with FLUSH/FUA
 */
struct r5l_io_unit {
        struct r5l_log *log;

        struct page *meta_page; /* store meta block */
        int meta_offset;        /* current offset in meta_page */

        struct bio *current_bio;/* current_bio accepting new data */

        atomic_t pending_stripe;/* how many stripes not flushed to raid */
        u64 seq;                /* seq number of the metablock */
        sector_t log_start;     /* where the io_unit starts */
        sector_t log_end;       /* where the io_unit ends */
        struct list_head log_sibling; /* log->running_ios */
        struct list_head stripe_list; /* stripes added to the io_unit */

        int state;
        bool need_split_bio;
        struct bio *split_bio;

        unsigned int has_flush:1;      /* include flush request */
        unsigned int has_fua:1;        /* include fua request */
        unsigned int has_null_flush:1; /* include empty flush request */
        /*
         * io isn't sent yet, flush/fua request can only be submitted till it's
         * the first IO in running_ios list
         */
        unsigned int io_deferred:1;

        struct bio_list flush_barriers;   /* size == 0 flush bios */
};

/* r5l_io_unit state */
enum r5l_io_unit_state {
        IO_UNIT_RUNNING = 0,    /* accepting new IO */
        IO_UNIT_IO_START = 1,   /* io_unit bio start writing to log,
                                 * don't accepting new bio */
        IO_UNIT_IO_END = 2,     /* io_unit bio finish writing to log */
        IO_UNIT_STRIPE_END = 3, /* stripes data finished writing to raid */
};

bool r5c_is_writeback(struct r5l_log *log)
{
        return (log != NULL &&
                log->r5c_journal_mode == R5C_JOURNAL_MODE_WRITE_BACK);
}

static sector_t r5l_ring_add(struct r5l_log *log, sector_t start, sector_t inc)
{
        start += inc;
        if (start >= log->device_size)
                start = start - log->device_size;
        return start;
}

static sector_t r5l_ring_distance(struct r5l_log *log, sector_t start,
                                  sector_t end)
{
        if (end >= start)
                return end - start;
        else
                return end + log->device_size - start;
}

static bool r5l_has_free_space(struct r5l_log *log, sector_t size)
{
        sector_t used_size;

        used_size = r5l_ring_distance(log, log->last_checkpoint,
                                        log->log_start);

        return log->device_size > used_size + size;
}

static void __r5l_set_io_unit_state(struct r5l_io_unit *io,
                                    enum r5l_io_unit_state state)
{
        if (WARN_ON(io->state >= state))
                return;
        io->state = state;
}

static void
r5c_return_dev_pending_writes(struct r5conf *conf, struct r5dev *dev)
{
        struct bio *wbi, *wbi2;

        wbi = dev->written;
        dev->written = NULL;
        while (wbi && wbi->bi_iter.bi_sector <
               dev->sector + STRIPE_SECTORS) {
                wbi2 = r5_next_bio(wbi, dev->sector);
                md_write_end(conf->mddev);
                bio_endio(wbi);
                wbi = wbi2;
        }
}

void r5c_handle_cached_data_endio(struct r5conf *conf,
                                  struct stripe_head *sh, int disks)
{
        int i;

        for (i = sh->disks; i--; ) {
                if (sh->dev[i].written) {
                        set_bit(R5_UPTODATE, &sh->dev[i].flags);
                        r5c_return_dev_pending_writes(conf, &sh->dev[i]);
                        bitmap_endwrite(conf->mddev->bitmap, sh->sector,
                                        STRIPE_SECTORS,
                                        !test_bit(STRIPE_DEGRADED, &sh->state),
                                        0);
                }
        }
}

void r5l_wake_reclaim(struct r5l_log *log, sector_t space);

/* Check whether we should flush some stripes to free up stripe cache */
void r5c_check_stripe_cache_usage(struct r5conf *conf)
{
        int total_cached;

        if (!r5c_is_writeback(conf->log))
                return;

        total_cached = atomic_read(&conf->r5c_cached_partial_stripes) +
                atomic_read(&conf->r5c_cached_full_stripes);

        /*
         * The following condition is true for either of the following:
         *   - stripe cache pressure high:
         *          total_cached > 3/4 min_nr_stripes ||
         *          empty_inactive_list_nr > 0
         *   - stripe cache pressure moderate:
         *          total_cached > 1/2 min_nr_stripes
         */
        if (total_cached > conf->min_nr_stripes * 1 / 2 ||
            atomic_read(&conf->empty_inactive_list_nr) > 0)
                r5l_wake_reclaim(conf->log, 0);
}

/*
 * flush cache when there are R5C_FULL_STRIPE_FLUSH_BATCH or more full
 * stripes in the cache
 */
void r5c_check_cached_full_stripe(struct r5conf *conf)
{
        if (!r5c_is_writeback(conf->log))
                return;

        /*
         * wake up reclaim for R5C_FULL_STRIPE_FLUSH_BATCH cached stripes
         * or a full stripe (chunk size / 4k stripes).
         */
        if (atomic_read(&conf->r5c_cached_full_stripes) >=
            min(R5C_FULL_STRIPE_FLUSH_BATCH(conf),
                conf->chunk_sectors >> STRIPE_SHIFT))
                r5l_wake_reclaim(conf->log, 0);
}

/*
 * Total log space (in sectors) needed to flush all data in cache
 *
 * To avoid deadlock due to log space, it is necessary to reserve log
 * space to flush critical stripes (stripes that occupying log space near
 * last_checkpoint). This function helps check how much log space is
 * required to flush all cached stripes.
 *
 * To reduce log space requirements, two mechanisms are used to give cache
 * flush higher priorities:
 *    1. In handle_stripe_dirtying() and schedule_reconstruction(),
 *       stripes ALREADY in journal can be flushed w/o pending writes;
 *    2. In r5l_write_stripe() and r5c_cache_data(), stripes NOT in journal
 *       can be delayed (r5l_add_no_space_stripe).
 *
 * In cache flush, the stripe goes through 1 and then 2. For a stripe that
 * already passed 1, flushing it requires at most (conf->max_degraded + 1)
 * pages of journal space. For stripes that has not passed 1, flushing it
 * requires (conf->raid_disks + 1) pages of journal space. There are at
 * most (conf->group_cnt + 1) stripe that passed 1. So total journal space
 * required to flush all cached stripes (in pages) is:
 *
 *     (stripe_in_journal_count - group_cnt - 1) * (max_degraded + 1) +
 *     (group_cnt + 1) * (raid_disks + 1)
 * or
 *     (stripe_in_journal_count) * (max_degraded + 1) +
 *     (group_cnt + 1) * (raid_disks - max_degraded)
 */
static sector_t r5c_log_required_to_flush_cache(struct r5conf *conf)
{
        struct r5l_log *log = conf->log;

        if (!r5c_is_writeback(log))
                return 0;

        return BLOCK_SECTORS *
                ((conf->max_degraded + 1) * atomic_read(&log->stripe_in_journal_count) +
                 (conf->raid_disks - conf->max_degraded) * (conf->group_cnt + 1));
}

/*
 * evaluate log space usage and update R5C_LOG_TIGHT and R5C_LOG_CRITICAL
 *
 * R5C_LOG_TIGHT is set when free space on the log device is less than 3x of
 * reclaim_required_space. R5C_LOG_CRITICAL is set when free space on the log
 * device is less than 2x of reclaim_required_space.
 */
static inline void r5c_update_log_state(struct r5l_log *log)
{
        struct r5conf *conf = log->rdev->mddev->private;
        sector_t free_space;
        sector_t reclaim_space;
        bool wake_reclaim = false;

        if (!r5c_is_writeback(log))
                return;

        free_space = r5l_ring_distance(log, log->log_start,
                                       log->last_checkpoint);
        reclaim_space = r5c_log_required_to_flush_cache(conf);
        if (free_space < 2 * reclaim_space)
                set_bit(R5C_LOG_CRITICAL, &conf->cache_state);
        else {
                if (test_bit(R5C_LOG_CRITICAL, &conf->cache_state))
                        wake_reclaim = true;
                clear_bit(R5C_LOG_CRITICAL, &conf->cache_state);
        }
        if (free_space < 3 * reclaim_space)
                set_bit(R5C_LOG_TIGHT, &conf->cache_state);
        else
                clear_bit(R5C_LOG_TIGHT, &conf->cache_state);

        if (wake_reclaim)
                r5l_wake_reclaim(log, 0);
}

/*
 * Put the stripe into writing-out phase by clearing STRIPE_R5C_CACHING.
 * This function should only be called in write-back mode.
 */
void r5c_make_stripe_write_out(struct stripe_head *sh)
{
        struct r5conf *conf = sh->raid_conf;
        struct r5l_log *log = conf->log;

        BUG_ON(!r5c_is_writeback(log));

        WARN_ON(!test_bit(STRIPE_R5C_CACHING, &sh->state));
        clear_bit(STRIPE_R5C_CACHING, &sh->state);

        if (!test_and_set_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
                atomic_inc(&conf->preread_active_stripes);
}

static void r5c_handle_data_cached(struct stripe_head *sh)
{
        int i;

        for (i = sh->disks; i--; )
                if (test_and_clear_bit(R5_Wantwrite, &sh->dev[i].flags)) {
                        set_bit(R5_InJournal, &sh->dev[i].flags);
                        clear_bit(R5_LOCKED, &sh->dev[i].flags);
                }
        clear_bit(STRIPE_LOG_TRAPPED, &sh->state);
}

/*
 * this journal write must contain full parity,
 * it may also contain some data pages
 */
static void r5c_handle_parity_cached(struct stripe_head *sh)
{
        int i;

        for (i = sh->disks; i--; )
                if (test_bit(R5_InJournal, &sh->dev[i].flags))
                        set_bit(R5_Wantwrite, &sh->dev[i].flags);
}

/*
 * Setting proper flags after writing (or flushing) data and/or parity to the
 * log device. This is called from r5l_log_endio() or r5l_log_flush_endio().
 */
static void r5c_finish_cache_stripe(struct stripe_head *sh)
{
        struct r5l_log *log = sh->raid_conf->log;

        if (log->r5c_journal_mode == R5C_JOURNAL_MODE_WRITE_THROUGH) {
                BUG_ON(test_bit(STRIPE_R5C_CACHING, &sh->state));
                /*
                 * Set R5_InJournal for parity dev[pd_idx]. This means
                 * all data AND parity in the journal. For RAID 6, it is
                 * NOT necessary to set the flag for dev[qd_idx], as the
                 * two parities are written out together.
                 */
                set_bit(R5_InJournal, &sh->dev[sh->pd_idx].flags);
        } else if (test_bit(STRIPE_R5C_CACHING, &sh->state)) {
                r5c_handle_data_cached(sh);
        } else {
                r5c_handle_parity_cached(sh);
                set_bit(R5_InJournal, &sh->dev[sh->pd_idx].flags);
        }
}

static void r5l_io_run_stripes(struct r5l_io_unit *io)
{
        struct stripe_head *sh, *next;

        list_for_each_entry_safe(sh, next, &io->stripe_list, log_list) {
                list_del_init(&sh->log_list);

                r5c_finish_cache_stripe(sh);

                set_bit(STRIPE_HANDLE, &sh->state);
                raid5_release_stripe(sh);
        }
}

static void r5l_log_run_stripes(struct r5l_log *log)
{
        struct r5l_io_unit *io, *next;

        assert_spin_locked(&log->io_list_lock);

        list_for_each_entry_safe(io, next, &log->running_ios, log_sibling) {
                /* don't change list order */
                if (io->state < IO_UNIT_IO_END)
                        break;

                list_move_tail(&io->log_sibling, &log->finished_ios);
                r5l_io_run_stripes(io);
        }
}

static void r5l_move_to_end_ios(struct r5l_log *log)
{
        struct r5l_io_unit *io, *next;

        assert_spin_locked(&log->io_list_lock);

        list_for_each_entry_safe(io, next, &log->running_ios, log_sibling) {
                /* don't change list order */
                if (io->state < IO_UNIT_IO_END)
                        break;
                list_move_tail(&io->log_sibling, &log->io_end_ios);
        }
}

static void __r5l_stripe_write_finished(struct r5l_io_unit *io);
static void r5l_log_endio(struct bio *bio)
{
        struct r5l_io_unit *io = bio->bi_private;
        struct r5l_io_unit *io_deferred;
        struct r5l_log *log = io->log;
        unsigned long flags;

        if (bio->bi_status)
                md_error(log->rdev->mddev, log->rdev);

        bio_put(bio);
        mempool_free(io->meta_page, log->meta_pool);

        spin_lock_irqsave(&log->io_list_lock, flags);
        __r5l_set_io_unit_state(io, IO_UNIT_IO_END);
        if (log->need_cache_flush && !list_empty(&io->stripe_list))
                r5l_move_to_end_ios(log);
        else
                r5l_log_run_stripes(log);
        if (!list_empty(&log->running_ios)) {
                /*
                 * FLUSH/FUA io_unit is deferred because of ordering, now we
                 * can dispatch it
                 */
                io_deferred = list_first_entry(&log->running_ios,
                                               struct r5l_io_unit, log_sibling);
                if (io_deferred->io_deferred)
                        schedule_work(&log->deferred_io_work);
        }

        spin_unlock_irqrestore(&log->io_list_lock, flags);

        if (log->need_cache_flush)
                md_wakeup_thread(log->rdev->mddev->thread);

        if (io->has_null_flush) {
                struct bio *bi;

                WARN_ON(bio_list_empty(&io->flush_barriers));
                while ((bi = bio_list_pop(&io->flush_barriers)) != NULL) {
                        bio_endio(bi);
                        atomic_dec(&io->pending_stripe);
                }
        }

        /* finish flush only io_unit and PAYLOAD_FLUSH only io_unit */
        if (atomic_read(&io->pending_stripe) == 0)
                __r5l_stripe_write_finished(io);
}

static void r5l_do_submit_io(struct r5l_log *log, struct r5l_io_unit *io)
{
        unsigned long flags;

        spin_lock_irqsave(&log->io_list_lock, flags);
        __r5l_set_io_unit_state(io, IO_UNIT_IO_START);
        spin_unlock_irqrestore(&log->io_list_lock, flags);

        /*
         * In case of journal device failures, submit_bio will get error
         * and calls endio, then active stripes will continue write
         * process. Therefore, it is not necessary to check Faulty bit
         * of journal device here.
         *
         * We can't check split_bio after current_bio is submitted. If
         * io->split_bio is null, after current_bio is submitted, current_bio
         * might already be completed and the io_unit is freed. We submit
         * split_bio first to avoid the issue.
         */
        if (io->split_bio) {
                if (io->has_flush)
                        io->split_bio->bi_opf |= REQ_PREFLUSH;
                if (io->has_fua)
                        io->split_bio->bi_opf |= REQ_FUA;
                submit_bio(io->split_bio);
        }

        if (io->has_flush)
                io->current_bio->bi_opf |= REQ_PREFLUSH;
        if (io->has_fua)
                io->current_bio->bi_opf |= REQ_FUA;
        submit_bio(io->current_bio);
}

/* deferred io_unit will be dispatched here */
static void r5l_submit_io_async(struct work_struct *work)
{
        struct r5l_log *log = container_of(work, struct r5l_log,
                                           deferred_io_work);
        struct r5l_io_unit *io = NULL;
        unsigned long flags;

        spin_lock_irqsave(&log->io_list_lock, flags);
        if (!list_empty(&log->running_ios)) {
                io = list_first_entry(&log->running_ios, struct r5l_io_unit,
                                      log_sibling);
                if (!io->io_deferred)
                        io = NULL;
                else
                        io->io_deferred = 0;
        }
        spin_unlock_irqrestore(&log->io_list_lock, flags);
        if (io)
                r5l_do_submit_io(log, io);
}

static void r5c_disable_writeback_async(struct work_struct *work)
{
        struct r5l_log *log = container_of(work, struct r5l_log,
                                           disable_writeback_work);
        struct mddev *mddev = log->rdev->mddev;

        if (log->r5c_journal_mode == R5C_JOURNAL_MODE_WRITE_THROUGH)
                return;
        pr_info("md/raid:%s: Disabling writeback cache for degraded array.\n",
                mdname(mddev));

        /* wait superblock change before suspend */
        wait_event(mddev->sb_wait,
                   !test_bit(MD_SB_CHANGE_PENDING, &mddev->sb_flags));

        mddev_suspend(mddev);
        log->r5c_journal_mode = R5C_JOURNAL_MODE_WRITE_THROUGH;
        mddev_resume(mddev);
}

static void r5l_submit_current_io(struct r5l_log *log)
{
        struct r5l_io_unit *io = log->current_io;
        struct bio *bio;
        struct r5l_meta_block *block;
        unsigned long flags;
        u32 crc;
        bool do_submit = true;

        if (!io)
                return;

        block = page_address(io->meta_page);
        block->meta_size = cpu_to_le32(io->meta_offset);
        crc = crc32c_le(log->uuid_checksum, block, PAGE_SIZE);
        block->checksum = cpu_to_le32(crc);
        bio = io->current_bio;

        log->current_io = NULL;
        spin_lock_irqsave(&log->io_list_lock, flags);
        if (io->has_flush || io->has_fua) {
                if (io != list_first_entry(&log->running_ios,
                                           struct r5l_io_unit, log_sibling)) {
                        io->io_deferred = 1;
                        do_submit = false;
                }
        }
        spin_unlock_irqrestore(&log->io_list_lock, flags);
        if (do_submit)
                r5l_do_submit_io(log, io);
}

static struct bio *r5l_bio_alloc(struct r5l_log *log)
{
        struct bio *bio = bio_alloc_bioset(GFP_NOIO, BIO_MAX_PAGES, log->bs);

        bio_set_op_attrs(bio, REQ_OP_WRITE, 0);
        bio->bi_bdev = log->rdev->bdev;
        bio->bi_iter.bi_sector = log->rdev->data_offset + log->log_start;

        return bio;
}

static void r5_reserve_log_entry(struct r5l_log *log, struct r5l_io_unit *io)
{
        log->log_start = r5l_ring_add(log, log->log_start, BLOCK_SECTORS);

        r5c_update_log_state(log);
        /*
         * If we filled up the log device start from the beginning again,
         * which will require a new bio.
         *
         * Note: for this to work properly the log size needs to me a multiple
         * of BLOCK_SECTORS.
         */
        if (log->log_start == 0)
                io->need_split_bio = true;

        io->log_end = log->log_start;
}

static struct r5l_io_unit *r5l_new_meta(struct r5l_log *log)
{
        struct r5l_io_unit *io;
        struct r5l_meta_block *block;

        io = mempool_alloc(log->io_pool, GFP_ATOMIC);
        if (!io)
                return NULL;
        memset(io, 0, sizeof(*io));

        io->log = log;
        INIT_LIST_HEAD(&io->log_sibling);
        INIT_LIST_HEAD(&io->stripe_list);
        bio_list_init(&io->flush_barriers);
        io->state = IO_UNIT_RUNNING;

        io->meta_page = mempool_alloc(log->meta_pool, GFP_NOIO);
        block = page_address(io->meta_page);
        clear_page(block);
        block->magic = cpu_to_le32(R5LOG_MAGIC);
        block->version = R5LOG_VERSION;
        block->seq = cpu_to_le64(log->seq);
        block->position = cpu_to_le64(log->log_start);

        io->log_start = log->log_start;
        io->meta_offset = sizeof(struct r5l_meta_block);
        io->seq = log->seq++;

        io->current_bio = r5l_bio_alloc(log);
        io->current_bio->bi_end_io = r5l_log_endio;
        io->current_bio->bi_private = io;
        bio_add_page(io->current_bio, io->meta_page, PAGE_SIZE, 0);

        r5_reserve_log_entry(log, io);

        spin_lock_irq(&log->io_list_lock);
        list_add_tail(&io->log_sibling, &log->running_ios);
        spin_unlock_irq(&log->io_list_lock);

        return io;
}

static int r5l_get_meta(struct r5l_log *log, unsigned int payload_size)
{
        if (log->current_io &&
            log->current_io->meta_offset + payload_size > PAGE_SIZE)
                r5l_submit_current_io(log);

        if (!log->current_io) {
                log->current_io = r5l_new_meta(log);
                if (!log->current_io)
                        return -ENOMEM;
        }

        return 0;
}

static void r5l_append_payload_meta(struct r5l_log *log, u16 type,
                                    sector_t location,
                                    u32 checksum1, u32 checksum2,
                                    bool checksum2_valid)
{
        struct r5l_io_unit *io = log->current_io;
        struct r5l_payload_data_parity *payload;

        payload = page_address(io->meta_page) + io->meta_offset;
        payload->header.type = cpu_to_le16(type);
        payload->header.flags = cpu_to_le16(0);
        payload->size = cpu_to_le32((1 + !!checksum2_valid) <<
                                    (PAGE_SHIFT - 9));
        payload->location = cpu_to_le64(location);
        payload->checksum[0] = cpu_to_le32(checksum1);
        if (checksum2_valid)
                payload->checksum[1] = cpu_to_le32(checksum2);

        io->meta_offset += sizeof(struct r5l_payload_data_parity) +
                sizeof(__le32) * (1 + !!checksum2_valid);
}

static void r5l_append_payload_page(struct r5l_log *log, struct page *page)
{
        struct r5l_io_unit *io = log->current_io;

        if (io->need_split_bio) {
                BUG_ON(io->split_bio);
                io->split_bio = io->current_bio;
                io->current_bio = r5l_bio_alloc(log);
                bio_chain(io->current_bio, io->split_bio);
                io->need_split_bio = false;
        }

        if (!bio_add_page(io->current_bio, page, PAGE_SIZE, 0))
                BUG();

        r5_reserve_log_entry(log, io);
}

static void r5l_append_flush_payload(struct r5l_log *log, sector_t sect)
{
        struct mddev *mddev = log->rdev->mddev;
        struct r5conf *conf = mddev->private;
        struct r5l_io_unit *io;
        struct r5l_payload_flush *payload;
        int meta_size;

        /*
         * payload_flush requires extra writes to the journal.
         * To avoid handling the extra IO in quiesce, just skip
         * flush_payload
         */
        if (conf->quiesce)
                return;

        mutex_lock(&log->io_mutex);
        meta_size = sizeof(struct r5l_payload_flush) + sizeof(__le64);

        if (r5l_get_meta(log, meta_size)) {
                mutex_unlock(&log->io_mutex);
                return;
        }

        /* current implementation is one stripe per flush payload */
        io = log->current_io;
        payload = page_address(io->meta_page) + io->meta_offset;
        payload->header.type = cpu_to_le16(R5LOG_PAYLOAD_FLUSH);
        payload->header.flags = cpu_to_le16(0);
        payload->size = cpu_to_le32(sizeof(__le64));
        payload->flush_stripes[0] = cpu_to_le64(sect);
        io->meta_offset += meta_size;
        mutex_unlock(&log->io_mutex);
}

static int r5l_log_stripe(struct r5l_log *log, struct stripe_head *sh,
                           int data_pages, int parity_pages)
{
        int i;
        int meta_size;
        int ret;
        struct r5l_io_unit *io;

        meta_size =
                ((sizeof(struct r5l_payload_data_parity) + sizeof(__le32))
                 * data_pages) +
                sizeof(struct r5l_payload_data_parity) +
                sizeof(__le32) * parity_pages;

        ret = r5l_get_meta(log, meta_size);
        if (ret)
                return ret;

        io = log->current_io;

        if (test_and_clear_bit(STRIPE_R5C_PREFLUSH, &sh->state))
                io->has_flush = 1;

        for (i = 0; i < sh->disks; i++) {
                if (!test_bit(R5_Wantwrite, &sh->dev[i].flags) ||
                    test_bit(R5_InJournal, &sh->dev[i].flags))
                        continue;
                if (i == sh->pd_idx || i == sh->qd_idx)
                        continue;
                if (test_bit(R5_WantFUA, &sh->dev[i].flags) &&
                    log->r5c_journal_mode == R5C_JOURNAL_MODE_WRITE_BACK) {
                        io->has_fua = 1;
                        /*
                         * we need to flush journal to make sure recovery can
                         * reach the data with fua flag
                         */
                        io->has_flush = 1;
                }
                r5l_append_payload_meta(log, R5LOG_PAYLOAD_DATA,
                                        raid5_compute_blocknr(sh, i, 0),
                                        sh->dev[i].log_checksum, 0, false);
                r5l_append_payload_page(log, sh->dev[i].page);
        }

        if (parity_pages == 2) {
                r5l_append_payload_meta(log, R5LOG_PAYLOAD_PARITY,
                                        sh->sector, sh->dev[sh->pd_idx].log_checksum,
                                        sh->dev[sh->qd_idx].log_checksum, true);
                r5l_append_payload_page(log, sh->dev[sh->pd_idx].page);
                r5l_append_payload_page(log, sh->dev[sh->qd_idx].page);
        } else if (parity_pages == 1) {
                r5l_append_payload_meta(log, R5LOG_PAYLOAD_PARITY,
                                        sh->sector, sh->dev[sh->pd_idx].log_checksum,
                                        0, false);
                r5l_append_payload_page(log, sh->dev[sh->pd_idx].page);
        } else  /* Just writing data, not parity, in caching phase */
                BUG_ON(parity_pages != 0);

        list_add_tail(&sh->log_list, &io->stripe_list);
        atomic_inc(&io->pending_stripe);
        sh->log_io = io;

        if (log->r5c_journal_mode == R5C_JOURNAL_MODE_WRITE_THROUGH)
                return 0;

        if (sh->log_start == MaxSector) {
                BUG_ON(!list_empty(&sh->r5c));
                sh->log_start = io->log_start;
                spin_lock_irq(&log->stripe_in_journal_lock);
                list_add_tail(&sh->r5c,
                              &log->stripe_in_journal_list);
                spin_unlock_irq(&log->stripe_in_journal_lock);
                atomic_inc(&log->stripe_in_journal_count);
        }
        return 0;
}

/* add stripe to no_space_stripes, and then wake up reclaim */
static inline void r5l_add_no_space_stripe(struct r5l_log *log,
                                           struct stripe_head *sh)
{
        spin_lock(&log->no_space_stripes_lock);
        list_add_tail(&sh->log_list, &log->no_space_stripes);
        spin_unlock(&log->no_space_stripes_lock);
}

/*
 * running in raid5d, where reclaim could wait for raid5d too (when it flushes
 * data from log to raid disks), so we shouldn't wait for reclaim here
 */
int r5l_write_stripe(struct r5l_log *log, struct stripe_head *sh)
{
        struct r5conf *conf = sh->raid_conf;
        int write_disks = 0;
        int data_pages, parity_pages;
        int reserve;
        int i;
        int ret = 0;
        bool wake_reclaim = false;

        if (!log)
                return -EAGAIN;
        /* Don't support stripe batch */
        if (sh->log_io || !test_bit(R5_Wantwrite, &sh->dev[sh->pd_idx].flags) ||
            test_bit(STRIPE_SYNCING, &sh->state)) {
                /* the stripe is written to log, we start writing it to raid */
                clear_bit(STRIPE_LOG_TRAPPED, &sh->state);
                return -EAGAIN;
        }

        WARN_ON(test_bit(STRIPE_R5C_CACHING, &sh->state));

        for (i = 0; i < sh->disks; i++) {
                void *addr;

                if (!test_bit(R5_Wantwrite, &sh->dev[i].flags) ||
                    test_bit(R5_InJournal, &sh->dev[i].flags))
                        continue;

                write_disks++;
                /* checksum is already calculated in last run */
                if (test_bit(STRIPE_LOG_TRAPPED, &sh->state))
                        continue;
                addr = kmap_atomic(sh->dev[i].page);
                sh->dev[i].log_checksum = crc32c_le(log->uuid_checksum,
                                                    addr, PAGE_SIZE);
                kunmap_atomic(addr);
        }
        parity_pages = 1 + !!(sh->qd_idx >= 0);
        data_pages = write_disks - parity_pages;

        set_bit(STRIPE_LOG_TRAPPED, &sh->state);
        /*
         * The stripe must enter state machine again to finish the write, so
         * don't delay.
         */
        clear_bit(STRIPE_DELAYED, &sh->state);
        atomic_inc(&sh->count);

        mutex_lock(&log->io_mutex);
        /* meta + data */
        reserve = (1 + write_disks) << (PAGE_SHIFT - 9);

        if (log->r5c_journal_mode == R5C_JOURNAL_MODE_WRITE_THROUGH) {
                if (!r5l_has_free_space(log, reserve)) {
                        r5l_add_no_space_stripe(log, sh);
                        wake_reclaim = true;
                } else {
                        ret = r5l_log_stripe(log, sh, data_pages, parity_pages);
                        if (ret) {
                                spin_lock_irq(&log->io_list_lock);
                                list_add_tail(&sh->log_list,
                                              &log->no_mem_stripes);
                                spin_unlock_irq(&log->io_list_lock);
                        }
                }
        } else {  /* R5C_JOURNAL_MODE_WRITE_BACK */
                /*
                 * log space critical, do not process stripes that are
                 * not in cache yet (sh->log_start == MaxSector).
                 */
                if (test_bit(R5C_LOG_CRITICAL, &conf->cache_state) &&
                    sh->log_start == MaxSector) {
                        r5l_add_no_space_stripe(log, sh);
                        wake_reclaim = true;
                        reserve = 0;
                } else if (!r5l_has_free_space(log, reserve)) {
                        if (sh->log_start == log->last_checkpoint)
                                BUG();
                        else
                                r5l_add_no_space_stripe(log, sh);
                } else {
                        ret = r5l_log_stripe(log, sh, data_pages, parity_pages);
                        if (ret) {
                                spin_lock_irq(&log->io_list_lock);
                                list_add_tail(&sh->log_list,
                                              &log->no_mem_stripes);
                                spin_unlock_irq(&log->io_list_lock);
                        }
                }
        }

        mutex_unlock(&log->io_mutex);
        if (wake_reclaim)
                r5l_wake_reclaim(log, reserve);
        return 0;
}

void r5l_write_stripe_run(struct r5l_log *log)
{
        if (!log)
                return;
        mutex_lock(&log->io_mutex);
        r5l_submit_current_io(log);
        mutex_unlock(&log->io_mutex);
}

int r5l_handle_flush_request(struct r5l_log *log, struct bio *bio)
{
        if (!log)
                return -ENODEV;

        if (log->r5c_journal_mode == R5C_JOURNAL_MODE_WRITE_THROUGH) {
                /*
                 * in write through (journal only)
                 * we flush log disk cache first, then write stripe data to
                 * raid disks. So if bio is finished, the log disk cache is
                 * flushed already. The recovery guarantees we can recovery
                 * the bio from log disk, so we don't need to flush again
                 */
                if (bio->bi_iter.bi_size == 0) {
                        bio_endio(bio);
                        return 0;
                }
                bio->bi_opf &= ~REQ_PREFLUSH;
        } else {
                /* write back (with cache) */
                if (bio->bi_iter.bi_size == 0) {
                        mutex_lock(&log->io_mutex);
                        r5l_get_meta(log, 0);
                        bio_list_add(&log->current_io->flush_barriers, bio);
                        log->current_io->has_flush = 1;
                        log->current_io->has_null_flush = 1;
                        atomic_inc(&log->current_io->pending_stripe);
                        r5l_submit_current_io(log);
                        mutex_unlock(&log->io_mutex);
                        return 0;
                }
        }
        return -EAGAIN;
}

/* This will run after log space is reclaimed */
static void r5l_run_no_space_stripes(struct r5l_log *log)
{
        struct stripe_head *sh;

        spin_lock(&log->no_space_stripes_lock);
        while (!list_empty(&log->no_space_stripes)) {
                sh = list_first_entry(&log->no_space_stripes,
                                      struct stripe_head, log_list);
                list_del_init(&sh->log_list);
                set_bit(STRIPE_HANDLE, &sh->state);
                raid5_release_stripe(sh);
        }
        spin_unlock(&log->no_space_stripes_lock);
}

/*
 * calculate new last_checkpoint
 * for write through mode, returns log->next_checkpoint
 * for write back, returns log_start of first sh in stripe_in_journal_list
 */
static sector_t r5c_calculate_new_cp(struct r5conf *conf)
{
        struct stripe_head *sh;
        struct r5l_log *log = conf->log;
        sector_t new_cp;
        unsigned long flags;

        if (log->r5c_journal_mode == R5C_JOURNAL_MODE_WRITE_THROUGH)
                return log->next_checkpoint;

        spin_lock_irqsave(&log->stripe_in_journal_lock, flags);
        if (list_empty(&conf->log->stripe_in_journal_list)) {
                /* all stripes flushed */
                spin_unlock_irqrestore(&log->stripe_in_journal_lock, flags);
                return log->next_checkpoint;
        }
        sh = list_first_entry(&conf->log->stripe_in_journal_list,
                              struct stripe_head, r5c);
        new_cp = sh->log_start;
        spin_unlock_irqrestore(&log->stripe_in_journal_lock, flags);
        return new_cp;
}

static sector_t r5l_reclaimable_space(struct r5l_log *log)
{
        struct r5conf *conf = log->rdev->mddev->private;

        return r5l_ring_distance(log, log->last_checkpoint,
                                 r5c_calculate_new_cp(conf));
}

static void r5l_run_no_mem_stripe(struct r5l_log *log)
{
        struct stripe_head *sh;

        assert_spin_locked(&log->io_list_lock);

        if (!list_empty(&log->no_mem_stripes)) {
                sh = list_first_entry(&log->no_mem_stripes,
                                      struct stripe_head, log_list);
                list_del_init(&sh->log_list);
                set_bit(STRIPE_HANDLE, &sh->state);
                raid5_release_stripe(sh);
        }
}

static bool r5l_complete_finished_ios(struct r5l_log *log)
{
        struct r5l_io_unit *io, *next;
        bool found = false;

        assert_spin_locked(&log->io_list_lock);

        list_for_each_entry_safe(io, next, &log->finished_ios, log_sibling) {
                /* don't change list order */
                if (io->state < IO_UNIT_STRIPE_END)
                        break;

                log->next_checkpoint = io->log_start;

                list_del(&io->log_sibling);
                mempool_free(io, log->io_pool);
                r5l_run_no_mem_stripe(log);

                found = true;
        }

        return found;
}

static void __r5l_stripe_write_finished(struct r5l_io_unit *io)
{
        struct r5l_log *log = io->log;
        struct r5conf *conf = log->rdev->mddev->private;
        unsigned long flags;

        spin_lock_irqsave(&log->io_list_lock, flags);
        __r5l_set_io_unit_state(io, IO_UNIT_STRIPE_END);

        if (!r5l_complete_finished_ios(log)) {
                spin_unlock_irqrestore(&log->io_list_lock, flags);
                return;
        }

        if (r5l_reclaimable_space(log) > log->max_free_space ||
            test_bit(R5C_LOG_TIGHT, &conf->cache_state))
                r5l_wake_reclaim(log, 0);

        spin_unlock_irqrestore(&log->io_list_lock, flags);
        wake_up(&log->iounit_wait);
}

void r5l_stripe_write_finished(struct stripe_head *sh)
{
        struct r5l_io_unit *io;

        io = sh->log_io;
        sh->log_io = NULL;

        if (io && atomic_dec_and_test(&io->pending_stripe))
                __r5l_stripe_write_finished(io);
}

static void r5l_log_flush_endio(struct bio *bio)
{
        struct r5l_log *log = container_of(bio, struct r5l_log,
                flush_bio);
        unsigned long flags;
        struct r5l_io_unit *io;

        if (bio->bi_status)
                md_error(log->rdev->mddev, log->rdev);

        spin_lock_irqsave(&log->io_list_lock, flags);
        list_for_each_entry(io, &log->flushing_ios, log_sibling)
                r5l_io_run_stripes(io);
        list_splice_tail_init(&log->flushing_ios, &log->finished_ios);
        spin_unlock_irqrestore(&log->io_list_lock, flags);
}

/*
 * Starting dispatch IO to raid.
 * io_unit(meta) consists of a log. There is one situation we want to avoid. A
 * broken meta in the middle of a log causes recovery can't find meta at the
 * head of log. If operations require meta at the head persistent in log, we
 * must make sure meta before it persistent in log too. A case is:
 *
 * stripe data/parity is in log, we start write stripe to raid disks. stripe
 * data/parity must be persistent in log before we do the write to raid disks.
 *
 * The solution is we restrictly maintain io_unit list order. In this case, we
 * only write stripes of an io_unit to raid disks till the io_unit is the first
 * one whose data/parity is in log.
 */
void r5l_flush_stripe_to_raid(struct r5l_log *log)
{
        bool do_flush;

        if (!log || !log->need_cache_flush)
                return;

        spin_lock_irq(&log->io_list_lock);
        /* flush bio is running */
        if (!list_empty(&log->flushing_ios)) {
                spin_unlock_irq(&log->io_list_lock);
                return;
        }
        list_splice_tail_init(&log->io_end_ios, &log->flushing_ios);
        do_flush = !list_empty(&log->flushing_ios);
        spin_unlock_irq(&log->io_list_lock);

        if (!do_flush)
                return;
        bio_reset(&log->flush_bio);
        log->flush_bio.bi_bdev = log->rdev->bdev;
        log->flush_bio.bi_end_io = r5l_log_flush_endio;
        log->flush_bio.bi_opf = REQ_OP_WRITE | REQ_PREFLUSH;
        submit_bio(&log->flush_bio);
}

static void r5l_write_super(struct r5l_log *log, sector_t cp);
static void r5l_write_super_and_discard_space(struct r5l_log *log,
        sector_t end)
{
        struct block_device *bdev = log->rdev->bdev;
        struct mddev *mddev;

        r5l_write_super(log, end);

        if (!blk_queue_discard(bdev_get_queue(bdev)))
                return;

        mddev = log->rdev->mddev;
        /*
         * Discard could zero data, so before discard we must make sure
         * superblock is updated to new log tail. Updating superblock (either
         * directly call md_update_sb() or depend on md thread) must hold
         * reconfig mutex. On the other hand, raid5_quiesce is called with
         * reconfig_mutex hold. The first step of raid5_quiesce() is waitting
         * for all IO finish, hence waitting for reclaim thread, while reclaim
         * thread is calling this function and waitting for reconfig mutex. So
         * there is a deadlock. We workaround this issue with a trylock.
         * FIXME: we could miss discard if we can't take reconfig mutex
         */
        set_mask_bits(&mddev->sb_flags, 0,
                BIT(MD_SB_CHANGE_DEVS) | BIT(MD_SB_CHANGE_PENDING));
        if (!mddev_trylock(mddev))
                return;
        md_update_sb(mddev, 1);
        mddev_unlock(mddev);

        /* discard IO error really doesn't matter, ignore it */
        if (log->last_checkpoint < end) {
                blkdev_issue_discard(bdev,
                                log->last_checkpoint + log->rdev->data_offset,
                                end - log->last_checkpoint, GFP_NOIO, 0);
        } else {
                blkdev_issue_discard(bdev,
                                log->last_checkpoint + log->rdev->data_offset,
                                log->device_size - log->last_checkpoint,
                                GFP_NOIO, 0);
                blkdev_issue_discard(bdev, log->rdev->data_offset, end,
                                GFP_NOIO, 0);
        }
}

/*
 * r5c_flush_stripe moves stripe from cached list to handle_list. When called,
 * the stripe must be on r5c_cached_full_stripes or r5c_cached_partial_stripes.
 *
 * must hold conf->device_lock
 */
static void r5c_flush_stripe(struct r5conf *conf, struct stripe_head *sh)
{
        BUG_ON(list_empty(&sh->lru));
        BUG_ON(!test_bit(STRIPE_R5C_CACHING, &sh->state));
        BUG_ON(test_bit(STRIPE_HANDLE, &sh->state));

        /*
         * The stripe is not ON_RELEASE_LIST, so it is safe to call
         * raid5_release_stripe() while holding conf->device_lock
         */
        BUG_ON(test_bit(STRIPE_ON_RELEASE_LIST, &sh->state));
        assert_spin_locked(&conf->device_lock);

        list_del_init(&sh->lru);
        atomic_inc(&sh->count);

        set_bit(STRIPE_HANDLE, &sh->state);
        atomic_inc(&conf->active_stripes);
        r5c_make_stripe_write_out(sh);

        if (test_bit(STRIPE_R5C_PARTIAL_STRIPE, &sh->state))
                atomic_inc(&conf->r5c_flushing_partial_stripes);
        else
                atomic_inc(&conf->r5c_flushing_full_stripes);
        raid5_release_stripe(sh);
}

/*
 * if num == 0, flush all full stripes
 * if num > 0, flush all full stripes. If less than num full stripes are
 *             flushed, flush some partial stripes until totally num stripes are
 *             flushed or there is no more cached stripes.
 */
void r5c_flush_cache(struct r5conf *conf, int num)
{
        int count;
        struct stripe_head *sh, *next;

        assert_spin_locked(&conf->device_lock);
        if (!conf->log)
                return;

        count = 0;
        list_for_each_entry_safe(sh, next, &conf->r5c_full_stripe_list, lru) {
                r5c_flush_stripe(conf, sh);
                count++;
        }

        if (count >= num)
                return;
        list_for_each_entry_safe(sh, next,
                                 &conf->r5c_partial_stripe_list, lru) {
                r5c_flush_stripe(conf, sh);
                if (++count >= num)
                        break;
        }
}

static void r5c_do_reclaim(struct r5conf *conf)
{
        struct r5l_log *log = conf->log;
        struct stripe_head *sh;
        int count = 0;
        unsigned long flags;
        int total_cached;
        int stripes_to_flush;
        int flushing_partial, flushing_full;

        if (!r5c_is_writeback(log))
                return;

        flushing_partial = atomic_read(&conf->r5c_flushing_partial_stripes);
        flushing_full = atomic_read(&conf->r5c_flushing_full_stripes);
        total_cached = atomic_read(&conf->r5c_cached_partial_stripes) +
                atomic_read(&conf->r5c_cached_full_stripes) -
                flushing_full - flushing_partial;

        if (total_cached > conf->min_nr_stripes * 3 / 4 ||
            atomic_read(&conf->empty_inactive_list_nr) > 0)
                /*
                 * if stripe cache pressure high, flush all full stripes and
                 * some partial stripes
                 */
                stripes_to_flush = R5C_RECLAIM_STRIPE_GROUP;
        else if (total_cached > conf->min_nr_stripes * 1 / 2 ||
                 atomic_read(&conf->r5c_cached_full_stripes) - flushing_full >
                 R5C_FULL_STRIPE_FLUSH_BATCH(conf))
                /*
                 * if stripe cache pressure moderate, or if there is many full
                 * stripes,flush all full stripes
                 */
                stripes_to_flush = 0;
        else
                /* no need to flush */
                stripes_to_flush = -1;

        if (stripes_to_flush >= 0) {
                spin_lock_irqsave(&conf->device_lock, flags);
                r5c_flush_cache(conf, stripes_to_flush);
                spin_unlock_irqrestore(&conf->device_lock, flags);
        }

        /* if log space is tight, flush stripes on stripe_in_journal_list */
        if (test_bit(R5C_LOG_TIGHT, &conf->cache_state)) {
                spin_lock_irqsave(&log->stripe_in_journal_lock, flags);
                spin_lock(&conf->device_lock);
                list_for_each_entry(sh, &log->stripe_in_journal_list, r5c) {
                        /*
                         * stripes on stripe_in_journal_list could be in any
                         * state of the stripe_cache state machine. In this
                         * case, we only want to flush stripe on
                         * r5c_cached_full/partial_stripes. The following
                         * condition makes sure the stripe is on one of the
                         * two lists.
                         */
                        if (!list_empty(&sh->lru) &&
                            !test_bit(STRIPE_HANDLE, &sh->state) &&
                            atomic_read(&sh->count) == 0) {
                                r5c_flush_stripe(conf, sh);
                                if (count++ >= R5C_RECLAIM_STRIPE_GROUP)
                                        break;
                        }
                }
                spin_unlock(&conf->device_lock);
                spin_unlock_irqrestore(&log->stripe_in_journal_lock, flags);
        }

        if (!test_bit(R5C_LOG_CRITICAL, &conf->cache_state))
                r5l_run_no_space_stripes(log);

        md_wakeup_thread(conf->mddev->thread);
}

static void r5l_do_reclaim(struct r5l_log *log)
{
        struct r5conf *conf = log->rdev->mddev->private;
        sector_t reclaim_target = xchg(&log->reclaim_target, 0);
        sector_t reclaimable;
        sector_t next_checkpoint;
        bool write_super;

        spin_lock_irq(&log->io_list_lock);
        write_super = r5l_reclaimable_space(log) > log->max_free_space ||
                reclaim_target != 0 || !list_empty(&log->no_space_stripes);
        /*
         * move proper io_unit to reclaim list. We should not change the order.
         * reclaimable/unreclaimable io_unit can be mixed in the list, we
         * shouldn't reuse space of an unreclaimable io_unit
         */
        while (1) {
                reclaimable = r5l_reclaimable_space(log);
                if (reclaimable >= reclaim_target ||
                    (list_empty(&log->running_ios) &&
                     list_empty(&log->io_end_ios) &&
                     list_empty(&log->flushing_ios) &&
                     list_empty(&log->finished_ios)))
                        break;

                md_wakeup_thread(log->rdev->mddev->thread);
                wait_event_lock_irq(log->iounit_wait,
                                    r5l_reclaimable_space(log) > reclaimable,
                                    log->io_list_lock);
        }

        next_checkpoint = r5c_calculate_new_cp(conf);
        spin_unlock_irq(&log->io_list_lock);

        if (reclaimable == 0 || !write_super)
                return;

        /*
         * write_super will flush cache of each raid disk. We must write super
         * here, because the log area might be reused soon and we don't want to
         * confuse recovery
         */
        r5l_write_super_and_discard_space(log, next_checkpoint);

        mutex_lock(&log->io_mutex);
        log->last_checkpoint = next_checkpoint;
        r5c_update_log_state(log);
        mutex_unlock(&log->io_mutex);

        r5l_run_no_space_stripes(log);
}

static void r5l_reclaim_thread(struct md_thread *thread)
{
        struct mddev *mddev = thread->mddev;
        struct r5conf *conf = mddev->private;
        struct r5l_log *log = conf->log;

        if (!log)
                return;
        r5c_do_reclaim(conf);
        r5l_do_reclaim(log);
}

void r5l_wake_reclaim(struct r5l_log *log, sector_t space)
{
        unsigned long target;
        unsigned long new = (unsigned long)space; /* overflow in theory */

        if (!log)
                return;
        do {
                target = log->reclaim_target;
                if (new < target)
                        return;
        } while (cmpxchg(&log->reclaim_target, target, new) != target);
        md_wakeup_thread(log->reclaim_thread);
}

void r5l_quiesce(struct r5l_log *log, int state)
{
        struct mddev *mddev;
        if (!log || state == 2)
                return;
        if (state == 0)
                kthread_unpark(log->reclaim_thread->tsk);
        else if (state == 1) {
                /* make sure r5l_write_super_and_discard_space exits */
                mddev = log->rdev->mddev;
                wake_up(&mddev->sb_wait);
                kthread_park(log->reclaim_thread->tsk);
                r5l_wake_reclaim(log, MaxSector);
                r5l_do_reclaim(log);
        }
}

bool r5l_log_disk_error(struct r5conf *conf)
{
        struct r5l_log *log;
        bool ret;
        /* don't allow write if journal disk is missing */
        rcu_read_lock();
        log = rcu_dereference(conf->log);

        if (!log)
                ret = test_bit(MD_HAS_JOURNAL, &conf->mddev->flags);
        else
                ret = test_bit(Faulty, &log->rdev->flags);
        rcu_read_unlock();
        return ret;
}

#define R5L_RECOVERY_PAGE_POOL_SIZE 256

struct r5l_recovery_ctx {
        struct page *meta_page;         /* current meta */
        sector_t meta_total_blocks;     /* total size of current meta and data */
        sector_t pos;                   /* recovery position */
        u64 seq;                        /* recovery position seq */
        int data_parity_stripes;        /* number of data_parity stripes */
        int data_only_stripes;          /* number of data_only stripes */
        struct list_head cached_list;

        /*
         * read ahead page pool (ra_pool)
         * in recovery, log is read sequentially. It is not efficient to
         * read every page with sync_page_io(). The read ahead page pool
         * reads multiple pages with one IO, so further log read can
         * just copy data from the pool.
         */
        struct page *ra_pool[R5L_RECOVERY_PAGE_POOL_SIZE];
        sector_t pool_offset;   /* offset of first page in the pool */
        int total_pages;        /* total allocated pages */
        int valid_pages;        /* pages with valid data */
        struct bio *ra_bio;     /* bio to do the read ahead */
};

static int r5l_recovery_allocate_ra_pool(struct r5l_log *log,
                                            struct r5l_recovery_ctx *ctx)
{
        struct page *page;

        ctx->ra_bio = bio_alloc_bioset(GFP_KERNEL, BIO_MAX_PAGES, log->bs);
        if (!ctx->ra_bio)
                return -ENOMEM;

        ctx->valid_pages = 0;
        ctx->total_pages = 0;
        while (ctx->total_pages < R5L_RECOVERY_PAGE_POOL_SIZE) {
                page = alloc_page(GFP_KERNEL);

                if (!page)
                        break;
                ctx->ra_pool[ctx->total_pages] = page;
                ctx->total_pages += 1;
        }

        if (ctx->total_pages == 0) {
                bio_put(ctx->ra_bio);
                return -ENOMEM;
        }

        ctx->pool_offset = 0;
        return 0;
}

static void r5l_recovery_free_ra_pool(struct r5l_log *log,
                                        struct r5l_recovery_ctx *ctx)
{
        int i;

        for (i = 0; i < ctx->total_pages; ++i)
                put_page(ctx->ra_pool[i]);
        bio_put(ctx->ra_bio);
}

/*
 * fetch ctx->valid_pages pages from offset
 * In normal cases, ctx->valid_pages == ctx->total_pages after the call.
 * However, if the offset is close to the end of the journal device,
 * ctx->valid_pages could be smaller than ctx->total_pages
 */
static int r5l_recovery_fetch_ra_pool(struct r5l_log *log,
                                      struct r5l_recovery_ctx *ctx,
                                      sector_t offset)
{
        bio_reset(ctx->ra_bio);
        ctx->ra_bio->bi_bdev = log->rdev->bdev;
        bio_set_op_attrs(ctx->ra_bio, REQ_OP_READ, 0);
        ctx->ra_bio->bi_iter.bi_sector = log->rdev->data_offset + offset;

        ctx->valid_pages = 0;
        ctx->pool_offset = offset;

        while (ctx->valid_pages < ctx->total_pages) {
                bio_add_page(ctx->ra_bio,
                             ctx->ra_pool[ctx->valid_pages], PAGE_SIZE, 0);
                ctx->valid_pages += 1;

                offset = r5l_ring_add(log, offset, BLOCK_SECTORS);

                if (offset == 0)  /* reached end of the device */
                        break;
        }

        return submit_bio_wait(ctx->ra_bio);
}

/*
 * try read a page from the read ahead page pool, if the page is not in the
 * pool, call r5l_recovery_fetch_ra_pool
 */
static int r5l_recovery_read_page(struct r5l_log *log,
                                  struct r5l_recovery_ctx *ctx,
                                  struct page *page,
                                  sector_t offset)
{
        int ret;

        if (offset < ctx->pool_offset ||
            offset >= ctx->pool_offset + ctx->valid_pages * BLOCK_SECTORS) {
                ret = r5l_recovery_fetch_ra_pool(log, ctx, offset);
                if (ret)
                        return ret;
        }

        BUG_ON(offset < ctx->pool_offset ||
               offset >= ctx->pool_offset + ctx->valid_pages * BLOCK_SECTORS);

        memcpy(page_address(page),
               page_address(ctx->ra_pool[(offset - ctx->pool_offset) >>
                                         BLOCK_SECTOR_SHIFT]),
               PAGE_SIZE);
        return 0;
}

static int r5l_recovery_read_meta_block(struct r5l_log *log,
                                        struct r5l_recovery_ctx *ctx)
{
        struct page *page = ctx->meta_page;
        struct r5l_meta_block *mb;
        u32 crc, stored_crc;
        int ret;

        ret = r5l_recovery_read_page(log, ctx, page, ctx->pos);
        if (ret != 0)
                return ret;

        mb = page_address(page);
        stored_crc = le32_to_cpu(mb->checksum);
        mb->checksum = 0;

        if (le32_to_cpu(mb->magic) != R5LOG_MAGIC ||
            le64_to_cpu(mb->seq) != ctx->seq ||
            mb->version != R5LOG_VERSION ||
            le64_to_cpu(mb->position) != ctx->pos)
                return -EINVAL;

        crc = crc32c_le(log->uuid_checksum, mb, PAGE_SIZE);
        if (stored_crc != crc)
                return -EINVAL;

        if (le32_to_cpu(mb->meta_size) > PAGE_SIZE)
                return -EINVAL;

        ctx->meta_total_blocks = BLOCK_SECTORS;

        return 0;
}

static void
r5l_recovery_create_empty_meta_block(struct r5l_log *log,
                                     struct page *page,
                                     sector_t pos, u64 seq)
{
        struct r5l_meta_block *mb;

        mb = page_address(page);
        clear_page(mb);
        mb->magic = cpu_to_le32(R5LOG_MAGIC);
        mb->version = R5LOG_VERSION;
        mb->meta_size = cpu_to_le32(sizeof(struct r5l_meta_block));
        mb->seq = cpu_to_le64(seq);
        mb->position = cpu_to_le64(pos);
}

static int r5l_log_write_empty_meta_block(struct r5l_log *log, sector_t pos,
                                          u64 seq)
{
        struct page *page;
        struct r5l_meta_block *mb;

        page = alloc_page(GFP_KERNEL);
        if (!page)
                return -ENOMEM;
        r5l_recovery_create_empty_meta_block(log, page, pos, seq);
        mb = page_address(page);
        mb->checksum = cpu_to_le32(crc32c_le(log->uuid_checksum,
                                             mb, PAGE_SIZE));
        if (!sync_page_io(log->rdev, pos, PAGE_SIZE, page, REQ_OP_WRITE,
                          REQ_SYNC | REQ_FUA, false)) {
                __free_page(page);
                return -EIO;
        }
        __free_page(page);
        return 0;
}

/*
 * r5l_recovery_load_data and r5l_recovery_load_parity uses flag R5_Wantwrite
 * to mark valid (potentially not flushed) data in the journal.
 *
 * We already verified checksum in r5l_recovery_verify_data_checksum_for_mb,
 * so there should not be any mismatch here.
 */
static void r5l_recovery_load_data(struct r5l_log *log,
                                   struct stripe_head *sh,
                                   struct r5l_recovery_ctx *ctx,
                                   struct r5l_payload_data_parity *payload,
                                   sector_t log_offset)
{
        struct mddev *mddev = log->rdev->mddev;
        struct r5conf *conf = mddev->private;
        int dd_idx;

        raid5_compute_sector(conf,
                             le64_to_cpu(payload->location), 0,
                             &dd_idx, sh);
        r5l_recovery_read_page(log, ctx, sh->dev[dd_idx].page, log_offset);
        sh->dev[dd_idx].log_checksum =
                le32_to_cpu(payload->checksum[0]);
        ctx->meta_total_blocks += BLOCK_SECTORS;

        set_bit(R5_Wantwrite, &sh->dev[dd_idx].flags);
        set_bit(STRIPE_R5C_CACHING, &sh->state);
}

static void r5l_recovery_load_parity(struct r5l_log *log,
                                     struct stripe_head *sh,
                                     struct r5l_recovery_ctx *ctx,
                                     struct r5l_payload_data_parity *payload,
                                     sector_t log_offset)
{
        struct mddev *mddev = log->rdev->mddev;
        struct r5conf *conf = mddev->private;

        ctx->meta_total_blocks += BLOCK_SECTORS * conf->max_degraded;
        r5l_recovery_read_page(log, ctx, sh->dev[sh->pd_idx].page, log_offset);
        sh->dev[sh->pd_idx].log_checksum =
                le32_to_cpu(payload->checksum[0]);
        set_bit(R5_Wantwrite, &sh->dev[sh->pd_idx].flags);

        if (sh->qd_idx >= 0) {
                r5l_recovery_read_page(
                        log, ctx, sh->dev[sh->qd_idx].page,
                        r5l_ring_add(log, log_offset, BLOCK_SECTORS));
                sh->dev[sh->qd_idx].log_checksum =
                        le32_to_cpu(payload->checksum[1]);
                set_bit(R5_Wantwrite, &sh->dev[sh->qd_idx].flags);
        }
        clear_bit(STRIPE_R5C_CACHING, &sh->state);
}

static void r5l_recovery_reset_stripe(struct stripe_head *sh)
{
        int i;

        sh->state = 0;
        sh->log_start = MaxSector;
        for (i = sh->disks; i--; )
                sh->dev[i].flags = 0;
}

static void
r5l_recovery_replay_one_stripe(struct r5conf *conf,
                               struct stripe_head *sh,
                               struct r5l_recovery_ctx *ctx)
{
        struct md_rdev *rdev, *rrdev;
        int disk_index;
        int data_count = 0;

        for (disk_index = 0; disk_index < sh->disks; disk_index++) {
                if (!test_bit(R5_Wantwrite, &sh->dev[disk_index].flags))
                        continue;
                if (disk_index == sh->qd_idx || disk_index == sh->pd_idx)
                        continue;
                data_count++;
        }

        /*
         * stripes that only have parity must have been flushed
         * before the crash that we are now recovering from, so
         * there is nothing more to recovery.
         */
        if (data_count == 0)
                goto out;

        for (disk_index = 0; disk_index < sh->disks; disk_index++) {
                if (!test_bit(R5_Wantwrite, &sh->dev[disk_index].flags))
                        continue;

                /* in case device is broken */
                rcu_read_lock();
                rdev = rcu_dereference(conf->disks[disk_index].rdev);
                if (rdev) {
                        atomic_inc(&rdev->nr_pending);
                        rcu_read_unlock();
                        sync_page_io(rdev, sh->sector, PAGE_SIZE,
                                     sh->dev[disk_index].page, REQ_OP_WRITE, 0,
                                     false);
                        rdev_dec_pending(rdev, rdev->mddev);
                        rcu_read_lock();
                }
                rrdev = rcu_dereference(conf->disks[disk_index].replacement);
                if (rrdev) {
                        atomic_inc(&rrdev->nr_pending);
                        rcu_read_unlock();
                        sync_page_io(rrdev, sh->sector, PAGE_SIZE,
                                     sh->dev[disk_index].page, REQ_OP_WRITE, 0,
                                     false);
                        rdev_dec_pending(rrdev, rrdev->mddev);
                        rcu_read_lock();
                }
                rcu_read_unlock();
        }
        ctx->data_parity_stripes++;
out:
        r5l_recovery_reset_stripe(sh);
}

static struct stripe_head *
r5c_recovery_alloc_stripe(struct r5conf *conf,
                          sector_t stripe_sect)
{
        struct stripe_head *sh;

        sh = raid5_get_active_stripe(conf, stripe_sect, 0, 1, 0);
        if (!sh)
                return NULL;  /* no more stripe available */

        r5l_recovery_reset_stripe(sh);

        return sh;
}

static struct stripe_head *
r5c_recovery_lookup_stripe(struct list_head *list, sector_t sect)
{
        struct stripe_head *sh;

        list_for_each_entry(sh, list, lru)
                if (sh->sector == sect)
                        return sh;
        return NULL;
}

static void
r5c_recovery_drop_stripes(struct list_head *cached_stripe_list,
                          struct r5l_recovery_ctx *ctx)
{
        struct stripe_head *sh, *next;

        list_for_each_entry_safe(sh, next, cached_stripe_list, lru) {
                r5l_recovery_reset_stripe(sh);
                list_del_init(&sh->lru);
                raid5_release_stripe(sh);
        }
}

static void
r5c_recovery_replay_stripes(struct list_head *cached_stripe_list,
                            struct r5l_recovery_ctx *ctx)
{
        struct stripe_head *sh, *next;

        list_for_each_entry_safe(sh, next, cached_stripe_list, lru)
                if (!test_bit(STRIPE_R5C_CACHING, &sh->state)) {
                        r5l_recovery_replay_one_stripe(sh->raid_conf, sh, ctx);
                        list_del_init(&sh->lru);
                        raid5_release_stripe(sh);
                }
}

/* if matches return 0; otherwise return -EINVAL */
static int
r5l_recovery_verify_data_checksum(struct r5l_log *log,
                                  struct r5l_recovery_ctx *ctx,
                                  struct page *page,
                                  sector_t log_offset, __le32 log_checksum)
{
        void *addr;
        u32 checksum;

        r5l_recovery_read_page(log, ctx, page, log_offset);
        addr = kmap_atomic(page);
        checksum = crc32c_le(log->uuid_checksum, addr, PAGE_SIZE);
        kunmap_atomic(addr);
        return (le32_to_cpu(log_checksum) == checksum) ? 0 : -EINVAL;
}

/*
 * before loading data to stripe cache, we need verify checksum for all data,
 * if there is mismatch for any data page, we drop all data in the mata block
 */
static int
r5l_recovery_verify_data_checksum_for_mb(struct r5l_log *log,
                                         struct r5l_recovery_ctx *ctx)
{
        struct mddev *mddev = log->rdev->mddev;
        struct r5conf *conf = mddev->private;
        struct r5l_meta_block *mb = page_address(ctx->meta_page);
        sector_t mb_offset = sizeof(struct r5l_meta_block);
        sector_t log_offset = r5l_ring_add(log, ctx->pos, BLOCK_SECTORS);
        struct page *page;
        struct r5l_payload_data_parity *payload;
        struct r5l_payload_flush *payload_flush;

        page = alloc_page(GFP_KERNEL);
        if (!page)
                return -ENOMEM;

        while (mb_offset < le32_to_cpu(mb->meta_size)) {
                payload = (void *)mb + mb_offset;
                payload_flush = (void *)mb + mb_offset;

                if (le16_to_cpu(payload->header.type) == R5LOG_PAYLOAD_DATA) {
                        if (r5l_recovery_verify_data_checksum(
                                    log, ctx, page, log_offset,
                                    payload->checksum[0]) < 0)
                                goto mismatch;
                } else if (le16_to_cpu(payload->header.type) == R5LOG_PAYLOAD_PARITY) {
                        if (r5l_recovery_verify_data_checksum(
                                    log, ctx, page, log_offset,
                                    payload->checksum[0]) < 0)
                                goto mismatch;
                        if (conf->max_degraded == 2 && /* q for RAID 6 */
                            r5l_recovery_verify_data_checksum(
                                    log, ctx, page,
                                    r5l_ring_add(log, log_offset,
                                                 BLOCK_SECTORS),
                                    payload->checksum[1]) < 0)
                                goto mismatch;
                } else if (le16_to_cpu(payload->header.type) == R5LOG_PAYLOAD_FLUSH) {
                        /* nothing to do for R5LOG_PAYLOAD_FLUSH here */
                } else /* not R5LOG_PAYLOAD_DATA/PARITY/FLUSH */
                        goto mismatch;

                if (le16_to_cpu(payload->header.type) == R5LOG_PAYLOAD_FLUSH) {
                        mb_offset += sizeof(struct r5l_payload_flush) +
                                le32_to_cpu(payload_flush->size);
                } else {
                        /* DATA or PARITY payload */
                        log_offset = r5l_ring_add(log, log_offset,
                                                  le32_to_cpu(payload->size));
                        mb_offset += sizeof(struct r5l_payload_data_parity) +
                                sizeof(__le32) *
                                (le32_to_cpu(payload->size) >> (PAGE_SHIFT - 9));
                }

        }

        put_page(page);
        return 0;

mismatch:
        put_page(page);
        return -EINVAL;
}

/*
 * Analyze all data/parity pages in one meta block
 * Returns:
 * 0 for success
 * -EINVAL for unknown playload type
 * -EAGAIN for checksum mismatch of data page
 * -ENOMEM for run out of memory (alloc_page failed or run out of stripes)
 */
static int
r5c_recovery_analyze_meta_block(struct r5l_log *log,
                                struct r5l_recovery_ctx *ctx,
                                struct list_head *cached_stripe_list)
{
        struct mddev *mddev = log->rdev->mddev;
        struct r5conf *conf = mddev->private;
        struct r5l_meta_block *mb;
        struct r5l_payload_data_parity *payload;
        struct r5l_payload_flush *payload_flush;
        int mb_offset;
        sector_t log_offset;
        sector_t stripe_sect;
        struct stripe_head *sh;
        int ret;

        /*
         * for mismatch in data blocks, we will drop all data in this mb, but
         * we will still read next mb for other data with FLUSH flag, as
         * io_unit could finish out of order.
         */
        ret = r5l_recovery_verify_data_checksum_for_mb(log, ctx);
        if (ret == -EINVAL)
                return -EAGAIN;
        else if (ret)
                return ret;   /* -ENOMEM duo to alloc_page() failed */

        mb = page_address(ctx->meta_page);
        mb_offset = sizeof(struct r5l_meta_block);
        log_offset = r5l_ring_add(log, ctx->pos, BLOCK_SECTORS);

        while (mb_offset < le32_to_cpu(mb->meta_size)) {
                int dd;

                payload = (void *)mb + mb_offset;
                payload_flush = (void *)mb + mb_offset;

                if (le16_to_cpu(payload->header.type) == R5LOG_PAYLOAD_FLUSH) {
                        int i, count;

                        count = le32_to_cpu(payload_flush->size) / sizeof(__le64);
                        for (i = 0; i < count; ++i) {
                                stripe_sect = le64_to_cpu(payload_flush->flush_stripes[i]);
                                sh = r5c_recovery_lookup_stripe(cached_stripe_list,
                                                                stripe_sect);
                                if (sh) {
                                        WARN_ON(test_bit(STRIPE_R5C_CACHING, &sh->state));
                                        r5l_recovery_reset_stripe(sh);
                                        list_del_init(&sh->lru);
                                        raid5_release_stripe(sh);
                                }
                        }

                        mb_offset += sizeof(struct r5l_payload_flush) +
                                le32_to_cpu(payload_flush->size);
                        continue;
                }

                /* DATA or PARITY payload */
                stripe_sect = (le16_to_cpu(payload->header.type) == R5LOG_PAYLOAD_DATA) ?
                        raid5_compute_sector(
                                conf, le64_to_cpu(payload->location), 0, &dd,
                                NULL)
                        : le64_to_cpu(payload->location);

                sh = r5c_recovery_lookup_stripe(cached_stripe_list,
                                                stripe_sect);

                if (!sh) {
                        sh = r5c_recovery_alloc_stripe(conf, stripe_sect);
                        /*
                         * cannot get stripe from raid5_get_active_stripe
                         * try replay some stripes
                         */
                        if (!sh) {
                                r5c_recovery_replay_stripes(
                                        cached_stripe_list, ctx);
                                sh = r5c_recovery_alloc_stripe(
                                        conf, stripe_sect);
                        }
                        if (!sh) {
                                pr_debug("md/raid:%s: Increasing stripe cache size to %d to recovery data on journal.\n",
                                        mdname(mddev),
                                        conf->min_nr_stripes * 2);
                                raid5_set_cache_size(mddev,
                                                     conf->min_nr_stripes * 2);
                                sh = r5c_recovery_alloc_stripe(conf,
                                                               stripe_sect);
                        }
                        if (!sh) {
                                pr_err("md/raid:%s: Cannot get enough stripes due to memory pressure. Recovery failed.\n",
                                       mdname(mddev));
                                return -ENOMEM;
                        }
                        list_add_tail(&sh->lru, cached_stripe_list);
                }

                if (le16_to_cpu(payload->header.type) == R5LOG_PAYLOAD_DATA) {
                        if (!test_bit(STRIPE_R5C_CACHING, &sh->state) &&
                            test_bit(R5_Wantwrite, &sh->dev[sh->pd_idx].flags)) {
                                r5l_recovery_replay_one_stripe(conf, sh, ctx);
                                list_move_tail(&sh->lru, cached_stripe_list);
                        }
                        r5l_recovery_load_data(log, sh, ctx, payload,
                                               log_offset);
                } else if (le16_to_cpu(payload->header.type) == R5LOG_PAYLOAD_PARITY)
                        r5l_recovery_load_parity(log, sh, ctx, payload,
                                                 log_offset);
                else
                        return -EINVAL;

                log_offset = r5l_ring_add(log, log_offset,
                                          le32_to_cpu(payload->size));

                mb_offset += sizeof(struct r5l_payload_data_parity) +
                        sizeof(__le32) *
                        (le32_to_cpu(payload->size) >> (PAGE_SHIFT - 9));
        }

        return 0;
}

/*
 * Load the stripe into cache. The stripe will be written out later by
 * the stripe cache state machine.
 */
static void r5c_recovery_load_one_stripe(struct r5l_log *log,
                                         struct stripe_head *sh)
{
        struct r5dev *dev;
        int i;

        for (i = sh->disks; i--; ) {
                dev = sh->dev + i;
                if (test_and_clear_bit(R5_Wantwrite, &dev->flags)) {
                        set_bit(R5_InJournal, &dev->flags);
                        set_bit(R5_UPTODATE, &dev->flags);
                }
        }
}

/*
 * Scan through the log for all to-be-flushed data
 *
 * For stripes with data and parity, namely Data-Parity stripe
 * (STRIPE_R5C_CACHING == 0), we simply replay all the writes.
 *
 * For stripes with only data, namely Data-Only stripe
 * (STRIPE_R5C_CACHING == 1), we load them to stripe cache state machine.
 *
 * For a stripe, if we see data after parity, we should discard all previous
 * data and parity for this stripe, as these data are already flushed to
 * the array.
 *
 * At the end of the scan, we return the new journal_tail, which points to
 * first data-only stripe on the journal device, or next invalid meta block.
 */
static int r5c_recovery_flush_log(struct r5l_log *log,
                                  struct r5l_recovery_ctx *ctx)
{
        struct stripe_head *sh;
        int ret = 0;

        /* scan through the log */
        while (1) {
                if (r5l_recovery_read_meta_block(log, ctx))
                        break;

                ret = r5c_recovery_analyze_meta_block(log, ctx,
                                                      &ctx->cached_list);
                /*
                 * -EAGAIN means mismatch in data block, in this case, we still
                 * try scan the next metablock
                 */
                if (ret && ret != -EAGAIN)
                        break;   /* ret == -EINVAL or -ENOMEM */
                ctx->seq++;
                ctx->pos = r5l_ring_add(log, ctx->pos, ctx->meta_total_blocks);
        }

        if (ret == -ENOMEM) {
                r5c_recovery_drop_stripes(&ctx->cached_list, ctx);
                return ret;
        }

        /* replay data-parity stripes */
        r5c_recovery_replay_stripes(&ctx->cached_list, ctx);

        /* load data-only stripes to stripe cache */
        list_for_each_entry(sh, &ctx->cached_list, lru) {
                WARN_ON(!test_bit(STRIPE_R5C_CACHING, &sh->state));
                r5c_recovery_load_one_stripe(log, sh);
                ctx->data_only_stripes++;
        }

        return 0;
}

/*
 * we did a recovery. Now ctx.pos points to an invalid meta block. New
 * log will start here. but we can't let superblock point to last valid
 * meta block. The log might looks like:
 * | meta 1| meta 2| meta 3|
 * meta 1 is valid, meta 2 is invalid. meta 3 could be valid. If
 * superblock points to meta 1, we write a new valid meta 2n.  if crash
 * happens again, new recovery will start from meta 1. Since meta 2n is
 * valid now, recovery will think meta 3 is valid, which is wrong.
 * The solution is we create a new meta in meta2 with its seq == meta
 * 1's seq + 10000 and let superblock points to meta2. The same recovery
 * will not think meta 3 is a valid meta, because its seq doesn't match
 */

/*
 * Before recovery, the log looks like the following
 *
 *   ---------------------------------------------
 *   |           valid log        | invalid log  |
 *   ---------------------------------------------
 *   ^
 *   |- log->last_checkpoint
 *   |- log->last_cp_seq
 *
 * Now we scan through the log until we see invalid entry
 *
 *   ---------------------------------------------
 *   |           valid log        | invalid log  |
 *   ---------------------------------------------
 *   ^                            ^
 *   |- log->last_checkpoint      |- ctx->pos
 *   |- log->last_cp_seq          |- ctx->seq
 *
 * From this point, we need to increase seq number by 10 to avoid
 * confusing next recovery.
 *
 *   ---------------------------------------------
 *   |           valid log        | invalid log  |
 *   ---------------------------------------------
 *   ^                              ^
 *   |- log->last_checkpoint        |- ctx->pos+1
 *   |- log->last_cp_seq            |- ctx->seq+10001
 *
 * However, it is not safe to start the state machine yet, because data only
 * parities are not yet secured in RAID. To save these data only parities, we
 * rewrite them from seq+11.
 *
 *   -----------------------------------------------------------------
 *   |           valid log        | data only stripes | invalid log  |
 *   -----------------------------------------------------------------
 *   ^                                                ^
 *   |- log->last_checkpoint                          |- ctx->pos+n
 *   |- log->last_cp_seq                              |- ctx->seq+10000+n
 *
 * If failure happens again during this process, the recovery can safe start
 * again from log->last_checkpoint.
 *
 * Once data only stripes are rewritten to journal, we move log_tail
 *
 *   -----------------------------------------------------------------
 *   |     old log        |    data only stripes    | invalid log  |
 *   -----------------------------------------------------------------
 *                        ^                         ^
 *                        |- log->last_checkpoint   |- ctx->pos+n
 *                        |- log->last_cp_seq       |- ctx->seq+10000+n
 *
 * Then we can safely start the state machine. If failure happens from this
 * point on, the recovery will start from new log->last_checkpoint.
 */
static int
r5c_recovery_rewrite_data_only_stripes(struct r5l_log *log,
                                       struct r5l_recovery_ctx *ctx)
{
        struct stripe_head *sh;
        struct mddev *mddev = log->rdev->mddev;
        struct page *page;
        sector_t next_checkpoint = MaxSector;

        page = alloc_page(GFP_KERNEL);
        if (!page) {
                pr_err("md/raid:%s: cannot allocate memory to rewrite data only stripes\n",
                       mdname(mddev));
                return -ENOMEM;
        }

        WARN_ON(list_empty(&ctx->cached_list));

        list_for_each_entry(sh, &ctx->cached_list, lru) {
                struct r5l_meta_block *mb;
                int i;
                int offset;
                sector_t write_pos;

                WARN_ON(!test_bit(STRIPE_R5C_CACHING, &sh->state));
                r5l_recovery_create_empty_meta_block(log, page,
                                                     ctx->pos, ctx->seq);
                mb = page_address(page);
                offset = le32_to_cpu(mb->meta_size);
                write_pos = r5l_ring_add(log, ctx->pos, BLOCK_SECTORS);

                for (i = sh->disks; i--; ) {
                        struct r5dev *dev = &sh->dev[i];
                        struct r5l_payload_data_parity *payload;
                        void *addr;

                        if (test_bit(R5_InJournal, &dev->flags)) {
                                payload = (void *)mb + offset;
                                payload->header.type = cpu_to_le16(
                                        R5LOG_PAYLOAD_DATA);
                                payload->size = cpu_to_le32(BLOCK_SECTORS);
                                payload->location = cpu_to_le64(
                                        raid5_compute_blocknr(sh, i, 0));
                                addr = kmap_atomic(dev->page);
                                payload->checksum[0] = cpu_to_le32(
                                        crc32c_le(log->uuid_checksum, addr,
                                                  PAGE_SIZE));
                                kunmap_atomic(addr);
                                sync_page_io(log->rdev, write_pos, PAGE_SIZE,
                                             dev->page, REQ_OP_WRITE, 0, false);
                                write_pos = r5l_ring_add(log, write_pos,
                                                         BLOCK_SECTORS);
                                offset += sizeof(__le32) +
                                        sizeof(struct r5l_payload_data_parity);

                        }
                }
                mb->meta_size = cpu_to_le32(offset);
                mb->checksum = cpu_to_le32(crc32c_le(log->uuid_checksum,
                                                     mb, PAGE_SIZE));
                sync_page_io(log->rdev, ctx->pos, PAGE_SIZE, page,
                             REQ_OP_WRITE, REQ_SYNC | REQ_FUA, false);
                sh->log_start = ctx->pos;
                list_add_tail(&sh->r5c, &log->stripe_in_journal_list);
                atomic_inc(&log->stripe_in_journal_count);
                ctx->pos = write_pos;
                ctx->seq += 1;
                next_checkpoint = sh->log_start;
        }
        log->next_checkpoint = next_checkpoint;
        __free_page(page);
        return 0;
}

static void r5c_recovery_flush_data_only_stripes(struct r5l_log *log,
                                                 struct r5l_recovery_ctx *ctx)
{
        struct mddev *mddev = log->rdev->mddev;
        struct r5conf *conf = mddev->private;
        struct stripe_head *sh, *next;

        if (ctx->data_only_stripes == 0)
                return;

        log->r5c_journal_mode = R5C_JOURNAL_MODE_WRITE_BACK;

        list_for_each_entry_safe(sh, next, &ctx->cached_list, lru) {
                r5c_make_stripe_write_out(sh);
                set_bit(STRIPE_HANDLE, &sh->state);
                list_del_init(&sh->lru);
                raid5_release_stripe(sh);
        }

        md_wakeup_thread(conf->mddev->thread);
        /* reuse conf->wait_for_quiescent in recovery */
        wait_event(conf->wait_for_quiescent,
                   atomic_read(&conf->active_stripes) == 0);

        log->r5c_journal_mode = R5C_JOURNAL_MODE_WRITE_THROUGH;
}

static int r5l_recovery_log(struct r5l_log *log)
{
        struct mddev *mddev = log->rdev->mddev;
        struct r5l_recovery_ctx *ctx;
        int ret;
        sector_t pos;

        ctx = kzalloc(sizeof(*ctx), GFP_KERNEL);
        if (!ctx)
                return -ENOMEM;

        ctx->pos = log->last_checkpoint;
        ctx->seq = log->last_cp_seq;
        INIT_LIST_HEAD(&ctx->cached_list);
        ctx->meta_page = alloc_page(GFP_KERNEL);

        if (!ctx->meta_page) {
                ret =  -ENOMEM;
                goto meta_page;
        }

        if (r5l_recovery_allocate_ra_pool(log, ctx) != 0) {
                ret = -ENOMEM;
                goto ra_pool;
        }

        ret = r5c_recovery_flush_log(log, ctx);

        if (ret)
                goto error;

        pos = ctx->pos;
        ctx->seq += 10000;

        if ((ctx->data_only_stripes == 0) && (ctx->data_parity_stripes == 0))
                pr_debug("md/raid:%s: starting from clean shutdown\n",
                         mdname(mddev));
        else
                pr_debug("md/raid:%s: recovering %d data-only stripes and %d data-parity stripes\n",
                         mdname(mddev), ctx->data_only_stripes,
                         ctx->data_parity_stripes);

        if (ctx->data_only_stripes == 0) {
                log->next_checkpoint = ctx->pos;
                r5l_log_write_empty_meta_block(log, ctx->pos, ctx->seq++);
                ctx->pos = r5l_ring_add(log, ctx->pos, BLOCK_SECTORS);
        } else if (r5c_recovery_rewrite_data_only_stripes(log, ctx)) {
                pr_err("md/raid:%s: failed to rewrite stripes to journal\n",
                       mdname(mddev));
                ret =  -EIO;
                goto error;
        }

        log->log_start = ctx->pos;
        log->seq = ctx->seq;
        log->last_checkpoint = pos;
        r5l_write_super(log, pos);

        r5c_recovery_flush_data_only_stripes(log, ctx);
        ret = 0;
error:
        r5l_recovery_free_ra_pool(log, ctx);
ra_pool:
        __free_page(ctx->meta_page);
meta_page:
        kfree(ctx);
        return ret;
}

static void r5l_write_super(struct r5l_log *log, sector_t cp)
{
        struct mddev *mddev = log->rdev->mddev;

        log->rdev->journal_tail = cp;
        set_bit(MD_SB_CHANGE_DEVS, &mddev->sb_flags);
}

static ssize_t r5c_journal_mode_show(struct mddev *mddev, char *page)
{
        struct r5conf *conf = mddev->private;
        int ret;

        if (!conf->log)
                return 0;

        switch (conf->log->r5c_journal_mode) {
        case R5C_JOURNAL_MODE_WRITE_THROUGH:
                ret = snprintf(
                        page, PAGE_SIZE, "[%s] %s\n",
                        r5c_journal_mode_str[R5C_JOURNAL_MODE_WRITE_THROUGH],
                        r5c_journal_mode_str[R5C_JOURNAL_MODE_WRITE_BACK]);
                break;
        case R5C_JOURNAL_MODE_WRITE_BACK:
                ret = snprintf(
                        page, PAGE_SIZE, "%s [%s]\n",
                        r5c_journal_mode_str[R5C_JOURNAL_MODE_WRITE_THROUGH],
                        r5c_journal_mode_str[R5C_JOURNAL_MODE_WRITE_BACK]);
                break;
        default:
                ret = 0;
        }
        return ret;
}

/*
 * Set journal cache mode on @mddev (external API initially needed by dm-raid).
 *
 * @mode as defined in 'enum r5c_journal_mode'.
 *
 */
int r5c_journal_mode_set(struct mddev *mddev, int mode)
{
        struct r5conf *conf = mddev->private;
        struct r5l_log *log = conf->log;

        if (!log)
                return -ENODEV;

        if (mode < R5C_JOURNAL_MODE_WRITE_THROUGH ||
            mode > R5C_JOURNAL_MODE_WRITE_BACK)
                return -EINVAL;

        if (raid5_calc_degraded(conf) > 0 &&
            mode == R5C_JOURNAL_MODE_WRITE_BACK)
                return -EINVAL;

        mddev_suspend(mddev);
        conf->log->r5c_journal_mode = mode;
        mddev_resume(mddev);

        pr_debug("md/raid:%s: setting r5c cache mode to %d: %s\n",
                 mdname(mddev), mode, r5c_journal_mode_str[mode]);
        return 0;
}
EXPORT_SYMBOL(r5c_journal_mode_set);

static ssize_t r5c_journal_mode_store(struct mddev *mddev,
                                      const char *page, size_t length)
{
        int mode = ARRAY_SIZE(r5c_journal_mode_str);
        size_t len = length;

        if (len < 2)
                return -EINVAL;

        if (page[len - 1] == '\n')
                len--;

        while (mode--)
                if (strlen(r5c_journal_mode_str[mode]) == len &&
                    !strncmp(page, r5c_journal_mode_str[mode], len))
                        break;

        return r5c_journal_mode_set(mddev, mode) ?: length;
}

struct md_sysfs_entry
r5c_journal_mode = __ATTR(journal_mode, 0644,
                          r5c_journal_mode_show, r5c_journal_mode_store);

/*
 * Try handle write operation in caching phase. This function should only
 * be called in write-back mode.
 *
 * If all outstanding writes can be handled in caching phase, returns 0
 * If writes requires write-out phase, call r5c_make_stripe_write_out()
 * and returns -EAGAIN
 */
int r5c_try_caching_write(struct r5conf *conf,
                          struct stripe_head *sh,
                          struct stripe_head_state *s,
                          int disks)
{
        struct r5l_log *log = conf->log;
        int i;
        struct r5dev *dev;
        int to_cache = 0;
        void **pslot;
        sector_t tree_index;
        int ret;
        uintptr_t refcount;

        BUG_ON(!r5c_is_writeback(log));

        if (!test_bit(STRIPE_R5C_CACHING, &sh->state)) {
                /*
                 * There are two different scenarios here:
                 *  1. The stripe has some data cached, and it is sent to
                 *     write-out phase for reclaim
                 *  2. The stripe is clean, and this is the first write
                 *
                 * For 1, return -EAGAIN, so we continue with
                 * handle_stripe_dirtying().
                 *
                 * For 2, set STRIPE_R5C_CACHING and continue with caching
                 * write.
                 */

                /* case 1: anything injournal or anything in written */
                if (s->injournal > 0 || s->written > 0)
                        return -EAGAIN;
                /* case 2 */
                set_bit(STRIPE_R5C_CACHING, &sh->state);
        }

        /*
         * When run in degraded mode, array is set to write-through mode.
         * This check helps drain pending write safely in the transition to
         * write-through mode.
         *
         * When a stripe is syncing, the write is also handled in write
         * through mode.
         */
        if (s->failed || test_bit(STRIPE_SYNCING, &sh->state)) {
                r5c_make_stripe_write_out(sh);
                return -EAGAIN;
        }

        for (i = disks; i--; ) {
                dev = &sh->dev[i];
                /* if non-overwrite, use writing-out phase */
                if (dev->towrite && !test_bit(R5_OVERWRITE, &dev->flags) &&
                    !test_bit(R5_InJournal, &dev->flags)) {
                        r5c_make_stripe_write_out(sh);
                        return -EAGAIN;
                }
        }

        /* if the stripe is not counted in big_stripe_tree, add it now */
        if (!test_bit(STRIPE_R5C_PARTIAL_STRIPE, &sh->state) &&
            !test_bit(STRIPE_R5C_FULL_STRIPE, &sh->state)) {
                tree_index = r5c_tree_index(conf, sh->sector);
                spin_lock(&log->tree_lock);
                pslot = radix_tree_lookup_slot(&log->big_stripe_tree,
                                               tree_index);
                if (pslot) {
                        refcount = (uintptr_t)radix_tree_deref_slot_protected(
                                pslot, &log->tree_lock) >>
                                R5C_RADIX_COUNT_SHIFT;
                        radix_tree_replace_slot(
                                &log->big_stripe_tree, pslot,
                                (void *)((refcount + 1) << R5C_RADIX_COUNT_SHIFT));
                } else {
                        /*
                         * this radix_tree_insert can fail safely, so no
                         * need to call radix_tree_preload()
                         */
                        ret = radix_tree_insert(
                                &log->big_stripe_tree, tree_index,
                                (void *)(1 << R5C_RADIX_COUNT_SHIFT));
                        if (ret) {
                                spin_unlock(&log->tree_lock);
                                r5c_make_stripe_write_out(sh);
                                return -EAGAIN;
                        }
                }
                spin_unlock(&log->tree_lock);

                /*
                 * set STRIPE_R5C_PARTIAL_STRIPE, this shows the stripe is
                 * counted in the radix tree
                 */
                set_bit(STRIPE_R5C_PARTIAL_STRIPE, &sh->state);
                atomic_inc(&conf->r5c_cached_partial_stripes);
        }

        for (i = disks; i--; ) {
                dev = &sh->dev[i];
                if (dev->towrite) {
                        set_bit(R5_Wantwrite, &dev->flags);
                        set_bit(R5_Wantdrain, &dev->flags);
                        set_bit(R5_LOCKED, &dev->flags);
                        to_cache++;
                }
        }

        if (to_cache) {
                set_bit(STRIPE_OP_BIODRAIN, &s->ops_request);
                /*
                 * set STRIPE_LOG_TRAPPED, which triggers r5c_cache_data()
                 * in ops_run_io(). STRIPE_LOG_TRAPPED will be cleared in
                 * r5c_handle_data_cached()
                 */
                set_bit(STRIPE_LOG_TRAPPED, &sh->state);
        }

        return 0;
}

/*
 * free extra pages (orig_page) we allocated for prexor
 */
void r5c_release_extra_page(struct stripe_head *sh)
{
        struct r5conf *conf = sh->raid_conf;
        int i;
        bool using_disk_info_extra_page;

        using_disk_info_extra_page =
                sh->dev[0].orig_page == conf->disks[0].extra_page;

        for (i = sh->disks; i--; )
                if (sh->dev[i].page != sh->dev[i].orig_page) {
                        struct page *p = sh->dev[i].orig_page;

                        sh->dev[i].orig_page = sh->dev[i].page;
                        clear_bit(R5_OrigPageUPTDODATE, &sh->dev[i].flags);

                        if (!using_disk_info_extra_page)
                                put_page(p);
                }

        if (using_disk_info_extra_page) {
                clear_bit(R5C_EXTRA_PAGE_IN_USE, &conf->cache_state);
                md_wakeup_thread(conf->mddev->thread);
        }
}

void r5c_use_extra_page(struct stripe_head *sh)
{
        struct r5conf *conf = sh->raid_conf;
        int i;
        struct r5dev *dev;

        for (i = sh->disks; i--; ) {
                dev = &sh->dev[i];
                if (dev->orig_page != dev->page)
                        put_page(dev->orig_page);
                dev->orig_page = conf->disks[i].extra_page;
        }
}

/*
 * clean up the stripe (clear R5_InJournal for dev[pd_idx] etc.) after the
 * stripe is committed to RAID disks.
 */
void r5c_finish_stripe_write_out(struct r5conf *conf,
                                 struct stripe_head *sh,
                                 struct stripe_head_state *s)
{
        struct r5l_log *log = conf->log;
        int i;
        int do_wakeup = 0;
        sector_t tree_index;
        void **pslot;
        uintptr_t refcount;

        if (!log || !test_bit(R5_InJournal, &sh->dev[sh->pd_idx].flags))
                return;

        WARN_ON(test_bit(STRIPE_R5C_CACHING, &sh->state));
        clear_bit(R5_InJournal, &sh->dev[sh->pd_idx].flags);

        if (log->r5c_journal_mode == R5C_JOURNAL_MODE_WRITE_THROUGH)
                return;

        for (i = sh->disks; i--; ) {
                clear_bit(R5_InJournal, &sh->dev[i].flags);
                if (test_and_clear_bit(R5_Overlap, &sh->dev[i].flags))
                        do_wakeup = 1;
        }

        /*
         * analyse_stripe() runs before r5c_finish_stripe_write_out(),
         * We updated R5_InJournal, so we also update s->injournal.
         */
        s->injournal = 0;

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

        if (do_wakeup)
                wake_up(&conf->wait_for_overlap);

        spin_lock_irq(&log->stripe_in_journal_lock);
        list_del_init(&sh->r5c);
        spin_unlock_irq(&log->stripe_in_journal_lock);
        sh->log_start = MaxSector;

        atomic_dec(&log->stripe_in_journal_count);
        r5c_update_log_state(log);

        /* stop counting this stripe in big_stripe_tree */
        if (test_bit(STRIPE_R5C_PARTIAL_STRIPE, &sh->state) ||
            test_bit(STRIPE_R5C_FULL_STRIPE, &sh->state)) {
                tree_index = r5c_tree_index(conf, sh->sector);
                spin_lock(&log->tree_lock);
                pslot = radix_tree_lookup_slot(&log->big_stripe_tree,
                                               tree_index);
                BUG_ON(pslot == NULL);
                refcount = (uintptr_t)radix_tree_deref_slot_protected(
                        pslot, &log->tree_lock) >>
                        R5C_RADIX_COUNT_SHIFT;
                if (refcount == 1)
                        radix_tree_delete(&log->big_stripe_tree, tree_index);
                else
                        radix_tree_replace_slot(
                                &log->big_stripe_tree, pslot,
                                (void *)((refcount - 1) << R5C_RADIX_COUNT_SHIFT));
                spin_unlock(&log->tree_lock);
        }

        if (test_and_clear_bit(STRIPE_R5C_PARTIAL_STRIPE, &sh->state)) {
                BUG_ON(atomic_read(&conf->r5c_cached_partial_stripes) == 0);
                atomic_dec(&conf->r5c_flushing_partial_stripes);
                atomic_dec(&conf->r5c_cached_partial_stripes);
        }

        if (test_and_clear_bit(STRIPE_R5C_FULL_STRIPE, &sh->state)) {
                BUG_ON(atomic_read(&conf->r5c_cached_full_stripes) == 0);
                atomic_dec(&conf->r5c_flushing_full_stripes);
                atomic_dec(&conf->r5c_cached_full_stripes);
        }

        r5l_append_flush_payload(log, sh->sector);
        /* stripe is flused to raid disks, we can do resync now */
        if (test_bit(STRIPE_SYNC_REQUESTED, &sh->state))
                set_bit(STRIPE_HANDLE, &sh->state);
}

int r5c_cache_data(struct r5l_log *log, struct stripe_head *sh)
{
        struct r5conf *conf = sh->raid_conf;
        int pages = 0;
        int reserve;
        int i;
        int ret = 0;

        BUG_ON(!log);

        for (i = 0; i < sh->disks; i++) {
                void *addr;

                if (!test_bit(R5_Wantwrite, &sh->dev[i].flags))
                        continue;
                addr = kmap_atomic(sh->dev[i].page);
                sh->dev[i].log_checksum = crc32c_le(log->uuid_checksum,
                                                    addr, PAGE_SIZE);
                kunmap_atomic(addr);
                pages++;
        }
        WARN_ON(pages == 0);

        /*
         * The stripe must enter state machine again to call endio, so
         * don't delay.
         */
        clear_bit(STRIPE_DELAYED, &sh->state);
        atomic_inc(&sh->count);

        mutex_lock(&log->io_mutex);
        /* meta + data */
        reserve = (1 + pages) << (PAGE_SHIFT - 9);

        if (test_bit(R5C_LOG_CRITICAL, &conf->cache_state) &&
            sh->log_start == MaxSector)
                r5l_add_no_space_stripe(log, sh);
        else if (!r5l_has_free_space(log, reserve)) {
                if (sh->log_start == log->last_checkpoint)
                        BUG();
                else
                        r5l_add_no_space_stripe(log, sh);
        } else {
                ret = r5l_log_stripe(log, sh, pages, 0);
                if (ret) {
                        spin_lock_irq(&log->io_list_lock);
                        list_add_tail(&sh->log_list, &log->no_mem_stripes);
                        spin_unlock_irq(&log->io_list_lock);
                }
        }

        mutex_unlock(&log->io_mutex);
        return 0;
}

/* check whether this big stripe is in write back cache. */
bool r5c_big_stripe_cached(struct r5conf *conf, sector_t sect)
{
        struct r5l_log *log = conf->log;
        sector_t tree_index;
        void *slot;

        if (!log)
                return false;

        WARN_ON_ONCE(!rcu_read_lock_held());
        tree_index = r5c_tree_index(conf, sect);
        slot = radix_tree_lookup(&log->big_stripe_tree, tree_index);
        return slot != NULL;
}

static int r5l_load_log(struct r5l_log *log)
{
        struct md_rdev *rdev = log->rdev;
        struct page *page;
        struct r5l_meta_block *mb;
        sector_t cp = log->rdev->journal_tail;
        u32 stored_crc, expected_crc;
        bool create_super = false;
        int ret = 0;

        /* Make sure it's valid */
        if (cp >= rdev->sectors || round_down(cp, BLOCK_SECTORS) != cp)
                cp = 0;
        page = alloc_page(GFP_KERNEL);
        if (!page)
                return -ENOMEM;

        if (!sync_page_io(rdev, cp, PAGE_SIZE, page, REQ_OP_READ, 0, false)) {
                ret = -EIO;
                goto ioerr;
        }
        mb = page_address(page);

        if (le32_to_cpu(mb->magic) != R5LOG_MAGIC ||
            mb->version != R5LOG_VERSION) {
                create_super = true;
                goto create;
        }
        stored_crc = le32_to_cpu(mb->checksum);
        mb->checksum = 0;
        expected_crc = crc32c_le(log->uuid_checksum, mb, PAGE_SIZE);
        if (stored_crc != expected_crc) {
                create_super = true;
                goto create;
        }
        if (le64_to_cpu(mb->position) != cp) {
                create_super = true;
                goto create;
        }
create:
        if (create_super) {
                log->last_cp_seq = prandom_u32();
                cp = 0;
                r5l_log_write_empty_meta_block(log, cp, log->last_cp_seq);
                /*
                 * Make sure super points to correct address. Log might have
                 * data very soon. If super hasn't correct log tail address,
                 * recovery can't find the log
                 */
                r5l_write_super(log, cp);
        } else
                log->last_cp_seq = le64_to_cpu(mb->seq);

        log->device_size = round_down(rdev->sectors, BLOCK_SECTORS);
        log->max_free_space = log->device_size >> RECLAIM_MAX_FREE_SPACE_SHIFT;
        if (log->max_free_space > RECLAIM_MAX_FREE_SPACE)
                log->max_free_space = RECLAIM_MAX_FREE_SPACE;
        log->last_checkpoint = cp;

        __free_page(page);

        if (create_super) {
                log->log_start = r5l_ring_add(log, cp, BLOCK_SECTORS);
                log->seq = log->last_cp_seq + 1;
                log->next_checkpoint = cp;
        } else
                ret = r5l_recovery_log(log);

        r5c_update_log_state(log);
        return ret;
ioerr:
        __free_page(page);
        return ret;
}

void r5c_update_on_rdev_error(struct mddev *mddev, struct md_rdev *rdev)
{
        struct r5conf *conf = mddev->private;
        struct r5l_log *log = conf->log;

        if (!log)
                return;

        if ((raid5_calc_degraded(conf) > 0 ||
             test_bit(Journal, &rdev->flags)) &&
            conf->log->r5c_journal_mode == R5C_JOURNAL_MODE_WRITE_BACK)
                schedule_work(&log->disable_writeback_work);
}

int r5l_init_log(struct r5conf *conf, struct md_rdev *rdev)
{
        struct request_queue *q = bdev_get_queue(rdev->bdev);
        struct r5l_log *log;
        char b[BDEVNAME_SIZE];

        pr_debug("md/raid:%s: using device %s as journal\n",
                 mdname(conf->mddev), bdevname(rdev->bdev, b));

        if (PAGE_SIZE != 4096)
                return -EINVAL;

        /*
         * The PAGE_SIZE must be big enough to hold 1 r5l_meta_block and
         * raid_disks r5l_payload_data_parity.
         *
         * Write journal and cache does not work for very big array
         * (raid_disks > 203)
         */
        if (sizeof(struct r5l_meta_block) +
            ((sizeof(struct r5l_payload_data_parity) + sizeof(__le32)) *
             conf->raid_disks) > PAGE_SIZE) {
                pr_err("md/raid:%s: write journal/cache doesn't work for array with %d disks\n",
                       mdname(conf->mddev), conf->raid_disks);
                return -EINVAL;
        }

        log = kzalloc(sizeof(*log), GFP_KERNEL);
        if (!log)
                return -ENOMEM;
        log->rdev = rdev;

        log->need_cache_flush = test_bit(QUEUE_FLAG_WC, &q->queue_flags) != 0;

        log->uuid_checksum = crc32c_le(~0, rdev->mddev->uuid,
                                       sizeof(rdev->mddev->uuid));

        mutex_init(&log->io_mutex);

        spin_lock_init(&log->io_list_lock);
        INIT_LIST_HEAD(&log->running_ios);
        INIT_LIST_HEAD(&log->io_end_ios);
        INIT_LIST_HEAD(&log->flushing_ios);
        INIT_LIST_HEAD(&log->finished_ios);
        bio_init(&log->flush_bio, NULL, 0);

        log->io_kc = KMEM_CACHE(r5l_io_unit, 0);
        if (!log->io_kc)
                goto io_kc;

        log->io_pool = mempool_create_slab_pool(R5L_POOL_SIZE, log->io_kc);
        if (!log->io_pool)
                goto io_pool;

        log->bs = bioset_create(R5L_POOL_SIZE, 0, BIOSET_NEED_BVECS);
        if (!log->bs)
                goto io_bs;

        log->meta_pool = mempool_create_page_pool(R5L_POOL_SIZE, 0);
        if (!log->meta_pool)
                goto out_mempool;

        spin_lock_init(&log->tree_lock);
        INIT_RADIX_TREE(&log->big_stripe_tree, GFP_NOWAIT | __GFP_NOWARN);

        log->reclaim_thread = md_register_thread(r5l_reclaim_thread,
                                                 log->rdev->mddev, "reclaim");
        if (!log->reclaim_thread)
                goto reclaim_thread;
        log->reclaim_thread->timeout = R5C_RECLAIM_WAKEUP_INTERVAL;

        init_waitqueue_head(&log->iounit_wait);

        INIT_LIST_HEAD(&log->no_mem_stripes);

        INIT_LIST_HEAD(&log->no_space_stripes);
        spin_lock_init(&log->no_space_stripes_lock);

        INIT_WORK(&log->deferred_io_work, r5l_submit_io_async);
        INIT_WORK(&log->disable_writeback_work, r5c_disable_writeback_async);

        log->r5c_journal_mode = R5C_JOURNAL_MODE_WRITE_THROUGH;
        INIT_LIST_HEAD(&log->stripe_in_journal_list);
        spin_lock_init(&log->stripe_in_journal_lock);
        atomic_set(&log->stripe_in_journal_count, 0);

        rcu_assign_pointer(conf->log, log);

        if (r5l_load_log(log))
                goto error;

        set_bit(MD_HAS_JOURNAL, &conf->mddev->flags);
        return 0;

error:
        rcu_assign_pointer(conf->log, NULL);
        md_unregister_thread(&log->reclaim_thread);
reclaim_thread:
        mempool_destroy(log->meta_pool);
out_mempool:
        bioset_free(log->bs);
io_bs:
        mempool_destroy(log->io_pool);
io_pool:
        kmem_cache_destroy(log->io_kc);
io_kc:
        kfree(log);
        return -EINVAL;
}

void r5l_exit_log(struct r5conf *conf)
{
        struct r5l_log *log = conf->log;

        conf->log = NULL;
        synchronize_rcu();

        flush_work(&log->disable_writeback_work);
        md_unregister_thread(&log->reclaim_thread);
        mempool_destroy(log->meta_pool);
        bioset_free(log->bs);
        mempool_destroy(log->io_pool);
        kmem_cache_destroy(log->io_kc);
        kfree(log);
}