xref: /linux/drivers/md/raid5-cache.c (revision 2ded370373a400c20cf0c6e941e724e61582a867)

/*
 * Copyright (C) 2015 Shaohua Li <shli@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 "md.h"
#include "raid5.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)

/*
 * reclaim runs every 1/4 disk size or 10G reclaimable space. This can prevent
 * recovery scans a very long log
 */
#define RECLAIM_MAX_FREE_SPACE (10 * 1024 * 1024 * 2) /* sector */
#define RECLAIM_MAX_FREE_SPACE_SHIFT (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

/*
 * r5c journal modes of the array: write-back or write-through.
 * write-through mode has identical behavior as existing log only
 * implementation.
 */
enum r5c_journal_mode {
	R5C_JOURNAL_MODE_WRITE_THROUGH = 0,
	R5C_JOURNAL_MODE_WRITE_BACK = 1,
};

/*
 * raid5 cache state machine
 *
 * With rhe 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;
	u64 next_cp_seq;

	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;
};

/*
 * 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;
};

/* 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;
}

/*
 * Put the stripe into writing-out phase by clearing STRIPE_R5C_CACHING.
 * This function should only be called in write-back mode.
 */
static 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);
}

/*
 * 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
		BUG(); /* write-back logic in next patch */
}

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_log_endio(struct bio *bio)
{
	struct r5l_io_unit *io = bio->bi_private;
	struct r5l_log *log = io->log;
	unsigned long flags;

	if (bio->bi_error)
		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)
		r5l_move_to_end_ios(log);
	else
		r5l_log_run_stripes(log);
	spin_unlock_irqrestore(&log->io_list_lock, flags);

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

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

	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);

	log->current_io = NULL;
	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);

	submit_bio(io->current_bio);
}

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);

	/*
	 * 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);
	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) {
		struct bio *prev = io->current_bio;

		io->current_bio = r5l_bio_alloc(log);
		bio_chain(io->current_bio, prev);

		submit_bio(prev);
	}

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

	r5_reserve_log_entry(log, io);
}

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;

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

	return 0;
}

static void r5l_wake_reclaim(struct r5l_log *log, sector_t space);
/*
 * 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)
{
	int write_disks = 0;
	int data_pages, parity_pages;
	int reserve;
	int i;
	int ret = 0;

	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))
			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 (!r5l_has_free_space(log, reserve)) {
		spin_lock(&log->no_space_stripes_lock);
		list_add_tail(&sh->log_list, &log->no_space_stripes);
		spin_unlock(&log->no_space_stripes_lock);

		r5l_wake_reclaim(log, reserve);
	} 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);
	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;
	/*
	 * 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;
	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);
}

static sector_t r5l_reclaimable_space(struct r5l_log *log)
{
	return r5l_ring_distance(log, log->last_checkpoint,
				 log->next_checkpoint);
}

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;
		log->next_cp_seq = io->seq;

		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;
	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)
		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_error)
		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;
	bio_set_op_attrs(&log->flush_bio, REQ_OP_WRITE, WRITE_FLUSH);
	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->flags, 0,
		BIT(MD_CHANGE_DEVS) | BIT(MD_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);
	}
}


static void r5l_do_reclaim(struct r5l_log *log)
{
	sector_t reclaim_target = xchg(&log->reclaim_target, 0);
	sector_t reclaimable;
	sector_t next_checkpoint;
	u64 next_cp_seq;

	spin_lock_irq(&log->io_list_lock);
	/*
	 * 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 = log->next_checkpoint;
	next_cp_seq = log->next_cp_seq;
	spin_unlock_irq(&log->io_list_lock);

	BUG_ON(reclaimable < 0);
	if (reclaimable == 0)
		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;
	log->last_cp_seq = next_cp_seq;
	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;
	r5l_do_reclaim(log);
}

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

	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) {
		/*
		 * This is a special case for hotadd. In suspend, the array has
		 * no journal. In resume, journal is initialized as well as the
		 * reclaim thread.
		 */
		if (log->reclaim_thread)
			return;
		log->reclaim_thread = md_register_thread(r5l_reclaim_thread,
					log->rdev->mddev, "reclaim");
	} else if (state == 1) {
		/* make sure r5l_write_super_and_discard_space exits */
		mddev = log->rdev->mddev;
		wake_up(&mddev->sb_wait);
		r5l_wake_reclaim(log, -1L);
		md_unregister_thread(&log->reclaim_thread);
		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;
}

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 */
};

static int r5l_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;

	if (!sync_page_io(log->rdev, ctx->pos, PAGE_SIZE, page, REQ_OP_READ, 0,
			  false))
		return -EIO;

	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 int r5l_recovery_flush_one_stripe(struct r5l_log *log,
					 struct r5l_recovery_ctx *ctx,
					 sector_t stripe_sect,
					 int *offset)
{
	struct r5conf *conf = log->rdev->mddev->private;
	struct stripe_head *sh;
	struct r5l_payload_data_parity *payload;
	int disk_index;

	sh = raid5_get_active_stripe(conf, stripe_sect, 0, 0, 0);
	while (1) {
		sector_t log_offset = r5l_ring_add(log, ctx->pos,
				ctx->meta_total_blocks);
		payload = page_address(ctx->meta_page) + *offset;

		if (le16_to_cpu(payload->header.type) == R5LOG_PAYLOAD_DATA) {
			raid5_compute_sector(conf,
					     le64_to_cpu(payload->location), 0,
					     &disk_index, sh);

			sync_page_io(log->rdev, log_offset, PAGE_SIZE,
				     sh->dev[disk_index].page, REQ_OP_READ, 0,
				     false);
			sh->dev[disk_index].log_checksum =
				le32_to_cpu(payload->checksum[0]);
			set_bit(R5_Wantwrite, &sh->dev[disk_index].flags);
		} else {
			disk_index = sh->pd_idx;
			sync_page_io(log->rdev, log_offset, PAGE_SIZE,
				     sh->dev[disk_index].page, REQ_OP_READ, 0,
				     false);
			sh->dev[disk_index].log_checksum =
				le32_to_cpu(payload->checksum[0]);
			set_bit(R5_Wantwrite, &sh->dev[disk_index].flags);

			if (sh->qd_idx >= 0) {
				disk_index = sh->qd_idx;
				sync_page_io(log->rdev,
					     r5l_ring_add(log, log_offset, BLOCK_SECTORS),
					     PAGE_SIZE, sh->dev[disk_index].page,
					     REQ_OP_READ, 0, false);
				sh->dev[disk_index].log_checksum =
					le32_to_cpu(payload->checksum[1]);
				set_bit(R5_Wantwrite,
					&sh->dev[disk_index].flags);
			}
		}

		ctx->meta_total_blocks += le32_to_cpu(payload->size);
		*offset += sizeof(struct r5l_payload_data_parity) +
			sizeof(__le32) *
			(le32_to_cpu(payload->size) >> (PAGE_SHIFT - 9));
		if (le16_to_cpu(payload->header.type) == R5LOG_PAYLOAD_PARITY)
			break;
	}

	for (disk_index = 0; disk_index < sh->disks; disk_index++) {
		void *addr;
		u32 checksum;

		if (!test_bit(R5_Wantwrite, &sh->dev[disk_index].flags))
			continue;
		addr = kmap_atomic(sh->dev[disk_index].page);
		checksum = crc32c_le(log->uuid_checksum, addr, PAGE_SIZE);
		kunmap_atomic(addr);
		if (checksum != sh->dev[disk_index].log_checksum)
			goto error;
	}

	for (disk_index = 0; disk_index < sh->disks; disk_index++) {
		struct md_rdev *rdev, *rrdev;

		if (!test_and_clear_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, stripe_sect, 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, stripe_sect, PAGE_SIZE,
				     sh->dev[disk_index].page, REQ_OP_WRITE, 0,
				     false);
			rdev_dec_pending(rrdev, rrdev->mddev);
			rcu_read_lock();
		}
		rcu_read_unlock();
	}
	raid5_release_stripe(sh);
	return 0;

error:
	for (disk_index = 0; disk_index < sh->disks; disk_index++)
		sh->dev[disk_index].flags = 0;
	raid5_release_stripe(sh);
	return -EINVAL;
}

static int r5l_recovery_flush_one_meta(struct r5l_log *log,
				       struct r5l_recovery_ctx *ctx)
{
	struct r5conf *conf = log->rdev->mddev->private;
	struct r5l_payload_data_parity *payload;
	struct r5l_meta_block *mb;
	int offset;
	sector_t stripe_sector;

	mb = page_address(ctx->meta_page);
	offset = sizeof(struct r5l_meta_block);

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

		payload = (void *)mb + offset;
		stripe_sector = raid5_compute_sector(conf,
						     le64_to_cpu(payload->location), 0, &dd, NULL);
		if (r5l_recovery_flush_one_stripe(log, ctx, stripe_sector,
						  &offset))
			return -EINVAL;
	}
	return 0;
}

/* copy data/parity from log to raid disks */
static void r5l_recovery_flush_log(struct r5l_log *log,
				   struct r5l_recovery_ctx *ctx)
{
	while (1) {
		if (r5l_read_meta_block(log, ctx))
			return;
		if (r5l_recovery_flush_one_meta(log, ctx))
			return;
		ctx->seq++;
		ctx->pos = r5l_ring_add(log, ctx->pos, ctx->meta_total_blocks);
	}
}

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;
	u32 crc;

	page = alloc_page(GFP_KERNEL | __GFP_ZERO);
	if (!page)
		return -ENOMEM;
	mb = page_address(page);
	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);
	crc = crc32c_le(log->uuid_checksum, mb, PAGE_SIZE);
	mb->checksum = cpu_to_le32(crc);

	if (!sync_page_io(log->rdev, pos, PAGE_SIZE, page, REQ_OP_WRITE,
			  WRITE_FUA, false)) {
		__free_page(page);
		return -EIO;
	}
	__free_page(page);
	return 0;
}

static int r5l_recovery_log(struct r5l_log *log)
{
	struct r5l_recovery_ctx ctx;

	ctx.pos = log->last_checkpoint;
	ctx.seq = log->last_cp_seq;
	ctx.meta_page = alloc_page(GFP_KERNEL);
	if (!ctx.meta_page)
		return -ENOMEM;

	r5l_recovery_flush_log(log, &ctx);
	__free_page(ctx.meta_page);

	/*
	 * 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 + 10 and let superblock points to meta2. The same recovery will
	 * not think meta 3 is a valid meta, because its seq doesn't match
	 */
	if (ctx.seq > log->last_cp_seq) {
		int ret;

		ret = r5l_log_write_empty_meta_block(log, ctx.pos, ctx.seq + 10);
		if (ret)
			return ret;
		log->seq = ctx.seq + 11;
		log->log_start = r5l_ring_add(log, ctx.pos, BLOCK_SECTORS);
		r5l_write_super(log, ctx.pos);
		log->last_checkpoint = ctx.pos;
		log->next_checkpoint = ctx.pos;
	} else {
		log->log_start = ctx.pos;
		log->seq = ctx.seq;
	}
	return 0;
}

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_CHANGE_DEVS, &mddev->flags);
}

/*
 * 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;

	BUG_ON(!r5c_is_writeback(log));

	/* more write-back logic in next patches */
	r5c_make_stripe_write_out(sh);
	return -EAGAIN;
}

/*
 * 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)
{
	if (!conf->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 (conf->log->r5c_journal_mode == R5C_JOURNAL_MODE_WRITE_THROUGH)
		return;
	BUG();  /* write-back logic in following patches */
}


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;

	/* 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;
	log->next_checkpoint = cp;

	__free_page(page);

	return r5l_recovery_log(log);
ioerr:
	__free_page(page);
	return ret;
}

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

	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);

	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);
	if (!log->bs)
		goto io_bs;

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

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

	log->r5c_journal_mode = R5C_JOURNAL_MODE_WRITE_THROUGH;

	if (r5l_load_log(log))
		goto error;

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

error:
	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 r5l_log *log)
{
	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);
}