OpenCloudOS-Kernel/drivers/md/raid5-ppl.c

/*
 * Partial Parity Log for closing the RAID5 write hole
 * Copyright (c) 2017, Intel Corporation.
 *
 * 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/blkdev.h>
#include <linux/slab.h>
#include <linux/crc32c.h>
#include <linux/flex_array.h>
#include <linux/async_tx.h>
#include <linux/raid/md_p.h>
#include "md.h"
#include "raid5.h"

/*
 * PPL consists of a 4KB header (struct ppl_header) and at least 128KB for
 * partial parity data. The header contains an array of entries
 * (struct ppl_header_entry) which describe the logged write requests.
 * Partial parity for the entries comes after the header, written in the same
 * sequence as the entries:
 *
 * Header
 *   entry0
 *   ...
 *   entryN
 * PP data
 *   PP for entry0
 *   ...
 *   PP for entryN
 *
 * An entry describes one or more consecutive stripe_heads, up to a full
 * stripe. The modifed raid data chunks form an m-by-n matrix, where m is the
 * number of stripe_heads in the entry and n is the number of modified data
 * disks. Every stripe_head in the entry must write to the same data disks.
 * An example of a valid case described by a single entry (writes to the first
 * stripe of a 4 disk array, 16k chunk size):
 *
 * sh->sector   dd0   dd1   dd2    ppl
 *            +-----+-----+-----+
 * 0          | --- | --- | --- | +----+
 * 8          | -W- | -W- | --- | | pp |   data_sector = 8
 * 16         | -W- | -W- | --- | | pp |   data_size = 3 * 2 * 4k
 * 24         | -W- | -W- | --- | | pp |   pp_size = 3 * 4k
 *            +-----+-----+-----+ +----+
 *
 * data_sector is the first raid sector of the modified data, data_size is the
 * total size of modified data and pp_size is the size of partial parity for
 * this entry. Entries for full stripe writes contain no partial parity
 * (pp_size = 0), they only mark the stripes for which parity should be
 * recalculated after an unclean shutdown. Every entry holds a checksum of its
 * partial parity, the header also has a checksum of the header itself.
 *
 * A write request is always logged to the PPL instance stored on the parity
 * disk of the corresponding stripe. For each member disk there is one ppl_log
 * used to handle logging for this disk, independently from others. They are
 * grouped in child_logs array in struct ppl_conf, which is assigned to
 * r5conf->log_private.
 *
 * ppl_io_unit represents a full PPL write, header_page contains the ppl_header.
 * PPL entries for logged stripes are added in ppl_log_stripe(). A stripe_head
 * can be appended to the last entry if it meets the conditions for a valid
 * entry described above, otherwise a new entry is added. Checksums of entries
 * are calculated incrementally as stripes containing partial parity are being
 * added. ppl_submit_iounit() calculates the checksum of the header and submits
 * a bio containing the header page and partial parity pages (sh->ppl_page) for
 * all stripes of the io_unit. When the PPL write completes, the stripes
 * associated with the io_unit are released and raid5d starts writing their data
 * and parity. When all stripes are written, the io_unit is freed and the next
 * can be submitted.
 *
 * An io_unit is used to gather stripes until it is submitted or becomes full
 * (if the maximum number of entries or size of PPL is reached). Another io_unit
 * can't be submitted until the previous has completed (PPL and stripe
 * data+parity is written). The log->io_list tracks all io_units of a log
 * (for a single member disk). New io_units are added to the end of the list
 * and the first io_unit is submitted, if it is not submitted already.
 * The current io_unit accepting new stripes is always at the end of the list.
 */

struct ppl_conf {
	struct mddev *mddev;

	/* array of child logs, one for each raid disk */
	struct ppl_log *child_logs;
	int count;

	int block_size;		/* the logical block size used for data_sector
				 * in ppl_header_entry */
	u32 signature;		/* raid array identifier */
	atomic64_t seq;		/* current log write sequence number */

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

struct ppl_log {
	struct ppl_conf *ppl_conf;	/* shared between all log instances */

	struct md_rdev *rdev;		/* array member disk associated with
					 * this log instance */
	struct mutex io_mutex;
	struct ppl_io_unit *current_io;	/* current io_unit accepting new data
					 * always at the end of io_list */
	spinlock_t io_list_lock;
	struct list_head io_list;	/* all io_units of this log */
	struct list_head no_mem_stripes;/* stripes to retry if failed to
					 * allocate io_unit */
};

#define PPL_IO_INLINE_BVECS 32

struct ppl_io_unit {
	struct ppl_log *log;

	struct page *header_page;	/* for ppl_header */

	unsigned int entries_count;	/* number of entries in ppl_header */
	unsigned int pp_size;		/* total size current of partial parity */

	u64 seq;			/* sequence number of this log write */
	struct list_head log_sibling;	/* log->io_list */

	struct list_head stripe_list;	/* stripes added to the io_unit */
	atomic_t pending_stripes;	/* how many stripes not written to raid */

	bool submitted;			/* true if write to log started */

	/* inline bio and its biovec for submitting the iounit */
	struct bio bio;
	struct bio_vec biovec[PPL_IO_INLINE_BVECS];
};

struct dma_async_tx_descriptor *
ops_run_partial_parity(struct stripe_head *sh, struct raid5_percpu *percpu,
		       struct dma_async_tx_descriptor *tx)
{
	int disks = sh->disks;
	struct page **xor_srcs = flex_array_get(percpu->scribble, 0);
	int count = 0, pd_idx = sh->pd_idx, i;
	struct async_submit_ctl submit;

	pr_debug("%s: stripe %llu\n", __func__, (unsigned long long)sh->sector);

	/*
	 * Partial parity is the XOR of stripe data chunks that are not changed
	 * during the write request. Depending on available data
	 * (read-modify-write vs. reconstruct-write case) we calculate it
	 * differently.
	 */
	if (sh->reconstruct_state == reconstruct_state_prexor_drain_run) {
		/* rmw: xor old data and parity from updated disks */
		for (i = disks; i--;) {
			struct r5dev *dev = &sh->dev[i];
			if (test_bit(R5_Wantdrain, &dev->flags) || i == pd_idx)
				xor_srcs[count++] = dev->page;
		}
	} else if (sh->reconstruct_state == reconstruct_state_drain_run) {
		/* rcw: xor data from all not updated disks */
		for (i = disks; i--;) {
			struct r5dev *dev = &sh->dev[i];
			if (test_bit(R5_UPTODATE, &dev->flags))
				xor_srcs[count++] = dev->page;
		}
	} else {
		return tx;
	}

	init_async_submit(&submit, ASYNC_TX_FENCE|ASYNC_TX_XOR_ZERO_DST, tx,
			  NULL, sh, flex_array_get(percpu->scribble, 0)
			  + sizeof(struct page *) * (sh->disks + 2));

	if (count == 1)
		tx = async_memcpy(sh->ppl_page, xor_srcs[0], 0, 0, PAGE_SIZE,
				  &submit);
	else
		tx = async_xor(sh->ppl_page, xor_srcs, 0, count, PAGE_SIZE,
			       &submit);

	return tx;
}

static struct ppl_io_unit *ppl_new_iounit(struct ppl_log *log,
					  struct stripe_head *sh)
{
	struct ppl_conf *ppl_conf = log->ppl_conf;
	struct ppl_io_unit *io;
	struct ppl_header *pplhdr;

	io = mempool_alloc(ppl_conf->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);
	atomic_set(&io->pending_stripes, 0);
	bio_init(&io->bio, io->biovec, PPL_IO_INLINE_BVECS);

	io->header_page = mempool_alloc(ppl_conf->meta_pool, GFP_NOIO);
	pplhdr = page_address(io->header_page);
	clear_page(pplhdr);
	memset(pplhdr->reserved, 0xff, PPL_HDR_RESERVED);
	pplhdr->signature = cpu_to_le32(ppl_conf->signature);

	io->seq = atomic64_add_return(1, &ppl_conf->seq);
	pplhdr->generation = cpu_to_le64(io->seq);

	return io;
}

static int ppl_log_stripe(struct ppl_log *log, struct stripe_head *sh)
{
	struct ppl_io_unit *io = log->current_io;
	struct ppl_header_entry *e = NULL;
	struct ppl_header *pplhdr;
	int i;
	sector_t data_sector = 0;
	int data_disks = 0;
	unsigned int entry_space = (log->rdev->ppl.size << 9) - PPL_HEADER_SIZE;
	struct r5conf *conf = sh->raid_conf;

	pr_debug("%s: stripe: %llu\n", __func__, (unsigned long long)sh->sector);

	/* check if current io_unit is full */
	if (io && (io->pp_size == entry_space ||
		   io->entries_count == PPL_HDR_MAX_ENTRIES)) {
		pr_debug("%s: add io_unit blocked by seq: %llu\n",
			 __func__, io->seq);
		io = NULL;
	}

	/* add a new unit if there is none or the current is full */
	if (!io) {
		io = ppl_new_iounit(log, sh);
		if (!io)
			return -ENOMEM;
		spin_lock_irq(&log->io_list_lock);
		list_add_tail(&io->log_sibling, &log->io_list);
		spin_unlock_irq(&log->io_list_lock);

		log->current_io = io;
	}

	for (i = 0; i < sh->disks; i++) {
		struct r5dev *dev = &sh->dev[i];

		if (i != sh->pd_idx && test_bit(R5_Wantwrite, &dev->flags)) {
			if (!data_disks || dev->sector < data_sector)
				data_sector = dev->sector;
			data_disks++;
		}
	}
	BUG_ON(!data_disks);

	pr_debug("%s: seq: %llu data_sector: %llu data_disks: %d\n", __func__,
		 io->seq, (unsigned long long)data_sector, data_disks);

	pplhdr = page_address(io->header_page);

	if (io->entries_count > 0) {
		struct ppl_header_entry *last =
				&pplhdr->entries[io->entries_count - 1];
		struct stripe_head *sh_last = list_last_entry(
				&io->stripe_list, struct stripe_head, log_list);
		u64 data_sector_last = le64_to_cpu(last->data_sector);
		u32 data_size_last = le32_to_cpu(last->data_size);

		/*
		 * Check if we can append the stripe to the last entry. It must
		 * be just after the last logged stripe and write to the same
		 * disks. Use bit shift and logarithm to avoid 64-bit division.
		 */
		if ((sh->sector == sh_last->sector + STRIPE_SECTORS) &&
		    (data_sector >> ilog2(conf->chunk_sectors) ==
		     data_sector_last >> ilog2(conf->chunk_sectors)) &&
		    ((data_sector - data_sector_last) * data_disks ==
		     data_size_last >> 9))
			e = last;
	}

	if (!e) {
		e = &pplhdr->entries[io->entries_count++];
		e->data_sector = cpu_to_le64(data_sector);
		e->parity_disk = cpu_to_le32(sh->pd_idx);
		e->checksum = cpu_to_le32(~0);
	}

	le32_add_cpu(&e->data_size, data_disks << PAGE_SHIFT);

	/* don't write any PP if full stripe write */
	if (!test_bit(STRIPE_FULL_WRITE, &sh->state)) {
		le32_add_cpu(&e->pp_size, PAGE_SIZE);
		io->pp_size += PAGE_SIZE;
		e->checksum = cpu_to_le32(crc32c_le(le32_to_cpu(e->checksum),
						    page_address(sh->ppl_page),
						    PAGE_SIZE));
	}

	list_add_tail(&sh->log_list, &io->stripe_list);
	atomic_inc(&io->pending_stripes);
	sh->ppl_io = io;

	return 0;
}

int ppl_write_stripe(struct r5conf *conf, struct stripe_head *sh)
{
	struct ppl_conf *ppl_conf = conf->log_private;
	struct ppl_io_unit *io = sh->ppl_io;
	struct ppl_log *log;

	if (io || test_bit(STRIPE_SYNCING, &sh->state) ||
	    !test_bit(R5_Wantwrite, &sh->dev[sh->pd_idx].flags) ||
	    !test_bit(R5_Insync, &sh->dev[sh->pd_idx].flags)) {
		clear_bit(STRIPE_LOG_TRAPPED, &sh->state);
		return -EAGAIN;
	}

	log = &ppl_conf->child_logs[sh->pd_idx];

	mutex_lock(&log->io_mutex);

	if (!log->rdev || test_bit(Faulty, &log->rdev->flags)) {
		mutex_unlock(&log->io_mutex);
		return -EAGAIN;
	}

	set_bit(STRIPE_LOG_TRAPPED, &sh->state);
	clear_bit(STRIPE_DELAYED, &sh->state);
	atomic_inc(&sh->count);

	if (ppl_log_stripe(log, sh)) {
		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;
}

static void ppl_log_endio(struct bio *bio)
{
	struct ppl_io_unit *io = bio->bi_private;
	struct ppl_log *log = io->log;
	struct ppl_conf *ppl_conf = log->ppl_conf;
	struct stripe_head *sh, *next;

	pr_debug("%s: seq: %llu\n", __func__, io->seq);

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

	mempool_free(io->header_page, ppl_conf->meta_pool);

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

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

static void ppl_submit_iounit_bio(struct ppl_io_unit *io, struct bio *bio)
{
	char b[BDEVNAME_SIZE];

	pr_debug("%s: seq: %llu size: %u sector: %llu dev: %s\n",
		 __func__, io->seq, bio->bi_iter.bi_size,
		 (unsigned long long)bio->bi_iter.bi_sector,
		 bdevname(bio->bi_bdev, b));

	submit_bio(bio);
}

static void ppl_submit_iounit(struct ppl_io_unit *io)
{
	struct ppl_log *log = io->log;
	struct ppl_conf *ppl_conf = log->ppl_conf;
	struct ppl_header *pplhdr = page_address(io->header_page);
	struct bio *bio = &io->bio;
	struct stripe_head *sh;
	int i;

	for (i = 0; i < io->entries_count; i++) {
		struct ppl_header_entry *e = &pplhdr->entries[i];

		pr_debug("%s: seq: %llu entry: %d data_sector: %llu pp_size: %u data_size: %u\n",
			 __func__, io->seq, i, le64_to_cpu(e->data_sector),
			 le32_to_cpu(e->pp_size), le32_to_cpu(e->data_size));

		e->data_sector = cpu_to_le64(le64_to_cpu(e->data_sector) >>
					     ilog2(ppl_conf->block_size >> 9));
		e->checksum = cpu_to_le32(~le32_to_cpu(e->checksum));
	}

	pplhdr->entries_count = cpu_to_le32(io->entries_count);
	pplhdr->checksum = cpu_to_le32(~crc32c_le(~0, pplhdr, PPL_HEADER_SIZE));

	bio->bi_private = io;
	bio->bi_end_io = ppl_log_endio;
	bio->bi_opf = REQ_OP_WRITE | REQ_FUA;
	bio->bi_bdev = log->rdev->bdev;
	bio->bi_iter.bi_sector = log->rdev->ppl.sector;
	bio_add_page(bio, io->header_page, PAGE_SIZE, 0);

	list_for_each_entry(sh, &io->stripe_list, log_list) {
		/* entries for full stripe writes have no partial parity */
		if (test_bit(STRIPE_FULL_WRITE, &sh->state))
			continue;

		if (!bio_add_page(bio, sh->ppl_page, PAGE_SIZE, 0)) {
			struct bio *prev = bio;

			bio = bio_alloc_bioset(GFP_NOIO, BIO_MAX_PAGES,
					       ppl_conf->bs);
			bio->bi_opf = prev->bi_opf;
			bio->bi_bdev = prev->bi_bdev;
			bio->bi_iter.bi_sector = bio_end_sector(prev);
			bio_add_page(bio, sh->ppl_page, PAGE_SIZE, 0);

			bio_chain(bio, prev);
			ppl_submit_iounit_bio(io, prev);
		}
	}

	ppl_submit_iounit_bio(io, bio);
}

static void ppl_submit_current_io(struct ppl_log *log)
{
	struct ppl_io_unit *io;

	spin_lock_irq(&log->io_list_lock);

	io = list_first_entry_or_null(&log->io_list, struct ppl_io_unit,
				      log_sibling);
	if (io && io->submitted)
		io = NULL;

	spin_unlock_irq(&log->io_list_lock);

	if (io) {
		io->submitted = true;

		if (io == log->current_io)
			log->current_io = NULL;

		ppl_submit_iounit(io);
	}
}

void ppl_write_stripe_run(struct r5conf *conf)
{
	struct ppl_conf *ppl_conf = conf->log_private;
	struct ppl_log *log;
	int i;

	for (i = 0; i < ppl_conf->count; i++) {
		log = &ppl_conf->child_logs[i];

		mutex_lock(&log->io_mutex);
		ppl_submit_current_io(log);
		mutex_unlock(&log->io_mutex);
	}
}

static void ppl_io_unit_finished(struct ppl_io_unit *io)
{
	struct ppl_log *log = io->log;
	unsigned long flags;

	pr_debug("%s: seq: %llu\n", __func__, io->seq);

	spin_lock_irqsave(&log->io_list_lock, flags);

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

	if (!list_empty(&log->no_mem_stripes)) {
		struct stripe_head *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);
	}

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

void ppl_stripe_write_finished(struct stripe_head *sh)
{
	struct ppl_io_unit *io;

	io = sh->ppl_io;
	sh->ppl_io = NULL;

	if (io && atomic_dec_and_test(&io->pending_stripes))
		ppl_io_unit_finished(io);
}

static void __ppl_exit_log(struct ppl_conf *ppl_conf)
{
	clear_bit(MD_HAS_PPL, &ppl_conf->mddev->flags);

	kfree(ppl_conf->child_logs);

	mempool_destroy(ppl_conf->meta_pool);
	if (ppl_conf->bs)
		bioset_free(ppl_conf->bs);
	mempool_destroy(ppl_conf->io_pool);
	kmem_cache_destroy(ppl_conf->io_kc);

	kfree(ppl_conf);
}

void ppl_exit_log(struct r5conf *conf)
{
	struct ppl_conf *ppl_conf = conf->log_private;

	if (ppl_conf) {
		__ppl_exit_log(ppl_conf);
		conf->log_private = NULL;
	}
}

static int ppl_validate_rdev(struct md_rdev *rdev)
{
	char b[BDEVNAME_SIZE];
	int ppl_data_sectors;
	int ppl_size_new;

	/*
	 * The configured PPL size must be enough to store
	 * the header and (at the very least) partial parity
	 * for one stripe. Round it down to ensure the data
	 * space is cleanly divisible by stripe size.
	 */
	ppl_data_sectors = rdev->ppl.size - (PPL_HEADER_SIZE >> 9);

	if (ppl_data_sectors > 0)
		ppl_data_sectors = rounddown(ppl_data_sectors, STRIPE_SECTORS);

	if (ppl_data_sectors <= 0) {
		pr_warn("md/raid:%s: PPL space too small on %s\n",
			mdname(rdev->mddev), bdevname(rdev->bdev, b));
		return -ENOSPC;
	}

	ppl_size_new = ppl_data_sectors + (PPL_HEADER_SIZE >> 9);

	if ((rdev->ppl.sector < rdev->data_offset &&
	     rdev->ppl.sector + ppl_size_new > rdev->data_offset) ||
	    (rdev->ppl.sector >= rdev->data_offset &&
	     rdev->data_offset + rdev->sectors > rdev->ppl.sector)) {
		pr_warn("md/raid:%s: PPL space overlaps with data on %s\n",
			mdname(rdev->mddev), bdevname(rdev->bdev, b));
		return -EINVAL;
	}

	if (!rdev->mddev->external &&
	    ((rdev->ppl.offset > 0 && rdev->ppl.offset < (rdev->sb_size >> 9)) ||
	     (rdev->ppl.offset <= 0 && rdev->ppl.offset + ppl_size_new > 0))) {
		pr_warn("md/raid:%s: PPL space overlaps with superblock on %s\n",
			mdname(rdev->mddev), bdevname(rdev->bdev, b));
		return -EINVAL;
	}

	rdev->ppl.size = ppl_size_new;

	return 0;
}

int ppl_init_log(struct r5conf *conf)
{
	struct ppl_conf *ppl_conf;
	struct mddev *mddev = conf->mddev;
	int ret = 0;
	int i;
	bool need_cache_flush;

	pr_debug("md/raid:%s: enabling distributed Partial Parity Log\n",
		 mdname(conf->mddev));

	if (PAGE_SIZE != 4096)
		return -EINVAL;

	if (mddev->level != 5) {
		pr_warn("md/raid:%s PPL is not compatible with raid level %d\n",
			mdname(mddev), mddev->level);
		return -EINVAL;
	}

	if (mddev->bitmap_info.file || mddev->bitmap_info.offset) {
		pr_warn("md/raid:%s PPL is not compatible with bitmap\n",
			mdname(mddev));
		return -EINVAL;
	}

	if (test_bit(MD_HAS_JOURNAL, &mddev->flags)) {
		pr_warn("md/raid:%s PPL is not compatible with journal\n",
			mdname(mddev));
		return -EINVAL;
	}

	ppl_conf = kzalloc(sizeof(struct ppl_conf), GFP_KERNEL);
	if (!ppl_conf)
		return -ENOMEM;

	ppl_conf->mddev = mddev;

	ppl_conf->io_kc = KMEM_CACHE(ppl_io_unit, 0);
	if (!ppl_conf->io_kc) {
		ret = -EINVAL;
		goto err;
	}

	ppl_conf->io_pool = mempool_create_slab_pool(conf->raid_disks, ppl_conf->io_kc);
	if (!ppl_conf->io_pool) {
		ret = -EINVAL;
		goto err;
	}

	ppl_conf->bs = bioset_create(conf->raid_disks, 0);
	if (!ppl_conf->bs) {
		ret = -EINVAL;
		goto err;
	}

	ppl_conf->meta_pool = mempool_create_page_pool(conf->raid_disks, 0);
	if (!ppl_conf->meta_pool) {
		ret = -EINVAL;
		goto err;
	}

	ppl_conf->count = conf->raid_disks;
	ppl_conf->child_logs = kcalloc(ppl_conf->count, sizeof(struct ppl_log),
				       GFP_KERNEL);
	if (!ppl_conf->child_logs) {
		ret = -ENOMEM;
		goto err;
	}

	atomic64_set(&ppl_conf->seq, 0);

	if (!mddev->external) {
		ppl_conf->signature = ~crc32c_le(~0, mddev->uuid, sizeof(mddev->uuid));
		ppl_conf->block_size = 512;
	} else {
		ppl_conf->block_size = queue_logical_block_size(mddev->queue);
	}

	for (i = 0; i < ppl_conf->count; i++) {
		struct ppl_log *log = &ppl_conf->child_logs[i];
		struct md_rdev *rdev = conf->disks[i].rdev;

		mutex_init(&log->io_mutex);
		spin_lock_init(&log->io_list_lock);
		INIT_LIST_HEAD(&log->io_list);
		INIT_LIST_HEAD(&log->no_mem_stripes);

		log->ppl_conf = ppl_conf;
		log->rdev = rdev;

		if (rdev) {
			struct request_queue *q;

			ret = ppl_validate_rdev(rdev);
			if (ret)
				goto err;

			q = bdev_get_queue(rdev->bdev);
			if (test_bit(QUEUE_FLAG_WC, &q->queue_flags))
				need_cache_flush = true;
		}
	}

	if (need_cache_flush)
		pr_warn("md/raid:%s: Volatile write-back cache should be disabled on all member drives when using PPL!\n",
			mdname(mddev));

	conf->log_private = ppl_conf;

	return 0;
err:
	__ppl_exit_log(ppl_conf);
	return ret;
}