Merge tag 'for-5.6/drivers-2020-01-27' of git://git.kernel.dk/linux-block

Pull block driver updates from Jens Axboe:
 "Like the core side, not a lot of changes here, just two main items:

   - Series of patches (via Coly) with fixes for bcache (Coly,
     Christoph)

   - MD pull request from Song"

* tag 'for-5.6/drivers-2020-01-27' of git://git.kernel.dk/linux-block: (31 commits)
  bcache: reap from tail of c->btree_cache in bch_mca_scan()
  bcache: reap c->btree_cache_freeable from the tail in bch_mca_scan()
  bcache: remove member accessed from struct btree
  bcache: print written and keys in trace_bcache_btree_write
  bcache: avoid unnecessary btree nodes flushing in btree_flush_write()
  bcache: add code comments for state->pool in __btree_sort()
  lib: crc64: include <linux/crc64.h> for 'crc64_be'
  bcache: use read_cache_page_gfp to read the superblock
  bcache: store a pointer to the on-disk sb in the cache and cached_dev structures
  bcache: return a pointer to the on-disk sb from read_super
  bcache: transfer the sb_page reference to register_{bdev,cache}
  bcache: fix use-after-free in register_bcache()
  bcache: properly initialize 'path' and 'err' in register_bcache()
  bcache: rework error unwinding in register_bcache
  bcache: use a separate data structure for the on-disk super block
  bcache: cached_dev_free needs to put the sb page
  md/raid1: introduce wait_for_serialization
  md/raid1: use bucket based mechanism for IO serialization
  md: introduce a new struct for IO serialization
  md: don't destroy serial_info_pool if serialize_policy is true
  ...

11 files changed, 469 insertions, 236 deletions

diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
index 9198c1b480d9..adf26a21fcd1 100644
--- a/drivers/md/bcache/bcache.h
+++ b/drivers/md/bcache/bcache.h
@@ -301,6 +301,7 @@ struct cached_dev {
 	struct block_device	*bdev;
 
 	struct cache_sb		sb;
+	struct cache_sb_disk	*sb_disk;
 	struct bio		sb_bio;
 	struct bio_vec		sb_bv[1];
 	struct closure		sb_write;
@@ -403,6 +404,7 @@ enum alloc_reserve {
 struct cache {
 	struct cache_set	*set;
 	struct cache_sb		sb;
+	struct cache_sb_disk	*sb_disk;
 	struct bio		sb_bio;
 	struct bio_vec		sb_bv[1];
 
diff --git a/drivers/md/bcache/bset.c b/drivers/md/bcache/bset.c
index cffcdc9feefb..4385303836d8 100644
--- a/drivers/md/bcache/bset.c
+++ b/drivers/md/bcache/bset.c
@@ -1257,6 +1257,11 @@ static void __btree_sort(struct btree_keys *b, struct btree_iter *iter,
 		 * Our temporary buffer is the same size as the btree node's
 		 * buffer, we can just swap buffers instead of doing a big
 		 * memcpy()
+		 *
+		 * Don't worry event 'out' is allocated from mempool, it can
+		 * still be swapped here. Because state->pool is a page mempool
+		 * creaated by by mempool_init_page_pool(), which allocates
+		 * pages by alloc_pages() indeed.
 		 */
 
 		out->magic	= b->set->data->magic;
diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
index 14d6c33b0957..fa872df4e770 100644
--- a/drivers/md/bcache/btree.c
+++ b/drivers/md/bcache/btree.c
@@ -734,34 +734,32 @@ static unsigned long bch_mca_scan(struct shrinker *shrink,
 
 	i = 0;
 	btree_cache_used = c->btree_cache_used;
-	list_for_each_entry_safe(b, t, &c->btree_cache_freeable, list) {
+	list_for_each_entry_safe_reverse(b, t, &c->btree_cache_freeable, list) {
 		if (nr <= 0)
 			goto out;
 
-		if (++i > 3 &&
-		    !mca_reap(b, 0, false)) {
+		if (!mca_reap(b, 0, false)) {
 			mca_data_free(b);
 			rw_unlock(true, b);
 			freed++;
 		}
 		nr--;
+		i++;
 	}
 
-	for (;  (nr--) && i < btree_cache_used; i++) {
-		if (list_empty(&c->btree_cache))
+	list_for_each_entry_safe_reverse(b, t, &c->btree_cache, list) {
+		if (nr <= 0 || i >= btree_cache_used)
 			goto out;
 
-		b = list_first_entry(&c->btree_cache, struct btree, list);
-		list_rotate_left(&c->btree_cache);
-
-		if (!b->accessed &&
-		    !mca_reap(b, 0, false)) {
+		if (!mca_reap(b, 0, false)) {
 			mca_bucket_free(b);
 			mca_data_free(b);
 			rw_unlock(true, b);
 			freed++;
-		} else
-			b->accessed = 0;
+		}
+
+		nr--;
+		i++;
 	}
 out:
 	mutex_unlock(&c->bucket_lock);
@@ -1069,7 +1067,6 @@ retry:
 	BUG_ON(!b->written);
 
 	b->parent = parent;
-	b->accessed = 1;
 
 	for (; i <= b->keys.nsets && b->keys.set[i].size; i++) {
 		prefetch(b->keys.set[i].tree);
@@ -1160,7 +1157,6 @@ retry:
 		goto retry;
 	}
 
-	b->accessed = 1;
 	b->parent = parent;
 	bch_bset_init_next(&b->keys, b->keys.set->data, bset_magic(&b->c->sb));
 
diff --git a/drivers/md/bcache/btree.h b/drivers/md/bcache/btree.h
index 76cfd121a486..f4dcca449391 100644
--- a/drivers/md/bcache/btree.h
+++ b/drivers/md/bcache/btree.h
@@ -121,8 +121,6 @@ struct btree {
 	/* Key/pointer for this btree node */
 	BKEY_PADDED(key);
 
-	/* Single bit - set when accessed, cleared by shrinker */
-	unsigned long		accessed;
 	unsigned long		seq;
 	struct rw_semaphore	lock;
 	struct cache_set	*c;
diff --git a/drivers/md/bcache/journal.c b/drivers/md/bcache/journal.c
index be2a2a201603..33ddc5269e8d 100644
--- a/drivers/md/bcache/journal.c
+++ b/drivers/md/bcache/journal.c
@@ -417,10 +417,14 @@ err:
 
 /* Journalling */
 
+#define nr_to_fifo_front(p, front_p, mask)	(((p) - (front_p)) & (mask))
+
 static void btree_flush_write(struct cache_set *c)
 {
 	struct btree *b, *t, *btree_nodes[BTREE_FLUSH_NR];
-	unsigned int i, n;
+	unsigned int i, nr, ref_nr;
+	atomic_t *fifo_front_p, *now_fifo_front_p;
+	size_t mask;
 
 	if (c->journal.btree_flushing)
 		return;
@@ -433,12 +437,50 @@ static void btree_flush_write(struct cache_set *c)
 	c->journal.btree_flushing = true;
 	spin_unlock(&c->journal.flush_write_lock);
 
+	/* get the oldest journal entry and check its refcount */
+	spin_lock(&c->journal.lock);
+	fifo_front_p = &fifo_front(&c->journal.pin);
+	ref_nr = atomic_read(fifo_front_p);
+	if (ref_nr <= 0) {
+		/*
+		 * do nothing if no btree node references
+		 * the oldest journal entry
+		 */
+		spin_unlock(&c->journal.lock);
+		goto out;
+	}
+	spin_unlock(&c->journal.lock);
+
+	mask = c->journal.pin.mask;
+	nr = 0;
 	atomic_long_inc(&c->flush_write);
 	memset(btree_nodes, 0, sizeof(btree_nodes));
-	n = 0;
 
 	mutex_lock(&c->bucket_lock);
 	list_for_each_entry_safe_reverse(b, t, &c->btree_cache, list) {
+		/*
+		 * It is safe to get now_fifo_front_p without holding
+		 * c->journal.lock here, because we don't need to know
+		 * the exactly accurate value, just check whether the
+		 * front pointer of c->journal.pin is changed.
+		 */
+		now_fifo_front_p = &fifo_front(&c->journal.pin);
+		/*
+		 * If the oldest journal entry is reclaimed and front
+		 * pointer of c->journal.pin changes, it is unnecessary
+		 * to scan c->btree_cache anymore, just quit the loop and
+		 * flush out what we have already.
+		 */
+		if (now_fifo_front_p != fifo_front_p)
+			break;
+		/*
+		 * quit this loop if all matching btree nodes are
+		 * scanned and record in btree_nodes[] already.
+		 */
+		ref_nr = atomic_read(fifo_front_p);
+		if (nr >= ref_nr)
+			break;
+
 		if (btree_node_journal_flush(b))
 			pr_err("BUG: flush_write bit should not be set here!");
 
@@ -454,17 +496,44 @@ static void btree_flush_write(struct cache_set *c)
 			continue;
 		}
 
+		/*
+		 * Only select the btree node which exactly references
+		 * the oldest journal entry.
+		 *
+		 * If the journal entry pointed by fifo_front_p is
+		 * reclaimed in parallel, don't worry:
+		 * - the list_for_each_xxx loop will quit when checking
+		 *   next now_fifo_front_p.
+		 * - If there are matched nodes recorded in btree_nodes[],
+		 *   they are clean now (this is why and how the oldest
+		 *   journal entry can be reclaimed). These selected nodes
+		 *   will be ignored and skipped in the folowing for-loop.
+		 */
+		if (nr_to_fifo_front(btree_current_write(b)->journal,
+				     fifo_front_p,
+				     mask) != 0) {
+			mutex_unlock(&b->write_lock);
+			continue;
+		}
+
 		set_btree_node_journal_flush(b);
 
 		mutex_unlock(&b->write_lock);
 
-		btree_nodes[n++] = b;
-		if (n == BTREE_FLUSH_NR)
+		btree_nodes[nr++] = b;
+		/*
+		 * To avoid holding c->bucket_lock too long time,
+		 * only scan for BTREE_FLUSH_NR matched btree nodes
+		 * at most. If there are more btree nodes reference
+		 * the oldest journal entry, try to flush them next
+		 * time when btree_flush_write() is called.
+		 */
+		if (nr == BTREE_FLUSH_NR)
 			break;
 	}
 	mutex_unlock(&c->bucket_lock);
 
-	for (i = 0; i < n; i++) {
+	for (i = 0; i < nr; i++) {
 		b = btree_nodes[i];
 		if (!b) {
 			pr_err("BUG: btree_nodes[%d] is NULL", i);
@@ -497,6 +566,7 @@ static void btree_flush_write(struct cache_set *c)
 		mutex_unlock(&b->write_lock);
 	}
 
+out:
 	spin_lock(&c->journal.flush_write_lock);
 	c->journal.btree_flushing = false;
 	spin_unlock(&c->journal.flush_write_lock);
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 77e9869345e7..3dea1d5acd5c 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -15,7 +15,6 @@
 #include "writeback.h"
 
 #include <linux/blkdev.h>
-#include <linux/buffer_head.h>
 #include <linux/debugfs.h>
 #include <linux/genhd.h>
 #include <linux/idr.h>
@@ -60,17 +59,18 @@ struct workqueue_struct *bch_journal_wq;
 /* Superblock */
 
 static const char *read_super(struct cache_sb *sb, struct block_device *bdev,
-			      struct page **res)
+			      struct cache_sb_disk **res)
 {
 	const char *err;
-	struct cache_sb *s;
-	struct buffer_head *bh = __bread(bdev, 1, SB_SIZE);
+	struct cache_sb_disk *s;
+	struct page *page;
 	unsigned int i;
 
-	if (!bh)
+	page = read_cache_page_gfp(bdev->bd_inode->i_mapping,
+				   SB_OFFSET >> PAGE_SHIFT, GFP_KERNEL);
+	if (IS_ERR(page))
 		return "IO error";
-
-	s = (struct cache_sb *) bh->b_data;
+	s = page_address(page) + offset_in_page(SB_OFFSET);
 
 	sb->offset		= le64_to_cpu(s->offset);
 	sb->version		= le64_to_cpu(s->version);
@@ -188,12 +188,10 @@ static const char *read_super(struct cache_sb *sb, struct block_device *bdev,
 	}
 
 	sb->last_mount = (u32)ktime_get_real_seconds();
-	err = NULL;
-
-	get_page(bh->b_page);
-	*res = bh->b_page;
+	*res = s;
+	return NULL;
 err:
-	put_bh(bh);
+	put_page(page);
 	return err;
 }
 
@@ -207,15 +205,15 @@ static void write_bdev_super_endio(struct bio *bio)
 	closure_put(&dc->sb_write);
 }
 
-static void __write_super(struct cache_sb *sb, struct bio *bio)
+static void __write_super(struct cache_sb *sb, struct cache_sb_disk *out,
+		struct bio *bio)
 {
-	struct cache_sb *out = page_address(bio_first_page_all(bio));
 	unsigned int i;
 
+	bio->bi_opf = REQ_OP_WRITE | REQ_SYNC | REQ_META;
 	bio->bi_iter.bi_sector	= SB_SECTOR;
-	bio->bi_iter.bi_size	= SB_SIZE;
-	bio_set_op_attrs(bio, REQ_OP_WRITE, REQ_SYNC|REQ_META);
-	bch_bio_map(bio, NULL);
+	__bio_add_page(bio, virt_to_page(out), SB_SIZE,
+			offset_in_page(out));
 
 	out->offset		= cpu_to_le64(sb->offset);
 	out->version		= cpu_to_le64(sb->version);
@@ -257,14 +255,14 @@ void bch_write_bdev_super(struct cached_dev *dc, struct closure *parent)
 	down(&dc->sb_write_mutex);
 	closure_init(cl, parent);
 
-	bio_reset(bio);
+	bio_init(bio, dc->sb_bv, 1);
 	bio_set_dev(bio, dc->bdev);
 	bio->bi_end_io	= write_bdev_super_endio;
 	bio->bi_private = dc;
 
 	closure_get(cl);
 	/* I/O request sent to backing device */
-	__write_super(&dc->sb, bio);
+	__write_super(&dc->sb, dc->sb_disk, bio);
 
 	closure_return_with_destructor(cl, bch_write_bdev_super_unlock);
 }
@@ -306,13 +304,13 @@ void bcache_write_super(struct cache_set *c)
 
 		SET_CACHE_SYNC(&ca->sb, CACHE_SYNC(&c->sb));
 
-		bio_reset(bio);
+		bio_init(bio, ca->sb_bv, 1);
 		bio_set_dev(bio, ca->bdev);
 		bio->bi_end_io	= write_super_endio;
 		bio->bi_private = ca;
 
 		closure_get(cl);
-		__write_super(&ca->sb, bio);
+		__write_super(&ca->sb, ca->sb_disk, bio);
 	}
 
 	closure_return_with_destructor(cl, bcache_write_super_unlock);
@@ -1275,6 +1273,9 @@ static void cached_dev_free(struct closure *cl)
 
 	mutex_unlock(&bch_register_lock);
 
+	if (dc->sb_disk)
+		put_page(virt_to_page(dc->sb_disk));
+
 	if (!IS_ERR_OR_NULL(dc->bdev))
 		blkdev_put(dc->bdev, FMODE_READ|FMODE_WRITE|FMODE_EXCL);
 
@@ -1350,7 +1351,7 @@ static int cached_dev_init(struct cached_dev *dc, unsigned int block_size)
 
 /* Cached device - bcache superblock */
 
-static int register_bdev(struct cache_sb *sb, struct page *sb_page,
+static int register_bdev(struct cache_sb *sb, struct cache_sb_disk *sb_disk,
 				 struct block_device *bdev,
 				 struct cached_dev *dc)
 {
@@ -1362,11 +1363,7 @@ static int register_bdev(struct cache_sb *sb, struct page *sb_page,
 	memcpy(&dc->sb, sb, sizeof(struct cache_sb));
 	dc->bdev = bdev;
 	dc->bdev->bd_holder = dc;
-
-	bio_init(&dc->sb_bio, dc->sb_bio.bi_inline_vecs, 1);
-	bio_first_bvec_all(&dc->sb_bio)->bv_page = sb_page;
-	get_page(sb_page);
-
+	dc->sb_disk = sb_disk;
 
 	if (cached_dev_init(dc, sb->block_size << 9))
 		goto err;
@@ -2136,8 +2133,8 @@ void bch_cache_release(struct kobject *kobj)
 	for (i = 0; i < RESERVE_NR; i++)
 		free_fifo(&ca->free[i]);
 
-	if (ca->sb_bio.bi_inline_vecs[0].bv_page)
-		put_page(bio_first_page_all(&ca->sb_bio));
+	if (ca->sb_disk)
+		put_page(virt_to_page(ca->sb_disk));
 
 	if (!IS_ERR_OR_NULL(ca->bdev))
 		blkdev_put(ca->bdev, FMODE_READ|FMODE_WRITE|FMODE_EXCL);
@@ -2259,7 +2256,7 @@ err_free:
 	return ret;
 }
 
-static int register_cache(struct cache_sb *sb, struct page *sb_page,
+static int register_cache(struct cache_sb *sb, struct cache_sb_disk *sb_disk,
 				struct block_device *bdev, struct cache *ca)
 {
 	const char *err = NULL; /* must be set for any error case */
@@ -2269,10 +2266,7 @@ static int register_cache(struct cache_sb *sb, struct page *sb_page,
 	memcpy(&ca->sb, sb, sizeof(struct cache_sb));
 	ca->bdev = bdev;
 	ca->bdev->bd_holder = ca;
-
-	bio_init(&ca->sb_bio, ca->sb_bio.bi_inline_vecs, 1);
-	bio_first_bvec_all(&ca->sb_bio)->bv_page = sb_page;
-	get_page(sb_page);
+	ca->sb_disk = sb_disk;
 
 	if (blk_queue_discard(bdev_get_queue(bdev)))
 		ca->discard = CACHE_DISCARD(&ca->sb);
@@ -2372,29 +2366,35 @@ static bool bch_is_open(struct block_device *bdev)
 static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
 			       const char *buffer, size_t size)
 {
-	ssize_t ret = -EINVAL;
-	const char *err = "cannot allocate memory";
+	const char *err;
 	char *path = NULL;
-	struct cache_sb *sb = NULL;
-	struct block_device *bdev = NULL;
-	struct page *sb_page = NULL;
+	struct cache_sb *sb;
+	struct cache_sb_disk *sb_disk;
+	struct block_device *bdev;
+	ssize_t ret;
 
+	ret = -EBUSY;
+	err = "failed to reference bcache module";
 	if (!try_module_get(THIS_MODULE))
-		return -EBUSY;
+		goto out;
 
 	/* For latest state of bcache_is_reboot */
 	smp_mb();
+	err = "bcache is in reboot";
 	if (bcache_is_reboot)
-		return -EBUSY;
+		goto out_module_put;
 
+	ret = -ENOMEM;
+	err = "cannot allocate memory";
 	path = kstrndup(buffer, size, GFP_KERNEL);
 	if (!path)
-		goto err;
+		goto out_module_put;
 
 	sb = kmalloc(sizeof(struct cache_sb), GFP_KERNEL);
 	if (!sb)
-		goto err;
+		goto out_free_path;
 
+	ret = -EINVAL;
 	err = "failed to open device";
 	bdev = blkdev_get_by_path(strim(path),
 				  FMODE_READ|FMODE_WRITE|FMODE_EXCL,
@@ -2411,57 +2411,63 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
 			if (!IS_ERR(bdev))
 				bdput(bdev);
 			if (attr == &ksysfs_register_quiet)
-				goto quiet_out;
+				goto done;
 		}
-		goto err;
+		goto out_free_sb;
 	}
 
 	err = "failed to set blocksize";
 	if (set_blocksize(bdev, 4096))
-		goto err_close;
+		goto out_blkdev_put;
 
-	err = read_super(sb, bdev, &sb_page);
+	err = read_super(sb, bdev, &sb_disk);
 	if (err)
-		goto err_close;
+		goto out_blkdev_put;
 
 	err = "failed to register device";
 	if (SB_IS_BDEV(sb)) {
 		struct cached_dev *dc = kzalloc(sizeof(*dc), GFP_KERNEL);
 
 		if (!dc)
-			goto err_close;
+			goto out_put_sb_page;
 
 		mutex_lock(&bch_register_lock);
-		ret = register_bdev(sb, sb_page, bdev, dc);
+		ret = register_bdev(sb, sb_disk, bdev, dc);
 		mutex_unlock(&bch_register_lock);
 		/* blkdev_put() will be called in cached_dev_free() */
 		if (ret < 0)
-			goto err;
+			goto out_free_sb;
 	} else {
 		struct cache *ca = kzalloc(sizeof(*ca), GFP_KERNEL);
 
 		if (!ca)
-			goto err_close;
+			goto out_put_sb_page;
 
 		/* blkdev_put() will be called in bch_cache_release() */
-		if (register_cache(sb, sb_page, bdev, ca) != 0)
-			goto err;
+		if (register_cache(sb, sb_disk, bdev, ca) != 0)
+			goto out_free_sb;
 	}
-quiet_out:
-	ret = size;
-out:
-	if (sb_page)
-		put_page(sb_page);
+
+done:
 	kfree(sb);
 	kfree(path);
 	module_put(THIS_MODULE);
-	return ret;
+	return size;
 
-err_close:
-	blkdev_put(bdev, FMODE_READ|FMODE_WRITE|FMODE_EXCL);
-err:
-	pr_info("error %s: %s", path, err);
-	goto out;
+out_put_sb_page:
+	put_page(virt_to_page(sb_disk));
+out_blkdev_put:
+	blkdev_put(bdev, FMODE_READ | FMODE_WRITE | FMODE_EXCL);
+out_free_sb:
+	kfree(sb);
+out_free_path:
+	kfree(path);
+	path = NULL;
+out_module_put:
+	module_put(THIS_MODULE);
+out:
+	pr_info("error %s: %s", path?path:"", err);
+	return ret;
 }
 
 
diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
index 3ad18246fcb3..e230052c2107 100644
--- a/drivers/md/md-bitmap.c
+++ b/drivers/md/md-bitmap.c
@@ -1019,8 +1019,6 @@ void md_bitmap_unplug(struct bitmap *bitmap)
 	/* look at each page to see if there are any set bits that need to be
 	 * flushed out to disk */
 	for (i = 0; i < bitmap->storage.file_pages; i++) {
-		if (!bitmap->storage.filemap)
-			return;
 		dirty = test_and_clear_page_attr(bitmap, i, BITMAP_PAGE_DIRTY);
 		need_write = test_and_clear_page_attr(bitmap, i,
 						      BITMAP_PAGE_NEEDWRITE);
@@ -1338,7 +1336,8 @@ void md_bitmap_daemon_work(struct mddev *mddev)
 				   BITMAP_PAGE_DIRTY))
 			/* bitmap_unplug will handle the rest */
 			break;
-		if (test_and_clear_page_attr(bitmap, j,
+		if (bitmap->storage.filemap &&
+		    test_and_clear_page_attr(bitmap, j,
 					     BITMAP_PAGE_NEEDWRITE)) {
 			write_page(bitmap, bitmap->storage.filemap[j], 0);
 		}
@@ -1790,8 +1789,8 @@ void md_bitmap_destroy(struct mddev *mddev)
 		return;
 
 	md_bitmap_wait_behind_writes(mddev);
-	mempool_destroy(mddev->wb_info_pool);
-	mddev->wb_info_pool = NULL;
+	if (!mddev->serialize_policy)
+		mddev_destroy_serial_pool(mddev, NULL, true);
 
 	mutex_lock(&mddev->bitmap_info.mutex);
 	spin_lock(&mddev->lock);
@@ -1908,7 +1907,7 @@ int md_bitmap_load(struct mddev *mddev)
 		goto out;
 
 	rdev_for_each(rdev, mddev)
-		mddev_create_wb_pool(mddev, rdev, true);
+		mddev_create_serial_pool(mddev, rdev, true);
 
 	if (mddev_is_clustered(mddev))
 		md_cluster_ops->load_bitmaps(mddev, mddev->bitmap_info.nodes);
@@ -2475,16 +2474,16 @@ backlog_store(struct mddev *mddev, const char *buf, size_t len)
 	if (backlog > COUNTER_MAX)
 		return -EINVAL;
 	mddev->bitmap_info.max_write_behind = backlog;
-	if (!backlog && mddev->wb_info_pool) {
-		/* wb_info_pool is not needed if backlog is zero */
-		mempool_destroy(mddev->wb_info_pool);
-		mddev->wb_info_pool = NULL;
-	} else if (backlog && !mddev->wb_info_pool) {
-		/* wb_info_pool is needed since backlog is not zero */
+	if (!backlog && mddev->serial_info_pool) {
+		/* serial_info_pool is not needed if backlog is zero */
+		if (!mddev->serialize_policy)
+			mddev_destroy_serial_pool(mddev, NULL, false);
+	} else if (backlog && !mddev->serial_info_pool) {
+		/* serial_info_pool is needed since backlog is not zero */
 		struct md_rdev *rdev;
 
 		rdev_for_each(rdev, mddev)
-			mddev_create_wb_pool(mddev, rdev, false);
+			mddev_create_serial_pool(mddev, rdev, false);
 	}
 	if (old_mwb != backlog)
 		md_bitmap_update_sb(mddev->bitmap);
diff --git a/drivers/md/md.c b/drivers/md/md.c
index 4e7c9f398bc6..4824d50526fa 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -125,74 +125,165 @@ static inline int speed_max(struct mddev *mddev)
 		mddev->sync_speed_max : sysctl_speed_limit_max;
 }
 
-static int rdev_init_wb(struct md_rdev *rdev)
+static void rdev_uninit_serial(struct md_rdev *rdev)
 {
-	if (rdev->bdev->bd_queue->nr_hw_queues == 1)
+	if (!test_and_clear_bit(CollisionCheck, &rdev->flags))
+		return;
+
+	kvfree(rdev->serial);
+	rdev->serial = NULL;
+}
+
+static void rdevs_uninit_serial(struct mddev *mddev)
+{
+	struct md_rdev *rdev;
+
+	rdev_for_each(rdev, mddev)
+		rdev_uninit_serial(rdev);
+}
+
+static int rdev_init_serial(struct md_rdev *rdev)
+{
+	/* serial_nums equals with BARRIER_BUCKETS_NR */
+	int i, serial_nums = 1 << ((PAGE_SHIFT - ilog2(sizeof(atomic_t))));
+	struct serial_in_rdev *serial = NULL;
+
+	if (test_bit(CollisionCheck, &rdev->flags))
 		return 0;
 
-	spin_lock_init(&rdev->wb_list_lock);
-	INIT_LIST_HEAD(&rdev->wb_list);
-	init_waitqueue_head(&rdev->wb_io_wait);
-	set_bit(WBCollisionCheck, &rdev->flags);
+	serial = kvmalloc(sizeof(struct serial_in_rdev) * serial_nums,
+			  GFP_KERNEL);
+	if (!serial)
+		return -ENOMEM;
 
-	return 1;
+	for (i = 0; i < serial_nums; i++) {
+		struct serial_in_rdev *serial_tmp = &serial[i];
+
+		spin_lock_init(&serial_tmp->serial_lock);
+		serial_tmp->serial_rb = RB_ROOT_CACHED;
+		init_waitqueue_head(&serial_tmp->serial_io_wait);
+	}
+
+	rdev->serial = serial;
+	set_bit(CollisionCheck, &rdev->flags);
+
+	return 0;
+}
+
+static int rdevs_init_serial(struct mddev *mddev)
+{
+	struct md_rdev *rdev;
+	int ret = 0;
+
+	rdev_for_each(rdev, mddev) {
+		ret = rdev_init_serial(rdev);
+		if (ret)
+			break;
+	}
+
+	/* Free all resources if pool is not existed */
+	if (ret && !mddev->serial_info_pool)
+		rdevs_uninit_serial(mddev);
+
+	return ret;
 }
 
 /*
- * Create wb_info_pool if rdev is the first multi-queue device flaged
- * with writemostly, also write-behind mode is enabled.
+ * rdev needs to enable serial stuffs if it meets the conditions:
+ * 1. it is multi-queue device flaged with writemostly.
+ * 2. the write-behind mode is enabled.
  */
-void mddev_create_wb_pool(struct mddev *mddev, struct md_rdev *rdev,
-			  bool is_suspend)
+static int rdev_need_serial(struct md_rdev *rdev)
 {
-	if (mddev->bitmap_info.max_write_behind == 0)
-		return;
+	return (rdev && rdev->mddev->bitmap_info.max_write_behind > 0 &&
+		rdev->bdev->bd_queue->nr_hw_queues != 1 &&
+		test_bit(WriteMostly, &rdev->flags));
+}
+
+/*
+ * Init resource for rdev(s), then create serial_info_pool if:
+ * 1. rdev is the first device which return true from rdev_enable_serial.
+ * 2. rdev is NULL, means we want to enable serialization for all rdevs.
+ */
+void mddev_create_serial_pool(struct mddev *mddev, struct md_rdev *rdev,
+			      bool is_suspend)
+{
+	int ret = 0;
 
-	if (!test_bit(WriteMostly, &rdev->flags) || !rdev_init_wb(rdev))
+	if (rdev && !rdev_need_serial(rdev) &&
+	    !test_bit(CollisionCheck, &rdev->flags))
 		return;
 
-	if (mddev->wb_info_pool == NULL) {
+	if (!is_suspend)
+		mddev_suspend(mddev);
+
+	if (!rdev)
+		ret = rdevs_init_serial(mddev);
+	else
+		ret = rdev_init_serial(rdev);
+	if (ret)
+		goto abort;
+
+	if (mddev->serial_info_pool == NULL) {
 		unsigned int noio_flag;
 
-		if (!is_suspend)
-			mddev_suspend(mddev);
 		noio_flag = memalloc_noio_save();
-		mddev->wb_info_pool = mempool_create_kmalloc_pool(NR_WB_INFOS,
-							sizeof(struct wb_info));
+		mddev->serial_info_pool =
+			mempool_create_kmalloc_pool(NR_SERIAL_INFOS,
+						sizeof(struct serial_info));
 		memalloc_noio_restore(noio_flag);
-		if (!mddev->wb_info_pool)
-			pr_err("can't alloc memory pool for writemostly\n");
-		if (!is_suspend)
-			mddev_resume(mddev);
+		if (!mddev->serial_info_pool) {
+			rdevs_uninit_serial(mddev);
+			pr_err("can't alloc memory pool for serialization\n");
+		}
 	}
+
+abort:
+	if (!is_suspend)
+		mddev_resume(mddev);
 }
-EXPORT_SYMBOL_GPL(mddev_create_wb_pool);
 
 /*
- * destroy wb_info_pool if rdev is the last device flaged with WBCollisionCheck.
+ * Free resource from rdev(s), and destroy serial_info_pool under conditions:
+ * 1. rdev is the last device flaged with CollisionCheck.
+ * 2. when bitmap is destroyed while policy is not enabled.
+ * 3. for disable policy, the pool is destroyed only when no rdev needs it.
  */
-static void mddev_destroy_wb_pool(struct mddev *mddev, struct md_rdev *rdev)
+void mddev_destroy_serial_pool(struct mddev *mddev, struct md_rdev *rdev,
+			       bool is_suspend)
 {
-	if (!test_and_clear_bit(WBCollisionCheck, &rdev->flags))
+	if (rdev && !test_bit(CollisionCheck, &rdev->flags))
 		return;
 
-	if (mddev->wb_info_pool) {
+	if (mddev->serial_info_pool) {
 		struct md_rdev *temp;
-		int num = 0;
+		int num = 0; /* used to track if other rdevs need the pool */
 
-		/*
-		 * Check if other rdevs need wb_info_pool.
-		 */
-		rdev_for_each(temp, mddev)
-			if (temp != rdev &&
-			    test_bit(WBCollisionCheck, &temp->flags))
+		if (!is_suspend)
+			mddev_suspend(mddev);
+		rdev_for_each(temp, mddev) {
+			if (!rdev) {
+				if (!mddev->serialize_policy ||
+				    !rdev_need_serial(temp))
+					rdev_uninit_serial(temp);
+				else
+					num++;
+			} else if (temp != rdev &&
+				   test_bit(CollisionCheck, &temp->flags))
 				num++;
-		if (!num) {
-			mddev_suspend(rdev->mddev);
-			mempool_destroy(mddev->wb_info_pool);
-			mddev->wb_info_pool = NULL;
-			mddev_resume(rdev->mddev);
 		}
+
+		if (rdev)
+			rdev_uninit_serial(rdev);
+
+		if (num)
+			pr_info("The mempool could be used by other devices\n");
+		else {
+			mempool_destroy(mddev->serial_info_pool);
+			mddev->serial_info_pool = NULL;
+		}
+		if (!is_suspend)
+			mddev_resume(mddev);
 	}
 }
 
@@ -2337,7 +2428,7 @@ static int bind_rdev_to_array(struct md_rdev *rdev, struct mddev *mddev)
 	pr_debug("md: bind<%s>\n", b);
 
 	if (mddev->raid_disks)
-		mddev_create_wb_pool(mddev, rdev, false);
+		mddev_create_serial_pool(mddev, rdev, false);
 
 	if ((err = kobject_add(&rdev->kobj, &mddev->kobj, "dev-%s", b)))
 		goto fail;
@@ -2375,7 +2466,7 @@ static void unbind_rdev_from_array(struct md_rdev *rdev)
 	bd_unlink_disk_holder(rdev->bdev, rdev->mddev->gendisk);
 	list_del_rcu(&rdev->same_set);
 	pr_debug("md: unbind<%s>\n", bdevname(rdev->bdev,b));
-	mddev_destroy_wb_pool(rdev->mddev, rdev);
+	mddev_destroy_serial_pool(rdev->mddev, rdev, false);
 	rdev->mddev = NULL;
 	sysfs_remove_link(&rdev->kobj, "block");
 	sysfs_put(rdev->sysfs_state);
@@ -2888,10 +2979,10 @@ state_store(struct md_rdev *rdev, const char *buf, size_t len)
 		}
 	} else if (cmd_match(buf, "writemostly")) {
 		set_bit(WriteMostly, &rdev->flags);
-		mddev_create_wb_pool(rdev->mddev, rdev, false);
+		mddev_create_serial_pool(rdev->mddev, rdev, false);
 		err = 0;
 	} else if (cmd_match(buf, "-writemostly")) {
-		mddev_destroy_wb_pool(rdev->mddev, rdev);
+		mddev_destroy_serial_pool(rdev->mddev, rdev, false);
 		clear_bit(WriteMostly, &rdev->flags);
 		err = 0;
 	} else if (cmd_match(buf, "blocked")) {
@@ -5277,6 +5368,57 @@ static struct md_sysfs_entry md_fail_last_dev =
 __ATTR(fail_last_dev, S_IRUGO | S_IWUSR, fail_last_dev_show,
        fail_last_dev_store);
 
+static ssize_t serialize_policy_show(struct mddev *mddev, char *page)
+{
+	if (mddev->pers == NULL || (mddev->pers->level != 1))
+		return sprintf(page, "n/a\n");
+	else
+		return sprintf(page, "%d\n", mddev->serialize_policy);
+}
+
+/*
+ * Setting serialize_policy to true to enforce write IO is not reordered
+ * for raid1.
+ */
+static ssize_t
+serialize_policy_store(struct mddev *mddev, const char *buf, size_t len)
+{
+	int err;
+	bool value;
+
+	err = kstrtobool(buf, &value);
+	if (err)
+		return err;
+
+	if (value == mddev->serialize_policy)
+		return len;
+
+	err = mddev_lock(mddev);
+	if (err)
+		return err;
+	if (mddev->pers == NULL || (mddev->pers->level != 1)) {
+		pr_err("md: serialize_policy is only effective for raid1\n");
+		err = -EINVAL;
+		goto unlock;
+	}
+
+	mddev_suspend(mddev);
+	if (value)
+		mddev_create_serial_pool(mddev, NULL, true);
+	else
+		mddev_destroy_serial_pool(mddev, NULL, true);
+	mddev->serialize_policy = value;
+	mddev_resume(mddev);
+unlock:
+	mddev_unlock(mddev);
+	return err ?: len;
+}
+
+static struct md_sysfs_entry md_serialize_policy =
+__ATTR(serialize_policy, S_IRUGO | S_IWUSR, serialize_policy_show,
+       serialize_policy_store);
+
+
 static struct attribute *md_default_attrs[] = {
 	&md_level.attr,
 	&md_layout.attr,
@@ -5294,6 +5436,7 @@ static struct attribute *md_default_attrs[] = {
 	&max_corr_read_errors.attr,
 	&md_consistency_policy.attr,
 	&md_fail_last_dev.attr,
+	&md_serialize_policy.attr,
 	NULL,
 };
 
@@ -5769,18 +5912,18 @@ int md_run(struct mddev *mddev)
 		goto bitmap_abort;
 
 	if (mddev->bitmap_info.max_write_behind > 0) {
-		bool creat_pool = false;
+		bool create_pool = false;
 
 		rdev_for_each(rdev, mddev) {
 			if (test_bit(WriteMostly, &rdev->flags) &&
-			    rdev_init_wb(rdev))
-				creat_pool = true;
-		}
-		if (creat_pool && mddev->wb_info_pool == NULL) {
-			mddev->wb_info_pool =
-				mempool_create_kmalloc_pool(NR_WB_INFOS,
-						    sizeof(struct wb_info));
-			if (!mddev->wb_info_pool) {
+			    rdev_init_serial(rdev))
+				create_pool = true;
+		}
+		if (create_pool && mddev->serial_info_pool == NULL) {
+			mddev->serial_info_pool =
+				mempool_create_kmalloc_pool(NR_SERIAL_INFOS,
+						    sizeof(struct serial_info));
+			if (!mddev->serial_info_pool) {
 				err = -ENOMEM;
 				goto bitmap_abort;
 			}
@@ -6025,8 +6168,9 @@ static void __md_stop_writes(struct mddev *mddev)
 			mddev->in_sync = 1;
 		md_update_sb(mddev, 1);
 	}
-	mempool_destroy(mddev->wb_info_pool);
-	mddev->wb_info_pool = NULL;
+	/* disable policy to guarantee rdevs free resources for serialization */
+	mddev->serialize_policy = 0;
+	mddev_destroy_serial_pool(mddev, NULL, true);
 }
 
 void md_stop_writes(struct mddev *mddev)
diff --git a/drivers/md/md.h b/drivers/md/md.h
index 5f86f8adb0a4..acd681939112 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -32,6 +32,16 @@
  * be retried.
  */
 #define	MD_FAILFAST	(REQ_FAILFAST_DEV | REQ_FAILFAST_TRANSPORT)
+
+/*
+ * The struct embedded in rdev is used to serialize IO.
+ */
+struct serial_in_rdev {
+	struct rb_root_cached serial_rb;
+	spinlock_t serial_lock;
+	wait_queue_head_t serial_io_wait;
+};
+
 /*
  * MD's 'extended' device
  */
@@ -110,12 +120,7 @@ struct md_rdev {
 					   * in superblock.
 					   */
 
-	/*
-	 * The members for check collision of write behind IOs.
-	 */
-	struct list_head wb_list;
-	spinlock_t wb_list_lock;
-	wait_queue_head_t wb_io_wait;
+	struct serial_in_rdev *serial;  /* used for raid1 io serialization */
 
 	struct work_struct del_work;	/* used for delayed sysfs removal */
 
@@ -201,9 +206,9 @@ enum flag_bits {
 				 * it didn't fail, so don't use FailFast
 				 * any more for metadata
 				 */
-	WBCollisionCheck,	/*
-				 * multiqueue device should check if there
-				 * is collision between write behind bios.
+	CollisionCheck,		/*
+				 * check if there is collision between raid1
+				 * serial bios.
 				 */
 };
 
@@ -263,12 +268,13 @@ enum mddev_sb_flags {
 	MD_SB_NEED_REWRITE,	/* metadata write needs to be repeated */
 };
 
-#define NR_WB_INFOS	8
-/* record current range of write behind IOs */
-struct wb_info {
-	sector_t lo;
-	sector_t hi;
-	struct list_head list;
+#define NR_SERIAL_INFOS		8
+/* record current range of serialize IOs */
+struct serial_info {
+	struct rb_node node;
+	sector_t start;		/* start sector of rb node */
+	sector_t last;		/* end sector of rb node */
+	sector_t _subtree_last; /* highest sector in subtree of rb node */
 };
 
 struct mddev {
@@ -487,13 +493,14 @@ struct mddev {
 					  */
 	struct work_struct flush_work;
 	struct work_struct event_work;	/* used by dm to report failure event */
-	mempool_t *wb_info_pool;
+	mempool_t *serial_info_pool;
 	void (*sync_super)(struct mddev *mddev, struct md_rdev *rdev);
 	struct md_cluster_info		*cluster_info;
 	unsigned int			good_device_nr;	/* good device num within cluster raid */
 
 	bool	has_superblocks:1;
 	bool	fail_last_dev:1;
+	bool	serialize_policy:1;
 };
 
 enum recovery_flags {
@@ -737,8 +744,10 @@ extern struct bio *bio_alloc_mddev(gfp_t gfp_mask, int nr_iovecs,
 extern void md_reload_sb(struct mddev *mddev, int raid_disk);
 extern void md_update_sb(struct mddev *mddev, int force);
 extern void md_kick_rdev_from_array(struct md_rdev * rdev);
-extern void mddev_create_wb_pool(struct mddev *mddev, struct md_rdev *rdev,
-				 bool is_suspend);
+extern void mddev_create_serial_pool(struct mddev *mddev, struct md_rdev *rdev,
+				     bool is_suspend);
+extern void mddev_destroy_serial_pool(struct mddev *mddev, struct md_rdev *rdev,
+				      bool is_suspend);
 struct md_rdev *md_find_rdev_nr_rcu(struct mddev *mddev, int nr);
 struct md_rdev *md_find_rdev_rcu(struct mddev *mddev, dev_t dev);
 
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index 201fd8aec59a..cd810e195086 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -29,6 +29,7 @@
 #include <linux/module.h>
 #include <linux/seq_file.h>
 #include <linux/ratelimit.h>
+#include <linux/interval_tree_generic.h>
 
 #include <trace/events/block.h>
 
@@ -50,55 +51,71 @@ static void lower_barrier(struct r1conf *conf, sector_t sector_nr);
 
 #include "raid1-10.c"
 
-static int check_and_add_wb(struct md_rdev *rdev, sector_t lo, sector_t hi)
+#define START(node) ((node)->start)
+#define LAST(node) ((node)->last)
+INTERVAL_TREE_DEFINE(struct serial_info, node, sector_t, _subtree_last,
+		     START, LAST, static inline, raid1_rb);
+
+static int check_and_add_serial(struct md_rdev *rdev, struct r1bio *r1_bio,
+				struct serial_info *si, int idx)
 {
-	struct wb_info *wi, *temp_wi;
 	unsigned long flags;
 	int ret = 0;
-	struct mddev *mddev = rdev->mddev;
-
-	wi = mempool_alloc(mddev->wb_info_pool, GFP_NOIO);
-
-	spin_lock_irqsave(&rdev->wb_list_lock, flags);
-	list_for_each_entry(temp_wi, &rdev->wb_list, list) {
-		/* collision happened */
-		if (hi > temp_wi->lo && lo < temp_wi->hi) {
-			ret = -EBUSY;
-			break;
-		}
+	sector_t lo = r1_bio->sector;
+	sector_t hi = lo + r1_bio->sectors;
+	struct serial_in_rdev *serial = &rdev->serial[idx];
+
+	spin_lock_irqsave(&serial->serial_lock, flags);
+	/* collision happened */
+	if (raid1_rb_iter_first(&serial->serial_rb, lo, hi))
+		ret = -EBUSY;
+	else {
+		si->start = lo;
+		si->last = hi;
+		raid1_rb_insert(si, &serial->serial_rb);
 	}
-
-	if (!ret) {
-		wi->lo = lo;
-		wi->hi = hi;
-		list_add(&wi->list, &rdev->wb_list);
-	} else
-		mempool_free(wi, mddev->wb_info_pool);
-	spin_unlock_irqrestore(&rdev->wb_list_lock, flags);
+	spin_unlock_irqrestore(&serial->serial_lock, flags);
 
 	return ret;
 }
 
-static void remove_wb(struct md_rdev *rdev, sector_t lo, sector_t hi)
+static void wait_for_serialization(struct md_rdev *rdev, struct r1bio *r1_bio)
+{
+	struct mddev *mddev = rdev->mddev;
+	struct serial_info *si;
+	int idx = sector_to_idx(r1_bio->sector);
+	struct serial_in_rdev *serial = &rdev->serial[idx];
+
+	if (WARN_ON(!mddev->serial_info_pool))
+		return;
+	si = mempool_alloc(mddev->serial_info_pool, GFP_NOIO);
+	wait_event(serial->serial_io_wait,
+		   check_and_add_serial(rdev, r1_bio, si, idx) == 0);
+}
+
+static void remove_serial(struct md_rdev *rdev, sector_t lo, sector_t hi)
 {
-	struct wb_info *wi;
+	struct serial_info *si;
 	unsigned long flags;
 	int found = 0;
 	struct mddev *mddev = rdev->mddev;
-
-	spin_lock_irqsave(&rdev->wb_list_lock, flags);
-	list_for_each_entry(wi, &rdev->wb_list, list)
-		if (hi == wi->hi && lo == wi->lo) {
-			list_del(&wi->list);
-			mempool_free(wi, mddev->wb_info_pool);
+	int idx = sector_to_idx(lo);
+	struct serial_in_rdev *serial = &rdev->serial[idx];
+
+	spin_lock_irqsave(&serial->serial_lock, flags);
+	for (si = raid1_rb_iter_first(&serial->serial_rb, lo, hi);
+	     si; si = raid1_rb_iter_next(si, lo, hi)) {
+		if (si->start == lo && si->last == hi) {
+			raid1_rb_remove(si, &serial->serial_rb);
+			mempool_free(si, mddev->serial_info_pool);
 			found = 1;
 			break;
 		}
-
+	}
 	if (!found)
-		WARN(1, "The write behind IO is not recorded\n");
-	spin_unlock_irqrestore(&rdev->wb_list_lock, flags);
-	wake_up(&rdev->wb_io_wait);
+		WARN(1, "The write IO is not recorded for serialization\n");
+	spin_unlock_irqrestore(&serial->serial_lock, flags);
+	wake_up(&serial->serial_io_wait);
 }
 
 /*
@@ -430,6 +447,8 @@ static void raid1_end_write_request(struct bio *bio)
 	int mirror = find_bio_disk(r1_bio, bio);
 	struct md_rdev *rdev = conf->mirrors[mirror].rdev;
 	bool discard_error;
+	sector_t lo = r1_bio->sector;
+	sector_t hi = r1_bio->sector + r1_bio->sectors;
 
 	discard_error = bio->bi_status && bio_op(bio) == REQ_OP_DISCARD;
 
@@ -499,12 +518,8 @@ static void raid1_end_write_request(struct bio *bio)
 	}
 
 	if (behind) {
-		if (test_bit(WBCollisionCheck, &rdev->flags)) {
-			sector_t lo = r1_bio->sector;
-			sector_t hi = r1_bio->sector + r1_bio->sectors;
-
-			remove_wb(rdev, lo, hi);
-		}
+		if (test_bit(CollisionCheck, &rdev->flags))
+			remove_serial(rdev, lo, hi);
 		if (test_bit(WriteMostly, &rdev->flags))
 			atomic_dec(&r1_bio->behind_remaining);
 
@@ -527,7 +542,8 @@ static void raid1_end_write_request(struct bio *bio)
 				call_bio_endio(r1_bio);
 			}
 		}
-	}
+	} else if (rdev->mddev->serialize_policy)
+		remove_serial(rdev, lo, hi);
 	if (r1_bio->bios[mirror] == NULL)
 		rdev_dec_pending(rdev, conf->mddev);
 
@@ -1479,6 +1495,7 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
 
 	for (i = 0; i < disks; i++) {
 		struct bio *mbio = NULL;
+		struct md_rdev *rdev = conf->mirrors[i].rdev;
 		if (!r1_bio->bios[i])
 			continue;
 
@@ -1506,18 +1523,12 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
 			mbio = bio_clone_fast(bio, GFP_NOIO, &mddev->bio_set);
 
 		if (r1_bio->behind_master_bio) {
-			struct md_rdev *rdev = conf->mirrors[i].rdev;
-
-			if (test_bit(WBCollisionCheck, &rdev->flags)) {
-				sector_t lo = r1_bio->sector;
-				sector_t hi = r1_bio->sector + r1_bio->sectors;
-
-				wait_event(rdev->wb_io_wait,
-					   check_and_add_wb(rdev, lo, hi) == 0);
-			}
+			if (test_bit(CollisionCheck, &rdev->flags))
+				wait_for_serialization(rdev, r1_bio);
 			if (test_bit(WriteMostly, &rdev->flags))
 				atomic_inc(&r1_bio->behind_remaining);
-		}
+		} else if (mddev->serialize_policy)
+			wait_for_serialization(rdev, r1_bio);
 
 		r1_bio->bios[i] = mbio;
 
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index d4d3b67ffbba..ba00e9877f02 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -6598,7 +6598,6 @@ raid5_show_group_thread_cnt(struct mddev *mddev, char *page)
 
 static int alloc_thread_groups(struct r5conf *conf, int cnt,
 			       int *group_cnt,
-			       int *worker_cnt_per_group,
 			       struct r5worker_group **worker_groups);
 static ssize_t
 raid5_store_group_thread_cnt(struct mddev *mddev, const char *page, size_t len)
@@ -6607,7 +6606,7 @@ raid5_store_group_thread_cnt(struct mddev *mddev, const char *page, size_t len)
 	unsigned int new;
 	int err;
 	struct r5worker_group *new_groups, *old_groups;
-	int group_cnt, worker_cnt_per_group;
+	int group_cnt;
 
 	if (len >= PAGE_SIZE)
 		return -EINVAL;
@@ -6630,13 +6629,11 @@ raid5_store_group_thread_cnt(struct mddev *mddev, const char *page, size_t len)
 		if (old_groups)
 			flush_workqueue(raid5_wq);
 
-		err = alloc_thread_groups(conf, new,
-					  &group_cnt, &worker_cnt_per_group,
-					  &new_groups);
+		err = alloc_thread_groups(conf, new, &group_cnt, &new_groups);
 		if (!err) {
 			spin_lock_irq(&conf->device_lock);
 			conf->group_cnt = group_cnt;
-			conf->worker_cnt_per_group = worker_cnt_per_group;
+			conf->worker_cnt_per_group = new;
 			conf->worker_groups = new_groups;
 			spin_unlock_irq(&conf->device_lock);
 
@@ -6672,16 +6669,13 @@ static struct attribute_group raid5_attrs_group = {
 	.attrs = raid5_attrs,
 };
 
-static int alloc_thread_groups(struct r5conf *conf, int cnt,
-			       int *group_cnt,
-			       int *worker_cnt_per_group,
+static int alloc_thread_groups(struct r5conf *conf, int cnt, int *group_cnt,
 			       struct r5worker_group **worker_groups)
 {
 	int i, j, k;
 	ssize_t size;
 	struct r5worker *workers;
 
-	*worker_cnt_per_group = cnt;
 	if (cnt == 0) {
 		*group_cnt = 0;
 		*worker_groups = NULL;
@@ -6882,7 +6876,7 @@ static struct r5conf *setup_conf(struct mddev *mddev)
 	struct disk_info *disk;
 	char pers_name[6];
 	int i;
-	int group_cnt, worker_cnt_per_group;
+	int group_cnt;
 	struct r5worker_group *new_group;
 	int ret;
 
@@ -6928,10 +6922,9 @@ static struct r5conf *setup_conf(struct mddev *mddev)
 	for (i = 0; i < PENDING_IO_MAX; i++)
 		list_add(&conf->pending_data[i].sibling, &conf->free_list);
 	/* Don't enable multi-threading by default*/
-	if (!alloc_thread_groups(conf, 0, &group_cnt, &worker_cnt_per_group,
-				 &new_group)) {
+	if (!alloc_thread_groups(conf, 0, &group_cnt, &new_group)) {
 		conf->group_cnt = group_cnt;
-		conf->worker_cnt_per_group = worker_cnt_per_group;
+		conf->worker_cnt_per_group = 0;
 		conf->worker_groups = new_group;
 	} else
 		goto abort;