diff --git a/drivers/md/md-bitmap.c b/drivers/md/md-bitmap.c
index 3ad1824..e230052 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 4e7c9f3..4824d50 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -125,76 +125,167 @@ 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 (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 (rdev && !rdev_need_serial(rdev) &&
+	    !test_bit(CollisionCheck, &rdev->flags))
 		return;
 
-	if (!test_bit(WriteMostly, &rdev->flags) || !rdev_init_wb(rdev))
-		return;
+	if (!is_suspend)
+		mddev_suspend(mddev);
 
-	if (mddev->wb_info_pool == NULL) {
+	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;
 
+		noio_flag = memalloc_noio_save();
+		mddev->serial_info_pool =
+			mempool_create_kmalloc_pool(NR_SERIAL_INFOS,
+						sizeof(struct serial_info));
+		memalloc_noio_restore(noio_flag);
+		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);
+}
+
+/*
+ * 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.
+ */
+void mddev_destroy_serial_pool(struct mddev *mddev, struct md_rdev *rdev,
+			       bool is_suspend)
+{
+	if (rdev && !test_bit(CollisionCheck, &rdev->flags))
+		return;
+
+	if (mddev->serial_info_pool) {
+		struct md_rdev *temp;
+		int num = 0; /* used to track if other rdevs need the pool */
+
 		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));
-		memalloc_noio_restore(noio_flag);
-		if (!mddev->wb_info_pool)
-			pr_err("can't alloc memory pool for writemostly\n");
+		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 (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);
 	}
 }
-EXPORT_SYMBOL_GPL(mddev_create_wb_pool);
-
-/*
- * destroy wb_info_pool if rdev is the last device flaged with WBCollisionCheck.
- */
-static void mddev_destroy_wb_pool(struct mddev *mddev, struct md_rdev *rdev)
-{
-	if (!test_and_clear_bit(WBCollisionCheck, &rdev->flags))
-		return;
-
-	if (mddev->wb_info_pool) {
-		struct md_rdev *temp;
-		int num = 0;
-
-		/*
-		 * Check if other rdevs need wb_info_pool.
-		 */
-		rdev_for_each(temp, mddev)
-			if (temp != rdev &&
-			    test_bit(WBCollisionCheck, &temp->flags))
-				num++;
-		if (!num) {
-			mddev_suspend(rdev->mddev);
-			mempool_destroy(mddev->wb_info_pool);
-			mddev->wb_info_pool = NULL;
-			mddev_resume(rdev->mddev);
-		}
-	}
-}
 
 static struct ctl_table_header *raid_table_header;
 
@@ -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;
+			    rdev_init_serial(rdev))
+				create_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) {
+		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 5f86f8a..acd6819 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 201fd8a..cd810e1 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;
+	sector_t lo = r1_bio->sector;
+	sector_t hi = lo + r1_bio->sectors;
+	struct serial_in_rdev *serial = &rdev->serial[idx];
 
-	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;
-		}
+	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 wb_info *wi;
+	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 serial_info *si;
 	unsigned long flags;
 	int found = 0;
 	struct mddev *mddev = rdev->mddev;
+	int idx = sector_to_idx(lo);
+	struct serial_in_rdev *serial = &rdev->serial[idx];
 
-	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);
+	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 d4d3b67..ba00e98 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;
diff --git a/include/linux/raid/pq.h b/include/linux/raid/pq.h
index 0832c9b..154e954 100644
--- a/include/linux/raid/pq.h
+++ b/include/linux/raid/pq.h
@@ -27,8 +27,8 @@ extern const char raid6_empty_zero_page[PAGE_SIZE];
 
 #include <errno.h>
 #include <inttypes.h>
-#include <limits.h>
 #include <stddef.h>
+#include <string.h>
 #include <sys/mman.h>
 #include <sys/time.h>
 #include <sys/types.h>
@@ -44,6 +44,9 @@ typedef uint64_t u64;
 #ifndef PAGE_SIZE
 # define PAGE_SIZE 4096
 #endif
+#ifndef PAGE_SHIFT
+# define PAGE_SHIFT 12
+#endif
 extern const char raid6_empty_zero_page[PAGE_SIZE];
 
 #define __init
@@ -59,7 +62,9 @@ extern const char raid6_empty_zero_page[PAGE_SIZE];
 #define enable_kernel_altivec()
 #define disable_kernel_altivec()
 
+#undef	EXPORT_SYMBOL
 #define EXPORT_SYMBOL(sym)
+#undef	EXPORT_SYMBOL_GPL
 #define EXPORT_SYMBOL_GPL(sym)
 #define MODULE_LICENSE(licence)
 #define MODULE_DESCRIPTION(desc)
diff --git a/lib/raid6/algos.c b/lib/raid6/algos.c
index 17417ee..bf1b476 100644
--- a/lib/raid6/algos.c
+++ b/lib/raid6/algos.c
@@ -124,6 +124,9 @@ const struct raid6_recov_calls *const raid6_recov_algos[] = {
 #define time_before(x, y) ((x) < (y))
 #endif
 
+#define RAID6_TEST_DISKS	8
+#define RAID6_TEST_DISKS_ORDER	3
+
 static inline const struct raid6_recov_calls *raid6_choose_recov(void)
 {
 	const struct raid6_recov_calls *const *algo;
@@ -146,7 +149,7 @@ static inline const struct raid6_recov_calls *raid6_choose_recov(void)
 }
 
 static inline const struct raid6_calls *raid6_choose_gen(
-	void *(*const dptrs)[(65536/PAGE_SIZE)+2], const int disks)
+	void *(*const dptrs)[RAID6_TEST_DISKS], const int disks)
 {
 	unsigned long perf, bestgenperf, bestxorperf, j0, j1;
 	int start = (disks>>1)-1, stop = disks-3;	/* work on the second half of the disks */
@@ -181,7 +184,8 @@ static inline const struct raid6_calls *raid6_choose_gen(
 				best = *algo;
 			}
 			pr_info("raid6: %-8s gen() %5ld MB/s\n", (*algo)->name,
-			       (perf*HZ) >> (20-16+RAID6_TIME_JIFFIES_LG2));
+				(perf * HZ * (disks-2)) >>
+				(20 - PAGE_SHIFT + RAID6_TIME_JIFFIES_LG2));
 
 			if (!(*algo)->xor_syndrome)
 				continue;
@@ -204,17 +208,24 @@ static inline const struct raid6_calls *raid6_choose_gen(
 				bestxorperf = perf;
 
 			pr_info("raid6: %-8s xor() %5ld MB/s\n", (*algo)->name,
-				(perf*HZ) >> (20-16+RAID6_TIME_JIFFIES_LG2+1));
+				(perf * HZ * (disks-2)) >>
+				(20 - PAGE_SHIFT + RAID6_TIME_JIFFIES_LG2 + 1));
 		}
 	}
 
 	if (best) {
-		pr_info("raid6: using algorithm %s gen() %ld MB/s\n",
-		       best->name,
-		       (bestgenperf*HZ) >> (20-16+RAID6_TIME_JIFFIES_LG2));
-		if (best->xor_syndrome)
-			pr_info("raid6: .... xor() %ld MB/s, rmw enabled\n",
-			       (bestxorperf*HZ) >> (20-16+RAID6_TIME_JIFFIES_LG2+1));
+		if (IS_ENABLED(CONFIG_RAID6_PQ_BENCHMARK)) {
+			pr_info("raid6: using algorithm %s gen() %ld MB/s\n",
+				best->name,
+				(bestgenperf * HZ * (disks-2)) >>
+				(20 - PAGE_SHIFT+RAID6_TIME_JIFFIES_LG2));
+			if (best->xor_syndrome)
+				pr_info("raid6: .... xor() %ld MB/s, rmw enabled\n",
+					(bestxorperf * HZ * (disks-2)) >>
+					(20 - PAGE_SHIFT + RAID6_TIME_JIFFIES_LG2 + 1));
+		} else
+			pr_info("raid6: skip pq benchmark and using algorithm %s\n",
+				best->name);
 		raid6_call = *best;
 	} else
 		pr_err("raid6: Yikes!  No algorithm found!\n");
@@ -228,27 +239,33 @@ static inline const struct raid6_calls *raid6_choose_gen(
 
 int __init raid6_select_algo(void)
 {
-	const int disks = (65536/PAGE_SIZE)+2;
+	const int disks = RAID6_TEST_DISKS;
 
 	const struct raid6_calls *gen_best;
 	const struct raid6_recov_calls *rec_best;
-	char *syndromes;
-	void *dptrs[(65536/PAGE_SIZE)+2];
-	int i;
+	char *disk_ptr, *p;
+	void *dptrs[RAID6_TEST_DISKS];
+	int i, cycle;
 
-	for (i = 0; i < disks-2; i++)
-		dptrs[i] = ((char *)raid6_gfmul) + PAGE_SIZE*i;
-
-	/* Normal code - use a 2-page allocation to avoid D$ conflict */
-	syndromes = (void *) __get_free_pages(GFP_KERNEL, 1);
-
-	if (!syndromes) {
+	/* prepare the buffer and fill it circularly with gfmul table */
+	disk_ptr = (char *)__get_free_pages(GFP_KERNEL, RAID6_TEST_DISKS_ORDER);
+	if (!disk_ptr) {
 		pr_err("raid6: Yikes!  No memory available.\n");
 		return -ENOMEM;
 	}
 
-	dptrs[disks-2] = syndromes;
-	dptrs[disks-1] = syndromes + PAGE_SIZE;
+	p = disk_ptr;
+	for (i = 0; i < disks; i++)
+		dptrs[i] = p + PAGE_SIZE * i;
+
+	cycle = ((disks - 2) * PAGE_SIZE) / 65536;
+	for (i = 0; i < cycle; i++) {
+		memcpy(p, raid6_gfmul, 65536);
+		p += 65536;
+	}
+
+	if ((disks - 2) * PAGE_SIZE % 65536)
+		memcpy(p, raid6_gfmul, (disks - 2) * PAGE_SIZE % 65536);
 
 	/* select raid gen_syndrome function */
 	gen_best = raid6_choose_gen(&dptrs, disks);
@@ -256,7 +273,7 @@ int __init raid6_select_algo(void)
 	/* select raid recover functions */
 	rec_best = raid6_choose_recov();
 
-	free_pages((unsigned long)syndromes, 1);
+	free_pages((unsigned long)disk_ptr, RAID6_TEST_DISKS_ORDER);
 
 	return gen_best && rec_best ? 0 : -EINVAL;
 }
diff --git a/lib/raid6/mktables.c b/lib/raid6/mktables.c
index 9c485df..f02e10f 100644
--- a/lib/raid6/mktables.c
+++ b/lib/raid6/mktables.c
@@ -56,8 +56,8 @@ int main(int argc, char *argv[])
 	uint8_t v;
 	uint8_t exptbl[256], invtbl[256];
 
-	printf("#include <linux/raid/pq.h>\n");
 	printf("#include <linux/export.h>\n");
+	printf("#include <linux/raid/pq.h>\n");
 
 	/* Compute multiplication table */
 	printf("\nconst u8  __attribute__((aligned(256)))\n"