Merge tag 'md/3.12' of git://neil.brown.name/md

Pull md update from Neil Brown:
 "Headline item is multithreading for RAID5 so that more IO/sec can be
  supported on fast (SSD) devices.  Also TILE-Gx SIMD suppor for RAID6
  calculations and an assortment of bug fixes"

* tag 'md/3.12' of git://neil.brown.name/md:
  raid5: only wakeup necessary threads
  md/raid5: flush out all pending requests before proceeding with reshape.
  md/raid5: use seqcount to protect access to shape in make_request.
  raid5: sysfs entry to control worker thread number
  raid5: offload stripe handle to workqueue
  raid5: fix stripe release order
  raid5: make release_stripe lockless
  md: avoid deadlock when dirty buffers during md_stop.
  md: Don't test all of mddev->flags at once.
  md: Fix apparent cut-and-paste error in super_90_validate
  raid6/test: replace echo -e with printf
  RAID: add tilegx SIMD implementation of raid6
  md: fix safe_mode buglet.
  md: don't call md_allow_write in get_bitmap_file.

4 files changed, 406 insertions, 40 deletions

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 9f13e13..adf4d7e 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -1180,7 +1180,7 @@ static int super_90_validate(struct mddev *mddev, struct md_rdev *rdev)
 			mddev->bitmap_info.offset =
 				mddev->bitmap_info.default_offset;
 			mddev->bitmap_info.space =
-				mddev->bitmap_info.space;
+				mddev->bitmap_info.default_space;
 		}
 
 	} else if (mddev->pers == NULL) {
@@ -3429,7 +3429,7 @@ safe_delay_store(struct mddev *mddev, const char *cbuf, size_t len)
 		mddev->safemode_delay = (msec*HZ)/1000;
 		if (mddev->safemode_delay == 0)
 			mddev->safemode_delay = 1;
-		if (mddev->safemode_delay < old_delay)
+		if (mddev->safemode_delay < old_delay || old_delay == 0)
 			md_safemode_timeout((unsigned long)mddev);
 	}
 	return len;
@@ -5144,7 +5144,7 @@ int md_run(struct mddev *mddev)
 	
 	set_bit(MD_RECOVERY_NEEDED, &mddev->recovery);
 	
-	if (mddev->flags)
+	if (mddev->flags & MD_UPDATE_SB_FLAGS)
 		md_update_sb(mddev, 0);
 
 	md_new_event(mddev);
@@ -5289,7 +5289,7 @@ static void __md_stop_writes(struct mddev *mddev)
 	md_super_wait(mddev);
 
 	if (mddev->ro == 0 &&
-	    (!mddev->in_sync || mddev->flags)) {
+	    (!mddev->in_sync || (mddev->flags & MD_UPDATE_SB_FLAGS))) {
 		/* mark array as shutdown cleanly */
 		mddev->in_sync = 1;
 		md_update_sb(mddev, 1);
@@ -5337,8 +5337,14 @@ static int md_set_readonly(struct mddev *mddev, struct block_device *bdev)
 		err = -EBUSY;
 		goto out;
 	}
-	if (bdev)
-		sync_blockdev(bdev);
+	if (bdev && !test_bit(MD_STILL_CLOSED, &mddev->flags)) {
+		/* Someone opened the device since we flushed it
+		 * so page cache could be dirty and it is too late
+		 * to flush.  So abort
+		 */
+		mutex_unlock(&mddev->open_mutex);
+		return -EBUSY;
+	}
 	if (mddev->pers) {
 		__md_stop_writes(mddev);
 
@@ -5373,14 +5379,14 @@ static int do_md_stop(struct mddev * mddev, int mode,
 		mutex_unlock(&mddev->open_mutex);
 		return -EBUSY;
 	}
-	if (bdev)
-		/* It is possible IO was issued on some other
-		 * open file which was closed before we took ->open_mutex.
-		 * As that was not the last close __blkdev_put will not
-		 * have called sync_blockdev, so we must.
+	if (bdev && !test_bit(MD_STILL_CLOSED, &mddev->flags)) {
+		/* Someone opened the device since we flushed it
+		 * so page cache could be dirty and it is too late
+		 * to flush.  So abort
 		 */
-		sync_blockdev(bdev);
-
+		mutex_unlock(&mddev->open_mutex);
+		return -EBUSY;
+	}
 	if (mddev->pers) {
 		if (mddev->ro)
 			set_disk_ro(disk, 0);
@@ -5628,10 +5634,7 @@ static int get_bitmap_file(struct mddev * mddev, void __user * arg)
 	char *ptr, *buf = NULL;
 	int err = -ENOMEM;
 
-	if (md_allow_write(mddev))
-		file = kmalloc(sizeof(*file), GFP_NOIO);
-	else
-		file = kmalloc(sizeof(*file), GFP_KERNEL);
+	file = kmalloc(sizeof(*file), GFP_NOIO);
 
 	if (!file)
 		goto out;
@@ -6420,6 +6423,20 @@ static int md_ioctl(struct block_device *bdev, fmode_t mode,
 						 !test_bit(MD_RECOVERY_NEEDED,
 							   &mddev->flags),
 						 msecs_to_jiffies(5000));
+	if (cmd == STOP_ARRAY || cmd == STOP_ARRAY_RO) {
+		/* Need to flush page cache, and ensure no-one else opens
+		 * and writes
+		 */
+		mutex_lock(&mddev->open_mutex);
+		if (atomic_read(&mddev->openers) > 1) {
+			mutex_unlock(&mddev->open_mutex);
+			err = -EBUSY;
+			goto abort;
+		}
+		set_bit(MD_STILL_CLOSED, &mddev->flags);
+		mutex_unlock(&mddev->open_mutex);
+		sync_blockdev(bdev);
+	}
 	err = mddev_lock(mddev);
 	if (err) {
 		printk(KERN_INFO 
@@ -6673,6 +6690,7 @@ static int md_open(struct block_device *bdev, fmode_t mode)
 
 	err = 0;
 	atomic_inc(&mddev->openers);
+	clear_bit(MD_STILL_CLOSED, &mddev->flags);
 	mutex_unlock(&mddev->open_mutex);
 
 	check_disk_change(bdev);
@@ -7817,7 +7835,7 @@ void md_check_recovery(struct mddev *mddev)
 				sysfs_notify_dirent_safe(mddev->sysfs_state);
 		}
 
-		if (mddev->flags)
+		if (mddev->flags & MD_UPDATE_SB_FLAGS)
 			md_update_sb(mddev, 0);
 
 		if (test_bit(MD_RECOVERY_RUNNING, &mddev->recovery) &&
diff --git a/drivers/md/md.h b/drivers/md/md.h
index 20f02c0..608050c 100644
--- a/drivers/md/md.h
+++ b/drivers/md/md.h
@@ -204,12 +204,16 @@ struct mddev {
 	struct md_personality		*pers;
 	dev_t				unit;
 	int				md_minor;
-	struct list_head 		disks;
+	struct list_head		disks;
 	unsigned long			flags;
 #define MD_CHANGE_DEVS	0	/* Some device status has changed */
 #define MD_CHANGE_CLEAN 1	/* transition to or from 'clean' */
 #define MD_CHANGE_PENDING 2	/* switch from 'clean' to 'active' in progress */
+#define MD_UPDATE_SB_FLAGS (1 | 2 | 4)	/* If these are set, md_update_sb needed */
 #define MD_ARRAY_FIRST_USE 3    /* First use of array, needs initialization */
+#define MD_STILL_CLOSED	4	/* If set, then array has not been opened since
+				 * md_ioctl checked on it.
+				 */
 
 	int				suspended;
 	atomic_t			active_io;
@@ -218,7 +222,7 @@ struct mddev {
 						       * are happening, so run/
 						       * takeover/stop are not safe
 						       */
-	int				ready; /* See when safe to pass 
+	int				ready; /* See when safe to pass
 						* IO requests down */
 	struct gendisk			*gendisk;
 
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 78ea443..7ff4f25 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -53,6 +53,7 @@
 #include <linux/cpu.h>
 #include <linux/slab.h>
 #include <linux/ratelimit.h>
+#include <linux/nodemask.h>
 #include <trace/events/block.h>
 
 #include "md.h"
@@ -60,6 +61,10 @@
 #include "raid0.h"
 #include "bitmap.h"
 
+#define cpu_to_group(cpu) cpu_to_node(cpu)
+#define ANY_GROUP NUMA_NO_NODE
+
+static struct workqueue_struct *raid5_wq;
 /*
  * Stripe cache
  */
@@ -72,6 +77,7 @@
 #define BYPASS_THRESHOLD	1
 #define NR_HASH			(PAGE_SIZE / sizeof(struct hlist_head))
 #define HASH_MASK		(NR_HASH - 1)
+#define MAX_STRIPE_BATCH	8
 
 static inline struct hlist_head *stripe_hash(struct r5conf *conf, sector_t sect)
 {
@@ -200,6 +206,49 @@ static int stripe_operations_active(struct stripe_head *sh)
 	       test_bit(STRIPE_COMPUTE_RUN, &sh->state);
 }
 
+static void raid5_wakeup_stripe_thread(struct stripe_head *sh)
+{
+	struct r5conf *conf = sh->raid_conf;
+	struct r5worker_group *group;
+	int thread_cnt;
+	int i, cpu = sh->cpu;
+
+	if (!cpu_online(cpu)) {
+		cpu = cpumask_any(cpu_online_mask);
+		sh->cpu = cpu;
+	}
+
+	if (list_empty(&sh->lru)) {
+		struct r5worker_group *group;
+		group = conf->worker_groups + cpu_to_group(cpu);
+		list_add_tail(&sh->lru, &group->handle_list);
+		group->stripes_cnt++;
+		sh->group = group;
+	}
+
+	if (conf->worker_cnt_per_group == 0) {
+		md_wakeup_thread(conf->mddev->thread);
+		return;
+	}
+
+	group = conf->worker_groups + cpu_to_group(sh->cpu);
+
+	group->workers[0].working = true;
+	/* at least one worker should run to avoid race */
+	queue_work_on(sh->cpu, raid5_wq, &group->workers[0].work);
+
+	thread_cnt = group->stripes_cnt / MAX_STRIPE_BATCH - 1;
+	/* wakeup more workers */
+	for (i = 1; i < conf->worker_cnt_per_group && thread_cnt > 0; i++) {
+		if (group->workers[i].working == false) {
+			group->workers[i].working = true;
+			queue_work_on(sh->cpu, raid5_wq,
+				      &group->workers[i].work);
+			thread_cnt--;
+		}
+	}
+}
+
 static void do_release_stripe(struct r5conf *conf, struct stripe_head *sh)
 {
 	BUG_ON(!list_empty(&sh->lru));
@@ -214,7 +263,12 @@ static void do_release_stripe(struct r5conf *conf, struct stripe_head *sh)
 		else {
 			clear_bit(STRIPE_DELAYED, &sh->state);
 			clear_bit(STRIPE_BIT_DELAY, &sh->state);
-			list_add_tail(&sh->lru, &conf->handle_list);
+			if (conf->worker_cnt_per_group == 0) {
+				list_add_tail(&sh->lru, &conf->handle_list);
+			} else {
+				raid5_wakeup_stripe_thread(sh);
+				return;
+			}
 		}
 		md_wakeup_thread(conf->mddev->thread);
 	} else {
@@ -239,12 +293,62 @@ static void __release_stripe(struct r5conf *conf, struct stripe_head *sh)
 		do_release_stripe(conf, sh);
 }
 
+static struct llist_node *llist_reverse_order(struct llist_node *head)
+{
+	struct llist_node *new_head = NULL;
+
+	while (head) {
+		struct llist_node *tmp = head;
+		head = head->next;
+		tmp->next = new_head;
+		new_head = tmp;
+	}
+
+	return new_head;
+}
+
+/* should hold conf->device_lock already */
+static int release_stripe_list(struct r5conf *conf)
+{
+	struct stripe_head *sh;
+	int count = 0;
+	struct llist_node *head;
+
+	head = llist_del_all(&conf->released_stripes);
+	head = llist_reverse_order(head);
+	while (head) {
+		sh = llist_entry(head, struct stripe_head, release_list);
+		head = llist_next(head);
+		/* sh could be readded after STRIPE_ON_RELEASE_LIST is cleard */
+		smp_mb();
+		clear_bit(STRIPE_ON_RELEASE_LIST, &sh->state);
+		/*
+		 * Don't worry the bit is set here, because if the bit is set
+		 * again, the count is always > 1. This is true for
+		 * STRIPE_ON_UNPLUG_LIST bit too.
+		 */
+		__release_stripe(conf, sh);
+		count++;
+	}
+
+	return count;
+}
+
 static void release_stripe(struct stripe_head *sh)
 {
 	struct r5conf *conf = sh->raid_conf;
 	unsigned long flags;
+	bool wakeup;
 
+	if (test_and_set_bit(STRIPE_ON_RELEASE_LIST, &sh->state))
+		goto slow_path;
+	wakeup = llist_add(&sh->release_list, &conf->released_stripes);
+	if (wakeup)
+		md_wakeup_thread(conf->mddev->thread);
+	return;
+slow_path:
 	local_irq_save(flags);
+	/* we are ok here if STRIPE_ON_RELEASE_LIST is set or not */
 	if (atomic_dec_and_lock(&sh->count, &conf->device_lock)) {
 		do_release_stripe(conf, sh);
 		spin_unlock(&conf->device_lock);
@@ -359,6 +463,7 @@ static void init_stripe(struct stripe_head *sh, sector_t sector, int previous)
 		raid5_build_block(sh, i, previous);
 	}
 	insert_hash(conf, sh);
+	sh->cpu = smp_processor_id();
 }
 
 static struct stripe_head *__find_stripe(struct r5conf *conf, sector_t sector,
@@ -491,7 +596,8 @@ get_active_stripe(struct r5conf *conf, sector_t sector,
 			if (atomic_read(&sh->count)) {
 				BUG_ON(!list_empty(&sh->lru)
 				    && !test_bit(STRIPE_EXPANDING, &sh->state)
-				    && !test_bit(STRIPE_ON_UNPLUG_LIST, &sh->state));
+				    && !test_bit(STRIPE_ON_UNPLUG_LIST, &sh->state)
+				    && !test_bit(STRIPE_ON_RELEASE_LIST, &sh->state));
 			} else {
 				if (!test_bit(STRIPE_HANDLE, &sh->state))
 					atomic_inc(&conf->active_stripes);
@@ -499,6 +605,10 @@ get_active_stripe(struct r5conf *conf, sector_t sector,
 				    !test_bit(STRIPE_EXPANDING, &sh->state))
 					BUG();
 				list_del_init(&sh->lru);
+				if (sh->group) {
+					sh->group->stripes_cnt--;
+					sh->group = NULL;
+				}
 			}
 		}
 	} while (sh == NULL);
@@ -3779,6 +3889,7 @@ static void raid5_activate_delayed(struct r5conf *conf)
 			if (!test_and_set_bit(STRIPE_PREREAD_ACTIVE, &sh->state))
 				atomic_inc(&conf->preread_active_stripes);
 			list_add_tail(&sh->lru, &conf->hold_list);
+			raid5_wakeup_stripe_thread(sh);
 		}
 	}
 }
@@ -4058,18 +4169,35 @@ static int chunk_aligned_read(struct mddev *mddev, struct bio * raid_bio)
  * head of the hold_list has changed, i.e. the head was promoted to the
  * handle_list.
  */
-static struct stripe_head *__get_priority_stripe(struct r5conf *conf)
+static struct stripe_head *__get_priority_stripe(struct r5conf *conf, int group)
 {
-	struct stripe_head *sh;
+	struct stripe_head *sh = NULL, *tmp;
+	struct list_head *handle_list = NULL;
+	struct r5worker_group *wg = NULL;
+
+	if (conf->worker_cnt_per_group == 0) {
+		handle_list = &conf->handle_list;
+	} else if (group != ANY_GROUP) {
+		handle_list = &conf->worker_groups[group].handle_list;
+		wg = &conf->worker_groups[group];
+	} else {
+		int i;
+		for (i = 0; i < conf->group_cnt; i++) {
+			handle_list = &conf->worker_groups[i].handle_list;
+			wg = &conf->worker_groups[i];
+			if (!list_empty(handle_list))
+				break;
+		}
+	}
 
 	pr_debug("%s: handle: %s hold: %s full_writes: %d bypass_count: %d\n",
 		  __func__,
-		  list_empty(&conf->handle_list) ? "empty" : "busy",
+		  list_empty(handle_list) ? "empty" : "busy",
 		  list_empty(&conf->hold_list) ? "empty" : "busy",
 		  atomic_read(&conf->pending_full_writes), conf->bypass_count);
 
-	if (!list_empty(&conf->handle_list)) {
-		sh = list_entry(conf->handle_list.next, typeof(*sh), lru);
+	if (!list_empty(handle_list)) {
+		sh = list_entry(handle_list->next, typeof(*sh), lru);
 
 		if (list_empty(&conf->hold_list))
 			conf->bypass_count = 0;
@@ -4087,14 +4215,32 @@ static struct stripe_head *__get_priority_stripe(struct r5conf *conf)
 		   ((conf->bypass_threshold &&
 		     conf->bypass_count > conf->bypass_threshold) ||
 		    atomic_read(&conf->pending_full_writes) == 0)) {
-		sh = list_entry(conf->hold_list.next,
-				typeof(*sh), lru);
-		conf->bypass_count -= conf->bypass_threshold;
-		if (conf->bypass_count < 0)
-			conf->bypass_count = 0;
-	} else
+
+		list_for_each_entry(tmp, &conf->hold_list,  lru) {
+			if (conf->worker_cnt_per_group == 0 ||
+			    group == ANY_GROUP ||
+			    !cpu_online(tmp->cpu) ||
+			    cpu_to_group(tmp->cpu) == group) {
+				sh = tmp;
+				break;
+			}
+		}
+
+		if (sh) {
+			conf->bypass_count -= conf->bypass_threshold;
+			if (conf->bypass_count < 0)
+				conf->bypass_count = 0;
+		}
+		wg = NULL;
+	}
+
+	if (!sh)
 		return NULL;
 
+	if (wg) {
+		wg->stripes_cnt--;
+		sh->group = NULL;
+	}
 	list_del_init(&sh->lru);
 	atomic_inc(&sh->count);
 	BUG_ON(atomic_read(&sh->count) != 1);
@@ -4127,6 +4273,10 @@ static void raid5_unplug(struct blk_plug_cb *blk_cb, bool from_schedule)
 			 */
 			smp_mb__before_clear_bit();
 			clear_bit(STRIPE_ON_UNPLUG_LIST, &sh->state);
+			/*
+			 * STRIPE_ON_RELEASE_LIST could be set here. In that
+			 * case, the count is always > 1 here
+			 */
 			__release_stripe(conf, sh);
 			cnt++;
 		}
@@ -4286,8 +4436,10 @@ static void make_request(struct mddev *mddev, struct bio * bi)
 	for (;logical_sector < last_sector; logical_sector += STRIPE_SECTORS) {
 		DEFINE_WAIT(w);
 		int previous;
+		int seq;
 
 	retry:
+		seq = read_seqcount_begin(&conf->gen_lock);
 		previous = 0;
 		prepare_to_wait(&conf->wait_for_overlap, &w, TASK_UNINTERRUPTIBLE);
 		if (unlikely(conf->reshape_progress != MaxSector)) {
@@ -4320,7 +4472,7 @@ static void make_request(struct mddev *mddev, struct bio * bi)
 						  previous,
 						  &dd_idx, NULL);
 		pr_debug("raid456: make_request, sector %llu logical %llu\n",
-			(unsigned long long)new_sector, 
+			(unsigned long long)new_sector,
 			(unsigned long long)logical_sector);
 
 		sh = get_active_stripe(conf, new_sector, previous,
@@ -4349,6 +4501,13 @@ static void make_request(struct mddev *mddev, struct bio * bi)
 					goto retry;
 				}
 			}
+			if (read_seqcount_retry(&conf->gen_lock, seq)) {
+				/* Might have got the wrong stripe_head
+				 * by accident
+				 */
+				release_stripe(sh);
+				goto retry;
+			}
 
 			if (rw == WRITE &&
 			    logical_sector >= mddev->suspend_lo &&
@@ -4788,14 +4947,14 @@ static int  retry_aligned_read(struct r5conf *conf, struct bio *raid_bio)
 	return handled;
 }
 
-#define MAX_STRIPE_BATCH 8
-static int handle_active_stripes(struct r5conf *conf)
+static int handle_active_stripes(struct r5conf *conf, int group,
+				 struct r5worker *worker)
 {
 	struct stripe_head *batch[MAX_STRIPE_BATCH], *sh;
 	int i, batch_size = 0;
 
 	while (batch_size < MAX_STRIPE_BATCH &&
-			(sh = __get_priority_stripe(conf)) != NULL)
+			(sh = __get_priority_stripe(conf, group)) != NULL)
 		batch[batch_size++] = sh;
 
 	if (batch_size == 0)
@@ -4813,6 +4972,39 @@ static int handle_active_stripes(struct r5conf *conf)
 	return batch_size;
 }
 
+static void raid5_do_work(struct work_struct *work)
+{
+	struct r5worker *worker = container_of(work, struct r5worker, work);
+	struct r5worker_group *group = worker->group;
+	struct r5conf *conf = group->conf;
+	int group_id = group - conf->worker_groups;
+	int handled;
+	struct blk_plug plug;
+
+	pr_debug("+++ raid5worker active\n");
+
+	blk_start_plug(&plug);
+	handled = 0;
+	spin_lock_irq(&conf->device_lock);
+	while (1) {
+		int batch_size, released;
+
+		released = release_stripe_list(conf);
+
+		batch_size = handle_active_stripes(conf, group_id, worker);
+		worker->working = false;
+		if (!batch_size && !released)
+			break;
+		handled += batch_size;
+	}
+	pr_debug("%d stripes handled\n", handled);
+
+	spin_unlock_irq(&conf->device_lock);
+	blk_finish_plug(&plug);
+
+	pr_debug("--- raid5worker inactive\n");
+}
+
 /*
  * This is our raid5 kernel thread.
  *
@@ -4836,7 +5028,9 @@ static void raid5d(struct md_thread *thread)
 	spin_lock_irq(&conf->device_lock);
 	while (1) {
 		struct bio *bio;
-		int batch_size;
+		int batch_size, released;
+
+		released = release_stripe_list(conf);
 
 		if (
 		    !list_empty(&conf->bitmap_list)) {
@@ -4860,8 +5054,8 @@ static void raid5d(struct md_thread *thread)
 			handled++;
 		}
 
-		batch_size = handle_active_stripes(conf);
-		if (!batch_size)
+		batch_size = handle_active_stripes(conf, ANY_GROUP, NULL);
+		if (!batch_size && !released)
 			break;
 		handled += batch_size;
 
@@ -4989,10 +5183,70 @@ stripe_cache_active_show(struct mddev *mddev, char *page)
 static struct md_sysfs_entry
 raid5_stripecache_active = __ATTR_RO(stripe_cache_active);
 
+static ssize_t
+raid5_show_group_thread_cnt(struct mddev *mddev, char *page)
+{
+	struct r5conf *conf = mddev->private;
+	if (conf)
+		return sprintf(page, "%d\n", conf->worker_cnt_per_group);
+	else
+		return 0;
+}
+
+static int alloc_thread_groups(struct r5conf *conf, int cnt);
+static ssize_t
+raid5_store_group_thread_cnt(struct mddev *mddev, const char *page, size_t len)
+{
+	struct r5conf *conf = mddev->private;
+	unsigned long new;
+	int err;
+	struct r5worker_group *old_groups;
+	int old_group_cnt;
+
+	if (len >= PAGE_SIZE)
+		return -EINVAL;
+	if (!conf)
+		return -ENODEV;
+
+	if (kstrtoul(page, 10, &new))
+		return -EINVAL;
+
+	if (new == conf->worker_cnt_per_group)
+		return len;
+
+	mddev_suspend(mddev);
+
+	old_groups = conf->worker_groups;
+	old_group_cnt = conf->worker_cnt_per_group;
+
+	conf->worker_groups = NULL;
+	err = alloc_thread_groups(conf, new);
+	if (err) {
+		conf->worker_groups = old_groups;
+		conf->worker_cnt_per_group = old_group_cnt;
+	} else {
+		if (old_groups)
+			kfree(old_groups[0].workers);
+		kfree(old_groups);
+	}
+
+	mddev_resume(mddev);
+
+	if (err)
+		return err;
+	return len;
+}
+
+static struct md_sysfs_entry
+raid5_group_thread_cnt = __ATTR(group_thread_cnt, S_IRUGO | S_IWUSR,
+				raid5_show_group_thread_cnt,
+				raid5_store_group_thread_cnt);
+
 static struct attribute *raid5_attrs[] =  {
 	&raid5_stripecache_size.attr,
 	&raid5_stripecache_active.attr,
 	&raid5_preread_bypass_threshold.attr,
+	&raid5_group_thread_cnt.attr,
 	NULL,
 };
 static struct attribute_group raid5_attrs_group = {
@@ -5000,6 +5254,54 @@ static struct attribute_group raid5_attrs_group = {
 	.attrs = raid5_attrs,
 };
 
+static int alloc_thread_groups(struct r5conf *conf, int cnt)
+{
+	int i, j;
+	ssize_t size;
+	struct r5worker *workers;
+
+	conf->worker_cnt_per_group = cnt;
+	if (cnt == 0) {
+		conf->worker_groups = NULL;
+		return 0;
+	}
+	conf->group_cnt = num_possible_nodes();
+	size = sizeof(struct r5worker) * cnt;
+	workers = kzalloc(size * conf->group_cnt, GFP_NOIO);
+	conf->worker_groups = kzalloc(sizeof(struct r5worker_group) *
+				conf->group_cnt, GFP_NOIO);
+	if (!conf->worker_groups || !workers) {
+		kfree(workers);
+		kfree(conf->worker_groups);
+		conf->worker_groups = NULL;
+		return -ENOMEM;
+	}
+
+	for (i = 0; i < conf->group_cnt; i++) {
+		struct r5worker_group *group;
+
+		group = &conf->worker_groups[i];
+		INIT_LIST_HEAD(&group->handle_list);
+		group->conf = conf;
+		group->workers = workers + i * cnt;
+
+		for (j = 0; j < cnt; j++) {
+			group->workers[j].group = group;
+			INIT_WORK(&group->workers[j].work, raid5_do_work);
+		}
+	}
+
+	return 0;
+}
+
+static void free_thread_groups(struct r5conf *conf)
+{
+	if (conf->worker_groups)
+		kfree(conf->worker_groups[0].workers);
+	kfree(conf->worker_groups);
+	conf->worker_groups = NULL;
+}
+
 static sector_t
 raid5_size(struct mddev *mddev, sector_t sectors, int raid_disks)
 {
@@ -5040,6 +5342,7 @@ static void raid5_free_percpu(struct r5conf *conf)
 
 static void free_conf(struct r5conf *conf)
 {
+	free_thread_groups(conf);
 	shrink_stripes(conf);
 	raid5_free_percpu(conf);
 	kfree(conf->disks);
@@ -5168,7 +5471,11 @@ static struct r5conf *setup_conf(struct mddev *mddev)
 	conf = kzalloc(sizeof(struct r5conf), GFP_KERNEL);
 	if (conf == NULL)
 		goto abort;
+	/* Don't enable multi-threading by default*/
+	if (alloc_thread_groups(conf, 0))
+		goto abort;
 	spin_lock_init(&conf->device_lock);
+	seqcount_init(&conf->gen_lock);
 	init_waitqueue_head(&conf->wait_for_stripe);
 	init_waitqueue_head(&conf->wait_for_overlap);
 	INIT_LIST_HEAD(&conf->handle_list);
@@ -5176,6 +5483,7 @@ static struct r5conf *setup_conf(struct mddev *mddev)
 	INIT_LIST_HEAD(&conf->delayed_list);
 	INIT_LIST_HEAD(&conf->bitmap_list);
 	INIT_LIST_HEAD(&conf->inactive_list);
+	init_llist_head(&conf->released_stripes);
 	atomic_set(&conf->active_stripes, 0);
 	atomic_set(&conf->preread_active_stripes, 0);
 	atomic_set(&conf->active_aligned_reads, 0);
@@ -5980,6 +6288,7 @@ static int raid5_start_reshape(struct mddev *mddev)
 
 	atomic_set(&conf->reshape_stripes, 0);
 	spin_lock_irq(&conf->device_lock);
+	write_seqcount_begin(&conf->gen_lock);
 	conf->previous_raid_disks = conf->raid_disks;
 	conf->raid_disks += mddev->delta_disks;
 	conf->prev_chunk_sectors = conf->chunk_sectors;
@@ -5996,8 +6305,16 @@ static int raid5_start_reshape(struct mddev *mddev)
 	else
 		conf->reshape_progress = 0;
 	conf->reshape_safe = conf->reshape_progress;
+	write_seqcount_end(&conf->gen_lock);
 	spin_unlock_irq(&conf->device_lock);
 
+	/* Now make sure any requests that proceeded on the assumption
+	 * the reshape wasn't running - like Discard or Read - have
+	 * completed.
+	 */
+	mddev_suspend(mddev);
+	mddev_resume(mddev);
+
 	/* Add some new drives, as many as will fit.
 	 * We know there are enough to make the newly sized array work.
 	 * Don't add devices if we are reducing the number of
@@ -6472,6 +6789,10 @@ static struct md_personality raid4_personality =
 
 static int __init raid5_init(void)
 {
+	raid5_wq = alloc_workqueue("raid5wq",
+		WQ_UNBOUND|WQ_MEM_RECLAIM|WQ_CPU_INTENSIVE|WQ_SYSFS, 0);
+	if (!raid5_wq)
+		return -ENOMEM;
 	register_md_personality(&raid6_personality);
 	register_md_personality(&raid5_personality);
 	register_md_personality(&raid4_personality);
@@ -6483,6 +6804,7 @@ static void raid5_exit(void)
 	unregister_md_personality(&raid6_personality);
 	unregister_md_personality(&raid5_personality);
 	unregister_md_personality(&raid4_personality);
+	destroy_workqueue(raid5_wq);
 }
 
 module_init(raid5_init);
diff --git a/drivers/md/raid5.h b/drivers/md/raid5.h
index 70c4932..2113ffa 100644
--- a/drivers/md/raid5.h
+++ b/drivers/md/raid5.h
@@ -197,6 +197,7 @@ enum reconstruct_states {
 struct stripe_head {
 	struct hlist_node	hash;
 	struct list_head	lru;	      /* inactive_list or handle_list */
+	struct llist_node	release_list;
 	struct r5conf		*raid_conf;
 	short			generation;	/* increments with every
 						 * reshape */
@@ -211,6 +212,8 @@ struct stripe_head {
 	enum check_states	check_state;
 	enum reconstruct_states reconstruct_state;
 	spinlock_t		stripe_lock;
+	int			cpu;
+	struct r5worker_group	*group;
 	/**
 	 * struct stripe_operations
 	 * @target - STRIPE_OP_COMPUTE_BLK target
@@ -321,6 +324,7 @@ enum {
 	STRIPE_OPS_REQ_PENDING,
 	STRIPE_ON_UNPLUG_LIST,
 	STRIPE_DISCARD,
+	STRIPE_ON_RELEASE_LIST,
 };
 
 /*
@@ -363,6 +367,19 @@ struct disk_info {
 	struct md_rdev	*rdev, *replacement;
 };
 
+struct r5worker {
+	struct work_struct work;
+	struct r5worker_group *group;
+	bool working;
+};
+
+struct r5worker_group {
+	struct list_head handle_list;
+	struct r5conf *conf;
+	struct r5worker *workers;
+	int stripes_cnt;
+};
+
 struct r5conf {
 	struct hlist_head	*stripe_hashtbl;
 	struct mddev		*mddev;
@@ -386,6 +403,7 @@ struct r5conf {
 	int			prev_chunk_sectors;
 	int			prev_algo;
 	short			generation; /* increments with every reshape */
+	seqcount_t		gen_lock;	/* lock against generation changes */
 	unsigned long		reshape_checkpoint; /* Time we last updated
 						     * metadata */
 	long long		min_offset_diff; /* minimum difference between
@@ -445,6 +463,7 @@ struct r5conf {
 	 */
 	atomic_t		active_stripes;
 	struct list_head	inactive_list;
+	struct llist_head	released_stripes;
 	wait_queue_head_t	wait_for_stripe;
 	wait_queue_head_t	wait_for_overlap;
 	int			inactive_blocked;	/* release of inactive stripes blocked,
@@ -458,6 +477,9 @@ struct r5conf {
 	 * the new thread here until we fully activate the array.
 	 */
 	struct md_thread	*thread;
+	struct r5worker_group	*worker_groups;
+	int			group_cnt;
+	int			worker_cnt_per_group;
 };
 
 /*