diff --git a/drivers/md/bitmap.c b/drivers/md/bitmap.c
index 220273e81ed6b2599b29dc031d4f7a87c486fb01..51315302a85e43ab651a4edaba742784d5e04af2 100644
--- a/drivers/md/bitmap.c
+++ b/drivers/md/bitmap.c
@@ -301,7 +301,7 @@ static int write_sb_page(mddev_t *mddev, long offset, struct page *page, int wai
 				       page);
 
 	if (wait)
-		wait_event(mddev->sb_wait, atomic_read(&mddev->pending_writes)==0);
+		md_super_wait(mddev);
 	return 0;
 }
 
@@ -828,8 +828,7 @@ int bitmap_unplug(struct bitmap *bitmap)
 					    wake_up_process(bitmap->writeback_daemon->tsk));
 			spin_unlock_irq(&bitmap->write_lock);
 		} else
-			wait_event(bitmap->mddev->sb_wait,
-				   atomic_read(&bitmap->mddev->pending_writes)==0);
+			md_super_wait(bitmap->mddev);
 	}
 	return 0;
 }
diff --git a/drivers/md/md.c b/drivers/md/md.c
index caa4add00c1b2240a3eb0579897587e67a51171e..199016932de500188c2fb0e04e8dacd6a5946f1f 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -330,18 +330,46 @@ static void free_disk_sb(mdk_rdev_t * rdev)
 static int super_written(struct bio *bio, unsigned int bytes_done, int error)
 {
 	mdk_rdev_t *rdev = bio->bi_private;
+	mddev_t *mddev = rdev->mddev;
 	if (bio->bi_size)
 		return 1;
 
 	if (error || !test_bit(BIO_UPTODATE, &bio->bi_flags))
-		md_error(rdev->mddev, rdev);
+		md_error(mddev, rdev);
 
-	if (atomic_dec_and_test(&rdev->mddev->pending_writes))
-		wake_up(&rdev->mddev->sb_wait);
+	if (atomic_dec_and_test(&mddev->pending_writes))
+		wake_up(&mddev->sb_wait);
 	bio_put(bio);
 	return 0;
 }
 
+static int super_written_barrier(struct bio *bio, unsigned int bytes_done, int error)
+{
+	struct bio *bio2 = bio->bi_private;
+	mdk_rdev_t *rdev = bio2->bi_private;
+	mddev_t *mddev = rdev->mddev;
+	if (bio->bi_size)
+		return 1;
+
+	if (!test_bit(BIO_UPTODATE, &bio->bi_flags) &&
+	    error == -EOPNOTSUPP) {
+		unsigned long flags;
+		/* barriers don't appear to be supported :-( */
+		set_bit(BarriersNotsupp, &rdev->flags);
+		mddev->barriers_work = 0;
+		spin_lock_irqsave(&mddev->write_lock, flags);
+		bio2->bi_next = mddev->biolist;
+		mddev->biolist = bio2;
+		spin_unlock_irqrestore(&mddev->write_lock, flags);
+		wake_up(&mddev->sb_wait);
+		bio_put(bio);
+		return 0;
+	}
+	bio_put(bio2);
+	bio->bi_private = rdev;
+	return super_written(bio, bytes_done, error);
+}
+
 void md_super_write(mddev_t *mddev, mdk_rdev_t *rdev,
 		   sector_t sector, int size, struct page *page)
 {
@@ -350,16 +378,54 @@ void md_super_write(mddev_t *mddev, mdk_rdev_t *rdev,
 	 * and decrement it on completion, waking up sb_wait
 	 * if zero is reached.
 	 * If an error occurred, call md_error
+	 *
+	 * As we might need to resubmit the request if BIO_RW_BARRIER
+	 * causes ENOTSUPP, we allocate a spare bio...
 	 */
 	struct bio *bio = bio_alloc(GFP_NOIO, 1);
+	int rw = (1<<BIO_RW) | (1<<BIO_RW_SYNC);
 
 	bio->bi_bdev = rdev->bdev;
 	bio->bi_sector = sector;
 	bio_add_page(bio, page, size, 0);
 	bio->bi_private = rdev;
 	bio->bi_end_io = super_written;
+	bio->bi_rw = rw;
+
 	atomic_inc(&mddev->pending_writes);
-	submit_bio((1<<BIO_RW)|(1<<BIO_RW_SYNC), bio);
+	if (!test_bit(BarriersNotsupp, &rdev->flags)) {
+		struct bio *rbio;
+		rw |= (1<<BIO_RW_BARRIER);
+		rbio = bio_clone(bio, GFP_NOIO);
+		rbio->bi_private = bio;
+		rbio->bi_end_io = super_written_barrier;
+		submit_bio(rw, rbio);
+	} else
+		submit_bio(rw, bio);
+}
+
+void md_super_wait(mddev_t *mddev)
+{
+	/* wait for all superblock writes that were scheduled to complete.
+	 * if any had to be retried (due to BARRIER problems), retry them
+	 */
+	DEFINE_WAIT(wq);
+	for(;;) {
+		prepare_to_wait(&mddev->sb_wait, &wq, TASK_UNINTERRUPTIBLE);
+		if (atomic_read(&mddev->pending_writes)==0)
+			break;
+		while (mddev->biolist) {
+			struct bio *bio;
+			spin_lock_irq(&mddev->write_lock);
+			bio = mddev->biolist;
+			mddev->biolist = bio->bi_next ;
+			bio->bi_next = NULL;
+			spin_unlock_irq(&mddev->write_lock);
+			submit_bio(bio->bi_rw, bio);
+		}
+		schedule();
+	}
+	finish_wait(&mddev->sb_wait, &wq);
 }
 
 static int bi_complete(struct bio *bio, unsigned int bytes_done, int error)
@@ -1382,7 +1448,7 @@ static void md_update_sb(mddev_t * mddev)
 	int sync_req;
 
 repeat:
-	spin_lock(&mddev->write_lock);
+	spin_lock_irq(&mddev->write_lock);
 	sync_req = mddev->in_sync;
 	mddev->utime = get_seconds();
 	mddev->events ++;
@@ -1405,11 +1471,11 @@ static void md_update_sb(mddev_t * mddev)
 	 */
 	if (!mddev->persistent) {
 		mddev->sb_dirty = 0;
-		spin_unlock(&mddev->write_lock);
+		spin_unlock_irq(&mddev->write_lock);
 		wake_up(&mddev->sb_wait);
 		return;
 	}
-	spin_unlock(&mddev->write_lock);
+	spin_unlock_irq(&mddev->write_lock);
 
 	dprintk(KERN_INFO 
 		"md: updating %s RAID superblock on device (in sync %d)\n",
@@ -1437,17 +1503,17 @@ static void md_update_sb(mddev_t * mddev)
 			/* only need to write one superblock... */
 			break;
 	}
-	wait_event(mddev->sb_wait, atomic_read(&mddev->pending_writes)==0);
+	md_super_wait(mddev);
 	/* if there was a failure, sb_dirty was set to 1, and we re-write super */
 
-	spin_lock(&mddev->write_lock);
+	spin_lock_irq(&mddev->write_lock);
 	if (mddev->in_sync != sync_req|| mddev->sb_dirty == 1) {
 		/* have to write it out again */
-		spin_unlock(&mddev->write_lock);
+		spin_unlock_irq(&mddev->write_lock);
 		goto repeat;
 	}
 	mddev->sb_dirty = 0;
-	spin_unlock(&mddev->write_lock);
+	spin_unlock_irq(&mddev->write_lock);
 	wake_up(&mddev->sb_wait);
 
 }
@@ -1989,6 +2055,7 @@ static int do_md_run(mddev_t * mddev)
 
 	mddev->recovery = 0;
 	mddev->resync_max_sectors = mddev->size << 1; /* may be over-ridden by personality */
+	mddev->barriers_work = 1;
 
 	/* before we start the array running, initialise the bitmap */
 	err = bitmap_create(mddev);
@@ -2107,7 +2174,7 @@ static int do_md_stop(mddev_t * mddev, int ro)
 			mddev->ro = 1;
 		} else {
 			bitmap_flush(mddev);
-			wait_event(mddev->sb_wait, atomic_read(&mddev->pending_writes)==0);
+			md_super_wait(mddev);
 			if (mddev->ro)
 				set_disk_ro(disk, 0);
 			blk_queue_make_request(mddev->queue, md_fail_request);
@@ -3796,13 +3863,13 @@ void md_write_start(mddev_t *mddev, struct bio *bi)
 
 	atomic_inc(&mddev->writes_pending);
 	if (mddev->in_sync) {
-		spin_lock(&mddev->write_lock);
+		spin_lock_irq(&mddev->write_lock);
 		if (mddev->in_sync) {
 			mddev->in_sync = 0;
 			mddev->sb_dirty = 1;
 			md_wakeup_thread(mddev->thread);
 		}
-		spin_unlock(&mddev->write_lock);
+		spin_unlock_irq(&mddev->write_lock);
 	}
 	wait_event(mddev->sb_wait, mddev->sb_dirty==0);
 }
@@ -4112,7 +4179,7 @@ void md_check_recovery(mddev_t *mddev)
 	if (mddev_trylock(mddev)==0) {
 		int spares =0;
 
-		spin_lock(&mddev->write_lock);
+		spin_lock_irq(&mddev->write_lock);
 		if (mddev->safemode && !atomic_read(&mddev->writes_pending) &&
 		    !mddev->in_sync && mddev->recovery_cp == MaxSector) {
 			mddev->in_sync = 1;
@@ -4120,7 +4187,7 @@ void md_check_recovery(mddev_t *mddev)
 		}
 		if (mddev->safemode == 1)
 			mddev->safemode = 0;
-		spin_unlock(&mddev->write_lock);
+		spin_unlock_irq(&mddev->write_lock);
 
 		if (mddev->sb_dirty)
 			md_update_sb(mddev);
diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
index fb6b866c28f5f41e84254cb233fac24782854b22..1cbf51fbd43fe4539862f39cd6b97e8932d6f36a 100644
--- a/drivers/md/raid1.c
+++ b/drivers/md/raid1.c
@@ -301,7 +301,7 @@ static int raid1_end_write_request(struct bio *bio, unsigned int bytes_done, int
 {
 	int uptodate = test_bit(BIO_UPTODATE, &bio->bi_flags);
 	r1bio_t * r1_bio = (r1bio_t *)(bio->bi_private);
-	int mirror, behind;
+	int mirror, behind = test_bit(R1BIO_BehindIO, &r1_bio->state);
 	conf_t *conf = mddev_to_conf(r1_bio->mddev);
 
 	if (bio->bi_size)
@@ -311,47 +311,54 @@ static int raid1_end_write_request(struct bio *bio, unsigned int bytes_done, int
 		if (r1_bio->bios[mirror] == bio)
 			break;
 
-	/*
-	 * this branch is our 'one mirror IO has finished' event handler:
-	 */
-	if (!uptodate) {
-		md_error(r1_bio->mddev, conf->mirrors[mirror].rdev);
-		/* an I/O failed, we can't clear the bitmap */
-		set_bit(R1BIO_Degraded, &r1_bio->state);
-	} else
+	if (error == -ENOTSUPP && test_bit(R1BIO_Barrier, &r1_bio->state)) {
+		set_bit(BarriersNotsupp, &conf->mirrors[mirror].rdev->flags);
+		set_bit(R1BIO_BarrierRetry, &r1_bio->state);
+		r1_bio->mddev->barriers_work = 0;
+	} else {
 		/*
-		 * Set R1BIO_Uptodate in our master bio, so that
-		 * we will return a good error code for to the higher
-		 * levels even if IO on some other mirrored buffer fails.
-		 *
-		 * The 'master' represents the composite IO operation to
-		 * user-side. So if something waits for IO, then it will
-		 * wait for the 'master' bio.
+		 * this branch is our 'one mirror IO has finished' event handler:
 		 */
-		set_bit(R1BIO_Uptodate, &r1_bio->state);
-
-	update_head_pos(mirror, r1_bio);
-
-	behind = test_bit(R1BIO_BehindIO, &r1_bio->state);
-	if (behind) {
-		if (test_bit(WriteMostly, &conf->mirrors[mirror].rdev->flags))
-			atomic_dec(&r1_bio->behind_remaining);
-
-		/* In behind mode, we ACK the master bio once the I/O has safely
-		 * reached all non-writemostly disks. Setting the Returned bit
-		 * ensures that this gets done only once -- we don't ever want to
-		 * return -EIO here, instead we'll wait */
-
-		if (atomic_read(&r1_bio->behind_remaining) >= (atomic_read(&r1_bio->remaining)-1) &&
-		    test_bit(R1BIO_Uptodate, &r1_bio->state)) {
-			/* Maybe we can return now */
-			if (!test_and_set_bit(R1BIO_Returned, &r1_bio->state)) {
-				struct bio *mbio = r1_bio->master_bio;
-				PRINTK(KERN_DEBUG "raid1: behind end write sectors %llu-%llu\n",
-				       (unsigned long long) mbio->bi_sector,
-				       (unsigned long long) mbio->bi_sector +
-				       (mbio->bi_size >> 9) - 1);
-				bio_endio(mbio, mbio->bi_size, 0);
+		r1_bio->bios[mirror] = NULL;
+		bio_put(bio);
+		if (!uptodate) {
+			md_error(r1_bio->mddev, conf->mirrors[mirror].rdev);
+			/* an I/O failed, we can't clear the bitmap */
+			set_bit(R1BIO_Degraded, &r1_bio->state);
+		} else
+			/*
+			 * Set R1BIO_Uptodate in our master bio, so that
+			 * we will return a good error code for to the higher
+			 * levels even if IO on some other mirrored buffer fails.
+			 *
+			 * The 'master' represents the composite IO operation to
+			 * user-side. So if something waits for IO, then it will
+			 * wait for the 'master' bio.
+			 */
+			set_bit(R1BIO_Uptodate, &r1_bio->state);
+
+		update_head_pos(mirror, r1_bio);
+
+		if (behind) {
+			if (test_bit(WriteMostly, &conf->mirrors[mirror].rdev->flags))
+				atomic_dec(&r1_bio->behind_remaining);
+
+			/* In behind mode, we ACK the master bio once the I/O has safely
+			 * reached all non-writemostly disks. Setting the Returned bit
+			 * ensures that this gets done only once -- we don't ever want to
+			 * return -EIO here, instead we'll wait */
+
+			if (atomic_read(&r1_bio->behind_remaining) >= (atomic_read(&r1_bio->remaining)-1) &&
+			    test_bit(R1BIO_Uptodate, &r1_bio->state)) {
+				/* Maybe we can return now */
+				if (!test_and_set_bit(R1BIO_Returned, &r1_bio->state)) {
+					struct bio *mbio = r1_bio->master_bio;
+					PRINTK(KERN_DEBUG "raid1: behind end write sectors %llu-%llu\n",
+					       (unsigned long long) mbio->bi_sector,
+					       (unsigned long long) mbio->bi_sector +
+					       (mbio->bi_size >> 9) - 1);
+					bio_endio(mbio, mbio->bi_size, 0);
+				}
 			}
 		}
 	}
@@ -361,8 +368,16 @@ static int raid1_end_write_request(struct bio *bio, unsigned int bytes_done, int
 	 * already.
 	 */
 	if (atomic_dec_and_test(&r1_bio->remaining)) {
+		if (test_bit(R1BIO_BarrierRetry, &r1_bio->state)) {
+			reschedule_retry(r1_bio);
+			/* Don't dec_pending yet, we want to hold
+			 * the reference over the retry
+			 */
+			return 0;
+		}
 		if (test_bit(R1BIO_BehindIO, &r1_bio->state)) {
 			/* free extra copy of the data pages */
+/* FIXME bio has been freed!!! */
 			int i = bio->bi_vcnt;
 			while (i--)
 				__free_page(bio->bi_io_vec[i].bv_page);
@@ -648,8 +663,9 @@ static int make_request(request_queue_t *q, struct bio * bio)
 	struct bio_list bl;
 	struct page **behind_pages = NULL;
 	const int rw = bio_data_dir(bio);
+	int do_barriers;
 
-	if (unlikely(bio_barrier(bio))) {
+	if (unlikely(!mddev->barriers_work && bio_barrier(bio))) {
 		bio_endio(bio, bio->bi_size, -EOPNOTSUPP);
 		return 0;
 	}
@@ -759,6 +775,10 @@ static int make_request(request_queue_t *q, struct bio * bio)
 	atomic_set(&r1_bio->remaining, 0);
 	atomic_set(&r1_bio->behind_remaining, 0);
 
+	do_barriers = bio->bi_rw & BIO_RW_BARRIER;
+	if (do_barriers)
+		set_bit(R1BIO_Barrier, &r1_bio->state);
+
 	bio_list_init(&bl);
 	for (i = 0; i < disks; i++) {
 		struct bio *mbio;
@@ -771,7 +791,7 @@ static int make_request(request_queue_t *q, struct bio * bio)
 		mbio->bi_sector	= r1_bio->sector + conf->mirrors[i].rdev->data_offset;
 		mbio->bi_bdev = conf->mirrors[i].rdev->bdev;
 		mbio->bi_end_io	= raid1_end_write_request;
-		mbio->bi_rw = WRITE;
+		mbio->bi_rw = WRITE | do_barriers;
 		mbio->bi_private = r1_bio;
 
 		if (behind_pages) {
@@ -1153,6 +1173,36 @@ static void raid1d(mddev_t *mddev)
 		if (test_bit(R1BIO_IsSync, &r1_bio->state)) {
 			sync_request_write(mddev, r1_bio);
 			unplug = 1;
+		} else if (test_bit(R1BIO_BarrierRetry, &r1_bio->state)) {
+			/* some requests in the r1bio were BIO_RW_BARRIER
+			 * requests which failed with -ENOTSUPP.  Hohumm..
+			 * Better resubmit without the barrier.
+			 * We know which devices to resubmit for, because
+			 * all others have had their bios[] entry cleared.
+			 */
+			int i;
+			clear_bit(R1BIO_BarrierRetry, &r1_bio->state);
+			clear_bit(R1BIO_Barrier, &r1_bio->state);
+			for (i=0; i < conf->raid_disks; i++)
+				if (r1_bio->bios[i]) {
+					struct bio_vec *bvec;
+					int j;
+
+					bio = bio_clone(r1_bio->master_bio, GFP_NOIO);
+					/* copy pages from the failed bio, as
+					 * this might be a write-behind device */
+					__bio_for_each_segment(bvec, bio, j, 0)
+						bvec->bv_page = bio_iovec_idx(r1_bio->bios[i], j)->bv_page;
+					bio_put(r1_bio->bios[i]);
+					bio->bi_sector = r1_bio->sector +
+						conf->mirrors[i].rdev->data_offset;
+					bio->bi_bdev = conf->mirrors[i].rdev->bdev;
+					bio->bi_end_io = raid1_end_write_request;
+					bio->bi_rw = WRITE;
+					bio->bi_private = r1_bio;
+					r1_bio->bios[i] = bio;
+					generic_make_request(bio);
+				}
 		} else {
 			int disk;
 			bio = r1_bio->bios[r1_bio->read_disk];
diff --git a/include/linux/raid/md.h b/include/linux/raid/md.h
index 91467a3c4a52c6c99d8b324d0429e4983cad6c13..13e7c4b62367f6e75d536e1eb124265694db50db 100644
--- a/include/linux/raid/md.h
+++ b/include/linux/raid/md.h
@@ -89,6 +89,7 @@ extern void md_print_devices (void);
 
 extern void md_super_write(mddev_t *mddev, mdk_rdev_t *rdev,
 			   sector_t sector, int size, struct page *page);
+extern void md_super_wait(mddev_t *mddev);
 extern int sync_page_io(struct block_device *bdev, sector_t sector, int size,
 			struct page *page, int rw);
 
diff --git a/include/linux/raid/md_k.h b/include/linux/raid/md_k.h
index 11629f92180ab966749ae273e045419d3f8c700e..d5854c2b27218e01b2449127394855fd2a5d0eda 100644
--- a/include/linux/raid/md_k.h
+++ b/include/linux/raid/md_k.h
@@ -122,6 +122,7 @@ struct mdk_rdev_s
 #define	Faulty		1		/* device is known to have a fault */
 #define	In_sync		2		/* device is in_sync with rest of array */
 #define	WriteMostly	4		/* Avoid reading if at all possible */
+#define	BarriersNotsupp	5		/* BIO_RW_BARRIER is not supported */
 
 	int desc_nr;			/* descriptor index in the superblock */
 	int raid_disk;			/* role of device in array */
@@ -210,6 +211,13 @@ struct mddev_s
 	int				degraded;	/* whether md should consider
 							 * adding a spare
 							 */
+	int				barriers_work;	/* initialised to true, cleared as soon
+							 * as a barrier request to slave
+							 * fails.  Only supported
+							 */
+	struct bio			*biolist; 	/* bios that need to be retried
+							 * because BIO_RW_BARRIER is not supported
+							 */
 
 	atomic_t			recovery_active; /* blocks scheduled, but not written */
 	wait_queue_head_t		recovery_wait;
diff --git a/include/linux/raid/raid1.h b/include/linux/raid/raid1.h
index 60e19b667548feccf6d8dd5cac96ab0c3420c3a5..292b98f2b408dd375154c9bf24569c5289c0f6ee 100644
--- a/include/linux/raid/raid1.h
+++ b/include/linux/raid/raid1.h
@@ -110,7 +110,9 @@ struct r1bio_s {
 #define	R1BIO_Uptodate	0
 #define	R1BIO_IsSync	1
 #define	R1BIO_Degraded	2
-#define	R1BIO_BehindIO   3
+#define	R1BIO_BehindIO	3
+#define	R1BIO_Barrier	4
+#define R1BIO_BarrierRetry 5
 /* For write-behind requests, we call bi_end_io when
  * the last non-write-behind device completes, providing
  * any write was successful.  Otherwise we call when