diff .prev/drivers/md/bitmap.c ./drivers/md/bitmap.c
--- .prev/drivers/md/bitmap.c	2007-02-07 13:03:56.000000000 +1100
+++ ./drivers/md/bitmap.c	2007-02-07 21:34:47.000000000 +1100
@@ -1160,6 +1160,22 @@ int bitmap_startwrite(struct bitmap *bit
 			return 0;
 		}
 
+		if (unlikely((*bmc & COUNTER_MAX) == COUNTER_MAX)) {
+			DEFINE_WAIT(__wait);
+			/* note that it is safe to do the prepare_to_wait
+			 * after the test as long as we do it before dropping
+			 * the spinlock.
+			 */
+			prepare_to_wait(&bitmap->overflow_wait, &__wait,
+					TASK_UNINTERRUPTIBLE);
+			spin_unlock_irq(&bitmap->lock);
+			bitmap->mddev->queue
+				->unplug_fn(bitmap->mddev->queue);
+			schedule();
+			finish_wait(&bitmap->overflow_wait, &__wait);
+			continue;
+		}
+
 		switch(*bmc) {
 		case 0:
 			bitmap_file_set_bit(bitmap, offset);
@@ -1169,7 +1185,7 @@ int bitmap_startwrite(struct bitmap *bit
 		case 1:
 			*bmc = 2;
 		}
-		BUG_ON((*bmc & COUNTER_MAX) == COUNTER_MAX);
+
 		(*bmc)++;
 
 		spin_unlock_irq(&bitmap->lock);
@@ -1207,6 +1223,9 @@ void bitmap_endwrite(struct bitmap *bitm
 		if (!success && ! (*bmc & NEEDED_MASK))
 			*bmc |= NEEDED_MASK;
 
+		if ((*bmc & COUNTER_MAX) == COUNTER_MAX)
+			wake_up(&bitmap->overflow_wait);
+
 		(*bmc)--;
 		if (*bmc <= 2) {
 			set_page_attr(bitmap,
@@ -1431,6 +1450,7 @@ int bitmap_create(mddev_t *mddev)
 	spin_lock_init(&bitmap->lock);
 	atomic_set(&bitmap->pending_writes, 0);
 	init_waitqueue_head(&bitmap->write_wait);
+	init_waitqueue_head(&bitmap->overflow_wait);
 
 	bitmap->mddev = mddev;
 
diff .prev/include/linux/raid/bitmap.h ./include/linux/raid/bitmap.h
--- .prev/include/linux/raid/bitmap.h	2007-02-07 13:03:56.000000000 +1100
+++ ./include/linux/raid/bitmap.h	2007-02-07 20:57:57.000000000 +1100
@@ -247,6 +247,7 @@ struct bitmap {
 
 	atomic_t pending_writes; /* pending writes to the bitmap file */
 	wait_queue_head_t write_wait;
+	wait_queue_head_t overflow_wait;
 
 };