diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 0b29bdb251050..62461239600fc 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -2593,7 +2593,6 @@ int btrfs_free_reserved_extent(struct btrfs_fs_info *fs_info,
 			       u64 start, u64 len, int delalloc);
 int btrfs_pin_reserved_extent(struct btrfs_trans_handle *trans, u64 start,
 			      u64 len);
-void btrfs_prepare_extent_commit(struct btrfs_fs_info *fs_info);
 int btrfs_finish_extent_commit(struct btrfs_trans_handle *trans);
 int btrfs_inc_extent_ref(struct btrfs_trans_handle *trans,
 			 struct btrfs_ref *generic_ref);
diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 0d110b7132c38..4209dbd6286e4 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2730,31 +2730,6 @@ btrfs_inc_block_group_reservations(struct btrfs_block_group *bg)
 	atomic_inc(&bg->reservations);
 }
 
-void btrfs_prepare_extent_commit(struct btrfs_fs_info *fs_info)
-{
-	struct btrfs_caching_control *next;
-	struct btrfs_caching_control *caching_ctl;
-	struct btrfs_block_group *cache;
-
-	down_write(&fs_info->commit_root_sem);
-
-	list_for_each_entry_safe(caching_ctl, next,
-				 &fs_info->caching_block_groups, list) {
-		cache = caching_ctl->block_group;
-		if (btrfs_block_group_done(cache)) {
-			cache->last_byte_to_unpin = (u64)-1;
-			list_del_init(&caching_ctl->list);
-			btrfs_put_caching_control(caching_ctl);
-		} else {
-			cache->last_byte_to_unpin = caching_ctl->progress;
-		}
-	}
-
-	up_write(&fs_info->commit_root_sem);
-
-	btrfs_update_global_block_rsv(fs_info);
-}
-
 /*
  * Returns the free cluster for the given space info and sets empty_cluster to
  * what it should be based on the mount options.
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 52ada47aff50d..96dbfc011f45d 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -155,6 +155,7 @@ static noinline void switch_commit_roots(struct btrfs_trans_handle *trans)
 	struct btrfs_transaction *cur_trans = trans->transaction;
 	struct btrfs_fs_info *fs_info = trans->fs_info;
 	struct btrfs_root *root, *tmp;
+	struct btrfs_caching_control *caching_ctl, *next;
 
 	down_write(&fs_info->commit_root_sem);
 	list_for_each_entry_safe(root, tmp, &cur_trans->switch_commits,
@@ -180,6 +181,45 @@ static noinline void switch_commit_roots(struct btrfs_trans_handle *trans)
 		spin_lock(&cur_trans->dropped_roots_lock);
 	}
 	spin_unlock(&cur_trans->dropped_roots_lock);
+
+	/*
+	 * We have to update the last_byte_to_unpin under the commit_root_sem,
+	 * at the same time we swap out the commit roots.
+	 *
+	 * This is because we must have a real view of the last spot the caching
+	 * kthreads were while caching.  Consider the following views of the
+	 * extent tree for a block group
+	 *
+	 * commit root
+	 * +----+----+----+----+----+----+----+
+	 * |\\\\|    |\\\\|\\\\|    |\\\\|\\\\|
+	 * +----+----+----+----+----+----+----+
+	 * 0    1    2    3    4    5    6    7
+	 *
+	 * new commit root
+	 * +----+----+----+----+----+----+----+
+	 * |    |    |    |\\\\|    |    |\\\\|
+	 * +----+----+----+----+----+----+----+
+	 * 0    1    2    3    4    5    6    7
+	 *
+	 * If the cache_ctl->progress was at 3, then we are only allowed to
+	 * unpin [0,1) and [2,3], because the caching thread has already
+	 * processed those extents.  We are not allowed to unpin [5,6), because
+	 * the caching thread will re-start it's search from 3, and thus find
+	 * the hole from [4,6) to add to the free space cache.
+	 */
+	list_for_each_entry_safe(caching_ctl, next,
+				 &fs_info->caching_block_groups, list) {
+		struct btrfs_block_group *cache = caching_ctl->block_group;
+
+		if (btrfs_block_group_done(cache)) {
+			cache->last_byte_to_unpin = (u64)-1;
+			list_del_init(&caching_ctl->list);
+			btrfs_put_caching_control(caching_ctl);
+		} else {
+			cache->last_byte_to_unpin = caching_ctl->progress;
+		}
+	}
 	up_write(&fs_info->commit_root_sem);
 }
 
@@ -2293,8 +2333,6 @@ int btrfs_commit_transaction(struct btrfs_trans_handle *trans)
 		goto unlock_tree_log;
 	}
 
-	btrfs_prepare_extent_commit(fs_info);
-
 	cur_trans = fs_info->running_transaction;
 
 	btrfs_set_root_node(&fs_info->tree_root->root_item,