Btrfs: remove no longer used function to run delayed refs asynchronously

It used to be called from only two places (truncate path and releasing a
transaction handle), but commits 28bad21257 ("btrfs: fix truncate
throttling") and db2462a6ad ("btrfs: don't run delayed refs in the end
transaction logic") removed their calls to this function, so it's not used
anymore. Just remove it and all its helpers.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/ctree.h

@@ -2701,8 +2701,6 @@ void btrfs_wait_nocow_writers(struct btrfs_block_group_cache *bg);
 void btrfs_put_block_group(struct btrfs_block_group_cache *cache);
 int btrfs_run_delayed_refs(struct btrfs_trans_handle *trans,
 			   unsigned long count);
-int btrfs_async_run_delayed_refs(struct btrfs_fs_info *fs_info,
-				 unsigned long count, u64 transid, int wait);
 void btrfs_cleanup_ref_head_accounting(struct btrfs_fs_info *fs_info,
 				  struct btrfs_delayed_ref_root *delayed_refs,
 				  struct btrfs_delayed_ref_head *head);

fs/btrfs/extent-tree.c

@@ -2876,91 +2876,6 @@ int btrfs_should_throttle_delayed_refs(struct btrfs_trans_handle *trans)
 	return btrfs_check_space_for_delayed_refs(trans->fs_info);
 }
 
-struct async_delayed_refs {
-	struct btrfs_root *root;
-	u64 transid;
-	int count;
-	int error;
-	int sync;
-	struct completion wait;
-	struct btrfs_work work;
-};
-
-static inline struct async_delayed_refs *
-to_async_delayed_refs(struct btrfs_work *work)
-{
-	return container_of(work, struct async_delayed_refs, work);
-}
-
-static void delayed_ref_async_start(struct btrfs_work *work)
-{
-	struct async_delayed_refs *async = to_async_delayed_refs(work);
-	struct btrfs_trans_handle *trans;
-	struct btrfs_fs_info *fs_info = async->root->fs_info;
-	int ret;
-
-	/* if the commit is already started, we don't need to wait here */
-	if (btrfs_transaction_blocked(fs_info))
-		goto done;
-
-	trans = btrfs_join_transaction(async->root);
-	if (IS_ERR(trans)) {
-		async->error = PTR_ERR(trans);
-		goto done;
-	}
-
-	/* Don't bother flushing if we got into a different transaction */
-	if (trans->transid > async->transid)
-		goto end;
-
-	ret = btrfs_run_delayed_refs(trans, async->count);
-	if (ret)
-		async->error = ret;
-end:
-	ret = btrfs_end_transaction(trans);
-	if (ret && !async->error)
-		async->error = ret;
-done:
-	if (async->sync)
-		complete(&async->wait);
-	else
-		kfree(async);
-}
-
-int btrfs_async_run_delayed_refs(struct btrfs_fs_info *fs_info,
-				 unsigned long count, u64 transid, int wait)
-{
-	struct async_delayed_refs *async;
-	int ret;
-
-	async = kmalloc(sizeof(*async), GFP_NOFS);
-	if (!async)
-		return -ENOMEM;
-
-	async->root = fs_info->tree_root;
-	async->count = count;
-	async->error = 0;
-	async->transid = transid;
-	if (wait)
-		async->sync = 1;
-	else
-		async->sync = 0;
-	init_completion(&async->wait);
-
-	btrfs_init_work(&async->work, btrfs_extent_refs_helper,
-			delayed_ref_async_start, NULL, NULL);
-
-	btrfs_queue_work(fs_info->extent_workers, &async->work);
-
-	if (wait) {
-		wait_for_completion(&async->wait);
-		ret = async->error;
-		kfree(async);
-		return ret;
-	}
-	return 0;
-}
-
 /*
  * this starts processing the delayed reference count updates and
  * extent insertions we have queued up so far.  count can be