Btrfs: don't re-enter when allocating a chunk

If we start running low on metadata space we will try to allocate a chunk,
which could then try to allocate a chunk to add the device entry.  The thing
is we allocate a chunk before we try really hard to make the allocation, so
we should be able to find space for the device entry.  Add a flag to the
trans handle so we know we're currently allocating a chunk so we can just
bail out if we try to allocate another chunk.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>

fs/btrfs/extent-tree.c

@@ -3570,6 +3570,10 @@ static int do_chunk_alloc(struct btrfs_trans_handle *trans,
 	int wait_for_alloc = 0;
 	int ret = 0;
 
+	/* Don't re-enter if we're already allocating a chunk */
+	if (trans->allocating_chunk)
+		return -ENOSPC;
+
 	space_info = __find_space_info(extent_root->fs_info, flags);
 	if (!space_info) {
 		ret = update_space_info(extent_root->fs_info, flags,
@@ -3612,6 +3616,8 @@ static int do_chunk_alloc(struct btrfs_trans_handle *trans,
 		goto again;
 	}
 
+	trans->allocating_chunk = true;
+
 	/*
 	 * If we have mixed data/metadata chunks we want to make sure we keep
 	 * allocating mixed chunks instead of individual chunks.
@@ -3638,6 +3644,7 @@ static int do_chunk_alloc(struct btrfs_trans_handle *trans,
 	check_system_chunk(trans, extent_root, flags);
 
 	ret = btrfs_alloc_chunk(trans, extent_root, flags);
+	trans->allocating_chunk = false;
 	if (ret < 0 && ret != -ENOSPC)
 		goto out;
 

fs/btrfs/transaction.c

@@ -385,6 +385,7 @@ start_transaction(struct btrfs_root *root, u64 num_items, int type,
 	h->qgroup_reserved = qgroup_reserved;
 	h->delayed_ref_elem.seq = 0;
 	h->type = type;
+	h->allocating_chunk = false;
 	INIT_LIST_HEAD(&h->qgroup_ref_list);
 	INIT_LIST_HEAD(&h->new_bgs);
 

fs/btrfs/transaction.h

@@ -68,6 +68,7 @@ struct btrfs_trans_handle {
 	struct btrfs_block_rsv *orig_rsv;
 	short aborted;
 	short adding_csums;
+	bool allocating_chunk;
 	enum btrfs_trans_type type;
 	/*
 	 * this root is only needed to validate that the root passed to