Btrfs: join the transaction in __btrfs_setxattr

With selinux on we end up calling __btrfs_setxattr when we create an inode,
which calls btrfs_start_transaction(). The problem is we've already called
that in btrfs_new_inode, and in btrfs_start_transaction we end up doing a
wait_current_trans(). If btrfs-transaction has started committing it will wait
for all handles to finish, while the other process is waiting for the
transaction to commit. This is fixed by using btrfs_join_transaction, which
won't wait for the transaction to commit. Thanks,

Signed-off-by: Josef Bacik <[e-mail]>

fs/btrfs/xattr.c

···
 	if (!path)
 		return -ENOMEM;
 
-	trans = btrfs_start_transaction(root, 1);
+	trans = btrfs_join_transaction(root, 1);
 	btrfs_set_trans_block_group(trans, inode);
 
 	/* first lets see if we already have this xattr */