BTRFS_FS_UNFINISHED_DROPS
if (test_bit(BTRFS_FS_UNFINISHED_DROPS, &fs_info->flags))
clear_and_wake_up_bit(BTRFS_FS_UNFINISHED_DROPS, &fs_info->flags);
ret = wait_on_bit(&fs_info->flags, BTRFS_FS_UNFINISHED_DROPS, TASK_INTERRUPTIBLE);
set_bit(BTRFS_FS_UNFINISHED_DROPS, &fs_info->flags);