f2fs: check free sections before disable checkpoint

'f2fs_is_checkpoint_ready()' checks free sections. If there is not
enough free sections, most f2fs operations will return -ENOSPC when
checkpoint is disabled.

It would be better to check free sections before disable checkpoint.
Signed-off-by: Wu Bo <bo.wu@vivo.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/segment.c

@@ -906,6 +906,8 @@ int f2fs_disable_cp_again(struct f2fs_sb_info *sbi, block_t unusable)
 	if (is_sbi_flag_set(sbi, SBI_CP_DISABLED_QUICK) &&
 		dirty_segments(sbi) > ovp_hole_segs)
 		return -EAGAIN;
+	if (has_not_enough_free_secs(sbi, 0, 0))
+		return -EAGAIN;
 	return 0;
 }