f2fs: fix to not account invalid blocks in get_left_section_blocks()

w/ LFS mode, in get_left_section_blocks(), we should not account the
blocks which were used before and now are invalided, otherwise those
blocks will be counted as freed one in has_curseg_enough_space(), result
in missing to trigger GC in time.

Cc: [e-mail]
Fixes: 249ad438e1d9 ("f2fs: add a method for calculating the remaining blocks in the current segment in LFS mode.")
Fixes: bf34c93d2645 ("f2fs: check curseg space before foreground GC")
Signed-off-by: Chao Yu <[e-mail]>
Signed-off-by: Jaegeuk Kim <[e-mail]>

fs/f2fs/segment.h

···
 static inline unsigned int get_left_section_blocks(struct f2fs_sb_info *sbi,
 					enum log_type type, unsigned int segno)
 {
-	if (f2fs_lfs_mode(sbi) && __is_large_section(sbi))
-		return CAP_BLKS_PER_SEC(sbi) - SEGS_TO_BLKS(sbi,
-			(segno - GET_START_SEG_FROM_SEC(sbi, segno))) -
+	if (f2fs_lfs_mode(sbi)) {
+		unsigned int used_blocks = __is_large_section(sbi) ? SEGS_TO_BLKS(sbi,
+				(segno - GET_START_SEG_FROM_SEC(sbi, segno))) : 0;
+		return CAP_BLKS_PER_SEC(sbi) - used_blocks -
 			CURSEG_I(sbi, type)->next_blkoff;
+	}
 	return CAP_BLKS_PER_SEC(sbi) - get_ckpt_valid_blocks(sbi, segno, true);
 }