[PATCH] f2fs: accurately adjust free_sections during free_segment_range

[Daeho Jeong <daeho43@gmail.com>]

From: Daeho Jeong <daehojeong@google.com>

In free_segment_range(), MAIN_SECS(sbi) is temporarily reduced by `secs`
while valid blocks in the truncated range are evacuated by GC.

However, if any sections within the truncated range were already free,
failing to deduct them from FREE_I(sbi)->free_sections leads to an
over-estimation of available space in the reduced main area, causing
inconsistent free section accounting.

Fix this by calculating the number of already-free sections in the
truncated range under segmap_lock, deducting them from free_sections upon
entering free_segment_range(), and restoring them under segmap_lock on exit.

Signed-off-by: Daeho Jeong <daehojeong@google.com>
Signed-off-by: Sunmin Jeong <s_min.jeong@samsung.com>
---
 fs/f2fs/gc.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/fs/f2fs/gc.c b/fs/f2fs/gc.c
index 787133ee2eb2..f3a6fc6d08ae 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -2200,8 +2200,9 @@ int f2fs_gc_range(struct f2fs_sb_info *sbi,
 static int free_segment_range(struct f2fs_sb_info *sbi,
 				unsigned int secs, bool dry_run)
 {
-	unsigned int next_inuse, start, end;
+	unsigned int secno, next_inuse, start, end, end_secno;
 	struct cp_control cpc = { CP_RESIZE, 0, 0, 0 };
+	unsigned int freed_secs = 0;
 	int gc_mode, gc_type;
 	int err = 0;
 	int type;
@@ -2210,6 +2211,7 @@ static int free_segment_range(struct f2fs_sb_info *sbi,
 	MAIN_SECS(sbi) -= secs;
 	start = MAIN_SECS(sbi) * SEGS_PER_SEC(sbi);
 	end = MAIN_SEGS(sbi) - 1;
+	end_secno = GET_SEC_FROM_SEG(sbi, end);
 
 	mutex_lock(&DIRTY_I(sbi)->seglist_lock);
 	for (gc_mode = 0; gc_mode < MAX_GC_POLICY; gc_mode++)
@@ -2221,6 +2223,14 @@ static int free_segment_range(struct f2fs_sb_info *sbi,
 			sbi->next_victim_seg[gc_type] = NULL_SEGNO;
 	mutex_unlock(&DIRTY_I(sbi)->seglist_lock);
 
+	spin_lock(&FREE_I(sbi)->segmap_lock);
+	for (secno = MAIN_SECS(sbi); secno <= end_secno; secno++) {
+		if (!test_bit(secno, FREE_I(sbi)->free_secmap))
+			freed_secs++;
+	}
+	FREE_I(sbi)->free_sections -= freed_secs;
+	spin_unlock(&FREE_I(sbi)->segmap_lock);
+
 	/* Move out cursegs from the target range */
 	for (type = CURSEG_HOT_DATA; type < NR_CURSEG_TYPE; type++) {
 		err = f2fs_allocate_segment_for_resize(sbi, type, start, end);
@@ -2245,6 +2255,9 @@ static int free_segment_range(struct f2fs_sb_info *sbi,
 		f2fs_bug_on(sbi, 1);
 	}
 out:
+	spin_lock(&FREE_I(sbi)->segmap_lock);
+	FREE_I(sbi)->free_sections += freed_secs;
+	spin_unlock(&FREE_I(sbi)->segmap_lock);
 	MAIN_SECS(sbi) += secs;
 	return err;
 }
-- 
2.55.0.691.gc56d675ccc-goog