[PATCH v2] 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`
to restrict block allocation to the safe remaining main area while valid
blocks in the truncated range are evacuated by GC.

However, FREE_I(sbi)->free_sections tracks the total number of free
sections across the whole filesystem. If any sections within the
truncated range were already free upon entering free_segment_range(),
failing to deduct them from free_sections causes the filesystem to
overestimate available free sections in the active, reduced main area.
This leads to inconsistent free section accounting during GC data
migration and can trigger unexpected allocation failures or assertion
errors when space is tight.

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

Fixes: b4b10061ef98 ("f2fs: refactor resize_fs to avoid meta updates in progress")
Cc: stable@vger.kernel.org
Signed-off-by: Daeho Jeong <daehojeong@google.com>
Signed-off-by: Sunmin Jeong <s_min.jeong@samsung.com>
---
v2: elaborate on the issue in the commit message.
---
 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;
 }
-- 
2.55.0.860.g4b6b3295ed-goog