[PATCH 5.10.y] f2fs: accurately adjust free_sections during free_segment_range

[Sasha Levin <sashal@kernel.org>]

From: Daeho Jeong <daehojeong@google.com>

[ Upstream commit 8c963d1738fdca400082ff5f9d99e083de4f4e70 ]

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>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
[ adapted the changes to free_segment_range()’s inline GC logic because the newer helper functions are absent. ]
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 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 379839f5b4b74..1831970b929c2 100644
--- a/fs/f2fs/gc.c
+++ b/fs/f2fs/gc.c
@@ -1855,8 +1855,9 @@ void f2fs_build_gc_manager(struct f2fs_sb_info *sbi)
 static int free_segment_range(struct f2fs_sb_info *sbi,
 				unsigned int secs, bool gc_only)
 {
-	unsigned int segno, next_inuse, start, end;
+	unsigned int segno, 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;
@@ -1865,6 +1866,7 @@ static int free_segment_range(struct f2fs_sb_info *sbi,
 	MAIN_SECS(sbi) -= secs;
 	start = MAIN_SECS(sbi) * sbi->segs_per_sec;
 	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++)
@@ -1876,6 +1878,14 @@ 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_PERSIST_TYPE; type++)
 		f2fs_allocate_segment_for_resize(sbi, type, start, end);
@@ -1913,6 +1923,9 @@ 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;
 }
-- 
2.53.0