[PATCH 3/3] f2fs: refresh superblock CRC after MAIN_AREA alignment fix

[Cheng Yongkang <teel4res@gmail.com>]

sanity_check_area_boundary() fixes the on-disk segment_count through
__f2fs_commit_super(..., false), which does not refresh the superblock
checksum.  segment_count is covered by the checksum, so the next mount
fails with -EFSCORRUPTED after the alignment fix.

Recompute the CRC over the modified superblock before writing it.  Use the
raw superblock's feature bit: sanity_check_area_boundary() runs from
read_raw_super_block(), before sbi->raw_super is assigned.

The stale-CRC trigger was reproduced 3/3 times; with this fix both
superblock copies end with segment_count=9 and a matching CRC, and the
next mount no longer reports an invalid checksum.

Assisted-by: LLM
Signed-off-by: Cheng Yongkang <teel4res@gmail.com>
---
 fs/f2fs/super.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/fs/f2fs/super.c b/fs/f2fs/super.c
index b90831e..7dcf15e 100644
--- a/fs/f2fs/super.c
+++ b/fs/f2fs/super.c
@@ -4023,6 +4023,13 @@ static inline bool sanity_check_area_boundary(struct f2fs_sb_info *sbi,
 		raw_super->segment_count = cpu_to_le32((main_end_blkaddr -
 				segment0_blkaddr) >> log_blocks_per_seg);
 
+		if (__F2FS_HAS_FEATURE(raw_super, F2FS_FEATURE_SB_CHKSUM)) {
+			u32 crc;
+
+			crc = f2fs_crc32(raw_super, offsetof(struct f2fs_super_block, crc));
+			raw_super->crc = cpu_to_le32(crc);
+		}
+
 		if (f2fs_readonly(sb) || f2fs_hw_is_readonly(sbi)) {
 			set_sbi_flag(sbi, SBI_NEED_SB_WRITE);
 			res = "internally";
-- 
2.34.1