f2fs: fix error path of __f2fs_build_free_nids

If NAT is corrupted, let scan_nat_page() return EFSCORRUPTED, so that,
caller can set SBI_NEED_FSCK flag into checkpoint for later repair by
fsck.

Also, this patch introduces a new fscorrupted error flag, and in above
scenario, it will persist the error flag into superblock synchronously
to avoid it has no luck to trigger a checkpoint to record SBI_NEED_FSCK
Signed-off-by: Zhiguo Niu <zhiguo.niu@unisoc.com>
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/node.c

@@ -2389,7 +2389,7 @@ static int scan_nat_page(struct f2fs_sb_info *sbi,
 		blk_addr = le32_to_cpu(nat_blk->entries[i].block_addr);
 
 		if (blk_addr == NEW_ADDR)
-			return -EINVAL;
+			return -EFSCORRUPTED;
 
 		if (blk_addr == NULL_ADDR) {
 			add_free_nid(sbi, start_nid, true, true);
@@ -2504,7 +2504,14 @@ static int __f2fs_build_free_nids(struct f2fs_sb_info *sbi,
 
 			if (ret) {
 				f2fs_up_read(&nm_i->nat_tree_lock);
+
+				if (ret == -EFSCORRUPTED) {
 					f2fs_err(sbi, "NAT is corrupt, run fsck to fix it");
+					set_sbi_flag(sbi, SBI_NEED_FSCK);
+					f2fs_handle_error(sbi,
+						ERROR_INCONSISTENT_NAT);
+				}
+
 				return ret;
 			}
 		}

include/linux/f2fs_fs.h

@@ -104,6 +104,7 @@ enum f2fs_error {
 	ERROR_CORRUPTED_VERITY_XATTR,
 	ERROR_CORRUPTED_XATTR,
 	ERROR_INVALID_NODE_REFERENCE,
+	ERROR_INCONSISTENT_NAT,
 	ERROR_MAX,
 };