f2fs: fix to handle looped node chain during recovery

There is no checksum in node block now, so bit-transition from hardware
can make node_footer.next_blkaddr being corrupted w/o any detection,
result in node chain becoming looped one.

For this condition, during recovery, in order to avoid running into dead
loop, let's detect it and just skip out.
Signed-off-by: Yunlei He <heyunlei@huawei.com>
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/recovery.c

@@ -242,6 +242,9 @@ static int find_fsync_dnodes(struct f2fs_sb_info *sbi, struct list_head *head,
 	struct curseg_info *curseg;
 	struct page *page = NULL;
 	block_t blkaddr;
+	unsigned int loop_cnt = 0;
+	unsigned int free_blocks = sbi->user_block_count -
+					valid_user_blocks(sbi);
 	int err = 0;
 
 	/* get node pages in the current segment */
@@ -294,6 +297,17 @@ static int find_fsync_dnodes(struct f2fs_sb_info *sbi, struct list_head *head,
 		if (IS_INODE(page) && is_dent_dnode(page))
 			entry->last_dentry = blkaddr;
 next:
+		/* sanity check in order to detect looped node chain */
+		if (++loop_cnt >= free_blocks ||
+			blkaddr == next_blkaddr_of_node(page)) {
+			f2fs_msg(sbi->sb, KERN_NOTICE,
+				"%s: detect looped node chain, "
+				"blkaddr:%u, next:%u",
+				__func__, blkaddr, next_blkaddr_of_node(page));
+			err = -EINVAL;
+			break;
+		}
+
 		/* check next segment */
 		blkaddr = next_blkaddr_of_node(page);
 		f2fs_put_page(page, 1);