f2fs: fix to detect looped node chain correctly

Below dmesg was printed when testing generic/388 of fstest:

F2FS-fs (zram1): find_fsync_dnodes: detect looped node chain, blkaddr:526615, next:526616
F2FS-fs (zram1): Cannot recover all fsync data errno=-22
F2FS-fs (zram1): Mounted with checkpoint version = 22300d0e
F2FS-fs (zram1): find_fsync_dnodes: detect looped node chain, blkaddr:526615, next:526616
F2FS-fs (zram1): Cannot recover all fsync data errno=-22

The reason is that we initialize free_blocks with free blocks of
filesystem, so if filesystem is full, free_blocks can be zero,
below condition will be true, so that, it will fail recovery.

if (++loop_cnt >= free_blocks ||
	blkaddr == next_blkaddr_of_node(page))

To fix this issue, initialize free_blocks with correct value which
includes over-privision blocks.
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/recovery.c

@@ -241,8 +241,8 @@ static int find_fsync_dnodes(struct f2fs_sb_info *sbi, struct list_head *head,
 	struct page *page = NULL;
 	block_t blkaddr;
 	unsigned int loop_cnt = 0;
-	unsigned int free_blocks = sbi->user_block_count -
-					valid_user_blocks(sbi);
+	unsigned int free_blocks = MAIN_SEGS(sbi) * sbi->blocks_per_seg -
+						valid_user_blocks(sbi);
 	int err = 0;
 
 	/* get node pages in the current segment */