f2fs: relax node version check for victim data in gc

- has_not_enough_free_secs
node_secs: 0  dent_secs: 0  freed:0  free_segments:103  reserved:104

          - f2fs_gc
             - get_victim_by_default
alloc_mode 0, gc_mode 1, max_search 2672, offset 4654, ofs_unit 1

                - do_garbage_collect
start_segno 3976, end_segno 3977   type 0

                  - is_alive
nid 22797, blkaddr 2131882, ofs_in_node 0, version 0x8/0x0

                   - gc_data_segment 766, segno 3976, block 512/426 not alive

So, this patch fixes subtle corrupted case where node version does not match
to summary version which results in infinite loop by gc.
Reported-by: Yunlei He <heyunlei@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/gc.c

@@ -555,8 +555,10 @@ static bool is_alive(struct f2fs_sb_info *sbi, struct f2fs_summary *sum,
 	get_node_info(sbi, nid, dni);
 
 	if (sum->version != dni->version) {
-		f2fs_put_page(node_page, 1);
-		return false;
+		f2fs_msg(sbi->sb, KERN_WARNING,
+				"%s: valid data with mismatched node version.",
+				__func__);
+		set_sbi_flag(sbi, SBI_NEED_FSCK);
 	}
 
 	*nofs = ofs_of_node(node_page);