f2fs: fix to avoid double unlock

On image that has verity and compression feature, if compressed pages
and non-compressed pages are mixed in one bio, we may double unlock
non-compressed page in below flow:

- f2fs_post_read_work
 - f2fs_decompress_work
  - f2fs_decompress_bio
   - __read_end_io
    - unlock_page
 - fsverity_enqueue_verify_work
  - f2fs_verity_work
   - f2fs_verify_bio
    - unlock_page

So it should skip handling non-compressed page in f2fs_decompress_work()
if verity is on.

Besides, add missing dec_page_count() in f2fs_verify_bio().
Signed-off-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -139,6 +139,8 @@ static void __read_end_io(struct bio *bio, bool compr, bool verity)
 			f2fs_decompress_pages(bio, page, verity);
 			continue;
 		}
+		if (verity)
+			continue;
 #endif
 
 		/* PG_error was set if any post_read step failed */
@@ -216,6 +218,7 @@ static void f2fs_verify_bio(struct bio *bio)
 		ClearPageUptodate(page);
 		ClearPageError(page);
 unlock:
+		dec_page_count(F2FS_P_SB(page), __read_io_type(page));
 		unlock_page(page);
 	}
 }