f2fs: compress: disallow disabling compress on non-empty compressed file

Compresse file and normal file has differ in i_addr addressing,
specifically addrs per inode/block. So, we will face data loss, if we
disable the compression flag on non-empty files. Therefore we should
disallow not only enabling but disabling the compression flag on
non-empty files.

Fixes: 4c8ff709 ("f2fs: support data compression")
Signed-off-by: Sungjong Seo <sj1557.seo@samsung.com>
Signed-off-by: Hyeong-Jun Kim <hj514.kim@samsung.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/f2fs.h

@@ -4179,8 +4179,7 @@ static inline bool f2fs_disable_compressed_file(struct inode *inode)
 
 	if (!f2fs_compressed_file(inode))
 		return true;
-	if (S_ISREG(inode->i_mode) &&
-		(get_dirty_pages(inode) || atomic_read(&fi->i_compr_blocks)))
+	if (S_ISREG(inode->i_mode) && F2FS_HAS_BLOCKS(inode))
 		return false;
 
 	fi->i_flags &= ~F2FS_COMPR_FL;