f2fs: compress: fix to check compress flag w/ .i_sem lock

It needs to check compress flag w/ .i_sem lock, otherwise, compressed
inode may be disabled after the check condition, it's not needed to
set compress option on non-compress inode.

Fixes: e1e8debe ("f2fs: add F2FS_IOC_SET_COMPRESS_OPTION ioctl")
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/file.c

@@ -4028,16 +4028,20 @@ static int f2fs_ioc_set_compress_option(struct file *filp, unsigned long arg)
 				sizeof(option)))
 		return -EFAULT;
 
-	if (!f2fs_compressed_file(inode) ||
-			option.log_cluster_size < MIN_COMPRESS_LOG_SIZE ||
-			option.log_cluster_size > MAX_COMPRESS_LOG_SIZE ||
-			option.algorithm >= COMPRESS_MAX)
+	if (option.log_cluster_size < MIN_COMPRESS_LOG_SIZE ||
+		option.log_cluster_size > MAX_COMPRESS_LOG_SIZE ||
+		option.algorithm >= COMPRESS_MAX)
 		return -EINVAL;
 
 	file_start_write(filp);
 	inode_lock(inode);
 
 	f2fs_down_write(&F2FS_I(inode)->i_sem);
+	if (!f2fs_compressed_file(inode)) {
+		ret = -EINVAL;
+		goto out;
+	}
+
 	if (f2fs_is_mmap_file(inode) || get_dirty_pages(inode)) {
 		ret = -EBUSY;
 		goto out;