int create_flush_cmd_control(struct f2fs_sb_info *sbi)
{
	dev_t dev = sbi->sb->s_bdev->bd_dev;
	struct flush_cmd_control *fcc;
	int err = 0;

	if (SM_I(sbi)->fcc_info) {
		fcc = SM_I(sbi)->fcc_info;
		goto init_thread;
	}

	fcc = kzalloc(sizeof(struct flush_cmd_control), GFP_KERNEL);
	if (!fcc)
		return -ENOMEM;
	atomic_set(&fcc->issued_flush, 0);
	atomic_set(&fcc->issing_flush, 0);
	init_waitqueue_head(&fcc->flush_wait_queue);
	init_llist_head(&fcc->issue_list);
	SM_I(sbi)->fcc_info = fcc;
	if (!test_opt(sbi, FLUSH_MERGE))
		return err;

init_thread:
	fcc->f2fs_issue_flush = kthread_run(issue_flush_thread, sbi,
				"f2fs_flush-%u:%u", MAJOR(dev), MINOR(dev));
	if (IS_ERR(fcc->f2fs_issue_flush)) {
		err = PTR_ERR(fcc->f2fs_issue_flush);
		kfree(fcc);
		SM_I(sbi)->fcc_info = NULL;
		return err;
	}

	return err;
}
A NULL pointer dereference occurs when the application dereferences a pointer that it expects to be valid, but is NULL, typically causing a crash or exit.