void build_free_nids(struct f2fs_sb_info *sbi, bool sync, bool mount)
{
	mutex_lock(&NM_I(sbi)->build_lock);
	__build_free_nids(sbi, sync, mount);
	mutex_unlock(&NM_I(sbi)->build_lock);
}

The product contains a concurrent code sequence that requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence operating concurrently.