if (!df) return;
void global_flush_tlb(void){ 	struct deferred_page *df, *next_df;	down_read(&init_mm.mmap_sem);	df = xchg(&df_list, NULL);	up_read(&init_mm.mmap_sem);	if (!df)		return;	flush_map((df && !df->next) ? df->address : 0);	for (; df; df = next_df) { 		next_df = df->next;		if (df->fpage) 			__free_page(df->fpage);		kfree(df);	} } 