if (down_trylock(&ipqnl_sem)) return; 
down(&ipqnl_sem); 
ipq_rcv_sk(struct sock *sk, int len){	do {		struct sk_buff *skb;		if (down_trylock(&ipqnl_sem))			return;					while ((skb = skb_dequeue(&sk->sk_receive_queue)) != NULL) {			ipq_rcv_skb(skb);			kfree_skb(skb);		}				up(&ipqnl_sem);	} while (ipqnl && ipqnl->sk_receive_queue.qlen);}
10457	/local/tlutelli/issta_data/temp/c/2005_temp/2005/10457/2a0a6ebee1d68552152ae8d4aeda91d806995dec/ip_queue.c/clean/net/ipv4/netfilter/ip_queue.c