[IPV4]: Fix BUG() in 2.6.x, udp_poll(), fragments + CONFIG_HIGHMEM

Steven Hand <Steven.Hand@cl.cam.ac.uk> wrote:
> 
> Reconstructed forward trace: 
> 
>   net/ipv4/udp.c:1334   spin_lock_irq() 
>   net/ipv4/udp.c:1336   udp_checksum_complete() 
> net/core/skbuff.c:1069   skb_shinfo(skb)->nr_frags > 1
> net/core/skbuff.c:1086   kunmap_skb_frag()
> net/core/skbuff.h:1087   local_bh_enable()
> kernel/softirq.c:0140   WARN_ON(irqs_disabled());

The receive queue lock is never taken in IRQs (and should never be) so
we can simply substitute bh for irq.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/udp.c

@@ -738,7 +738,7 @@ int udp_ioctl(struct sock *sk, int cmd, unsigned long arg)
 			unsigned long amount;
 
 			amount = 0;
-			spin_lock_irq(&sk->sk_receive_queue.lock);
+			spin_lock_bh(&sk->sk_receive_queue.lock);
 			skb = skb_peek(&sk->sk_receive_queue);
 			if (skb != NULL) {
 				/*
@@ -748,7 +748,7 @@ int udp_ioctl(struct sock *sk, int cmd, unsigned long arg)
 				 */
 				amount = skb->len - sizeof(struct udphdr);
 			}
-			spin_unlock_irq(&sk->sk_receive_queue.lock);
+			spin_unlock_bh(&sk->sk_receive_queue.lock);
 			return put_user(amount, (int __user *)arg);
 		}
 
@@ -848,12 +848,12 @@ static int udp_recvmsg(struct kiocb *iocb, struct sock *sk, struct msghdr *msg,
 	/* Clear queue. */
 	if (flags&MSG_PEEK) {
 		int clear = 0;
-		spin_lock_irq(&sk->sk_receive_queue.lock);
+		spin_lock_bh(&sk->sk_receive_queue.lock);
 		if (skb == skb_peek(&sk->sk_receive_queue)) {
 			__skb_unlink(skb, &sk->sk_receive_queue);
 			clear = 1;
 		}
-		spin_unlock_irq(&sk->sk_receive_queue.lock);
+		spin_unlock_bh(&sk->sk_receive_queue.lock);
 		if (clear)
 			kfree_skb(skb);
 	}
@@ -1334,7 +1334,7 @@ unsigned int udp_poll(struct file *file, struct socket *sock, poll_table *wait)
 		struct sk_buff_head *rcvq = &sk->sk_receive_queue;
 		struct sk_buff *skb;
 
-		spin_lock_irq(&rcvq->lock);
+		spin_lock_bh(&rcvq->lock);
 		while ((skb = skb_peek(rcvq)) != NULL) {
 			if (udp_checksum_complete(skb)) {
 				UDP_INC_STATS_BH(UDP_MIB_INERRORS);
@@ -1345,7 +1345,7 @@ unsigned int udp_poll(struct file *file, struct socket *sock, poll_table *wait)
 				break;
 			}
 		}
-		spin_unlock_irq(&rcvq->lock);
+		spin_unlock_bh(&rcvq->lock);
 
 		/* nothing to see, move along */
 		if (skb == NULL)