netdev - Re: DNS (?) not working on G5 (64-bit powerpc) (was [net-next,v3,3/3] udp: try to avoid 2 cache miss on dequeue)

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Date:   Fri, 23 Jun 2017 16:59:06 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Hannes Frederic Sowa <hannes@...essinduktion.org>,
        Paolo Abeni <pabeni@...hat.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org
Subject: Re: DNS (?) not working on G5 (64-bit powerpc) (was [net-next,v3,3/3] udp: try to avoid 2 cache miss on dequeue)

Hannes Frederic Sowa <hannes@...essinduktion.org> writes:

> On Thu, Jun 22, 2017, at 22:57, Paolo Abeni wrote:
>> 
>> Can you please check if the following patch fixes the issue? Only
>> compiled tested here.
>> 
>> Thanks!!!
>> ---
>> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
>> index 067a607..80d89fe 100644
>> --- a/net/ipv4/udp.c
>> +++ b/net/ipv4/udp.c
>> @@ -1446,16 +1446,19 @@ static struct sk_buff
>> *__first_packet_length(struct sock *sk,
>>  {
>>  	struct sk_buff *skb;
>>  
>> -       while ((skb = skb_peek(rcvq)) != NULL &&
>> -              udp_lib_checksum_complete(skb)) {
>> -               __UDP_INC_STATS(sock_net(sk), UDP_MIB_CSUMERRORS,
>> -                               IS_UDPLITE(sk));
>> -               __UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS,
>> -                               IS_UDPLITE(sk));
>> -               atomic_inc(&sk->sk_drops);
>> -               __skb_unlink(skb, rcvq);
>> -               *total += skb->truesize;
>> -               kfree_skb(skb);
>> +       while ((skb = skb_peek(rcvq)) != NULL) {
>> +               if (udp_lib_checksum_complete(skb)) {
>> +                       __UDP_INC_STATS(sock_net(sk), UDP_MIB_CSUMERRORS,
>> +                                       IS_UDPLITE(sk));
>> +                       __UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS,
>> +                                       IS_UDPLITE(sk));
>> +                       atomic_inc(&sk->sk_drops);
>> +                       __skb_unlink(skb, rcvq);
>> +                       *total += skb->truesize;
>> +                       kfree_skb(skb);
>> +               } else {
>> +                       udp_set_dev_scratch(skb);
>
> It needs a "break;" here.
>
>> +               }
>>  	}
>>  	return skb;
>>  }

That works!

$ wget google.com
--2017-06-23 16:56:31--  http://google.com/
Resolving proxy.pmdw.com (proxy.pmdw.com)... 10.1.2.3
Connecting to proxy.pmdw.com (proxy.pmdw.com)|10.1.2.3|:3128... connected.
Proxy request sent, awaiting response... 302 Found
Location: http://www.google.com.au/?gfe_rd=cr&ei=n7tMWeb9JYPr8wfg4LXYAQ [following]
--2017-06-23 16:56:31--  http://www.google.com.au/?gfe_rd=cr&ei=n7tMWeb9JYPr8wfg4LXYAQ
Reusing existing connection to proxy.pmdw.com:3128.
Proxy request sent, awaiting response... 200 OK
Length: unspecified [text/html]
Saving to: ‘index.html’


The patch had whitespace issues or something and I had to apply it by
hand, here's what I actually tested.

cheers

diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 067a607917f9..d3227c1bbe8e 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -1446,16 +1446,20 @@ static struct sk_buff *__first_packet_length(struct sock *sk,
 {
 	struct sk_buff *skb;
 
-	while ((skb = skb_peek(rcvq)) != NULL &&
-	       udp_lib_checksum_complete(skb)) {
-		__UDP_INC_STATS(sock_net(sk), UDP_MIB_CSUMERRORS,
-				IS_UDPLITE(sk));
-		__UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS,
-				IS_UDPLITE(sk));
-		atomic_inc(&sk->sk_drops);
-		__skb_unlink(skb, rcvq);
-		*total += skb->truesize;
-		kfree_skb(skb);
+	while ((skb = skb_peek(rcvq)) != NULL) {
+		if (udp_lib_checksum_complete(skb)) {
+			__UDP_INC_STATS(sock_net(sk), UDP_MIB_CSUMERRORS,
+					IS_UDPLITE(sk));
+			__UDP_INC_STATS(sock_net(sk), UDP_MIB_INERRORS,
+					IS_UDPLITE(sk));
+			atomic_inc(&sk->sk_drops);
+			__skb_unlink(skb, rcvq);
+			*total += skb->truesize;
+			kfree_skb(skb);
+		} else {
+			udp_set_dev_scratch(skb);
+			break;
+		}
 	}
 	return skb;
 }