Subject: Re: [PATCH net-next 5/6] udpv6: Add lockless sendmsg() support

From: Vlad Yasevich <[email-masked]>
Date: Mon, 02 Feb 2015 15:42:16 -0500

On 01/31/2015 03:49 PM, Sergei Shtylyov wrote:
> Hello.
> 
> On 1/31/2015 6:40 PM, Vladislav Yasevich wrote:
> 
>> This commit adds the same functionaliy to IPv6 that
>> commit 903ab86d195cca295379699299c5fc10beba31c7
>> Author: Herbert Xu <[email-masked]>
>> Date:   Tue Mar 1 02:36:48 2011 +0000
> 
>>      udp: Add lockless transmit path
> 
>> added to IPv4.
> 
>> UDP transmit path can now run without a socket lock,
>> thus allowing multiple threads to send to a single socket
>> more efficiently.
>> This is only used when corking/MSG_MORE is not used.
> 
>> Signed-off-by: Vladislav Yasevich <[email-masked]>
>> ---
>>   net/ipv6/udp.c | 24 ++++++++++++++++++++----
>>   1 file changed, 20 insertions(+), 4 deletions(-)
> 
>> diff --git a/net/ipv6/udp.c b/net/ipv6/udp.c
>> index 67a3d70..d048d46 100644
>> --- a/net/ipv6/udp.c
>> +++ b/net/ipv6/udp.c
> [...]
>> @@ -1307,6 +1308,20 @@ do_udp_sendmsg:
>>           goto do_confirm;
>>   back_from_confirm:
>>
>> +    /* Lockless fast path for the non-corking case */
>> +    if (!corkreq) {
>> +        struct sk_buff *skb;
>>
>> +        skb = ip6_make_skb(sk, getfrag, msg, ulen,
>> +                   sizeof(struct udphdr), hlimit, tclass, opt,
>> +                   &fl6, (struct rt6_info *)dst,
>> +                   msg->msg_flags, dontfrag);
>> +        err = PTR_ERR(skb);
> 
>    You should use PTR_ERR_OR_ZERO() here, I think.
> 

That particular code was stolen from ipv4/udp.c.  You are
right, we can use PTR_ERR_OR_ZERO() and simplify the following
check as well.

Will fix.

Thanks
-vlad

> [...]
> WBR, Sergei