Subject: Re: [PATCH 1/4] [UDP]: fix send buffer check

From: Hideo AOKI <[email-masked]>
Date: Thu, 20 Dec 2007 22:43:17 -0500

Hello,

David Miller wrote:

>> diff -pruN net-2.6/net/ipv4/ip_output.c net-2.6-udp-take11a1-p1/net/ipv4/ip_output.c
>> --- net-2.6/net/ipv4/ip_output.c	2007-12-11 10:54:55.000000000 -0500
>> +++ net-2.6-udp-take11a1-p1/net/ipv4/ip_output.c	2007-12-17 14:42:31.000000000 -0500
>> @@ -1004,6 +1004,11 @@ alloc_new_skb:
>>  					frag = &skb_shinfo(skb)->frags[i];
>>  				}
>>  			} else if (i < MAX_SKB_FRAGS) {
>> +				if (atomic_read(&sk->sk_wmem_alloc) + PAGE_SIZE
>> +				    > 2 * sk->sk_sndbuf) {
>> +					err = -ENOBUFS;
>> +					goto error;
>> +				}
>>  				if (copy > PAGE_SIZE)
>>  					copy = PAGE_SIZE;
>>  				page = alloc_pages(sk->sk_allocation, 0);
> 
> If we are going to do this, we need to add the same check to
> skb_append_datato_frags() which is invoked via ip_ufo_append_data().
> 
> We also have to be very careful in this area.  One problem we had a
> long time ago was that we would socket account when fragmenting an
> outgoing frame.  This was bogus because even if the socket had enough
> space for one full sized frame, the packet send would fail because it
> could not fit the space for both the original frame and the
> fragmented copy of it.
> 
> This situation was cured by simply not enforcing accounting for the
> fragmented copy.  It is valid because after we fragment, we keep
> the fragmented copy but free the original.
> 
> This doesn't apply directly to this specific patch, but it is
> something to keep in mind when doing these changes.

Hello,

Thank you for sharing your experience.

Let me investigate this code and skb_append_datato_frags().

I'll include the check code in next patch set if it is really needed.

Regards,
Hideo

-- 
Hitachi Computer Products (America) Inc.