Subject: Re: [PATCH] netfilter : struct xt_table_info diet

From: Patrick McHardy <[email-masked]>
Date: Thu, 15 Nov 2007 13:26:40 +0100

Eric Dumazet wrote:
> On Wed, 14 Nov 2007 18:19:41 +0100
> Patrick McHardy <[email-masked]> wrote:
> 
>>>diff --git a/net/ipv4/netfilter/arp_tables.c b/net/ipv4/netfilter/arp_tables.c
>>>index 2909c92..ed3bd0b 100644
>>>--- a/net/ipv4/netfilter/arp_tables.c
>>>+++ b/net/ipv4/netfilter/arp_tables.c
>>>@@ -811,7 +811,7 @@ static int do_replace(void __user *user, unsigned int len)
>>> 		return -ENOPROTOOPT;
>>> 
>>> 	/* overflow check */
>>>-	if (tmp.size >= (INT_MAX - sizeof(struct xt_table_info)) / NR_CPUS -
>>>+	if (tmp.size >= (INT_MAX - XT_TABLE_INFO_SZ) / NR_CPUS -
>>> 			SMP_CACHE_BYTES)
>>
>>
>>Shouldn't NR_CPUs be replaced by nr_cpu_ids here? I'm wondering
>>why we still include NR_CPUs in the calculation at all though,
>>unlike in 2.4, we don't allocate one huge area of memory anymore
>>but do one allocation per CPU. IIRC it even was you who changed
>>that.
> 
> 
> Yes, doing an allocation per possible cpu was better than one giant 
> allocation (memory savings and NUMA aware)
> 
> Well, technically speaking you are right, we may also replace these 
> divides per NR_CPUS by nr_cpu_ids (or even better : num_possible_cpus())
> 
> Because with NR_CPUS=4096, we actually limit tmp.size to about 524000,
>  what a shame ! :)

We actually had complaints about number of rule limitations, but that
was more likely caused by vmalloc limits :) But of course we do need
to include the number of CPUs in the check, I misread the code.