Subject: Re: [PATCH v5 6/8] tcp buffer limitation: per-cgroup limit

From: Glauber Costa <[email-masked]>
Date: Wed, 5 Oct 2011 12:08:04 +0400

On 10/04/2011 04:48 PM, Eric Dumazet wrote:
> Le mardi 04 octobre 2011 à 16:17 +0400, Glauber Costa a écrit :
>> This patch uses the "tcp_max_mem" field of the kmem_cgroup to
>> effectively control the amount of kernel memory pinned by a cgroup.
>>
>> We have to make sure that none of the memory pressure thresholds
>> specified in the namespace are bigger than the current cgroup.
>>
>> Signed-off-by: Glauber Costa<[email-masked]>
>> CC: David S. Miller<[email-masked]>
>> CC: Hiroyouki Kamezawa<[email-masked]>
>> CC: Eric W. Biederman<[email-masked]>
>> ---
>
>
>> --- a/include/net/tcp.h
>> +++ b/include/net/tcp.h
>> @@ -256,6 +256,7 @@ extern int sysctl_tcp_thin_dupack;
>>   struct mem_cgroup;
>>   struct tcp_memcontrol {
>>   	/* per-cgroup tcp memory pressure knobs */
>> +	int tcp_max_memory;
>>   	atomic_long_t tcp_memory_allocated;
>>   	struct percpu_counter tcp_sockets_allocated;
>>   	/* those two are read-mostly, leave them at the end */
>> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
>
> So tcp_max_memory is an "int".
>
>
>> +static u64 tcp_read_limit(struct cgroup *cgrp, struct cftype *cft)
>> +{
>> +	struct mem_cgroup *memcg = mem_cgroup_from_cont(cgrp);
>> +	return memcg->tcp.tcp_max_memory<<  PAGE_SHIFT;
>> +}
>
> 1) Typical integer overflow here.
>
> You need :
>
> return ((u64)memcg->tcp.tcp_max_memory)<<  PAGE_SHIFT;

Thanks for spotting this, Eric.

>
> 2) Could you add const qualifiers when possible to your pointers ?

Well, I'll go over the patches again and see where I can add them.
Any specific place site you're concerned about?