Subject: Re: linux-next: Tree for June 5

From: Mike Travis <[email-masked]>
Date: Fri, 06 Jun 2008 07:13:00 -0700

Vegard Nossum wrote:
> On Fri, Jun 6, 2008 at 3:33 PM, Mike Travis <[email-masked]> wrote:
>> Vegard Nossum wrote:
>>> I reproced it with gc 4.1.2. I think the error is somewhere in kernel/sched.c.
>>>
>>> static int __build_sched_domains(const cpumask_t *cpu_map,
>>>                                  struct sched_domain_attr *attr)
>>> {
>>> ...
>>>         for (i = 0; i < MAX_NUMNODES; i++) {
>>> ...
>>>                 sg = kmalloc_node(sizeof(struct sched_group), GFP_KERNEL, i);
>>> ...
>>>
>>> This code is calling into the allocator with a spurious value of i,
>>> which causes SLAB to use an index (of 4 in my case) that is out of
>>> bounds for its nodelist array (at least it hasn't been initialized).
>>>
>>> This bit of code (a bit further down, inside the same loop) is also dubious:
>>>
>>>                         sg = kmalloc_node(sizeof(struct sched_group),
>>>                                           GFP_KERNEL, i);
>>>                         if (!sg) {
>>>                                 printk(KERN_WARNING
>>>                                 "Can not alloc domain group for node %d\n", j);
>>>                                 goto error;
>>>                         }
>>>
>>> Where it passes i to kmalloc_node() but reports an allocation for node
>>> j. Which one is correct?
>>>
> 
> Hm, I think I'm wrong and the code is correct. However...
> 
>>> Hope this helps, will send an update if I find out more.
>>>
>>>
>>> Vegard
>>>
>> Thanks Vegard for tracking this down.  My thoughts were along the same
>> wavelength... ;-)
> 
> I applied this patch
> @@ -7133,6 +7133,14 @@ static int __build_sched_domains(const
> cpumask_t *cpu_map,
>                 cpus_clear(*covered);
> 
>                 cpus_and(*nodemask, *nodemask, *cpu_map);
> +
> +               printk("node %d\n", i);
> +               for (j = 0; j < NR_CPUS; ++j)
> +                       printk("%c", cpu_isset(j, *nodemask) ? 'X' : '.');
> +               printk("\n");
> +
> +               printk("empty = %d\n", cpus_empty(*nodemask));
> +
>                 if (cpus_empty(*nodemask)) {
>                         sched_group_nodes[i] = NULL;
>                         continue;
> 
> and it shows some really strange output, maybe it makes sense to you:
> 
> (the X means cpu is in the node)
> 
> Total of 2 processors activated (11976.24 BogoMIPS).
> node 0
> XX..............................................................................
> ................................................................................
> ................................................................................
> ...............
> empty = 0
> node 1
> XX..............................................................................
> ................................................................................
> ................................................................................
> ...............
> empty = 0
> l3 = cachep->nodelists[0] (size-64) = ffff81003f824340
> node 2
> ................................................................................
> ................................................................................
> ................................................................................
> ...............
> empty = 1
> node 3
> ................................................................................
> ................................................................................
> ................................................................................
> ...............
> empty = 1
> node 4
> X...............................................................................
> ................................................................................
> ................................................................................
> ...............
> empty = 0
> 
> This is a P4 3.0GHz with 1 physical CPU (but HT, so two logical CPUs).
> Yet node 4 is claimed to have a cpu too. That's bogus!
> 
> (But I don't think it's an error in sched.c any more, probably the
> code that sets up the node maps.)
> 
> 
> Vegard
> 

Could you send me the full console log and your config file?  The setup of
the node_to_cpumask map is dependent on the early discovery (usually in the
apic code) and there's been some changes in that area recently.

Thanks,
Mike