Re: linux-next: Tree for June 5

Vegard Nossum
2008-06-06T12:34:18Z

On Fri, Jun 6, 2008 at 1:57 PM, Ingo Molnar <mingo@elte.hu> wrote:
>
> * Andrew Morton <akpm@linux-foundation.org> wrote:
>
>> Good
>>
>> a9ad585c8a18f7ba754b85f5786976609b9d7d29
>> Author: Mike Travis <travis@sgi.com> 2008-05-12 12:21:12
>> Committer: Thomas Gleixner <tglx@linutronix.de> 2008-05-23 09:07:47
>> Parent: 543e21916497be5a4005fd5820264ce1de9bd56d (x86: restore pda nodenumber field)
>> Child: 78d49c6d890aee9cf8aea371011c9d7b0121b822 (x86: remove static boot_cpu_pda array v2)
>> Branch:
>> Follows: v2.6.26-rc2
>> Precedes: next-20080526
>>
>> x86: remove the static 256k node_to_cpumask_map
>>
>> crash, as described earlier.
>
> thanks for tracking it down! This was the origin of the commit:
>
> # tip/x86/numa: a9ad585: x86: remove the static 256k node_to_cpumask_map
>
> which has been in -tip since May 12 and in linux-next for two weeks
> AFAICS, which is beyond the point of being something freshly wrong.
>
> So i suspect something more subtle here. What compiler version are you
> using? This crash is not something that has been found in testing before
> - i use rather new compilers, gcc 4.2.2 most of the time. Previous
> compilers miscompile the kernel seriously so it's not usable for our
> regression testing grid.
>

Hi,

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?

Hope this helps, will send an update if I find out more.

Vegard

--
"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
-- E. W. Dijkstra, EWD1036