On Fri, Jun 6, 2008 at 3:33 PM, Mike Travis [off-list ref] wrote:

quoted

Vegard Nossum wrote:

quoted

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...

quoted

quoted

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