Re: [PATCH] sched_groups are expected to be circular linked list,make it so right after allocation

[Igor Mammedov]

On 05/09/2012 01:52 PM, Peter Zijlstra wrote:
> On Wed, 2012-05-09 at 13:44 +0200, Igor Mammedov wrote:
> > This patch fixes only build_sched_groups path, but there is another fail path
> > that results in below OOPS.
> > build_overlap_sched_groups() may exit without setting groups and later it will crash
> > init_sched_groups_power as well.
>
> if that allocation fails? Or is there another fail path?

build_overlap_sched_groups(struct sched_domain *sd, int cpu)
...
                if (cpumask_test_cpu(cpu, sg_span))
                        groups = sg;
...

above test fails and leaves local var groups set to NULL
and before exit there is:

  sd->groups = groups;

which resets sd->groups to NULL and I'm not sure if it is correct at all to skip this
assignment if groups == NULL.

> >   But I just don't know how to fix it, so I've just
> > posted partial fix that reduces crash frequency.
>
>
> > And I have to admit that
> > cpu_active_mask and siblings map are busted but we either should not exit from builder
> > funcs with NULL group or BUG there if it is impossible to come-up with sane group
> > for insane domain span.
>
> I'm perfectly OK with taking the machine down, provided we can output
> useful messages as to what is broken first..

--
-----
 Igor
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