Re: [RFC][PATCH 06/11] perf, x86: PEBS infrastructure

[Peter Zijlstra <peterz@infradead.org>]

On Wed, 2010-03-03 at 18:38 +0100, Robert Richter wrote:
> > +     fake_cpuc = kmalloc(sizeof(*fake_cpuc), GFP_KERNEL | __GFP_ZERO);
> > +     if (!fake_cpuc)
> > +             return -ENOMEM;
> > +
> > +     c = x86_pmu.get_event_constraints(fake_cpuc, event);
> > +
> > +     if (!c || !c->weight)
> > +             ret = -ENOSPC;
> > +
> > +     if (x86_pmu.put_event_constraints)
> > +             x86_pmu.put_event_constraints(fake_cpuc, event);
> 
> A fake cpu with the struct filled with zeros will cause a null pointer
> exception in amd_get_event_constraints():
> 
>         struct amd_nb *nb = cpuc->amd_nb;

That should result in nb == NULL, right? which is checked slightly
further in the function.

> Shouldn't x86_schedule_events() sufficient to decide if a single
> counter is available? I did not yet look at group events, this might
> happen there too.

Sure, but we will only attempt scheduling them at enable time, this is a
creation time check, failing to create an unschedulable event seems
prudent.