Re: [PATCH 5/9] perf/x86: implement cross-HT corruption bug workaround

Maria Dimakopoulou
2014-06-05T14:01:28Z

Are you saying it is illegal to call kmalloc() from
this context?

kmalloc is needed because we need to allocate
a new constraint struct since the static constraint
cannot be modified.

Worst case we can statically allocate a second
constraint struct in the event struct.

On Thu, Jun 5, 2014 at 4:48 PM, Peter Zijlstra <peterz@infradead.org> wrote:
> On Wed, Jun 04, 2014 at 11:34:14PM +0200, Stephane Eranian wrote:
>
>> +static struct event_constraint *
>> +intel_get_excl_constraints(struct cpu_hw_events *cpuc, struct perf_event *event,
>> + struct event_constraint *c)
>> +{
>
>> + if (!(c->flags & PERF_X86_EVENT_DYNAMIC)) {
>> +
>> + /*
>> + * in case we fail, we assume no counter
>> + * is supported to be on the safe side
>> + */
>> + cx = kmalloc(sizeof(*cx), GFP_KERNEL);
>> + if (!cx)
>> + return &emptyconstraint;
>> +
>
> Ok, so forgive me if I'm wrong, but the way we get here is through:
>
> x86_schedule_event()
> ->start_scheduling()
> spin_lock()
> ->get_event_constraints()
> intel_get_excl_constraints()
> kmalloc(.gfp=GFP_KERNEL)
>
> How can that ever work?