Re: [PATCH 01/10] perf,x86: Fix event/group validation

[Stephane Eranian]

On Thu, May 21, 2015 at 6:29 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> On Thu, 2015-05-21 at 06:27 -0700, Stephane Eranian wrote:
>> Or are you talking about a preemption while executing x86_schedule_events()?
>
> That.
>
> And we can of course cure that by an earlier patch I send; but I find it
> a much simpler rule to just never allow modifying global state for
> validation.

I can see  validation being preempted, but not the context switch code path.
Is that what you are talking about?

You are saying validate_group() is in the middle of x86_schedule_events()
using fake_cpuc, when it gets preempted. The context switch code when it loads
the new thread's PMU state calls x86_schedule_events() which modifies the
cpuc->event_list[]->hwc. But this is cpuc vs. fake_cpuc again. So yes, the calls
nest but they do not touch the same state. And when you eventually come back
to validate_group() you are back to using the fake_cpuc. So I am still not clear
on how the corruption can happen.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/