Re: [perf] perf_fuzzer causes crash in intel_pmu_drain_pebs_nhm()

[Vince Weaver]

On Mon, 1 Mar 2021, Liang, Kan wrote:

> https://lore.kernel.org/lkml/tip-01330d7288e0050c5aaabc558059ff91589e67cd@xxxxxxxxxxxxxx/
> The patch is an SW workaround for some old CPUs (HSW and earlier), which may
> set 0 to the PEBS status. It adds a check in the intel_pmu_drain_pebs_nhm().
> It tries to minimize the impact of the defect by avoiding dropping the PEBS
> records which have PEBS status 0.
> But, it doesn't correct the PEBS status, which may bring problems,
> especially for the large PEBS.
> It's possible that all the PEBS records in a large PEBS have the PEBS status
> 0. If so, the first get_next_pebs_record_by_bit() in the
> __intel_pmu_pebs_event() returns NULL. The at = NULL. Since it's a large PEBS,
> the 'count' parameter must > 1. The second get_next_pebs_record_by_bit() will
> crash.
> 
> Could you please revert the patch and check whether it fixes your issue?

I've reverted that patch and my test-case no longer triggers the issue.

I'll restart a longer fuzzing run to see if any other issues turn up.

Thanks,

Vince