Re: Perf: BUG: kernel NULL pointer dereference, address: 0000000000000198

[Ravi Bangoria <ravi.bangoria@amd.com>]

On 03-Nov-22 9:42 PM, Ravi Bangoria wrote:
> On 03-Nov-22 6:03 PM, Peter Zijlstra wrote:
>> On Thu, Nov 03, 2022 at 05:15:30PM +0530, Ravi Bangoria wrote:
>>
>>> Sorry was distracted a bit. So, this seems to be happening because of
>>> race between amd_pmu_enable_all() and perf event NMI. Something like:
>>>
>>>   amd_pmu_enable_all()
>>>   {
>>>       if (!test_bit(idx, cpuc->active_mask))
>>>
>>>   --->/* perf NMI entry */
>>>       ...
>>>       x86_pmu_stop() {
>>>           __clear_bit(hwc->idx, cpuc->active_mask);
>>>           cpuc->events[hwc->idx] = NULL;
>>>       }
>>>       ...
>>>   <---/* perf NMI exit */
>>>
>>>       amd_pmu_enable_event(cpuc->events[idx]);
>>>   }
>>
>> Hmm, do you have more information?
> 
> I've extracted function graph logs from crash dump and uploaded it here:
> https://github.com/BangoriaRavi/function_graph/blob/main/trace.function_graph.dat
> 
> crash was on CPU1.

git bisect let me to a BRS patch:

    commit ada543459cab7f653dcacdaba4011a8bb19c627c
    Author: Stephane Eranian <eranian@google.com>
    Date:   Tue Mar 22 15:15:07 2022 -0700

    perf/x86/amd: Add AMD Fam19h Branch Sampling support

    Add support for the AMD Fam19h 16-deep branch sampling feature as
    described in the AMD PPR Fam19h Model 01h Revision B1.  This is a model
    specific extension. It is not an architected AMD feature.

Thanks,
Ravi