Re: [PATCH 2/2] perf/x86/amd: Don't allow pre-emption in amd_pmu_lbr_reset()

[Sandipan Das]

On 10/24/2023 10:04 PM, Peter Zijlstra wrote:
> On Tue, Oct 24, 2023 at 06:30:38PM +0200, Peter Zijlstra wrote:
>> On Tue, Oct 24, 2023 at 11:04:06AM -0500, Mario Limonciello wrote:
>>
>>>> IIRC this is the hotplug thread running a teardown function on that CPU
>>>> itself. It being a strict per-cpu thread should not trip
>>>> smp_processor_id() wanrs.
>>>>
>>>
>>> BUG: using smp_processor_id() in preemptible [00000000] code: rtcwake/2960
>>> caller is amd_pmu_lbr_reset+0x19/0xc0
>>> CPU: 104 PID: 2960 Comm: rtcwake Not tainted 6.6.0-rc6-00002-g3e2c7f3ac51f
>>
>> Very much not the cpuhp/%u thread :/, let me try and figure out how that
>> happens.
> 
> Uhh, my bad, these are the PREPARE/DEAD handlers, they run before online
> and after dying. The CPU is completely dead. Running lbr_reset() here
> makes no sense.
> 
> Did that want to be in amd_pmu_cpu_dying() ?
> 

Agreed, it should have gone into the cpu_dying() callback. lbr_reset() is called
once from cpu_starting() so I wonder if its necessary to call it again in the
CPU offline path.