Re: [PATCH v2 24/24] perf: Make perf_pmu_unregister() useable

[Ravi Bangoria]

Hi Peter,

>> Apparently not, it ends up with:
>>
>>   ------------[ cut here ]------------
>>   WARNING: CPU: 145 PID: 5459 at kernel/events/core.c:281 event_function+0xd2/0xf0
>>   WARNING: CPU: 145 PID: 5459 at kernel/events/core.c:286 event_function+0xd6/0xf0
> 
>>    remote_function+0x4f/0x70
>>    generic_exec_single+0x7f/0x160
>>    smp_call_function_single+0x110/0x160
>>    event_function_call+0x98/0x1d0
>>    _perf_event_disable+0x41/0x70
>>    perf_event_for_each_child+0x40/0x90
>>    _perf_ioctl+0xac/0xb00
>>    perf_ioctl+0x45/0x80
> 
> Took me a long while trying to blame this on the 'event->parent =
> NULL;', but AFAICT this is a new, unrelated issue.
> 
> What I think happens is this perf_ioctl(DISABLE) vs pmu_detach_events()
> race, where the crux is that perf_ioctl() path does not take
> event2->mutex which allows the following interleave:

This one was only with perf_fuzzer, so pmu_detach_events() code path was
not invoked.

Thanks,
Ravi