Re: REGRESSION linux-next since Nov 16th, perf tool broken (at least on s390)

[Thomas Richter <tmricht@linux.ibm.com>]

On 11/22/23 11:07, Peter Zijlstra wrote:
> On Wed, Nov 22, 2023 at 08:38:28AM +0100, Thomas Richter wrote:
>> perf tool fails on linux-next since Nov 16th on s390 when invoking perf on
>> any PMU event, as in
>>
>>   # perf stat -e cycles -- true
>>
>>    Performance counter stats for 'true':
>>
>>      <not supported>      cycles                                                               
>>
>>        0.000598399 seconds time elapsed
>>
>>        0.000055000 seconds user
>>        0.000567000 seconds sys
>>
>>   # perf stat -e pai_ext/NNPA_ALL/ -C0 -- true
>>   event syntax error: 'pai_ext/NNPA_ALL/'
>>                        \___ Bad event or PMU
>>
>>   Unable to find PMU or event on a PMU of 'pai_ext'
>>
>>   Initial error:
>>   event syntax error: 'pai_ext/NNPA_ALL/'
>>                        \___ Cannot find PMU `pai_ext'. Missing kernel support?
>>   #
>>
>> This error is caused by following commit, which got into linux-next around November 15th:
>>
>> commit 652ffc2104ec1f69dd4a46313888c33527145ccf
>> Author: Greg KH <gregkh@linuxfoundation.org>
>> Date:   Mon Jun 12 15:09:09 2023 +0200
>>
>>     perf/core: Fix narrow startup race when creating the perf nr_addr_filters sysfs file
>>
>>     Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
>>     Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
>>     Link: https://lkml.kernel.org/r/2023061204-decal-flyable-6090@gregkh
>>
>> This commit adds function pmu_dev_is_visible() as the PMU bus function
>> to make sysfs attribute files visible.
>> On a failing system these sysfs attribute files are exported:
> 
> Does this help? I'm not entirely sure on the is_visible thing, but the
> way I understand it, it was only supposed to hide the nr_filters thing,
> not the entire group and @n helps select the attribute.
> 
> Greg, did I get that right?

Yes, the is_visible call back function hides whole group, not just this
one attribute.

static struct attribute *pmu_dev_attrs[] = {    <--- This group controlled by is_visibly                              
        &dev_attr_type.attr,                                                  
        &dev_attr_perf_event_mux_interval_ms.attr,                            
        &dev_attr_nr_addr_filters.attr,                                       
        NULL,                                                                 
};    
static struct attribute_group pmu_dev_attr_group = {                          
        .is_visible = pmu_dev_is_visible,                                     
        .attrs = pmu_dev_attrs,                                               
};

So is_visible call back hides whole pmu_dev_attrs group with all 3 files.

> 
> Also, spurious return... clearly I should've woken up before merging
> that patch... oh well.
> 
> 

-- 
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
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