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?
> 
> Also, spurious return... clearly I should've woken up before merging
> that patch... oh well.
> 
> ---
> 
> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 4f0c45ab8d7d..59b332cce9e7 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -11417,12 +11417,10 @@ static umode_t pmu_dev_is_visible(struct kobject *kobj, struct attribute *a, int
>  	struct device *dev = kobj_to_dev(kobj);
>  	struct pmu *pmu = dev_get_drvdata(dev);
>  
> -	if (!pmu->nr_addr_filters)
> +	if (n == 2 && !pmu->nr_addr_filters)
>  		return 0;
>  
>  	return a->mode;
> -
> -	return 0;
>  }
>  
>  static struct attribute_group pmu_dev_attr_group = {

Yep, this fixes the issue. As you can see, the type file etc is exported again:


# ll /sys/devices/pai_crypto/
total 0
drwxr-xr-x. 2 root root    0 Nov 23 12:19 events
drwxr-xr-x. 2 root root    0 Nov 23 12:19 format
-rw-r--r--. 1 root root 4096 Nov 23 12:19 perf_event_mux_interval_ms
lrwxrwxrwx. 1 root root    0 Nov 23 12:18 subsystem -> ../../bus/event_source
-r--r--r--. 1 root root 4096 Nov 23 12:19 type
-rw-r--r--. 1 root root 4096 Nov 23 12:19 uevent
# perf stat -a -e pai_crypto/KM_DEA/ -- true

 Performance counter stats for 'system wide':

                 0      pai_crypto/KM_DEA/                                                    

       0.000983239 seconds time elapsed
#

This looks very and and you have my 
Tested-by: Thomas Richter <tmricht@linux.ibm.com

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