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

[Peter Zijlstra <peterz@infradead.org>]

On Wed, Nov 22, 2023 at 03:38:36PM +0100, Thomas Richter wrote:
> 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.

Right, so patchlet I send should only result in hiding n==2, which is
that nr_addr_filters thing IIUC.