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

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Nov 23, 2023 at 08:54:19AM +0100, Thomas Richter wrote:
> On 11/22/23 10:31, Greg KH 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:
> >>
> >> #  ll /sys/devices/pai_ext/
> >> drwxr-xr-x. 2 root root    0 Nov 21 14:59 events
> >> drwxr-xr-x. 2 root root    0 Nov 21 14:59 format
> >> lrwxrwxrwx. 1 root root    0 Nov 21 14:43 subsystem -> ../../bus/event_source
> >> -rw-r--r--. 1 root root 4096 Nov 21 14:43 uevent
> >> #
> > 
> > /sys/devices/pai_ext/ is a real device?  Why there?  That's a very odd
> > location, what type of device is this?
> 
> S390 has 5 different PMU devices, all show up at /sys/devices/ directory:
> drwxr-xr-x   4 root root 0 Nov 22 14:30 cpum_cf
> drwxr-xr-x   4 root root 0 Nov 22 14:30 cpum_cf_diag
> drwxr-xr-x   4 root root 0 Nov 22 14:30 cpum_sf
> drwxr-xr-x   4 root root 0 Nov 22 14:30 pai_crypto
> drwxr-xr-x   4 root root 0 Nov 22 14:30 pai_ext

And that's messed up, we need to put them in the "proper" place, in
either a bus-specific directory, or somewhere lower, they shouldn't be
in the "root" of the device hierarchy which is what I think started this
whole conversation a while ago.

I'll work on that as a different patch...

thanks,

greg k-h