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 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 = {