[PATCH 5.14 817/849] s390/cpumf: cpum_cf PMU displays invalid value after hotplug remove

Greg Kroah-Hartman
2021-11-16T01:16:09Z

From: Thomas Richter <tmricht@linux.ibm.com>

commit 9d48c7afedf91a02d03295837ec76b2fb5e7d3fe upstream.

When a CPU is hotplugged while the perf stat -e cycles command is
running, a wrong (very large) value is displayed immediately after the
CPU removal:

Check the values, shouldn't be too high as in
time counts unit events
1.001101919 29261846 cycles
2.002454499 17523405 cycles
3.003659292 24361161 cycles
4.004816983 18446744073638406144 cycles
5.005671647 <not counted> cycles
...

The CPU hotplug off took place after 3 seconds.
The issue is the read of the event count value after 4 seconds when
the CPU is not available and the read of the counter returns an
error. This is treated as a counter value of zero. This results
in a very large value (0 - previous_value).

Fix this by detecting the hotplugged off CPU and report 0 instead
of a very large number.

Cc: stable@vger.kernel.org
Fixes: a029a4eab39e ("s390/cpumf: Allow concurrent access for CPU Measurement Counter Facility")
Reported-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Thomas Richter <tmricht@linux.ibm.com>
Reviewed-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/s390/kernel/perf_cpum_cf.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

--- a/arch/s390/kernel/perf_cpum_cf.c
+++ b/arch/s390/kernel/perf_cpum_cf.c
@@ -679,8 +679,10 @@ static void cpumf_pmu_stop(struct perf_e
false);
if (cfdiag_diffctr(cpuhw, event->hw.config_base))
cfdiag_push_sample(event, cpuhw);
- } else
+ } else if (cpuhw->flags & PMU_F_RESERVED) {
+ /* Only update when PMU not hotplugged off */
hw_perf_event_update(event);
+ }
hwc->state |= PERF_HES_UPTODATE;
}
}