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; } }