s390/cpumf: cpum_cf PMU displays invalid value after hotplug remove

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: [email protected]
Fixes: a029a4eab39e ("s390/cpumf: Allow concurrent access for CPU Measurement Counter Facility")
Reported-by: Sumanth Korikkar <[email protected]>
Signed-off-by: Thomas Richter <[email protected]>
Reviewed-by: Sumanth Korikkar <[email protected]>
Signed-off-by: Vasily Gorbik <[email protected]>

0 files changed, 0 insertions, 0 deletions