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commit9d48c7afedupstream. 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:a029a4eab3("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>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.