RFR: 8255716: AArch64: Regression: JVM crashes if manually offline a core

[Andrew Dinn]

On Sun, 1 Nov 2020 12:26:15 GMT, Patrick Zhang <qpzhang at openjdk.org> wrote:

> Please review this change that removed the unnecessary check **cpu_lines == os::processor_count()** from VM_Version::get_os_cpu_info inside src/hotspot/os_cpu/linux_aarch64/vm_version_linux_aarch64.cpp. 
> 
> This **assertion** is practically not needed. While a test system with some cores intentionally turned off, e.g. via echo 0 > /sys/devices/system/cpu/cpu1/online, **java -version** would crash, building openjdk on this system would fail too. 
> 
> This regression issue was introduced by https://github.com/openjdk/jdk/commit/ec9bee68
> 
> Testing:
> - java -version, building openjdk as smoke tests
> - jtreg tier1 as sanity check

Marked as reviewed by adinn (Reviewer).

@cnqpzhang I agree this guarantee needs removing as it breaks a valid case.

@AntonKozlov If the code that sets the A53MAC property really needs to be based on the cpu count obtained from /proc/cpuinfo then you need to rework things so that the OS-specific code can communicate the requisite info to the os agnostic vm_version code. Could you raise a new JIRA for that and propose a fix?

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PR: https://git.openjdk.java.net/jdk/pull/983