RFR: 8339648: ZGC: Division by zero in rule_major_allocation_rate

[Matthias Baesken]

On Fri, 6 Sep 2024 10:26:19 GMT, Matthias Baesken <mbaesken at openjdk.org> wrote:

> The HS jtreg test gc/stringdedup/TestStringDeduplicationAgeThreshold_ZGenerational
> shows this error when running with ubsan enabled 
> 
> src/hotspot/share/gc/z/zDirector.cpp:491:74: runtime error: division by zero
>     #0 0x7f09886401d4 in rule_major_allocation_rate src/hotspot/share/gc/z/zDirector.cpp:491
>     #1 0x7f09886401d4 in start_gc src/hotspot/share/gc/z/zDirector.cpp:822
>     #2 0x7f09886401d4 in ZDirector::run_thread() src/hotspot/share/gc/z/zDirector.cpp:912
>     #3 0x7f098c1404e8 in ZThread::run_service() src/hotspot/share/gc/z/zThread.cpp:29
>     #4 0x7f09897cac19 in ConcurrentGCThread::run() src/hotspot/share/gc/shared/concurrentGCThread.cpp:48
>     #5 0x7f098bb46b0a in Thread::call_run() src/hotspot/share/runtime/thread.cpp:225
>     #6 0x7f098b1a9881 in thread_native_entry src/hotspot/os/linux/os_linux.cpp:858

So we should avoid the division in case the divisor is zero and rewrite the coding a bit.

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PR Comment: https://git.openjdk.org/jdk/pull/20888#issuecomment-2333770996