RFR: 8336911: ZGC: Division by zero in heuristics after JDK-8332717 [v2]

[Matthias Baesken]

> When running with ubsan enabled binaries, the following issue is reported,
> e.g. in test
> compiler/uncommontrap/TestDeoptOOM_ZGenerational.jtr
> also in gc/z/TestSmallHeap.jtr
> 
> 
> jdk/src/hotspot/share/gc/z/zDirector.cpp:537:84: runtime error: division by zero
>     #0 0x7f422495bd1f in calculate_young_to_old_worker_ratio src/hotspot/share/gc/z/zDirector.cpp:537
>     #1 0x7f422495bd1f in select_worker_threads src/hotspot/share/gc/z/zDirector.cpp:694
>     #2 0x7f42282a0d97 in select_worker_threads src/hotspot/share/gc/z/zDirector.cpp:689
>     #3 0x7f42282a0d97 in initial_workers src/hotspot/share/gc/z/zDirector.cpp:784
>     #4 0x7f42282a2485 in initial_workers src/hotspot/share/gc/z/zDirector.cpp:795
>     #5 0x7f42282a2485 in start_minor_gc src/hotspot/share/gc/z/zDirector.cpp:797
>     #6 0x7f42282a2485 in start_gc src/hotspot/share/gc/z/zDirector.cpp:826
>     #7 0x7f42282a2485 in ZDirector::run_thread() src/hotspot/share/gc/z/zDirector.cpp:912
>     #8 0x7f422840bdd8 in ZThread::run_service() src/hotspot/share/gc/z/zThread.cpp:29
>     #9 0x7f4225ab6979 in ConcurrentGCThread::run() src/hotspot/share/gc/shared/concurrentGCThread.cpp:48
>     #10 0x7f4227e1137a in Thread::call_run() src/hotspot/share/runtime/thread.cpp:225
>     #11 0x7f42274619b1 in thread_native_entry src/hotspot/os/linux/os_linux.cpp:858
>     #12 0x7f422c8d36e9 in start_thread (/lib64/libpthread.so.0+0xa6e9) (BuildId: 9a146bd267419cb6a8cf08d7c602953a0f2e12c5)
>     #13 0x7f422c1dc58e in clone (/lib64/libc.so.6+0x11858e) (BuildId: f2d1cb1ef49f8c47d43a4053910ba6137673ccce)
> 
> 
> The division by 0 leads to  'infinity'  on most of our platforms. So instead of relying on this behavior, we can add a small check and  set 'infinity'  for divisor == 0.

Matthias Baesken has updated the pull request incrementally with one additional commit since the last revision:

  adjustment from xmas - Update src/hotspot/share/gc/z/zDirector.cpp
  
  Co-authored-by: Axel Boldt-Christmas <xmas1915 at gmail.com>

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/21304/files
  - new: https://git.openjdk.org/jdk/pull/21304/files/5debdae2..3b5ffc53

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21304&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21304&range=00-01

  Stats: 14 lines in 1 file changed: 12 ins; 0 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/21304.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21304/head:pull/21304

PR: https://git.openjdk.org/jdk/pull/21304