RFR: 8254877: GCLogPrecious::_lock rank constrains what locks you are allowed to have when crashing

[Erik Österlund]

Today, when you crash, the GCLogPrecious::_lock is taken. This effectively limits you to only get clean crash reports if you crash or assert without holding a lock of rank tty or lower. It is arguably difficult to know what locks you are going to have when crashing. Therefore, I don't think the precious GC log should constrain possible crashing contexts in that fashion.

This patch inserts the precious GC lines into a linked list instead, that can be traversed concurrently, without holding any locks. This allows you to crash in contexts where "low" ranked locks are held.

I have manually verified that the hs_err precious GC log looks identical before and after my change.

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Commit messages:
 - 8254877: GCLogPrecious::_lock rank constrains what locks you are allowed to have when crashing

Changes: https://git.openjdk.java.net/jdk/pull/900/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=900&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8254877
  Stats: 50 lines in 2 files changed: 41 ins; 2 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/900.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/900/head:pull/900

PR: https://git.openjdk.java.net/jdk/pull/900