RFR: 8271406: Kitchensink failed with "assert(early->flag() == current->flag()) failed: Should be the same"

[Zhengyu Gu]

There is a narrow race window if nmt baseline is executed between reserving a virtual region and setting it nmt type, that can result the assertion failure.

Thanks @coleenp for testing the patch, as it is an Oracle internal test.

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Commit messages:
 - 8271406

Changes: https://git.openjdk.java.net/jdk/pull/8906/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8906&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8271406
  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8906.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8906/head:pull/8906

PR: https://git.openjdk.java.net/jdk/pull/8906