[jdk17u] RFR: 8271215: Fix data races in G1PeriodicGCTask

[Larry-N]

Tested with tier1

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Commit messages:
 - Backport f2c359a8826e51a92f6a7c6917f2c3d223c24488

Changes: https://git.openjdk.java.net/jdk17u/pull/51/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk17u&pr=51&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8271215
  Stats: 4 lines in 1 file changed: 4 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk17u/pull/51.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk17u pull/51/head:pull/51

PR: https://git.openjdk.java.net/jdk17u/pull/51