[jdk17] RFR: 8271251: JavaThread::java_suspend() fails with "fatal error: Illegal threadstate encountered: 6"

[Patricio Chilano Mateo]

Hi,

Please review this small patch. When self-suspending, a JavaThread might reach SafepointSynchronize::block() with a state of _thread_in_vm which is not listed as a valid state for safepoint polling. There are a couple of simple ways to fix this. As suggested by @dholmes-ora  we can avoid the handshake machinery altogether and directly self-suspend. Since this issue is intermittent and in tier7 which I didn't run as many times as other lower tiers it escaped my testing of 8270085.

Testing in mach5 tiers1-7. I also reproduced the test failures locally and verified that now both hs202t002.java and ThreadSuspendSelf.java are passing. 

Thanks,
Patricio

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Commit messages:
 - fix self-suspend handshake

Changes: https://git.openjdk.java.net/jdk17/pull/283/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk17&pr=283&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8271251
  Stats: 25 lines in 1 file changed: 13 ins; 7 del; 5 mod
  Patch: https://git.openjdk.java.net/jdk17/pull/283.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk17 pull/283/head:pull/283

PR: https://git.openjdk.java.net/jdk17/pull/283