[jdk21u-dev] RFR: 8342449: reimplement: JDK-8327114 Attach in Linux may have wrong behavior when pid == ns_pid

[Goetz Lindenmaier]

I backport this for parity with 21.0.11-oracle.

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Commit messages:
 - backport 93e889b48cb6eb6872201a28ee19d8fd17c5d821

Changes: https://git.openjdk.org/jdk21u-dev/pull/2560/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk21u-dev&pr=2560&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8342449
  Stats: 169 lines in 1 file changed: 70 ins; 65 del; 34 mod
  Patch: https://git.openjdk.org/jdk21u-dev/pull/2560.diff
  Fetch: git fetch https://git.openjdk.org/jdk21u-dev.git pull/2560/head:pull/2560

PR: https://git.openjdk.org/jdk21u-dev/pull/2560