RFR: 8366659: ObjectMonitor::wait() can deadlock with a suspension request [v8]

[Anton Artemov]

> Hi, please consider the following changes:
> 
> If suspension is allowed when a thread is re-entering an object monitor (OM), then a deadlock is possible:
> 
> The waiting thread is made to be a successor and is unparked. Upon a suspension request, the thread will suspend itself whilst clearing the successor. The OM will be left unlocked (not grabbed by any thread), while the other threads are parked until a thread grabs the OM and the exits it. The suspended thread is on the entry-list and can be selected as a successor again. None of other threads can be woken up to grab the OM until the suspended thread has been resumed and successfully releases the OM.
> 
> This can happen in two places where the successor could be suspended: 
> 1:
> https://github.com/openjdk/jdk/blob/6322aaba63b235cb6c73d23a932210af318404ec/src/hotspot/share/runtime/objectMonitor.cpp#L1897
> 
> 2:
> https://github.com/openjdk/jdk/blob/6322aaba63b235cb6c73d23a932210af318404ec/src/hotspot/share/runtime/objectMonitor.cpp#L1149
> 
> The issues are addressed by not allowing suspension in case 1, and by handling the suspension request at a later stage, after the thread has grabbed the OM in `reenter_internal()` in case 2. In case of a suspension request, the thread exits the OM and enters it again once resumed. 
> 
> The JVMTI `waited` event posting (2nd one) is postponed until the suspended thread is resumed and has entered the OM again.  The `enter` to the OM (in case `ExitOnSuspend` did exit) is done without posting any events.
> 
> Tests are added for both scenarios. 
> 
> Tested in tiers 1 - 7.

Anton Artemov has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains 22 commits:

 - Merge remote-tracking branch 'origin/master' into JDK-8366659-OM-wait-suspend-deadlock
 - 8366659: Fixed the test.
 - Merge remote-tracking branch 'origin/master' into JDK-8366659-OM-wait-suspend-deadlock
 - 8366659: Fixed lines in tests.
 - Merge remote-tracking branch 'origin/master' into JDK-8366659-OM-wait-suspend-deadlock
 - 8366659: Added a comment to a boolean arg for enter()
 - Merge remote-tracking branch 'origin/master' into JDK-8366659-OM-wait-suspend-deadlock
 - Merge remote-tracking branch 'origin/master' into JDK-8366659-OM-wait-suspend-deadlock
 - 8366659: Fixed new lines.
 - Merge remote-tracking branch 'origin/master' into JDK-8366659-OM-wait-suspend-deadlock
 - ... and 12 more: https://git.openjdk.org/jdk/compare/ff851de8...2ac18b94

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Changes: https://git.openjdk.org/jdk/pull/27040/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27040&range=07
  Stats: 469 lines in 3 files changed: 397 ins; 44 del; 28 mod
  Patch: https://git.openjdk.org/jdk/pull/27040.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27040/head:pull/27040

PR: https://git.openjdk.org/jdk/pull/27040