RFR: 8273695: Safepoint deadlock on VMOperation_lock [v4]

[Robbin Ehn]

> We should not do any processing in SM::should_process().
> The query is used to determine if we need to process safepoint/handshakes and with this change StackWaterMark.
> When locking a Mutex which may be acquired in such processing, we must release that Mutex before we can start processing, otherwise we can deadlock.
> 
> This change adds a method to determine if StackWaterMarkSet::on_safepoint() will do any processing.
> In that case there are poll is armed, we do not allow suspend handshakes and there is no safepoint and no non-suspend handshakes, we still return true if StackWaterMarkSet needs processing.
> Thus the code querying should release any such Mutex and call process SM::process_if_requested().
> 
> The cross_modify_fence() do not have any such state, so we still need to emit that before returning false if poll is armed.
> 
> Passes t1-t4 and local stressing.

Robbin Ehn has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains seven additional commits since the last revision:

 - Fixed comment
 - Merge branch 'master' into 8273695-swm-should-proc
 - Fixed spelling
 - Merge branch 'master' into 8273695-swm-should-proc
 - Added update poll values and fixed PR comments
 - Removed string dedup test from problem list
 - Check SWS for processing

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/5613/files
  - new: https://git.openjdk.java.net/jdk/pull/5613/files/e5b52cda..72b98111

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=5613&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=5613&range=02-03

  Stats: 16153 lines in 342 files changed: 12065 ins; 1711 del; 2377 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5613.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5613/head:pull/5613

PR: https://git.openjdk.java.net/jdk/pull/5613