RFR: 8262197: JDK-8242032 uses wrong contains_reference() in assertion code

[Thomas Schatzl]

Hi all,

  can I have reviews for this change that fixes use of the wrong HeapRegionRemSet::contains_reference() method, causing a thread lock the same mutex again, resulting in problems like assertion failures?

The code in question has been introduced in JDK-8242032:


    +    // Rechecking if the region is coarsened, while holding the lock.
    +    if (is_region_coarsened(from_hrm_ind)) {
    +      assert(contains_reference(from), "We just found " PTR_FORMAT " in the Coarse table", p2i(from));
    +      return;
    +    }

The problem is the call to `contains_reference`, which locks the same lock that "we know we are already locking" per the comment above. Correct is using `contains_reference_locked` added for just this purpose.

In the original change the PR already mentioned that the situation where this condition should hold could not be reproduced - now we know that it actually occurs ;) 

Testing: tier1. Trying to reproduce with the original some of the failing tests without luck - however the problematic line and the fix is very obvious.

Thanks,
  Thomas

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

Commit messages:
 - Use correct contains_reference_locked

Changes: https://git.openjdk.java.net/jdk/pull/2690/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=2690&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8262197
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/2690.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/2690/head:pull/2690

PR: https://git.openjdk.java.net/jdk/pull/2690