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

[Kim Barrett]

On Tue, 23 Feb 2021 13:22:25 GMT, Thomas Schatzl <tschatzl at openjdk.org> wrote:

> 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

Marked as reviewed by kbarrett (Reviewer).

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